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THE WORMAN SERIES IN MODERN LANGUAGE.
A COMPLETE COURSE IN GERMAN.
By JAMES H. WORMAN, AM.
EMBRACING
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PREFACE.
DURING the past few years great advances have
been made in astronomical science. A new hori-
zontal parallax of the sun has been established.
This has materially altered the estimated distances,
etc., of the planets. The sun is much nearer us than
we supposed, and light has lost a little of its wonder-
ful velocity. , Much additional information has been
obtained concerning Meteors and Shooting Stars.
The investigations connected with Spectrum Analy-
sis have been especially suggestive. Thus on every
hand the facts of Astronomy have been accumulat-
ing. As yet, however, they are scattered through
many expensive foreign works, and are consequently
beyond the reach of most of our schools. It has
been the aim of the author to collect in this little
volume the most interesting features of these larger
works. Believing that Natural Science is full of fas-
cination, he has sought to weave the story of those
far-distant worlds into a form that may attract the
attention and kindle the enthusiasm of the pupil.
The work is not written for the information of scien-
tific men, but for the inspiration of youth. The
pages therefore are not burdened with a multitude
924232
6 PREFACE.
of figures which no memory could possibly retain,
Mathematical tables and data, Questions for Re-
view, and also a Guide to the Constellations, are
given in the Appendix, where they may be useful
for constant reference.
The author would call particular attention to the
method of classifying the measurements of Space,
and the practical treatment of the subjects . of
Parallax, Harvest Moon, Eclipses, the Seasons,
Phases of the Moon, Time, Nebular Hypothesis,
&c.
To teachers heretofore compelled to use a cum-
bersome set of charts, it is hoped that the star maps
here offered will present a welcome substitute. The
geometrical figures showing the actual appearance
of the constellations, will relieve the mind confused
with the idea of numberless rivers, serpents, and
classical heroes. The brightest stars only are given,
since in practice it is found that pupils remember
the general outlines alone.
Finally, the author commits this little work to
the hands of the young, to whose instruction he has
consecrated the energies of his life, in the earnest
hope that, loving Nature in all her varied phases,
they may come to understand somewhat of the wis-
dom, power, beneficence, and grandeur displayed i
the Divine harmony of the Universe.
"One God, one law, one element,
And one far-off Divine event
To which the whole creation moves."
PREFACE.
The following works, among others, have been freely
suited in preparing this volume:
The Heavens Guillernin.
Astronomy Chambers.
Introduction to Astronomy Hind.
Solar System Hind.
Popular Astronomy Airy.
Popular Astronomy Arago.
Astronomy Norton.
Astronomy Robinson.
Astronomy Loomis.
Age of Fable Bulfiuch.
Poetry of Science Hunt.
Outlines of Astronomy Herschel.
Popular Astronomy Mitchell.
Astronomy and Physics Whewell.
Annual of Scientific Discovery Kneeland.
The Chemical News.
PUBLISHERS' NOTICE. Teachers will find in each edition of
this Series certain changes ; not such, however, as to cause any
inconvenience in the use of all the editions in the same class.
These are to be considered, not as corrections of errors, but as
improvements suggested by the constant advance made in science,
and by practical work in the school-room. The publishers are
determined to spare no expense in making this Series increasing-
ly worthy of the unprecedented success it has attained.
SUGGESTIONS TO TEACHERS.
THIS work is designed to be recited in the topical method.
On naming the title of a paragraph, the pupil should be able to
draw on the blackboard the diagram, if any is given, and state
the substance of what is contained in the book. It will be
noticed that the cyder of topics, in treating of the planets and
also of the constellations, is uniform. If a portion of the class
write their topics in full upon the blackboard, it will be found
a valuable exercise in spelling, punctuation, and composition.
Eveiy point which can be illustrated in the heavens should be
shown to the class. No description or apparatus can equal tho
'reality in the sky. After a constellation has been traced, the
pupil should be practised in star-map drawing. Much profit-
able instruction can be obtained in this way. For the pur-
pose of more easily finding the heavenly bodies at any time,
WHITALL'S MOVABLE PLANISPHERE is of great service. It
may be procured of the publishers of this work. " Orreries
are of little account." A tellurian is invaluable in explaining
Precession of the Equinoxes, Eclipses, Phases of the Moon, etc.
Messrs. A. S. Barnes & Co., New York City, furnish a good instru-
ment at a low price. The article on " Celestial Measurements,"
near the close of the work, should be constantly referred to dur-
ing the term. In the figures, the right-hand side represents the
west and the left-hand the east. When it is important to obtain
this idea correctly, the book should be held up toward the south-
ern sky.
Never let a pupil recite, a lesson, nor answer a question, except
it be a mere definition, in the language of the book, Thje text is
designed to interest and instruct the pupil ; the recitation should
afford him an opportunity of expressing what he has learned, in
his own style and words.
TABLE OF CONTENTS.
CELESTIAL MAP.
I. INTRODUCTION.
PAG
HISTORY OF ASTRONOMY 16
SPACE 35
THE THREE SYSTEMS OF CIRCLES . . .37
II. THE SOLAR SYSTEM . . 43
THE SUN 46
THE PLANETS 65
VULCAN 82
MERCURY . 83
VENUS 89
THE EARTH .96
THE SEASONS no
PRECESSION AND NUTATION . . .120
REFRACTION, ABERRATION AND PARALLAX . 130
THE MOON . . . . -139
ECLIPSES 155
THE TIDES ....... 165
MARS . . . 168
THE MINOR PLANETS . . . , .172
JUPITER .... ... 175
SATURN 182
URANUS .189
NEPTUNE 191
METEORS AND SHOOTING STARS . . 194
12 TABLE OF CONTENTS.
PAGI
COMETS 206
ZODIACAL LIGHT 217
III. THE SIDEREAL SYSTEM . . 219
THE STARS 221
THE CONSTELLATIONS 234
NORTHERN CIRCUMPOLAR CONSTELLATIONS . 234
EQUATORIAL CONSTELLATIONS . . . .242
SOUTHERN CONSTELLATIONS . . . 263
DOUBLE STARS, COLORED STARS, VARIABLE
STARS, CLUSTERS, MAGELLANIC CLOUDS,
NEBULA, &C 265
THE MILKY WAY 280
THE NEBULAR HYPOTHESIS . . . .282
CELESTIAL CHEMISTRY. SPECTRUM ANALYSIS 284
TIME . . .288
CELESTIAL MEASUREMENTS . . . .298
APPENDIX 311
TABLES 312
QUESTIONS 315
GUIDE TO THE CONSTELLATIONS . . .331
INDEX. . 335
INTRODUCTION.
ASTRONOMY (astron, a star, and nomos, a law) treats
of the Heavenly Bodies the sun, nioon, planets,
stars, and, as our globe itself is a planet, of the
earth also. It is, above all others, a science that
cultivates the powers of the imagination. Yet all
its theories and distances are based upon the most
rigorous mathematical demonstrations. Thus the
study has at once the beauty of poetry and the ex-
actness of Geometry.
The Appearance of the Heavens to an Observer.
The great dome of the sky filled with glittering
stars is one of the most sublime spectacles in nature.
To enjoy this fully, a night must be chosen when
the air is clear, and the moon is absent. "We then
gaze upon a deep blue, an immense expanse studded
with stars of varied color and brilliancy. Some
shine with a vivid light, perpetually changing and
twinkling; others, more constant, beam tranquilly
and softly upon us ; while many just tremble into
our sight, like a Avave that, struggling to reach some
far-off land, dies as it touches the shore. In the
presence of such weird and wondrous beauty, the
14 INTRODUCTION.
tenderest sentinients of the heart are aroused a
feeling of awy and reverence, of softened melan-
choly 2aii'gled;w;ith a-, thought of God, comes over
us,' and awakens the better nature within us. Those
far-off lights seem full of meaning to us, could we
but read their holy message ; they become real and
sentient, and, like the soft eyes in pictures, look lov-
ingly and inquiringly upon us. We come into com-
munion with another life, and the soul asserts its
immortality more strongly than ever before. We
are humbled as we gaze upon the infinity of worlds,
and strive to comprehend their enormous distances,
their magnificent retinue of suns. The powers of
the mind are aroused, and eager questionings crowd
upon us. What are those glittering fires? What
their distances from us ? Are they worlds like our
own ? Do living, thinking beings dwell upon them ?
Are they carelessly scattered through infinite space,
or is there an order of the universe ? Can we ever
hope to fathom those mysterious depths, or are they
closed to us forever ? Many of these problems have
been solved ; others yet await the astronomer whose
keen eye shall be strong enough to read the myste-
rious scroll of the heavens. Two hundred genera-
tions of study have revealed to us such startling
facts, that we wonder how man in his feebleness
can grasp so much, see so far, and penetrate so
deeply into the mysteries of the universe. Astron-
omy has measured the distance of many of the stars,
and of all the planets ; computed their weight and
INTRODUCTION. 15
size, their days, years, and seasons, with many ot
their physical features ; made a map of the moon, in
some respects more perfect than any map of the
earth ; tracked the comers in their immense sidereal
journeys, marking their paths to a nicety of which
we can scarcely conceive, and at last it has analyzed
the structure of the sun and far-off stars, announ-
cing the very elements of which they are composed.
Observing for several evenings those stars which
shine with a clear distinct light, we notice that they
change their position with respect to the others.
They are therefore called "planets" (literally, wan-
derers). Others remain immovable, and shine with
a shifting, twinkling light. They are termed the
"fixed stars" although it is now known that they
also are in motion the most rapid of any known
even to Astronomy but through such immense or-
bits that they seem to us stationary. Then, too,
diagonally girdling the heavens, is a whitish, vapory
belt the Milky Way. This is composed of multi-
tudes of millions of suns of which our own sun
itself is one so far removed from us that their light
mingles, and makes only a fleecy whiteness. This
magnificent panorama of the heavens is before us,
inviting our study, and waiting to make kn wn to us
the grandest revelations of science.
16 INTRODUCTION.
DESCRIPTIVE ASTRONOMY.
HISTOEY.
ASTRONOMY is the most ancient of all sciences.
The study of the stars is doubtless as old as man
himself, and hence many of its discoveries date back
of authentic records, amid the dim mysteries of tra-
dition. In tracing its history, we shall speak only
of those prominent facts which will best enable us to
understand its progress and glorious achievements.
THE CHINESE. This people boast much of their
astronomical discoveries. Indeed their emperor
claims a celestial ancestry, and styles himself " Son
of the Sun." They possess an account of a conjunc-
tion of four planets and the moon, which must have
occurred a century before the Flood. They have
also the first record of an eclipse of the sun, which
took place about two hundred and twenty years* after
the Deluge. It is reported that one of their kings,
two thousand years before Christ, put to death the
principal officers of state because they had failed to
calculate an approaching eclipse.
* October 13, 2127 B. c.
HISTORY. 17
THE CHALDEANS. The Chaldean shepherds, watch-
ing their flocks by night under the open sky, could
not fail to become familiar with many of the move-
ments of the heavenly bodies. When Alexander
took Babylon, two centuries before Christ, he found
in that city a record of their observations reaching
back about nineteen centuries, or nearly to the con-
fusion of tongues at the Tower of Babel. The
Chaldeans divided the day into twelve hours, in-
vented the sun-dial, and also discovered the " Saros "
or "Chaldean Period," which is the length of time
in which the eclipses of the sun and moon repeat
themselves in the same order.
THE GRECIANS. In the seventh century B. c.,
Tholes, noted for his electrical discoveries, acquired
much renown, and established the first school of
Astronomy in Greece. He taught that the earth is
round, and that the moon receives her light from
the sun. He introduced the division of the earth's
surface into zones, and the theory of the obliquity
of the ecliptic. He also predicted an eclipse of the
sun which is memorable in ancient history as having
terminated a war between the Medes and Lydians.
These nations were engaged in a fierce battle, but
the awe produced by the darkening of the sun was
so great, that both sides threw down their arms and
made peace. Thales had two pupils, Anaximander
and Anaxagoras. The first of these taught that the
stars are suns, and that the planets are inhabited.
He erected the first sun-dial, at Sparta. The second
18 INTRODUCTION.
maintained that there is but one God, that the sun
is solid, and as large as the country of Greece, and
attempted to explain eclipses and other celestial
phenomena by natural causes. For his audacity
and impiety, as his countryman considered it, he
and his family were doomed to perpetual banish-
ment.
Pythagoras founded the second celebrated astro-
nomical school, at Crotona, at which were educated
hundreds of enthusiastic pupils. He knew the
causes of eclipses, and calculated them by means of
the Saros. He was most emphatically a dreamer.
He conceived a system of the universe, in many re-
. spects correct ; yet he advanced no proof, and made
few converts to his views, and they were soon well-
nigh forgoften. He held that the sun is the centre
of the solar system, and that the planets revolve
about it in circular orbits ; that the earth revolves
daily on its axis, and yearly around the sun ; that
Venus is both morning and evening star ; that the
planets are inhabited and he even attempted to
calculate the size of some of the animals in the
moon ; that the planets are placed at intervals cor-
responding to the scale in music, and that they move
in harmony, making the "music of the spheres,"
but that this celestial concert is heard only by the
gods the ears of man being too gross for such
divine melody.
^ Eudoxus, who lived in the fourth century B. c., in-
vented the theory of the Crystalline Spheres. He
HISTORY. 19
held that the heavenly bodies are set, like gems, in
hollow, transparent, crystal globes, which are so
pure that they do not obstruct our view, while they
all revolve around the earth. The planets are
placed in one globe, but have a power of moving
themselves, under the guidance as Aristotle taught
of a tutelary genius, who resides in each, and
rules over it as the mind rules ove** the body.
Hipparclms, who flourished in the second century
B. c., has been called the " Newton of Antiquity."
He was the most celebrated of the Greek astrono-
mers. He calculated the length of the year to with-
in six minutes, discovered the precession of the equi-
noxes, and made the first catalogue of the stars
1081 in number.
THE EGYPTIANS. Egypt, as well as Chaldea, was
noted for its knowledge of the sciences long before
they were cultivated in Greece. It was the practice
of the Greek philosophers, before aspiring to the
rank of teacher, to travel for years through these
countries, and gather wisdom at its fountain-head.
Pythagoras spent thirty years in this manner. Two
hundred years after Pythagoras, the celebrated
school of Alexandria was established. Here were
concentrated in vast libraries and princely halls
nearly all the wisdom and learning of the world.
Here flourished all the sciences and arts, under the
patronage of munificent kings. At this school Ptol-
emy, a Grecian, wrote his great work, the "Alma-
gest," which for fourteen centuries was the text-
20 INTRODUCTION.
book of astronomers. In this work was given what
is known as the "Ptolemaic System." It was
founded largely upon the materials gathered by
previous astronomers, such as Hipparchus, whom
we have already mentioned, and Eratosthenes, who
computed the size of the earth by the means even
now considered the best the measurement of an
arc of the meridian.
PTOLEMAIC THEORY. The movements of the planets
were to the ancients extremely complex. Venus, for
instance, was sometimes seen as " evening star" in
the west, and then again as " morning star" in the
east. Sometimes she seemed to be moving in the
same direction as the sun, then going apparently
behind the sun, appeared to pass on again in a
course directly opposite. At one time she would
recede from the sun more and more slowly and
coyly, until she would appear to be entirely station-
ary; then she would retrace her steps, and seem
to meet the sun. All these facts were attempted
to be accounted for by an incongruous system of
" cycles and epicycles," as it is called. The advo-
cates of this theory assumed that every planet re-
volves in a circle, and that the earth is the fixed
centre around which the sun and the heavenly bodies
move. They then conceived that a bar, or some-
thing equivalent, is connected at one end with the
earth ; that at some part of this bar the sun is at-
tached ; while between that and the earth, Venus is
fastened not to the bar directly, but to a sort of
HISTORY. 21
crank ; and further on, Mercury is hitched on in the
same way. In the cut, let A be the earth, S the sun,
ABDF the bar (real or imaginary), BC the short
bar or crank to which Venus is tied, D E another
bar for Mercury, F G another bar, with still another
short crank, at the end of which, H, Mars is attached.
THE PTOLEMAIC THEORY.
Thus they had a complete system. They did not
exactly understand the nature of these bars
whether they were real or only imaginary but they
did comprehend their action, as they thought ; and
so they supposed the bar revolved, carrying the sun
and planets along in a large circle about the earth ;
while all the short cranks kept flying around, thus
sweeping each planet through a smaller circle. By
this theory, we can see that the planets would
sometimes go in front of the sun and sometimes
behind; and their places were so accurately pre-
dicted, that the error could not be detected by the
rude instruments then in use. As soon as a new
motion of one of the heavenly bodies was discov-
ered, a new crank, and of course a new circle, was
22 INTRODUCTION.
added to account for the fact. Thus the system
became more and more complicated, until a com-
bination of five cranks and circles was necessary to
make the planet Mars keep pace with the Ptolemaic
theory. No wonder that Alfonso, king of Castile,
and a very celebrated patron of Astronomy, revolted
at the cumbersome machinery, and cried out, "If
I had been consulted at the creation, I could have
done the thing better than that !"
ASTROLOGY. After the death of Ptolemy, Astron-
omy ceased to be cultivated as a science. The
Romans, engrossed with schemes of conquest, never
produced a single great astronomer. Indeed, when
Julius Caesar reformed the calendar, he obtained the
assistance, not of a Roman, but of Sosigenes an Alex-
andrian. The Arabians studied the stars merely for
purposes of soothsaying and prophecy. They pro-
fessed to foretell the future by the appearance of the
planets or stars. All of the ancient astronomers
shared more or less in this superstition. Tiberius,
emperor of Rome, practised Astrology. Hippoc-
rates himself, the " Father of Medicine " who flour-
ished in the 4th century B. C., ranked it among the
most important branches of knowledge for the phy-
sician. Star-diviners were held in the greatest
estimation. The system continued to increase in
credit until the Middle Ages, when it was at its
height of popularity. The issue of any important
undertaking, or the fortunes of an individual, were
foretold by the astrologer, who drew up a Horoscope,
HISTORY. 23
representing the position of the stars and planets at
the beginning of the enterprise, or at the birth of
the person. It was a complete and complicated
system, and contained regular rules, which guided
the interpretation, and which were so abstruse
that they required years for their entire mastery.
Venus foretold love; Mars, war; the Pleiades,*
storms at sea. The ignorant were not alone the
dupes of this visionary system. Lord Bacon be-
lieved in it most firmly. As late even as the reign
of Charles II., Lilly, a famous astrologer of that
time, was called before a committee of the House of
Commons to give his opinion on the probable issue
of some enterprise then under consideration. How-
ever foolish the system of Astrology itself may have
been, it preserved the science of Astronomy during
the Dark Ages, and prompted to accurate observa-
tion and diligent study of the heavens.
THE COPERNICAN SYSTEM. About the middle of
the sixteenth centta'y, Copernicus, breaking uway
from the theory of Ptolemy, which was still taught
in all the institutions of learning in Europe, revived
the theory of Pythagoras. He saw how beautiful-
ly simple is the idea of considering the sun the
grand centre about which revolve the earth and all
the planets. He noticed how constantly, when we
arc riding swiftly, we forget our own motion, and
think that the trees and fences are gliding by us in
* Plc'-3\i-dcz.
24 INTRODUCTION.
the contrary direction. He applied this thought to
the movements of the heavenly bodies, and main-
tained that, instead of all the starry host revolving
about the earth once in twenty-four hours, the earth
simply turns on its own axis : that this produces
the apparent daily revolution of the sun and stars ;
while the yearly motion of the earth about the sun,
transferred in the same manner to that body, would
account for its various movements. Though Coper-
nicus thus simplified so greatly the Ptolemaic the-
ory, he yet found that the idea of circular orbits for
the planets would not explain all the phenomena ;
he therefore still retained the " cycles and epicycles"
that Alfonso had so heartily condemned. For forty
years this illustrious astronomer carried on his ob-
servations in the upper part of a humble, dilapi-
dated farm-house, through the roof of which he had
an unobstructed view of the sky. The work con-
taining his theory was at last published just in time
to be laid upon his death-bed.
TYCHO BEAHE, a celebrated Danish astronomer,
next propounded a modification of the Copernican
system. He rejected the idea of cycles and epi-
cycles, but, influenced by certain passages of Scrip-
ture, maintained, with Ptolemy, that the earth is the
centre, and that all the heavenly bodies revolve
about it daily in circular orbits. Brahe was a noble-
man of wealth, and, in addition, received large sums
from the Government. He erected a magnificent
observatory, and made many beautiful and rare in-
HISTORY. 25
struments. Clad in his robes of state, he watched
the heavens with the intelligence of a philosopher
and the splendor of a king. His indefatigable in-
dustry and zeal resulted in the accumulation of a
vast fund of astronomical knowledge, which, how-
ever, he lacked the wit to apply to any further ad-
vance in science. His pupil, Kepler, saw these facts,
and in his fruitful mind they germinated into three
great truths, called Kepler's laws. These constitute
almost the sum of astronomical knowledge, and form
one of the most precious conquests of the human
mind. They are the three arches of the bridge over
which Astronomy crossed the gulf between the Ptol-
emaic and Copernican systems.
KEPLER'S LAWS. Kepler, taking the investigations
of his master, Tycho Brahe, determined to find what
is the exact shape of the orbits of the planets. He
adopted the Copernican theory, that the sun is
the centre of the system. At that time all be-
lieved the orbits to be circular. Since, as they said,
the circle is perfect, is the most beautiful figure in
nature, has neither beginning nor ending, therefore
it is the only form worthy of God, and He must
have used it for the orbits of the worlds He has
made. Imbued with this romantic view, Kepler
commenced with a rigorous comparison of the
places of the planet Mars, as observed by Brahe,
with the places as stated by the best tables that
could be computed on the circular theory. For a
time they agreed, but in certain portions of the
2
26
INTRODUCTION.
orbit tlie observations of Brahe would not fit tlie
computed place by eight minutes of a degree. Be-
lieving that so good an astronomer could not be
mistaken as to the facts, Kepler exclaimed, " Out of
these eight minutes we will construct a new theory
that will explain the movements of all planets." He
resumed his work, and for eight years continued to
imagine every conceivable hypothesis, and then pa-
tiently to test it "hunt it down," as he called it.
Each in turn proved false, until nineteen had been
tried. He then determined to abandon the circle
and adopt another form. The ellipse suggested itself
to his mind. Let us see how this figure is made.
Attach a thread to two pins, as at F F in the
figure ; next move a pencil along with the thread,
the latter being kept tightly stretched, and the point
will mark a curve which is flattened in proportion
HIHTOBY. 27
to the length of the string we use, the longer the
string, the nearer a circle will the figure become.
This figure is the ellipse. The two points F F are
called the foci (singular, focus). We can now under-
stand Kepler's attempt, and the glorious triumph
which crowned his seventeen years of unflagging toil.
First Law. With this figure he constructed an
orbit, having the sun at the centre, and again fol-
lowed the planet Mars in its course. But very soon
there was as great discrepancy between the observed
and computed places as before. Undismayed by
this failure, Kepler assumed another hypothesis.
He determined to place the sun at one of the foci
of the ellipse, and once more "hunted down" the
theory. For a whole year he traced the planet
along the imaginary orbit, and it did not diverge.
The truth was discovered at last, and Kepler an-
nounced his first great law
PLANETS BEVOLVE IN ELLIPSES, WITH THE SUN AT
ONE FOCUS.
Second Law. Kepler knew that the planets do
not move with equal velocity in. the different parts
of their orbits. He next set about establish-
ing some law by which this speed could be deter-
mined, and the place of the planet computed. He
drew an ellipse, and marked the various positions of
the planet Mars once more. He soon found that
when at its perihelion (point nearest the sun) it
moves the fastest, but when at its aphelion (point
furthest from the sun) it moves the slowest. Once
28 INTRODUCTION.
more he " hunted down" various hypotheses, until
at last he discovered that while in going from B to
A the planet moves very slowly, and from D to C
Fig. 3.
very rapidly; yet the space inclosed between the
lines S B and S A is equal to that inclosed between
S D and S C. Hence the second law
A LINE CONNECTING THE CENTRE OF THE EARTH WITH
THE CENTRE OF THE SUN, PASSES OVER EQUAL SPACES IN
EQUAL TIMES.
Third ,Laiv. Kepler, not satisfied with the dis-
covery of these laws, now determined to ascertain
if there were not some relation existing between the
times of the revolution of the planets about the sun
and their distances from that body. With the same
wonderful patience, he took the figures of Tycho
Brahe, and began to compare them. He tried them
in every imaginable relation. Next he took their
squares, then he attempted their cubes, and lastly
he combined the squares and the cubes. Here was
the secret ; but he toiled around it, made a blunder,
HISTORY. 29
and waited for months, until, once more, his patience
triumphed, and he reached the third law
THE SQUARES OF THE TIMES OF REVOLUTION OF THE
PLANETS ABOUT THE SUN, ARE PROPORTIONAL TO THE
CUBES OF THEIR MEAN DISTANCES FROM THE SUN.*
In rapture over the discovery of these three laws,
so marked by that divine simplicity which pervades
all the laws of nature, Kepler exclaimed, "Nothing
holds me. The die is cast. The book is written, to
be read now or by posterity, I care not which. It
may well wait a century for a reader, since God has
waited six thousand years for an observer."f
Galileo. Contemporary with Kepler was the great
Florentine philosopher, Galileo. He discovered the
laws of the pendulum and of falling bodies, as we
have already learned in Natural Philosophy. He,
however, was educated in and believed the Ptolemaic
theory. A disciple of the Copernican theory hap-
pening to come to Pisa, where Galileo was teaching
* For example : The square of Jupiter's period is to the square
of Mars' period, as the cube of Jupiter's distance is to the cube
of Mars' distance ; or, representing the earth's time of revolu-
tion by P, and her distance from the sun by p, then letting D and
d represent the same in another planet, we have the proportion
P 2 : D 2 : : p* : d 3 .
f Kepler, strangely enough, believed in the " Music of the
Spheres." He made Saturn and Jupiter take the bass, Mars the
tenor, Earth and Venus the counter, and Mercury the treble.
This shows what a streak of folly or superstition may run
through the character of the noblest man. However, as John-
son says, a mass of metal may be gold, though there be in it a
little vein of tin.
30 INTRODUCTION.
as professor in the University, drew his attention to
its simplicity and beauty. His clear discriminating
mind perceived its perfection, and he henceforth
advocated it with all the ardor of his unconquerable
zeal. Soon after he learned that one Jansen, a Dutch
watchmaker, had invented a contrivance for making
distant objects appear near. With his profound
knowledge of optics and philosophical instruments,
Galileo instantly caught the idea, and soon had a
telescope completed that would magnify thirty times.
It was a very simple affair only a piece of lead
pipe with glasses set at each end ; but it was the
first telescope ever made, and destined to over-
throw the old Ptolemaic theory, and revolutionize
the whole science of Astronomy.
Discoveries made ivith the telescope. Galileo now
examined the moon. He saw its mountains and val-
leys, and watched the dense shadows sweep over its
plains. On January 8, 1610, he turned the telescope
toward Jupiter. Near it he saw three bright stars,
as he considered them, which were invisible to the
naked eye. The next night he noticed that those
stars had changed their relative positions. Aston-
ished and perplexed, he waited three days for a fair
night in which to resume his observations. The
fourth night was favorable, and he again found
the three stars had shifted. Night after night he
watched them, discovered a fourth star, and finally
found that they were all rapidly revolving around
Jupiter, each in its elliptical orbit, with its own rate
HISTORY. 31
of motion, and all accompanying the planet in its
journey around the sun. Here \vas a miniature
Copernican system, hung up in the sky for all to see
and examine for themselves.
Reception of the discoveries. Galileo met with the
most bitter opposition. Many refused to look through
the telescope lest they might become victims of the
philosopher's magic. Some prated of the wickedness
of digging out valleys in the fair face of the moon.
Others doggedly clung to the theory they had held
from their youth up. As a specimen of the arguments
adduced against the new system, the following by
Sizzi is a fair instance. " There are seven windows
in the head, through which the air is admitted to the
body, to enlighten, to warm, and to nourish it, two
nostrils, two eyes, two ears, and one mouth. So in
the heavens there are two favorable stars, Jupiter and
Venus ; two unpropitious, Mars and Saturn ; two
luminaries, the Sun and Moon ; and Mercury alone,
undecided and indifferent. From which, and from
many other phenomena of Nature, such as the seven
metals, etc., we gather that the number of planets is
necessarily seven. Moreover, the satellites are in-
visible to the naked eye, can exercise no influence
over the earth, and would be useless, and therefore
do not exist. Besides, the week is divided into seven
days, which are named from the seven planets. Now,
if we increase the number of planets, this whole
system falls to the ground."
NEWTON. As we have seen, the truth of the Co-
32 INTKODUCTION.
pernican system was fully established by the discov-
eries of Galileo with his telescope. Philosophers
gradually adopted this view, and the Ptolemaic
theory became a relic of the past. In 1666, Newton,
a young man of twenty-four years, was spending a
season in the country, on account of the plague
which prevailed at Cambridge, his place of resi-
dence. One day, while sitting in a garden, an apple
chanced to fall to the ground near him. Reflecting
upon the strange power that causes all bodies thus
to descend to the earth, and remembering that this
force continues, even when we ascend to the tops of
high mountains, the thought occurred to his mind,
' ' May not this same force extend to a great distance
out in space ? Does it not reach the moon ?"
Laws of Motion. To understand the philosophy
of the reasoning that now occupied the mind of
Newton, let us apply the laws of motion as we have
learned them in Philosophy. When a body is once
set in motion, it will continue to move forever in a
straight line, unless another force is applied. As
there is no friction in space, the planets do not lose
any of their original velocity, but move now with the
same speed which they received in the beginning
from the Divine hand. But this would make them
all pass through straight, and not circular orbits.
What causes the curve? Obviously another force.
For example : I. throw a stone into the air. It
moves not in a straight line, but in a curve, because
the earth constantly bends it downward.
HISTORY. 33
Application. Just so the moon is moving around
the earth, not in a straight line, but in a curve. Can
it not be that the earth bends it downward, just as
it does the stone ? Newton knew that a stone falls
toward the earth sixteen feet the first second. He
imagined, after a careful study of Kepler's laws,
that the attraction of the earth diminishes according
to the square of the distance. He knew (according
to the measurement then received) that a body on
the surface of the earth is four thousand miles from
the centre. He applied this imaginary law. Sup-
pose it is removed four thousand miles from the
surface of the earth, or eight thousand miles from
the centre. Then, as it is twice as far from the
centre, its weight will be diminished 2 2 , or 4 times.
If it were placed 3, 4, 5, 10 times further away, its
weight would then decrease 9, 16, 25, 100 times.
If, then, the stone at the surface of the earth (four
thousand miles from the centre) falls sixteen feet
the first second, at eight thousand miles it would
fall only four feet ; at 240,000 miles, or the distance
of the moon, it would fall only about one-twentieth
of an inch (exactly .053). Now the question arose,
" How far does the moon fall toward the earth, i. e.,
bend from a straight line, every second ?" For sev-
enteen years, with a patience rivalling Kepler's, this
philosopher toiled over interminable columns of fig-
ures to find how much the moon's path around the
earth curves each second. He reached the result
at last. It was nearly, but not quite exact. Disap-
34 INTRODUCTION.
pointed, he laid aside his calculations. Repeatedly
he reviewed them, but could not find a mistake. At
length, while in London, he learned of a new and
more accurate measurement of the distance from the
circumference to the centre of the earth. He has-
tened home, inserted this new value in his calcula-
tions, and soon found that the result would be cor-
rect. Overpowered by the thought of the grand
truth just before him, his hand faltered, and he
called upon a friend to complete the computation.
From the moon, Newton passed on to the other
heavenly bodies, calculating and testing their orbits.
At last he turned his attention to the sun, and, by
reasoning equally conclusive, proved that the attrac-
tion of that great central orb compels all the planets
to revolve about it in elliptical orbits, and holds
them with an irresistible power in their appointed
paths. At last he announced this grand Law of
Gravitation :
EVERY PARTICLE OF MATTER IN THE UNIVERSE AT-
TRACTS EVERY OTHER PARTICLE OF MATTER WITH A
FORCE DIRECTLY PROPORTIONAL TO ITS QUANTITY OF
MATTER, AND DECREASING AS THE SQUARE OF THE DIS-
TANCE INCREASES.
SPACE. 35
SPACE.
We now in imagination pass into space, which
stretches out in every direction without bounds or
measures. We look up to the heavens and try to
locate some object among the mazes of the stars,
We are bewildered, and immediately feel the neces-
sity of some system of measurement. Let us try to
understand the one adopted by astronomers.
THE CELESTIAL SPHERE. The blue arch of the sky,
as it appears to be spread above us, is termed the
Celestial Sphere. There are two points to be no-
ticed here. First, that so far distant is this imagi-
nary arch from us, that if any two parallel lines from
different parts of the earth are drawn to this sphere,
they will apparently intersect. Of course this can-
not be the fact ; but the distance is so immense, that
we are unable to distinguish the little difference of
four or even eight thousand miles, and the two lines
will seem to unite : so we must consider this great
earth as a mere speck or point at the centre of the
Celestial Sphere. Second, that we must even neg-
lect the entire diameter of the earth's orbit, so that
if we should draw two parallel lines, one from each
end of the earth's orbit, to the sphere, although
these lines would be 183,000,000 miles apart, yet
they would be extended so far that we could not
separate them, and they would appear to pierce the
sphere at the same point ; which is to say, that at
\
36 INTRODUCTION.
that enormous distance, 183,000,000 miles shrink to
a point. Consequently, in all parts of the earth, and
in every part of the earth's orbit, we see the fixed
stars in the same place. This sphere of stars sur-
rounds the earth on every side. In the daytime we
cannot see the stars because of the superior light of
the sun ; but with a telescope they can be traced,
and an astronomer will find certain stars as well at
noon as at midnight. Indeed, when looking at the
sky from the bottom of a deep well or lofty chimney,
if a bright star happens to be directly overhead, it
can be seen with the naked eye even at midday. In
this way it is said a celebrated optician was first led
to think of there being stars by day as well as by
night. One half of the sphere is constantly visible
to us ; and so far distant are the stars, that we see
just as much of the sphere as we would if the upper
part of the earth were removed, and we were to
stand four thousand miles further away, or at the
very centre of the earth, where our view would be
bounded by a great circle of the earth. On the con-
cave surface of the celestial sphere there are imag-
ined to be drawn three systems of circles : the HORI-
ZON, the EQUINOCTIAL, and the ECLIPTIC Systems.
Each of these has (1) its Principal Circle, (2) its
Subordinate Circles, (3) its Points, and (4) its Meas-
SPACE. 37
I. THE HORIZON SYSTEM.
(a) The PRINCIPAL CIKCLE is the Rational Horizon.
This is the great circle that, passing through the
centre of the earth, separates the visible from the
invisible heavens. The Sensible Horizon is the small
1 circle where the earth and sky seem to meet ; it is
parallel to the rational horizon, but distant from it
the semi-diameter of the earth. No two places have
the same sensible horizon : any two on opposite
sides of the earth have the same rational horizon.
(b) THE- SUBOEDINATE CIRCLES. These are the
Prime Vertical circle and the Meridian. A vertical
Circle is one passing through the poles of the horizon
the zenith and nadir). The Prime Vertical is a
* ertical circle passing through the East and West
points. The Meridian is a vertical circle passing
hrough the North and South points.
(c) POINTS. These are the Zenith, the Nadir, the
N., S., E., and W. points. The Zenith is the point
"lirectly overhead, and the Nadir the one directly
Underfoot. They are also the poles of the horizon
i. e., the points where the axis of the horizon
pierces fche celestial sphere. The N., S., E., and W.
points are familiar to all.
(d) MEASUREMENTS. These are Azimuth, Ampli-
tude, Altitude, and Zenith distance.
Azimuth is the distance from the meridian, meas-
ured East or "West, on the horizon (to a vertical
circle passing through the object).
38 INTRODUCTION.
Amplitude (the complement of Azimuth) is the
distance from the Prime Vertical, measured on the
horizon, North or South.
Altitude is the distance from the horizon, meas-
ured on a vertical circle toward the zenith.
Zenith distance (the complement of Altitude) is the
distance from the zenith, measured on a vertical
circle, toward the horizon.
The Horizon System is the one commonly used
in observations with Mural Circles and Transit In-
struments.
IE. THE EQUINOCTIAL SYSTEM.
(a) The PRINCIPAL CIRCLE is the Equinoctial. This
is the Celestial Equator, or the earth's equator, ex-
tended to the Celestial Sphere.
(b) SUBORDINATE CIRCLES. These are the Hour
Circles (Right Ascension Meridians) and the Decli-
nation Parallels. The Hour Circles are thus lo-
cated. The Equinoctial is divided into 360, equal
to twenty-four hours of motion thus making 15
equal to one hour of motion. Through these divi-
sions run twenty-four meridians, each constituting
an hour of motion (time) or 15 of space. The
Hoar Circles may be conceived as meridians of ter-
restrial longitude (15 apart) extended to the Celes-
tial Sphere. (See Colures, p. 40.)
The Declination Parallels are small circles par-
allel to the Equinoctial ; or they may be conceived
SPACE. 39
as the parallels of terrestrial latitude extended to
the Celestial Sphere.
(c) The POINTS are the Celestial Poles and the
Equinoxes. The Celestial Poles are the points where
the axis of the earth extended pierces the Celestial
Sphere, and are the extremities of the celestial axis,
just as the poles of the earth are the extremities of
the earth's axis. The North Point is marked very
nearly by the North Star, and every direction from
that is reckoned South, and every direction toward
that is reckoned North, however it may conflict with
our ideas of the points of the compass.
The Equinoxes are the points where the Equi-
noctial and the Ecliptic (the sun's apparent path
through the heavens) intersect.
(d) The MEASUKEMENTS are Eight Ascension (B. A.),
Declination, and Polar Distance.
Hight Ascension is distance from the Vernal Equi-
nox, measured on the equinoctial eastward. B. A.
corresponds to terrestrial longitude, and may ex-
tend to 360 East, instead of 180 as on the earth.
E. A. is never measured westward. The starting
point is the meridian passing through the vernal
equinox; as the meridian passing through Green-
wich is the point from which terrestrial longitude
is measured.
Declination is distance from the equinoctial, meas-
ured on any vertical circle or meridian North or
South. It corresponds to terrestrial latitude.
Polar distance (the complement of Declination) is
4:0 INTRODUCTION.
the distance from the Pole, measured on a vertical
circle.
The Equinoctial System is largely used by modern
astronomers., and accompanies the Equatorial Tele-
scope, Sidereal Clock, and Chronographs of the best
Observatories.
III. THE ECLIPTIC SYSTEM.
(a) The PKINCIPAL CIRCLE is the Ecliptic. This is
the earth's orbit about the sun, or the apparent
path of the sun in the heavens. It is inclined to
the equinoctial 23 28', which measures the inclina-
tion of the Earth's Equator to its orbit, and is called
the obliquity of the ecliptic.
(6) The SUBORDINATE CIRCLES are Circles of Celestial
Longitude, the Colures, and Parallels of Celestial
Latitude.
The Circles of Celestial Longitude are now less
employed. They are measured on the Ecliptic, as
circles of Bight Ascension (E. A.) are now measured
on the Equinoctial.
The Colures are two principal meridians ; the
Equinoctial Colure is the meridian passing through
the equinoxes ; the Solstitial Colure is the meridian
passing through the solstitial points.
The Parallels of Celestial Latitude are now little
used, but are small circles drawn parallel to the
ecliptic, as parallels of declination are now drawn
parallel to the equinoctial.
SPACE. 41
(c) The POINTS are the Poles of the Ecliptic, the
Equinoxes, and the Solstices.
The Poles of the Ecliptic are the points where the
axis of the earth's orbit meets the Celestial Sphere.
(Little used.)
The Equinoxes are the points where the ecliptic
intersects the equinoctial. The place where the
sun crosses the equinoctial* in going North, which
occurs about the 21st of March, is called the Vernal
Equinox. The place where the sun crosses the
equinoctial in going South, which occurs about the
21st of September, is called the Autumnal Equinox.
The Solstices are the two points of "the ecliptic most
distant from the Equator ; or they may be con-
sidered to mark the sun's furthest declination, North
and South of the equinoctial. The Summer Sol-
stice occurs about the 22d of June ; the Winter Sol-
stice occurs about the 22d of December.
(d) The MEASUREMENTS are celestial longitude and
latitude.
Celestial longitude is distance from the Vernal Equi-
nox measured on the ecliptic, eastward.
Celestial latitude is distance from the ecliptic meas-
ured on a Subordinate circle, north or south.
THE ZODIAC.
A belt of the Celestial Sphere, 8 on each side of
the ecliptic, is styled the 'Zodiac. This is of very
" This is what is commonly called " crossing the line."
42 INTRODUCTION.
high antiquity, having been in use among the an-
cient Hindoos and Egyptians. The Zodiac is di-
vided into twelve equal parts of 30 each called
Signs, to each of which a fanciful name is given.
The following are the names of the
SIGNS or THE ZODIAC.
Aries T
Taurus
Gemini n
Cancer
Leo si
Virgo m
Libra ^
Scorpio TTL
Sagittarius *
Capricornus V3
Aquarius ^
Pisces . , . ^
"The first, T, indicates the horns of the Earn;
the second, , the head and horns of the Bull ; the
barb attached to a sort of letter m, designates the
Scorpion ; the arrow, # , sufficiently points to Sagit-
tarius ; v3 is formed from the Greek letters <rp, the
two first letters of rpfyos, a goat. Finally, a bal-
ance, the flowing of water, and two fishes, tied by
a string, may be imagined in =^, ^r, and x, the signs
of Libra, Aquarius, and Pisces."
She Sdar SjjBtem.
In them hath He set a tabernacle for the sun."
PSALM xix 4.
THE SOLAR SYSTEM.
THE Solar System is mainly comprised within the
limits of the Zodiac. It consists of
1. The Sun the centre."
2. The major planets Vulcan (undetermined), Mercury,
Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune.
3. The minor planets, at present one hundred and seventeen
in number. (The paths of some extend a little outside
the Zodiac.)
4 The satellites or moons, eighteen in number, which re-
volve around the different planets.
5. Meteors and shooting-stars.
6. Nine comets whose orbits have been computed, and
over two hundred of which little is known.
7. The Zodiacal Light.
HOW WE AKE TO IMAGINE THE SOLAR SYSTEM TO OUR-
SELVES. We are to think of it as suspended in
space ; being held up, not by any visible object, but
in accordance with the law of Universal Gravitation
discovered by Newton, whereby each planet attracts
every other planet and is in turn attracted by alL
First, the Sun, a great central globe, so vast as
to overcome the attraction of all the planets, and
compel them to circle around him ; next, the planets,
each turning on its axis while it flies around the
46 THE SOLAB SYSTEM.
sun^in an elliptical orbit; then, accompanying these,
the satellites, each revolving about its own planet,
while all whirl in a dizzy waltz about the central
orb ; next, the comets, rushing across the planetary
orbits at irregular intervals of time and space ; and
finally, shooting-stars and meteors darting hither
and thither, interweaving all in apparently inextri-
cable confusion. To make the picture more wonder-
ful still, every member is flying with an inconceiv-
able velocity, and yet with such accuracy that the
solar system is the most perfect timepiece known.
THE SUN.
Sign, , a buckler with its boss.
DISTANCE. The sun's average distance from the
earth is about ^1^ million miles. Since the orbit of
the earth is elliptical, and the sun is situated at one
of its foci, the earth is nearly 3,000,000 miles further
from the sun in aphelion than in perihelion. As we
attempt to locate the heavenly bodies in space, we
are immediately startled by the enormous figures
employed. The first number, 91,500,000 miles, is
far beyond our grasp. Let us try to comprehend it.
If there were air to convey a sound from the sun to
the earth, and a noise could be made loud enough to
pass that distance, it would require over fourteen
years for it to come to us. Suppose a railroad
THE SUN. 47
could be built to the sun. An express-train, travel*
ling day and night, at the rate of thirty miles an
hour, would require 341 years to reach its desti-
nation. Ten generations would be born and would
die ; the young men would become gray-haired, and
their great-grandchildren v ould forget the story of
the beginning of that wonderful journey, and could
find it only in history, as we now read of Queen
Elizabeth or of Shakspeare ; the eleventh generation
would see the solar depot at the end of the route.
Yet this enormous distance of 91,500,000 miles is
used as the unit for expressing celestial distances
as the foot-rule fop measuring space ; and astron-
omers speak of so many times the sun's distance
as we speak of so many feet or inches.
The LIGHT OP THE SUN. This is equal to 5,563
wax-candles held at a distance of one foot from the
eye. It would require 800,000 full-moons to pro-
duce a day as brilliant~as one of cloudless sunshine.
THE HEAT OF THE SUN. The amount of heat we
receive annually is sufficient to melt a layer of ice
thirty-eight yards in thickness, extending over the
whole earth. Yet the' sunbeam is only -sTroVinr part
as intense as it is at the surface of the sun. More-
over, the heat and light stream off into space equally
in every direction. Of this vast flood only one
twenty-three hundred millionth part reaches the
earth. It is said that if the heat of the sun were
produced by the burning of coal, it would require a
layer ten feet in thickness, extending over the whole
48 THE SOLAR SYSTEM.
sun, to feed the flame a single hour. Were the sun
a solid body of coal, it would burn up at this rate in
forty-six centuries. Sir John Herschel says that if
a solid cylinder of ice 45 miles in diameter and
200,000 miles long were plunged, end first, into the
sun, it would melt in a second of time.
APPARENT SIZE. It appears to be about a half de-
gree in diameter, so that 360 disks like the sun, laid
side by side, would make a half circle of the celestial
sphere. It seems a little larger to us in winter than
in summer, as we are 3,000,000 miles nearer it. If
we represent the luminous surface of the sun when
at its average (mean) distance by 1000, the same sur-
face will be represented to us when in aphelion (July)
by 940, and when in perihelion (January) by 1072.
DIMENSIONS. Its diameter is about 850,000 miles.*
Let us try to understand this amount by comparison.
A mountain upon the surface of the sun, to bear
the same proportion to the globe itself as the Dha-
walaghiri of the Himalayas does to the earth, would
have to be about six hundred miles high.
Again: Suppose the sun were hollow, and the
earth, as in the cut (Fig. 4), placed at the centre, not
only would there be room for the moon to revolve
in its regular orbit within the shell, but that would
stretch off in every direction 200,000 miles beyond.
Its volume is 1,245,000 times that of the earth
* Pythagoras, whose theory of the universe was in so many
respects very like the one we receive, believed the sun to be
44,000 miles from the earth, and 75 miles in diameter.
THE SUN. 49
t. e., it would take 1,245,000 earths to make a globe
the size of the sun. Its mass is 674 times that of
all the rest of the solar system. Its weight may be
expressed in tons thus,
1 , 910 , 278 , 070 , 000 , 000 , 000 , 000 , 000 , 000,
Fig. 4.
a number which is meaningless to our imagination,
but yet represents a force of attraction which holds
our own earth and all the planets steadily in their
places ; while it fills the mind with an indescribable
awe as we think of that Being who made the sun,
and holds it in the very palm of his hand.
50 THE SOLAR SYSTEM.
The density of the sun is only about one-fourth
that of the earth, or 1.43 that of water, so that
the weight of a body transferred from the earth to
the sun would not be increased in proportion to the
comparative size of the two. On account also of
the vast size of the sun, its surface is so far from
its centre that the attraction is largely diminished,
since that decreases, we remember, as the square of
the distance. However, a man weighing at the
earth's equator 150 Ibs., at the sun's equator would
weigh about 4,080 Ibs., a force of attraction that
would inevitably and instantly crush him. At the
earth's equator a stone falls 16 feet the first second ;
at the sun's equator it would fall 437 feet.
TELESCOPIC APPEARANCE OF THE SUN : SUN-SPOTS.
We may sometimes examine the sun at early morning
or late in the afternoon with the naked eye, and at mid-
day by using a smoked glass. The disk will appear
to us perfectly distinct and circular, and with no
spot to dim its brightness. If we use, however, a
telescope of moderate power, taking the precaution
to properly shield the eye with a colored eye-piece,
we shall find its surf ace sprinkled with irregular spots,
somewhat as shown in the accompanying figure.
Curious opinions concerning solar spots. The nat-
ural purity of the sun seems to have been formerly
an article of faith among astronomers, and therefore
on no account to be called in question. Scheiner,
it is said, having reported to his superior that he
had seen spots on the sun's face, was abruptly dis-
THE SUN.
51
missed with these remarks : " I have read Aristotle's
writings from end to end many times, and I assure
you I do not find anything in them similar to that
which you mention. Go, my son, tranquillize your-
self ; be assured that what you take for spots are
the faults of your glasses or your own eyes."
SUN IN TELESCOPE.
Discovery of the solar spots. They seem to have
been noticed as early as 807 A. D., although the tel-
escope was not invented until 1610, and Galileo dis-
covered the solar spots in the following year. We
52 THE SOLAR SYSTEM.
read in the log-book of the good ship Bichard of
Arundell, on a voyage, in 1590, to the coast of
Guinea, that " on the 7, at the going downe of the
sunne, we saw a great black spot in the sunne ; and
the 8 day, both at rising and setting, we saw the
like, which spot to me seeming was about the big-
nesse of a shilling, being in 5 degrees of latitude,
and still there came a great billow out of the souther
board."
Number and location of spots. Sometimes, but
rarely, the disk is clear. During a period of ten
years, observations were made on 1982 days, on 372
of which there were no spots seen. As many as
two hundred spots have been noticed at one time.
They are found in two belts, one on each side of
the equator, within not less than 8 nor more than
35 of latitude. They seem to herd together the
length of the straggling group being generally par-
allel to the equator.
The size of the spots. It is not uncommon to find
a spot with a surface larger than that of the earth.
Schroter measured one more than 29,000 miles in
diameter. Sir J. W. Herschel calculated that one
which he saw was 50,000 miles in diameter. In
1843 one was seen which was 14,816 miles across,
and was visible to the naked eye for an entire
week. On the day of the eclipse in 1858, a spot
over 107,000 miles broad was distinctly seen, and
attracted general attention in this country. Some
who read this paragraph will doubtless recall its ap-
THE SUN.
53
Fig. 6.
pearance. In 1839, Captain Davis saw one which
he computed was not less than 186,000 miles long,
and had an area of twenty-five billion square miles.
If these are deep openings in the luminous atmos-
phere of the sun, what an abyss must that be at
"the bottom of which our earth could lie like a
boulder in the crater of a volcano !"
The spots consist of distinct part*. From the ac-
companying representation it will be seen that the
spots generally consist of one or more dark portions
called the umbra, and around that a grayish portion
styled the pe-
numbra (pene,
almost, and um-
bra, black).
Sometimes, how-
ever, umbrae ap-
pear without a
penumbra, and
vice versa. The
umbra itself has
generally a
dense black
centre, called the
nucleus. Besides
this, the umbra is sometimes divided by luminous
bridges.
The spots are in motion. They change from day
to day; but they all have a common movement.
About fourteen days are required for a spot to pass
SUN SPOTS.
54 THE SOLAR SYSTEM.
across the disk of the sun from the eastern side or
limb to the western ; in fourteen days it reappears,
changed in form perhaps, but generally recognizable.
The spots change their rapidity and apparent form
as they pass across the dish A spot is seen on the
eastern limb ; day by day it progresses, with a grad-
ually increasing rapidity, until it reaches the cen-
CHANGE IN SPOTS AS THEY CROSS THE DISK.
tre ; it now gradually loses its rapidity, and finally
disappears on the western limb. The diagram il-
lustrates the apparent change which takes place in
the form. Suppose at first it is of an oval shape ;
as it approaches the centre it apparently widens
and becomes circular. Having passed that point,
it becomes more and more oval until it disappears.
This change in the spots proves the sun's rotation
on its axis. These changes can be accounted for
only on the supposition that the sun revolves on its
axis : indeed, they are the precise effects which the
THE SUN.
55
laws of perspective demand in that case. About
twenty-seven days (27 d., 7 h.) elapse from the ap-
pearance of a spot on the eastern limb before it
reappears a second time. During this time the
earth has gone forward in its orbit, so that the
location of the observer is changed ; allowing for
this, the sun's time of rotation is about twenty-
five days (25 d., 8 h., 10 m. : Langier.)
SYNODIC AND SIDEREAL BBVOLUTION.
Synodic and sidereal revolution of the spots. We
can easily understand why we make an allowance
for the motion of the earth in its orbit. Suppose a
56 THE SOLAR SYSTEM.
solar spot at a, on a line passing from the centre of
the earth to the centre of the sun. For the spot to
pass around the sun and come into that same posi-
tion again, requires about twenty-seven days. But
during this time, the earth has passed on from T to
T'. The spot has not only travelled around to a
again, but also beyond that to a', or the distance
from a to a' more than an entire revolution. To do
this requires, as we have said, about two days. A
revolution from a around to a' is called a synodic,
and one from a around to a again is called a sidereal
revolution.
The spots apparently do not always move in
straight lines. Sometimes their path curves toward
SEPTEMBER.
Fig. 9.
the north, and sometimes toward the south, as ID
the figure. This can be explained only on the sup-
position that the sun's axis is inclined to the
ecliptic (7 15').
The spots have a motion of their own. Besides the
motion already named as assigned to the sun's rota-
tion, the spots seem to have a motion of their own,
THE SUN. 57
and this fact is undoubtedly the cause of the va-
riation in the estimates made of the time of the
sun's revolution on its axis. A spot near the equator
Fig. 10.
performs a synodic revolution in about twenty-five
days, while one half way to either pole requires
twenty-eight days. One spot was noticed which
had a motion three times greater than that of clouds
driven along by the most violent hurricane. Again,
immense cyclones occasionally pass over the surface
with fearful rapidity, producing rotation and sudden
changes in. the spots. At other times, however, the
spots seem " to set sail and move across the disk of
the sun like gondolas over a silver sea."
The spots change their real form. Spots break out
and then disappear under the very eye of the astron-
omer. Wollaston saw one that seemed to be shat-
3*
58 THE SOLAR SYSTEM.
tered like a fragment of ice when it is thrown on a
frozen surface, breaking into pieces, and sliding off
in every direction. Sometimes one divides itself
into several nuclei, while again several nuclei com-
bine into one. Occasionally a spot will remain for
six or eight rotations, while often one will last
only half an hour. In one case, Sir. W. Herschel
relates that when examining a spot through his
telescope, he turned away for a moment, and on
looking back it was gone.
The appearance of the spots is periodical. It is a re-
markable fact that the numberof spots increases and
diminishes through a regular interval of about 11.11
years. These variations seem also to be connected
with periodical variations in the aurora, and magnet-
ic earth-currents, which interfere with the telegraph.
The regular increase and diminution in the spots
was discovered by Schwabe of Prussia, who watched
the sun so carefully that it is said, " for thirty year
the sun never appeared above the horizon without
being confronted by his imperturbable telescope.'
Besides this, it has now been found that the activity
of the sun's spots goes through another regular
period of about 56 years. Independently of this
conclusion, it has also been discovered that the
aurora has a similar period of 56 years.
The spots are influenced by the planets. They ap-
pear to be especially sensitive to the approach of
Venus, on account of its nearness, and of Jupiter,
because of its size. The area of the spots exposed
THE SUN. 59
to view from the earth is uniformly greatest when
Venus is on the opposite side of the sun from us,
and least when on the same side. When both
"Venus and Jupiter are on the side of the sun op-
posite to us, the spots are much larger than when
Venus alone is in that position. In part explana-
tion of this influence of the planets, we may suppose
that they, in some manner, modify reflection on the
disk of the sun exposed to their action, and thus
cause a condensation of gases.
The spots do not influence the fruitfulness of the sea-
son. Sir W. Herschel first advanced the idea that
years of abundant spots would be years also of plen-
tiful harvest. This is not now generally received.
What two years could be more dissimilar than 1859
and 1860 ? Both abounded in solar spots, yet one
was a fruitful year and the other almost one of
famine in Europe.
The spots are cooler tJian the surrounding surface.
It seems that the breaking out of a spot sensibly
diminishes the temperature of that portion of the
sun's disk. The faculae, on the other hand, do not
increase the temperature. (Secchi.)
The spots are depressions below the luminous surface.
This was thought probable before, but is conclu-
sively proved by the photographs of the sun, which
have been taken in large numbers of late at Kew
Observatory.
Comparative brightness of spots and sun. If we
represent the ordinary brightness of the sun by
60
THE SOLAE SYSTEM.
1,000, then that of the penumbra would be 469, and
that of the nucleus 7. There may be much light
and heat radiated by a spot, which seems totally
black as compared with the sun : we remember that
when we look through even a Drummond light at
the sun, it appears as a black spot on the disk of
that luminary.
Faculce, tvillow-leaf, and mottled appearance. Be-
sides the variety of
spots already de-
scribed, there are
other curious ap-
pearances worthy of
note. Bright ridges
or streaks appear,
which constitute the
most brilliant por-
tions of the sun.
These are called fa-
culce. They vary
from barely discern-
ible, softly-gleaming
tracts 1,000 miles long, to lofty, piled-up, mountain-
ous regions 40,000 miles long and 4,000 broad. Out-
side of the spots, the entire disk of the sun is covered
with minute shady dots, giving it a mottled appear-
ance not unlike that of the skin of an orange, though
less coarse. Under a large telescope the surface seems
to be entirely made up of luminous masses, imperfectly
separated by dark dots called pores. These masses are
THE SUN.
61
said by Mr. Nasmyth to have a "willow-leaf" shape ;
many observers apply other descriptive terms, such
as " rice grains," " untidy circular masses," " things
twice as long as broad," " granules," etc. The ac-
companying cut represents the willow-leafed struc-
ture of the luminous surface, and also the " bridges"
Pig. 12.
WILLOW-LBAF.
spanning the solar spot. Indeed, it is said that
the spots themselves always have their origin in a
"pore" which appears to slowly increase and as-
sume the blackness of an umbra, after which the
penumbra begins to appear.
PHYSICAL CONSTITUTION OF THE SUN. Of the consti-
62 THE SOLAR SYSTEM.
tution of the sun, and consequent cause of the
solar spots, very little is definitely known. We shall
notice the various theories now adopted by different
astronomers.
WILSON'S THEORY. This theory supposes that the
sun is composed of a solid, dark globe, surrounded
by three atmospheres. The first, nearest the black
body of the sun, is a dense, cloudy covering, pos-
sessing high reflecting power. The second is called
the photosphere. It consists of an incandescent gas,
and is the seat of the light and heat of the sun.
The third, or outer one, is transparent, very like our
atmosphere. According to this theory, the spots
are to be explained in the following manner. They
are simply openings in these atmospheres made by
powerful upward currents. At the bottom of these
chasms we see the dark sun as a mtdeus at the
centre, and around this the cloudy atmosphere the
penumbra. This explains a black spot with its
penumbra. Sometimes the opening in the photo-
sphere may be smaller than that in the inner or
cloudy atmosphere; in that case there will be a
black spot without a penumbra. It will be natural
to suppose that when the heated gas of the photo-
sphere or second atmosphere is thus violently rent
asunder by an eruption or current from below,
luminous ridges will be formed on every side of
the opening by the heaped-up gas. This will ac-
count for the faculce surrounding the sun-spots.
It will be natural, also, to suppose that sometimes
THE SUN. 63
the cloudy atmosphere below will close up first over
the dark surface of the sun, leaving only an open-
ing through the photosphere, disclosing at the bot-
tom a grayish surface of penumbra. We can readily
Fig. 13.
WILSON S THEORY.
see, also, how, as the sun revolving on its axis brings
a spot nearer and nearer to the centre, thus giving us
a more direct view of the opening, we can see
more and more of the dark body. Then as it passes
by the centre the nucleus will disappear, until
finally we can see only the side of the fissure, the
64 THE SOLAR SYSTEM.
penumbra, which, in its turn, will pass from our
sight. The existence of an outer atmosphere will
account for the fact that the sun's margin is not so
bright as its centre.
EJRCHHOFF'S THEORY. This view differs essentially
from that of Wilson. It considers the sun as an
intensely white-hot solid or fluid body surrounded
by a dense atmosphere of flame, filled with sub-
stances volatilized by the vivid heat. Changes of
temperature take place, which give rise to tornadoes
and violent tempests. Descending currents pro-
duce openings filled with clouds, which appear as
black spots on the sun's disk. A cloud once formed
becomes a screen to shield the upper regions from
the direct heat of the body of the sun. Thus a
lighter cloud is produced, which gives the appear-
ance of a penumbra around the spots.
Spectrum analysis. The hypothesis just given of
the constitution of the sun rests upon the discov-
eries of the spectroscope. This subject will be
treated hereafter under the head of Celestial Chem-
istry. Wilson's theory is time-honored, but compli-
cated ; Kirchhoff's is modern, and partakes of the
simplicity of true science.
THE HEAT OF THE SUN. This subject is not under-
stood. Many theories have been advanced, but
none has. been generally adopted. Some have
supposed the heat is produced by condensation,
whereby the size of the sun is being constantly de-
creased. The dynamic theory accounts for the heat
THE PLANETS. 65
and the solar spots by assuming that there are vast
numbers of meteors revolving around the sun, and
that these constantly rain down upon the surface of
that luminary. Their motion being stopped and
changed to heat, feeds this great central fire. Were
Mercury to strike the sun in this way, it would
generate sufficient heat to compensate the loss by
radiation for seven years. Many suppose that the
heat of the sun is gradually diminishing. Of this
we may be assured, there is enough to support life
on our globe for millions of years yet to come.
THE PLANETS.
WE shall describe these in regular order, passing
outward from the sun. In this journey we shall ex-
amine each planet in turn, noticing its distance,
size, length of its year, duration of day and night,
temperature of the climate, the number of its moons,
and many other interesting facts, showing how much
we can T mow of its world-life in spite of its wonder-
ful distance. We shall encounter the earth in our
imaginary wanderings through space, and shall ex-
plain many celestial phenomena already partially
familiar to us. In all these worlds we shall find
traces of the same Divine hand, moulding and
directing in conformity to one universal plan. The
laws of light and heat will be invariable. The law
66 THE SOLAR SYSTEM.
of gravitation, which causes a stone to fall to the
ground, will be found to apply equally to the- most
distant planets. Even the very elements of which
they are composed will be familiar to us, so that a
book of natural science published here would, in all
its general features, answer for use in a school on
Mars or Jupiter.
CHARACTERISTICS COMMON TO THE PLANETS. (Hind.)
1. They move in the same invariable direction
around the sun ; their course, as viewed from the
north side of the ecliptic, being contrary to the
motion of the hands of a watch.
2. They describe oval or elliptical paths round
the sun not, however, differing greatly from circles.
3. Their orbits are more or less inclined to the
ecliptic, and intersect it in two points, which are the
nodes one half of the orbit lying north and the
other south of the earth's path.
4. They are opaque bodies like the earth, and
shine by reflecting the light they receive from the
sun.
5. They revolve upon their axes in the same way
as the earth. This we know by telescopic observa-
tion to be the case with many planets, and by anal-
ogy the rule may be extended to all. Hence they
will have the alternation of day and night like the
inhabitants of the earth ; but their days are of dif-
ferent lengths from our own.
6. Agreeably to the principles of gravitation, their
velocity is greatest at those parts of their orbit
THE PLANETS. 67
which are nearest the sun, and least at the parts
which are most distant from it ; in other words,
they move quickest in perihelion, and slowest in
aphelion.
COMPARISON OF THE TWO GROUPS OF THE MAJOR
PLANETS. (Chambers.} Separating the major plan-
ets into two groups, if we take Mercury, Venus, the
Earth, and Mars as belonging to the interior, and
Jupiter, Saturn, Uranus, and Neptune to the exterior
group, we shall find that they differ in the following
respects :
1. The interior planets, with the exception of the
earth, are not, so far as we know, attended by any
satellite, while the exterior planets all have satel-
lites. We can but consider this as one of the
many instances to be met with, in the universe, of
the beneficence of the Creator, and that the satel-
lites of these remote planets are designed to com-
pensate for the small amount of light their primaries
receive from the sun, owing to their great distance
from that luminary.
2. The average density of the first group consid-
erably exceeds that of the second, the approximate
ratio being 5 : 1.
3. The mean duration of the axial rotations, or
mean length of the day of the interior planets, is
much longer than that of the exterior ; the average
in the former case being about twenty-four hours,
but in the latter only about ten hours.
THE PROPERTIES OF THE ELLIPSE. In the figure, S
68
THE SOLAK SYSTEM.
and S' are the foci of the ellipse ; AC is the major
axis ; BD, the minor or conjugate axis ; O, the centre :
or, astronomically, OA is the semi-axis-major or mean
distance, OB the semi-axis-minor: the ratio of OS
to OA is the eccentricity ; the least distance, SA, is
the perihelion distance / the greatest distance, SO,
the aphelion distance.
Fig. 14.
CHARACTERISTICS OF PLANETARY ORBIT. It will not
be difficult to follow in the mind the additional
Fig. 15.
PLANETABT ORBITS.
characteristics of a planet's orbit. The orbit or
ellipse just given is laid on a plane surface. Now,
THE PLANETS. 69
incline it slightly, as compared with some other
fixed plane ring, as in the cut. The astronomical
fixed plane is the ecliptic. Imagine a planet follow-
ing the inclined ellipse ; at some point it must rise
above the level of the fixed plane : this point is
called the ascending node, and the opposite point of
intersection is termed the descending node. A line
connecting the two nodes is called the line of the
nodes. The longitude of the node is its distance from
the first point of Aries, measured on the ecliptic,
eastward. In this way we can get a very correct
idea of a planetary orbit in space.
COMPARATIVE SIZE OF PLANETS. (Chambers.) The
following scheme will assist in obtaining a correct
notion of the magnitude of the planetary system.
Choose a level field or common ; on it place a globe
two feet in diameter for the Sun : Vulcan will then
be represented by a small pin's head, at a distance
of about 27 feet from the centre of the ideal sun ;
Mercury by a mustard-seed, at a distance of 82
feet ; Venus by a pea, at a distance of 142 feet ; the
Earth, also, by a pea, at a distance of 215 feet;
Mars by a small pepper-corn, at a distance of 327
feet; the minor planets by grains of sand, at dis-
tances varying from 500 to 600 feet. If space will
permit, we may place a moderate-sized orange
nearly one-quarter of a mile distant from the start-
ing point to represent Jupiter ; a small orange two-
fifths of a mile for Saturn ; a full-sized cherry three-
quarters of a mile distant for Uranus ; and lastly, a
70 THE SOLAR SYSTEM.
pluin 1 miles off for Neptune, the most distant planet
yet known. Extending this scheme, we should find
that the aphelion distance of Encke's comet would
Pig. 16.
COMPARATIVE SIZE OP PLANETS.
be at 880 feet; the aphelion distance of Donati's
comet of 1858 at 6 miles ; and the nearest fixed star
at 7,500 miles.
THE PLANETS. 71
According to this scale, the daily motion of
Vulcan in its orbit would be 4f feet ; of Mercury, 3
feet ; of Venus, 2 feet ; of the Earth, 1| feet ; of
Mars, 1 feet ; of Jupiter, 10J inches ; of Saturn,
7J inches ; of Uranus, 5 inches ; and of Neptune, 4
inches. This illustrates the fact that the orbital
velocity of a planet decreases as its distance from
the sun increases.
CONJUNCTIONS OF PLANETS. The grouping together
of two or more planets within a limited area of the
heavens is a rare event. The earliest record we
have is the one of Chinese origin, already mentioned
on page 16, wherein it is stated that a conjunction of
Mars, Jupiter, Saturn, and Mercury occurred in the
Fig. 17.
VENUS AND JUPITER IN CONJUNCTION, JANUARY 30, 1868.
reign of the Emperor Chuenhio. Astronomers tell I
us that this actually took place Feb. 28, 2446 B. c.,
and that they were between 10 and 18 of Pisces.
This was before the Deluge, so that the fact must
72 THE SOLAR SYSTEM.
have been afterward calculated and chronicled in
their records. In 1859, Venus and Jupiter came so
near each other that they appeared to the naked eye
as one object. In 1725, Venus, Mercury, Jupiter,
and Mars appeared in the same field of the telescope,
ARE THE PLANETS INHABITED? This question is
one which very naturally arises, when we think of
the planets as worlds in so many respects similar
to our own. We can give no satisfactory answer.
Many think that the only object God can possibly
have in making any world is to form an abode for
man. Our own earth was evidently fitted up, al-
though perhaps not created, for this express pur-
pose. Everywhere about us we find proofs of
special forethought and adaptation. Coal and oil
in the earth for fuel and light, forests for timber,
metals in the mountains for machinery, rivers for
navigation, and level plains for corn. Our own
bodies, the air, light, and heat are all fitted to each
other with exquisite nicety. When we turn to the
planets, we do not know but God has other races of
intelligent beings who inhabit them, or even entirely
different ends to attain. Of this, however, we are
assured, that, if inhabited, the conditions on which
life is supported vary much from those familiar
to us. We shall notice these more especially as we
speak of the different planets. We shall see (1) how
they differ in light and heat, from seven times our
usual temperature to less than -5-^-5- ; (2) in the in-
tensity of the force of gravity, from 2 \ times that of
THE PLANETS. 73
the earth to less than -$ ; (3) in the constitution of
the planet itself, from a density J heavier than that
of the earth to one nearly that of cork. The tem-
perature sweeps downward through a scale of over
Fig. 18.
SIZE OF SUN AS SEEN PROM THB PLANETS.
2,000 in passing from Mercury to Uranus. No hu-
man being could reside on the former, while we
4
74 THE SOLAR SYSTEM.
cannot conceive of any polar inhabitant who could
endure the intense cold of the latter. At the sun,
one of our pounds would weigh 27 pounds ; on our
moon the pound weight would become only about
2 ounces ; while on Vesta, one of the planetoids,
a man could easily spring sixty feet in the air and
sustain no shock. Yet while we speak of these
peculiarities, we do not know what modification of
the atmosphere or physical features may exist even
on Mercury to temper the heat, or on Uranus to
reduce the cold. With, however, all these diversi-
ties, we must admit the power of an all-wise
Creator to create beings adapted to the life and
the land, however different from our own. The
Power that prepared a world for us, could as easily
and perfectly prepare one for other races. May
it not be that the same love of diversity, which will
not make two leaves after the same pattern nor two
pebbles of the same size, delights in worlds peopled
by races as diverse ? While, then, we cannot affirm
that the planets are inhabited, analogy would lead
us to think that they are, and that the most
distant star that shines in the arch of heaven is
filled with living beings under the care and govern-
ment of Him who enlivens the densest forest
with the hum of insects, and populates even a
drop of water with its teeming millions of animal-
eulso.
DmsiOKS OF THE PLANETS. The planets are di-
vided into two classes : (1) Inferior, or those whose
THE PLANETS. 75
orbits are within that of the earth viz., Mercury,
Venus ; (2) Superior, or those whose orbits are be-
yond that of the earth Mars, Jupiter, Saturn,
Uranus, Neptune.
MOTIONS OF A PLANET AS SEEN FROM THE SUN.
Could we stand at the sun and watch the movements
of the planets, they would all be seen to be revolv-
ing with different velocities in the order of the
zodiacal signs. But to us, standing on one of the
planets, itself in motion, the effect is changed. To
an observer at the sun all the motions would be real,
while to us many are only apparent. The position
of a planet, as seen from the centre of the sun, is
called its heliocentric place ; as seen from the centre
of the earth, its geocentric place. When Yenus is at
inferior conjunction, an observer at the sun would
see it in the opposite part of the heavens from that
in which it would appear to him if viewed from the
earth.
MOTIONS OF AN INFERIOR PLANET. An inferior
planet is never seen by us in the part of the sky
opposite to the sun at the time of observation. It
cannot recede from him as much as 90, or \ the
circumference, since it moves in an orbit entirely
enclosed by the orbit of the earth. Twice in every
revolution it is in conjunction ( & ) with the sun, an
inferior conjunction (A) when it comes between the
earth and the sun, and a superior conjunction (B)
when the sun lies between it and the earth. (See
Fig. 19.)
76
THE SOLAK SYSTEM.
When the planet attains its greatest distance east
or west (as we see it) from the sun, it is said to be
at its greatest elongation, or in quadrature ( n ).
QUADRATURE AND CONJUNCTION.
When passing from B to A it is east of the sun, and
from A to B it is west of the sun. When east of the
sun, it sets later than the sun, and hence is " evening
star : " when west of the sun, it rises earlier than the
sun, and hence is " morning star." An inferior planet
is never visible when in superior conjunction, as its
light is then lost in the greater brilliancy of the sun.
THE PLANETS.
77
When in inferior conjunction, it sometimes passes in
front of the sun, and appears to us as a round black
spot swiftly moving across his disk. This is called
a transit.
RETROGRADE MOTION.
Retrograde motion of an inferior ]danet. Suppose
the earth to be at A, and the planet at B. Now,
while the earth is passing to F, the planet will pass
to D the arc AF being shorter than BD, because
the nearer a planet is to the sun the greater its
velocity. While the planet is at B, we locate it a >
C on the ecliptic, in Gemini ; but at D, it appears
to us to be at G, in Taurus. So that the planet has
retrograded through "an entire sign on the ecliptic,
while its course all the while has been directly for-s
78 THE SOLAR SYSTEM.
ward in the order of the signs ; and to an observer at
the sun, such would have been its motion.
Phases of an inferior planet An inferior planet
presents all the phases of the moon. At superior
conjunction, the whole illumined disk is turned to-
ward us ; but the planet is lost in the sun's rays :
therefore neither Mercury nor Venus ever presents a
full circular appearance, like the full moon. A little
before or after superior conjunction, an inferior
Fig. 21.
>** JT\ O (V.
^^O^o^-^
4) .ft,
^^0^
PHASES OF AN INFERIOR PLANET.
planet may be seen with a telescope ; but the whole
of the light side is not turned toward us, and so the
planet appears gibbous, like the moon between first
quarter and full. In quadrature, the planet shows
us only one-half its illumined disk ; this decreases,
becoming more and more crescent toward inferior
conjunction, at which time the unillumined side is
toward us.
MOTIONS OF A SUPEKIOB PLANET. The superior
planet moves in an orbit which entirely surrounds
THE PLANETS. 79
that of the earth. When the earth is at E (Fig.
22), the planet at L is said to be in opposition to the
sun. It is then at its greatest distance from him
180. The planet is on the meridian at midnight
while the sun is on the corresponding meridian on
the opposite side of the earth ; or the planet may be
rising when the sun is just setting. When the
planet is at N, it is in conjunction, and being lost in
the sun's rays is invisible to us.
Retrograde ' 'motion of a superior planet. Suppose
the earth to be at E and the planet at L, and that
we move on to G while the planet passes on to O
the distance EG being longer than LO (just the
reverse of what takes place in the movements of
the inferior planets) ; at E, we should locate the
planet at P on the ecliptic, in the sign Cancer ; but
at G, it would appear to us at Q, in the sign Gemini,
having apparently retrograded on the ecliptic the
distance PQ, while it was all the while moving on in
the direct order of the signs. Now, suppose the
earth moves on to I and the planet to U, we should
then see it at the point W, further on in the ecliptic
than Q, which indicates direct motion again, and
at some point near Q the planet must have appeared
without motion. After this, it will continue direct
until the earth has completed a large portion of her
orbit, as we shall easily see by imagining various
positions of the earth and planet, and then drawing
lines as we have just done, noticing whether they
indicate direct or retrograde motion. The greater
80
THE SOLAR SYSTEM.
the distance of a planet the less it will retrograde,
as we shall perceive by drawing another orbit out-
side the one represented in the cut, and making the
same suppositions concerning it as those we have
already explained.
RETROGRADE MOTION OF A SUPERIOR PLANET.
SIDEREAL AND SYNODIC KEVOLUTION. The interval
of time required by a planet to perform a revolution
from one fixed star back to it again, is termed a
sidereal revolution (sidus, a star).
1. The interval of time between two similar con-
THE PLANETS. 81
junctions of an inferior planet with the earth and
sun is termed a synodic revolution. Were the earth
at rest, there would be no difference between a
sidereal and a synodic revolution, and the planet
would come into conjunction twice in each revolution.
Since, however, the earth is in motion, it follows
that after the planet has completed its sidereal
revolution, it must then overtake the earth before
they can both come again into the same position
with regard to the sun. The faster a planet moves,
the sooner it can do this. Mercury, travelling at
the greater speed and on an inner orbit, accom-
plishes it much quicker than Yenus. The synodic
period always exceeds the sidereal.
2. The interval between two successive conjunc-
tions or oppositions of a superior planet is termed a
synodic revolution. Since the earth moves so much
faster than any superior planet, it follows that after
it has completed a sidereal revolution it must then
overtake the planet before they can come again into
the same position with regard to the sun. The
slower the planet moves, the sooner it can do this.
Uranus, making a sidereal revolution in eighty-four
years, can be overtaken more quickly than Mars,
which makes one in less than two years. It conse-
quently requires over a second revolution to catch up
with Mars, ^ of one to overtake Jupiter, and but
little over y^ of one to come up with Uranus. In-
deed, the earth repasses Neptune in two days after
it has finished a sidereal revolution.
82 THE SOLAR SYSTEM.
PLANETS AS EVENING AND MORNING STARS. The in-
ferior planets are evening stars from superior to
inferior conjunction, and the superior planets from
opposition to conjunction. During the other half
of their revolutions they are morning stars.
Mercury, evening star 2 months.
Venus, " " 9J '"
Mars, " " 13
Jupiter, " " 6J
Saturn, " " 6
Uranus, " " 6 "
To avoid filling the text with a multiplicity of
figures, many interesting items are condensed in
tables at the close of the volume.
VULCAN.
SUPPOSED DISCOVERY. Le Verrier, having detected
an error in the assumed motion of Mercury, sug-
gested, in the fall of 1859, that there may be an
interior planet, which is the cause of this disturb-
ance. On this being made public, M. Lescarbault,
a French physician, and an amateur astronomer,
stated that on March 26 of that year he had seen a
dark body pass across the sun's disk, and that this
might have been the unknown planet. Le Verrier
visited him, and found his instruments rough and
home-made, but singularly accurate. His clock was
a simple pendulum, consisting of an ivory ball hang-
MERCURY. 83
ing from. a nail by a silk thread. His observations
were on prescription paper, covered with grease
and laudanum. His calculations were chalked on a
board, which he planed off to make room for fresh
ones. Le Verrier became satisfied that a new planet
had been really discovered by this enthusiastic ob-
server, and congratulated him upon his deserved
success. On March 20, 1862, Mr. Lummis, of Man-
chester, England, noticed a rapidly-moving, dark
spot, apparently the transit of an inner planet.
Many other instances are given of a somewhat sim-
ilar character. As yet, however, the existence of
the planet is not generally conceded. The name
Vulcan and the sign of a hammer have been given
to it. Its distance from the sun has been estimated
at 13,000,000 miles, and its periodic time (its year)
at 20 days.
MEECUEY.
The fleetest of the gods. Sign, , his wand.
DESCRIPTION. Mercury is nearest to the sun of
any of the definitely known planets. , When the sky
is very clear, we may sometimes see it, just after
the setting of the sun, as a bright sparkling star,
near the western horizon. Its elevation increases
evening by evening, but never exceeds 30.* If we
watch it closely, we shall find that it again ap-
* This distance varies much, owing to the eccentricity of Mcr
cury's orbit.
84 THE SOLAR SYSTEM.
proaclies the sun and becomes lost in his rays.
Some days afterward, just before sunrise, we can see
the same star in the east, rising higher each morn-
ing, until its greatest elevation equals that which it
before attained in the west. Thus the planet appears
to slowly but steadily oscillate like a pendulum, to
and fro from one side to the other of the sun. The
ancients, deceived by this, failed to discover the iden-
tity of the two stars, and called the morning star
Apollo, the god of day, and the evening star Mer-
cury, the god of thieves, who walk to and fro in the
night-time seeking plunder. The Greeks gave to
Mercury the additional name of "The Sparkling
One." The astrologists looked upon it as the malig-
nant planet. The chemists, because of its extreme
swiftness, applied the name to quicksilver. The most
ancient account that we have of this planet is given
by Ptolemy, in his Almagest ; he states its location
on the 15th of November, 265 B. c. The Chinese
also state that on June 9, 118 A. D., it was near the
Beehive, a cluster of stars in Cancer. Astronomers
tell us that, according to the best calculations, it
was at that date within less than 1 of that group.
On account of the nearness of Mercury to the sun,
it is difficult to be detected.* It is said that Coper-
nicus, an old man of seventy, lamented in his last
moments that, much as he had tried, he had never
* An old English writer by the name of Goad, in 1686, humor-
ously termed this planet, " A squinting lacquey of the sun, who
seldom shows his head in these parts, as if he were in debt"
MERCURY. 85
been able to see it. In our latitude and climate,
we can generally easily detect it if we watch for it
at the time of its greatest elongation or quadrature,
as given in the almanac.
MOTION IN SPACE. It revolves about the sun at a
mean distance of 35,000,000 miles. Its orbit is the
most eccentric (flattened) of any among the eight
principal planets, so that although when in peri-
helion it approaches to within 28,000,000 miles, in
aphelion it speeds away 15,000,000 miles farther, or
to the distance of 43,000,000 miles. Being so near
the sun, its motion in its orbit is correspondingly
rapid viz., 30 miles per second. At this rate. of
speed, we could cross the Atlantic Ocean in two
minutes. The Mercurial year comprises only about
88 days, or nearly three of our months. Mercury
revolves upon its axis in about the same time as the
earth, so that the length of the Mercurial day is
nearly the same as that of the terrestrial one.
Though Mercury thus completes a sidereal revolu-
tion around the sun in 88 days, yet to pass from one
inferior or superior conjunction to the same again (a
synodic revolution) requires 116 days. The reason
of this is, as already explained, that when Mercury
comes around to the same spot in its orbit again,
the earth has gone forward, and it requires 28 days
for the planet to overtake us.
DISTANCE FROM THE EARTH. This varies still more
than its distance from the sun. At inferior conjunc-
tion it is between the earth and the sun, and its dis-
86 THE SOLAR SYSTEM.
tance from us is the difference between the distance
of the earth and the planet from the sun : at supe-
rior conjunction it is the sum of these distances. Its
apparent diameter in these different positions varies
in the same proportion as the distances, or as three
to one. The greatest and least distances vary ac-
cording as either planet may happen to be in aphe-
lion or perihelion. If at inferior conjunction Mer-
cury is in aphelion and the earth in perihelion, its
distance from us is only 90,000,000 - 43,000,000 =
47,000,000 miles. If at superior conjunction Mer-
cury is in aphelion and the earth in aphelion also,
its distance from us is 93,000,000 + 43,000,000 =
136,000,000 miles.
DIMENSIONS. Mercury is about 3,000 miles in di-
ameter. Its volume is about -fa that of the earth
i. e., it would require twenty globes as large as Mer-
cury to make one the size of the earth, or 25,000,000
to equal the sun. Yet as it is | denser than the
earth, its weight is nearly ^ that of the earth, and
a stone let drop upon its surface would fall 7J feet
the first second. Its specific gravity is about that
of tin. A pound weight removed to Mercury would
weigh only about seven ounces.
SEASONS. As Mercury's axis is much inclined
from a perpendicular, its seasons are peculiar.
There are no distinct frigid zones; but large re-
gions near the poles have six weeks continuous day
and torrid heat, alternating with a night of equal
length and arctic cold. The sun shines perpendic-
MERCUKY.
87
ularly upon the torrid zone only at the equinoxes,
while he sinks far toward the southern horizon at
one solstice, and as far toward the northern hori-
zon at the other. The equatorial regions, there-
fore, modify their temperature during each rev-
Fig. 29
ORBIT AND SEASONS OF MERCURY.
olution from torrid to temperate, and the tropical
heat is experienced alternately toward the north
and south of what we call the temperate zones.
There is no marked distinction of zones as with
us, but each zone changes its character twice
during the Mercurial year, or eight times during
the terrestrial one. An inhabitant of Mercury
88 THE SOLAR SYSTEM.
must be accustomed to the most sudden and vio-
lent vicissitudes of temperature. At one time the
sun not only thus pours down its vertical rays, and in
a few weeks after sinks far down toward the horizon,
but, on account of Mercury's elliptical orbit, when in
perihelion the planet approaches so near the sun that
the heat and light are ten times as great as that we
receive, while in aphelion it recedes so as to reduce
the amount to four and a half times (the average,
however, is seven times), a temperature sufficient to
turn water to steam, and even to melt many of the
metals. This entire round of transitions is swept
through four times during one terrestrial year. The
relative length of the days and nights is much more
variable than with us. The sun, apparently seven
times as large as it seems to us, must be a magnifi-
cent spectacle, and illumine every object with insuf-
ferable brilliancy. The evening sky is, however,
lighted by no moon.
TELESCOPIC FEATURES. Under the telescope, Mer-
cury presents all the phases of the moon, from a
slender crescent to gibbous, when its light is lost
in that of the sun. These phases prove that Mer-
cury is spherical, and shines by the light reflected
from the sun. When in quadrature, it can some-
times be detected with a telescope in daylight.
Being an inferior planet, we can never see it when
full, and hence the brightest, nor when nearest the
earth, as then its dark side is turned toward us.
Owing to the dazzling light, and the vapors almost
VENUS. 89
always hanging around our horizon, this planet has
not received much attention of late ; the cuts here
given, and the remarks concerning its physical fea-
tures, are based upon the observations of the older
astronomers. It is thought by some to have a
dense atmosphere loaded with clouds, which would
materially diminish the intensity of the sun, and
perhaps make Mercury quite habitable. Sir W.
Herschel, however, emphatically denies this, and
asserts that the atmosphere is too insignificant to
be detected. There are some dark bands about its
equator. It has lofty mountains, which intercept
the light of the sun, and deep valleys plunged in
shade. One mountain has been ascertained to be
about ten miles in height, which is -3^5- of the di-
ameter of the planet. The height of the Dhawa-
laghiri of the Himalayas is less than 29,000 feet,
or y^Vir P ar ^ of the earth's diameter.
VENUS.
The Queen of Beauty. Sign ? , a looking-glass.
DESCRIPTION. Venus, the next in order to Mer-
cury, is the most brilliant of all the planets. When
visible before sunrise, she was called by the ancients
Phosphorus, Lucifer, or the Morning Star, and when
she shone in the evening after sunset, Hesperus, Ves-
per, or the Evening Star. She presents the same
appearances as Mercury. Owing, however, to the
greater diameter of her orbit, her apparent oscillations
90 THE SOLAB SYSTEM.
are nearly 48 east and west of the sun,* or about
18 more than those of Mercury. She is therefore
seen much earlier in the morning and much later at
night. She is " morning star" from inferior to supe-
rior conjunction, and " evening star" from superior
to inferior conjunction. She is the most brilliant
about five weeks before and after inferior conjunc-
tion, at which time the planet is bright enough to
cast a shadow at night. If, in addition, at this time
of greatest brilliancy, Yenus is at or near her high-
est north latitude, she may be seen with the naked
eye in full daylight.t This occurs once in eight
years, in which interval the earth and planet return
to the same situation in their orbits ; eight complete
revolutions of the earth about the sun occupying
nearly the same time as thirteen of Venus. This
happened last in February, 1862. A less degree
of brilliancy is attained once in twenty-nine months,
under somewhat the same circumstances.
MOTION IN SPACE. Unlike Mercury, Venus has
an orbit the most circular of any of the principal
* This distance varies but little, owing to the slight eccentricity
^>f Venus's orbit.
t Arago relates that Bonaparte, upon repairing to the Luxem-
bourg, when the Directory was about to give him a fete, was
much surprised at seeing the multitude paying more attention to
the heavens above the palace than to him or his brilliant staff.
Upon inquiry, he learned that these curious persons were observ-
ing with astonishment a star which they supposed to be that of
the Conqueror of Italy. The emperor himself was not indifferent
when his piercing eye caught the clear lustre of Venus smiling
upon him at midday.
VENUS. 91
planets. Her mean distance from the sun is about
66,000,000 miles, which varies at aphelion and peri-
helion within the limits of a half million miles against
15,000,000 miles in the case of the former planet.
She makes a complete revolution around the sun in
about 225 da} r s, at the mean rate of 22 miles per
second ; hence her year is equal to about seven and
one half of our months. This is a sidereal revolu-
tion, as it would appear to an observer at the sun,
but a synodic revolution is 584 days. Mercury, we
remember, catches up with the earth in 28 days after
it reaches the point where it left the earth at the
last inferior conjunction. But it takes Venus nearly
two and a half revolutions to overtake the earth and
come into the same conjunction again. This grows
out of the fact that Yenus has a longer orbit to
travel through, and moves only about one-fifth faster
than the earth, while Mercury travels nearly twice
as fast. The planet revolves upon its axis in about
24 hours ; so the day does not differ in length essen-
tially from ours.
DISTANCE FROM THE EARTH. The distance of Ve-
nus from the earth, like that of Mercury, when in
inferior conjunction, is the difference between the
distances* of these two planets from the sun, and
when in superior conjunction the sum of these dis-
tances.
* Let the pupil calculate the distances of the earth and Venus
from each other, when in perihelion and aphelion, as hi the case
ol Mercury, (See tables in Appendix.)
92
THE SOLAR SYSTEM.
The figure represents its apparent dimensions at
the extreme, mean, and least distances from us.
The variation is nearly as the numbers 10, 18, and
65. It would be natural to think that the planet is
the brightest when the nearest, and thus the largest,
Fig. 24.
EXTREME, MEAN, AND LEAST APPARENT SIZE OP VENUS.
but we should remember that then the bright side
is toward the sun, and the unillumined side toward
us. Indeed, at the period of greatest brilliancy of
which we have spoken, only about one-fourth of
the light is visible. At this time, however, many
observers have noticed the entire contour of the
planet to be of a dull gray hue, as seen in the cut.
DIMENSIONS. Venus is about 7,500 miles in diame-
ter. The volume of the planet is about four-fifths
that of the earth, while the density is about the same.
A stone let fall upon its surface would fall 14 feet in
VENUS. 93
the first second : a pound weight removed to its
equator would weigh about five-sixths of a pound.
From this we see that the force of gravity does not
decrease exactly in proportion to the size of the
planet, any more than it increases with the mass of
the sun. The reason of this is, that the body is
brought nearer the mass of the small planet, and
so feels its attraction more fully than when far out
upon the extreme circumference of a large body,
the attraction increasing as the square of the dis-
tance from the particles decreases.
SEASONS. As the axis of Yenus is very much in-
clined from a perpendicular, its seasons are similar
to those of Mercury. The torrid and temperate
Fig. 25
VENUS AT ITS SOLSTICE.
zones overlap each other ; the polar regions having
alternately at one solstice a torrid temperature, and
at the other a prolonged arctic cold. The inequality
94 THE SOLAR SYSTEM.
of the nights is very marked. The heat and light are
double that of the earth, while the circular form of
its orbit gives nearly an equal length to its four
seasons.
If the inclination of its axis is 75, as some as-
tronomers hold, its tropics must be 75 from the
equator, and its polar circles 75 from the poles.
The torrid zone is, therefore, 150 in width. The
torrid and frigid zones inteiiap through a space of
60, midway between the equator and poles.
TELESCOPIC FEATURES. Venus, being an interior
planet, presents, like Mercury, all the phases of the
moon. This fact was discovered by Galileo, and was
among the first achievements of his telescopic obser-
vations. It had been argued against the Coperni-
;an system that, if true, Venus should wax and wane
Aike the moon. Indeed, Copernicus himself boldly
declared that if means of seeing the planets more
distinctly were ever invented, Venus would be found
to present such phases. Galileo, with his telescope,
proved this fact, and, by overthrowing that objec-
tion, again vindicated the Copernican theory. This
planet is not sensibly flattened at the poles. It is
thought to have a dense, cloudy atmosphere. This
was established by the fact that at the transit of
Venus over the sun in 1761 and 1769, a faint ring
of light was observed to surround the black
disk of the planet. The evidence of an atmosphere,
as well as of mountains, rests very much upon the
peculiar appearance attending its crescent s ape.
VENUS.
95
(1.) The luminous part does not end abruptly ; on
the contrary, its light diminishes gradually, which
diminution may be entirely explained by the twi-
light on the planet. The existence of an atmosphere
Pig. 26.
CRESCENT AND SPOTS OP VENU9.
which diffuses the rays of light into regions where
the sun has already set, has hence been inferred.
Thus, on Venus, the evenings, like ours, are lighted
by twilight, and the mornings by dawn. (2.) The
edge of the enlightened portion 'of the planet is un-
even and irregular. This appearance is doubtless
the effect of shadows cast by mountains. Spots
have been noticed on its disk which are considered
to be traceable to clouds. Indeed, Herschel thinks
that we never see the real body of the planet, but
only its atmosphere loaded with vapors, which may
mitigate the glare of the intense sunshine.
SATELLITES. Venus is not known to have any
moon.
THE SOLAR SYSTEM.
THE EAUTH.
Sign, 0, a circle with Equator and Meridian.
The Earth is the next planet we meet in passing
outward from the sun. To the beginner, it seems
strange enough to class our world among the heav-
enly bodies. They are brilliant, while it is dark and
opaque ; they appear light and airy, while it is solid
and firm ; we see in it no motion, while they are
constantly changing their position ; they seem mere
points in the sky, while it is vast and extended. Yet
at the very beginning we are to consider the earth
as a planet shining brightly in the heavens, and
appearing to other worlds as a star does to us : we
are to learn that it is in motion, flying through its
orbit with inconceivable velocity ; that it is not fixed,
but hanging in space, held by an invisible power of
gravitation which it cannot evade ; that it is small
and insignificant beside the mighty globes that so
gently shine upon us in the far-off sky; that our
earth is only one atom in a universe of worlds, all
firm and solid, and equally well fitted to be the abode
of life.
DIMENSIONS. The earth is not "round like a bah 1 ,"
but flattened at the poles. Its form is that of an
oblate spheroid. Its polar diameter is about 7,899
miles, and its equatorial about 7,925^. The com-
pression is, therefore, about 26J miles. (See table
THE EARTH.
97
in Appendix.) If we represent the earth by a globe
one yard in diameter, the polar diameter would be
one-tenth of an inch too long. It has been recently
Fig. 27.
THE EARTH IN SPACE.
shown that the equator itself is not a perfect circle,
but is somewhat flattened, since the diameter which
98 THE SOLAR SYSTEM.
pierces the meridian 14 east of Greenwich is two
miles longer than the one at right angles to it. The
circumference of the earth is about 25,000 miles.
Its density is about 5J times that of water. Its
weight is
6,069,000,000,000,000,000,000 tons.
The inequalities of its surface, arising from build-
ings, valleys, mountains, etc., have been likened to
the roughness on the rind of an orange. This is
not an exaggeration. On a globe sixteen inches in
diameter, the land, to be in proportion, should be
represented by the thinnest writing-paper, the hills
by small grains of sand, and elevated ranges by
thick drawing-paper. To represent the deepest
wells or mines, a scratch might be made that would
be invisible except with a glass. The water in the
ocean could be shown by a brush dipped in color
and lightly drawn over the bed of the sea.
THE KOTUNDITY or THE EARTH. This is shown in
various ways, among which are the following : (1)
By the fact that vessels have sailed around the earth ;*
* It is curious, in connection with this well-known fact, lo re-
call the arguments urged by the Spanish philosophers against
the reasoning of Columbus, when he assured them that he
could arrive at Asia just as certainly by sailing west as
east. "How," they asked, "can the earth be round? If
it were, then on the opposite side the rain would fall upward,
trees would grow with their branches down, and everything
would be topsy-turvy. Eveiy object on its surface would cer-
tainly fall off; and if a ship by siiVng west should get around
THE EARTH. 9 ( J
(2) when a ship is coming into port w.e see the masts
first ; (3) the shadow of the earth on the moon is
circular; (4) the polar star seems higher in the
heavens as we pass north ; (5) the horizon expands
as we ascend an eminence.* If we climb to the top
of a hill, we can see further than when on the plain
at its foot. Our eyesight is not improved ; it is only
because ordinarily the curvature of the earth shuts
off the view of distant objects, but when we ascend
to a higher point, we can see farther over the side
of the earth. The curvature is eight inches per
mile, 2 2 x 8 in - = 32 inches for two miles, 3 2 x 8 in - for
three miles, etc. An object of these respective
heights would be just hidden at these distances.
APPARENT AND REAL MOTION. In endeavoring to
understand the various appearances of the heavenly
bodies, it is well to remember how in daily life we
transfer motion. On the cars, when in rapid move-
ment, the fences and trees seem to glide by us,
there, it would never be able to climb up the side of the earth
and get back again. How can a ship sail up hill ?"
* The histoiy of aeronautic adventure affords a curious illustra-
tion of this same principle. The late Mr. Sadler, the celebrated
aeronaut, ascended on one occasion in a balloon from Dublin,
and was wafted across the Irish Channel, when, on his approach
to the Welsh coast, the balloon descended nearly to the surface
of the sea. By this time the sun was set, and the shades of even-
ing began to close in. He threw out nearly all his ballast, and
suddenly sprang upward to a great height, and by so doing
brought his horizon to dip below the sun, producing the whole
phenomenon of a western sunrise. Subsequently descending in
Wales, he, of course, witnessed a second sunset on the same
evening.
100 THE SOLAR SYSTEM.
while we sit still and watch them pass. On a
bridge, when we are at rest, we follow the undula-
tions of the waves, until at last we come to think
that they are stationary and we are sweeping down
stream. "In the cabin of a large vessel going
smoothly before the wind on still waterj or drawn
along a canal, not the smallest indication acquaints
us with the ' way it is making.' We read, sit,
walk, as if we were on land. If we throw a ball
into the air, it falls back into our hand ; if we drop
it, it alights at our feet. Insects buzz around us
as in the free air, and smoke ascends in the same
manner as it would do in an apartment on shore.
If, indeed, we come on deck, the case is in some
respects different ; the air, not being carried along
with us, drifts away smoke and other light bodies
such as feathers cast upon it, apparently in the
opposite direction to that of the ship's progress ;
but in reality they remain at rest, and we leave
them behind in the air."*
DIURNAL EEVOLUTION OF THE EARTH AROUND ITS
Axis. The earth, in constantly turning from west
* " And what is the earth itself but the good ship we are sailing
in through the universe, bound round the sun ; and as we sit
here in one of the ' berths,' we are unconscious of there being
any 'way' at all upon the vessel. On deck, too, out in the open
air, it's all the same as long as we keep our eyes on the ship;
but immediately we look over the sides and the horizon is but
the 'gunwale' of our vessel we see the blue tide of the great
ocean around us go drifting by the ship, and sparkling with its
million stars as the waters of the sea itself sparkle at night be-
tween the tropics "
THE EARTH. '101
to east, elevates our horizon above the stars on
the west, and depresses it below the stars on the
east. As the horizon appears to us to be sta-
tionary, we assign the motion to the stars, think-
ing those on the west whichjit pajsses 6vei> and
hides to have sunk belo^.it or
those on the east it has.
moved above it or risen. So, also, the horizon is
depressed below the sun, and we call it sunrise;
it is elevated above the sun, and we call it sunset.
We thus see that the diurnal movement of the sun
by day and stars by night is a mere optical delu-
sion that here as elsewhere we simply transfer
motion. This seems easy enough for us to under-
stand, because the explanation makes it so simple ;
but it was the " stone of stumbling" to ancient as-
tronomers for two thousand years. Copernicus him-
self, it is said, first thought of the true solution while
riding on a vessel and noticing how he insensibly
transferred the movement of the ship to the objects
on the shore. How much grander the beautiful
simplicity of this theory than the cumbersome com-
plexity of the old Ptolemaic belief !
Diurnal motion of the Sun. The explanation
just given illustrates the apparent motion of the
sun, and the cause of day and night. Suppose S to
be the sun. E, the earth, turning upon its axis
EF from west to east, has half its surface only illu-
minated at one time by the sun. To a person at
D, the sun is in the horizon and day commences,
102
THE SOLAR SYSTEM.
the luminary appearing to rise higher and higher
in the heavens with a westerly motion, as the ob-
server is carried forward easterly by the earth's
diurnal rotation to A, where he has the sun in his
i
f>. t -Vjxrt
DAILY MOTION OP THE BUN.
meridian, and it is consequently noon. The sun
then begins to decline in the sky until the specta-
tor arrives at B, where it sets, or is again in the
horizon on the west side, and night begins. He
moves on to C, which marks his position at midnight,
the sun being then on the meridian of places on
the opposite part of the earth, and he is then brought
round again to D, the point of sunrise, when another
day commences. (Hind.)
The unequal rate of diurnal motion. Different
points upon .the surface of the earth revolve with
different velocities. At the two poles the speed of
rotation is nothing, while at the equator it is great-
est, or over 1,000 miles per hour. At Quito, the
circle of latitude is much longer than one at the
mouth of the St. Lawrence, and the velocities vary
in the same proportion. The former place moves
THE EABTH. 103
at the rate of about 1,038 miles per hour ; the lat-
ter, 450 miles. In our latitude (41) the speed is
about 780 miles per hour. We do not perceive
this wonderful velocity with which we are flying
through the air, because the air moves with
us.* Yet were the earth suddenly to stop its
rotation, the terrible shock would, without doubt,
destroy the entire race of man, and we, with houses,
trees, rocks, and even the oceans, in one confused
mass, would be hurled headlong into space. On
the other hand, were the rate of rotation to increase,
the length of the day would be proportionately short-
ened, and the weight of all bodies decreased by the
centrifugal force thus produced. Indeed, if the
rotary movement should become swift enough to
* An ingenious inventor once suggested that we should utilize
the earth's rotation, as the most simple and economical, as well
as rapid mode of locomotion that could be conceived. This was
to be accomplished by rising in a balloon to a height inacces-
sible to aerial currents. The balloon, remaining immovable in
this calm region, would simply await the moment when the
earth, rotating underneath, would present the place of destination
to the eyes of travellers, who would then descend. A well-
regulated watch and an exact knowledge of longitudes would
thus render travelling possible from east to west, all voyages
north or south naturally being interdicted. This suggestion has
only one fault ; it supposes that the atmospheric strata do not
revolve with the earth. Upon that hypothesis, since we rotate
in our latitude with the velocity of 333 yards hi a second, there
would result a wind in the contrary direction ten times more
violent than the most terrible hurricane. Is not the absence of
such a state of things a convincing proof of the participation of
the atmospheric envelope in the general movement ? (Guillemin.)
104
THE SOLAR SYSTEM.
reduce the day to 84 minutes, or about ^\ its pres-
ent length, the force of gravity would be overcome,
and, at the equator, all bodies would be without
weight; if the speed were still further increased,
loose bodies would fly off from the earth like water
from a grindstone when swiftly turned, while we
should be compelled to constantly "hold on" to
avoid sharing the same fate. But against such a
catastrophe we are assured by the immutability of
God's laws. " He is the same yesterday, to-day,
and forever." The earth has not varied in its revo-
lution T -jj of a second in 2,000 years.
Unequal diurnal orbits of the stars. Let O repre-
sent our position on the earth's surface, E Z B our
meridian ; E I B K our horizon ; P and P' the north
THE EARTH. 105
and south poles, Z the zenith, Z' the nadir; and
GICK the celestial equator. Now PB, it will be
seen, is the elevation of the north pole above the
horizon, or the latitude of the place. Suppose we
should see a star at A, on the meridian below the
pole. The earth revolves in the direction GIG; the
star will therefore move along A L to Z, when it is
on the meridian above the pole. It continues its
course along the dotted line around to A again, when
it is on the meridian below the pole, having made a
complete circuit around the pole, but not having
descended below our horizon. A star rising at B
would just touch the horizon ; one at I would move
on the celestial equator, and would be above the
horizon as long time as it is below twelve hours in
each case ; a star rising at M, would just come above
the horizon and set again at N.
Unequal diurnal velocities of the stars. The stars
appear to us to be set in a concave shell which ro-
tates daily about the earth. As different parts of
the earth really revolve with varying velocities, so
the stars appear to revolve at different rates of speed.
Those near the pole, having a small orbit, revolve
very slowly, while those near the celestial equator
move at the greatest speed.
Appearance of the stars' at different places on the
earth. Were we placed at the north pole, Polaris
would be directly overhead, and the stars would
seem to pass around us in circles parallel to the
horizon, and increasing in diameter from the upper
5*
106 THE SOLAR SYSTEM.
to lower ones. Were we placed at the equator, the
pole-star would be at the horizon, and the stars
would move in circles exactly perpendicular to the
horizon, and decreasing in diameter, north and south
from those in the zenith, while we could see one
half of the path of each star. Were we placed in the
southern hemisphere, the circumpolar stars would
rotate about the south pole, and the others in cir-
cles resembling those in our sky, only the points of
direction would be reversed to correspond with the
pole. Were we placed at the south pole, the ap-
pearance would be the same as at the north pole,
except that there is no star to mark the direction of
the earth's axis.
MOTION OF THE EARTH IN SPACE ABOUT THE SUN.
The earth revolves in an elliptical path about the
sun at a mean distance of 91 \ million of miles. This
path is called the ecliptic ; its eccentricity, which is
greater than that of the orbit of Venus, changes
about j-oo~f oTo P er cen tury, so that in time the orbit
would become circular, were it not that after the
lapse of some thousands of years, the eccentricity
will begin to increase again, and will thus vary
through all ages within definite, although yet un-
determined limits. Its entire circumference is near-
ly 600,000,000 miles, and the earth pursues this
wonderful journey at the rate of 18 miles per second.
This revolution of the earth about the sun gives rise
to various phenomena, of which we shall now proceed
to speak.
THE EARTH. 107
1. Change in the appearance of the heavens in differ-
ent months. This is the natural result of the revolu-
tion of the earth about the sun. In Fig. 30, suppose
Fig. 30.
APPEARANCE OF THE HEAVENS IN DIFFERENT SEASONS.
A B C D to be the orbit of the earth, and E F G
H the sphere of the fixed stars, surrounding the
sun in every direction. When our globe is at A, the
stars about E are on the meridian at midnight.
Being seen from the earth in the opposite quarter
108 THE SOLAR SYSTEM.
to the sun, they are most favorably placed for obser-
vation. The stars at G, on the contrary, will be invisible,
for the sun intervenes between them and the earth :
they are on the meridian of the spectator about the
same time as the sun, and are always hidden in his
rays. In three months the earth has passed over
one-fourth of her orbit, and has arrived at B. Stars
about F now appear on the meridian at midnight,
while those at E, which previously occupied their
places, have descended toward the west and are
becoming lost in the sun's refulgence, while those
about G are just coming into sight in the east. In
three months more the earth is situated at C, and
stars about G shine in the midnight sky, those at F
having, in their turn, vanished in the west. Stars
at E are on the meridian at noon, and consequently
hidden in daylight ; and those about H are just
escaping from the sun's rays, and commencing their
appearance in the east. One revolution of the
earth brings the same stars again on the meridian
at midnight. Thus it is that the earth's motion
round the sun as a centre explains the varied aspect
of the heavens in the summer and winter skies.
(Hind.)
2. Yearly path of the sun through the heavens. We
have spoken of the diurnal motion of the sun. "We
now speak of its second apparent motion its yearly
path among the stars.* If we look at the accom-
* This yearly movement of the sun among the fixed stars is
not as apparent to us as his daily motion, because his superior
THE EARTH. 109
panying plate (Fig. 31), we can see how the motion
of the earth in its orbit is also transferred to the
sun, and causes him to appear to us to travel in a
fixed path through the heavens. When the earth is
in any part of the ecliptic, the sun seems to us to be
in the point directly opposite. For example, when
the earth is in Libra (==)* autumnal equinox the
sun is in Aries (T) vernal equinox; when the sun
enters the next sign, Taurus (), the earth in fact
has passed on to Scorpio (^). Thus as the earth
moves through her orbit, the sun seems to pass
through the same path along the opposite side of the
ecliptic, making the entire circuit of the heavens in
the year, and returning at the end of that time to the
same place among the stars. If the earth could leave
a shining line as it passes through its orbit about the
sun, we should see the sun apparently moving along
this same line on the opposite side of the circle.
We therefore define the ecliptic as the real orbit of
the earth about the sun, or the apparent path of the sun
through the heavens. The ecliptic crosses the celes-
tial equator at two points. These are called the
light blots out the stars. But if we notice a star at the western
horizon just at sunset, we can tell what constellation the sun is
then hi : now wait two or three nights, and we shall find that star
is set, and another has taken its place. Thus we can trace the
sun through the year in his path among the fixed stars.
* When we say " the earth is hi Libra," we mean that a spec-
tator placed at the sun would see the earth hi that part of the
heavens which is occupied by the sign Libra.
110 THE SOLAR SYSTEM.
3. An apparent movement of the sun, north and
south. Having now spoken of the apparent diurnal
and annual motions of the sun, there yet remains a
third motion, which has doubtless oftentimes at-
tracted our attention. In summer, at midday, the
sun is high in the heavens ; in the winter, quite low,
near the southern horizon. In summer he is a long
time above the horizon ; in the winter, a short time.
In summer he rises and sets north of the east and
west points ; in winter, south of the east and west
points. This subject is so intimately connected with
the next, that we shall understand it best when taken
in connection with it.
4. CHANGE OF THE SEASONS. VARIATION IN LENGTH
OF DAY AND NIGHT. By closely studying the accom-
panying illustration and imagining the various posi-
tions of the earth in its orbit, let us try to under-
stand the several points.
I. Obliquity of the ecliptic. The axis of the earth
is inclined 23J from a perpendicular to its orbit.
This angle is called the obliquity of the ecliptic.
II. Parallelism of the axis. In all parts of the
orbit, the axis of the earth is parallel to itself and
constantly points toward the North Star.* This is
only an instance of what is very familiar to us all.
Nature reveals to us nothing more permanent than
the axis of rotation in anything that is rapidly
turned. It is its rotation which keeps a boy's hoop
* There is a slight variation from this, which we shall soon
notice.
THE EARTH.
Fig. 31.
Ill
THB ORBIT OF THE EABTH-
112 THE SOLAR SYSTEM.
from falling. For the same reason a quoit retains
its direction when whirled, and it will keep in the
same plane at whatever angle it may be thrown.
A man slating a roof wishes to throw a slate to the
ground ; he simply whirls it, and as it descends it
will strike on the edge without breaking. As long
as a top spins there is no danger of its falling,
since its tendency to preserve parallel its axis of
rotation is greater than the attraction of the earth.
This wonderful law would lead us to think that
the axis of the earth always points in the same
direction, even if we did not know it from direct
observation.
III. TJie rays of the sun strike the various por-
tions of the earth, when in any position, at different
angles. Example. "When the earth is in Libra, and
also when in Aries, the rays strike vertically at the
equator, and more and more obliquely in the northern
and southern hemispheres, as the distance from the
equator increases, until at the poles they strike
almost horizontally. This variation in the direction
of the rays produces a corresponding variation in
the intensity of the sun's heat and light at dif-
ferent places, and accounts for the difference between
the torrid and polar regions.
IV. As the earth changes its position the angle at
which the rays strike any portion is varied. Ex-
ample. Take the earth as it enters Capricornus
(\s) and the sun in Cancer () He is now over-
head, 23J north of the equator. His rays strike
THE EARTH. 113
less obliquely in tire northern hemisphere than
when the earth was in Libra. Let six months
elapse : the earth is now in Cancer and the sun in
Capricornus; and he is overhead, 23J south of
the equator. His rays strike less obliquely in the
southern hemisphere than before, but in the northern
hemisphere more obliquely. These six months have
changed the direction of the sun's rays on every
part of the earth's surface. This accounts for the dif-
ference in temperature between summer and winter.
V. The Equinoxes. At the equinoxes one half
of each hemisphere is illuminated : hence the
name Equinox (cequus, equal, and nox, night). At
these points of the orbit the days and nights are
equal over the entire earth,* each being twelve
hours in length.
VI. Northern and southern hemispheres unequally
illuminated. While one half of the earth is con-
stantly illuminated, at all points in the orbit except
the equinoxes the proportion of the northern or
southern hemisphere which is in daylight or dark-
ness varies. When more than half of a hemi-
sphere is in the light, its days are longer than
the nights, and vice versa.
VII. The seasons and the comparative length of
days and nights in the South Temperate Zone, at any
specified time, are the reverse of those in the North
Temperate Zone, except at the Equinoxes, where the
days and nights are of equal length.
* Except a small space at each pole.
114 THE SOLAB SYSTEM.
VIII. The earth at the Summer Solstice. When
the earth is at the summer solstice, about the
21st of June, the sun is overhead 23J north of the
equator, and if its vertical rays could leave a gold-
en line on the surface of the earth as it revolves, they
would mark the Tropic of Cancer. The sun is at
its furthest northern declination, ascends the high-
est it is ever seen above our horizon, and rises and
sets 23 J north of the east and west points. It seems
now to stand still in its northern and southern course,
and hence the name Solstice (sol, the sun, sto, to
stand). The days in the north temperate zone
are longer than the nights. It is our summer, and
the 21st of June is the longest day of the year. In
the south temperate zone it is winter, and the
shortest day of the year. The circle that sepa-
rates day from night extends 23^ beyond the
north pole, and if the sun's rays could in like manner
leave a golden line on that day, they would trace
on the earth the Arctic Circle. It is the noon of
the long six months polar day. The reverse is
true at the Antarctic Circle, and it is there the
midnight of the long six months polar night.
IX. The earth at the Autumnal Equinox. The
earth crosses the aphelion point the 1st of July,
when it is at its furthest distance from the sun,
which is then said to be in apogee. The sun each
day rising and setting a trifle farther toward the
south, passes through a lower circuit in the heavens.
We reach the autumnal equinox the 22d of Sep-
THE EABTH. 115
tember. The sun being now on the equinoctial, if
its vertical rays could leave a line of golden light,
they would -mark on the earth the circle of the
equator. It is autumn in the north temperate zone
'and spring in the south temperate zone. The days
and nights are equal over the whole earth, the sun
rising at 6 A. M. and setting at 6 p. M., exactly in the
east and west where the equinoctial intersects the
horizon.
X. The earth at the Winter Solstice. The sun
after passing the equinoctial "crossing the line,"
as it is called sinks lower toward the southern ho-
rizon each day. We reach the winter solstice the
21st of December. The sun is now directly overhead
23J south of the equator, and if its rays could
leave a line of golden light they would mark on
the earth's surface the Tropic of Capricorn. It
is at its furthest southern declination, and rises and
sets 23J south of the east and west points. It
is our winter, and the 21st of December is the short-
est day of the year. In the south temperate
zone it is summer, and the longest day of the
year. The circle that separates day from night
extends 23J beyond the south pole, and if the sun's
rays in like manner could leave a line of golden light
they would mark the Antarctic Circle. It is there
the noon of the long six months polar day. At
the Arctic Circle the reverse is true ; the rays fall
23| short of the north pole, and it is there the
midnight of the long six months polar night. Here
116 THE SOLAR SYSTEM.
again the sun appears to us to stand still a day
or two before retracing its course, and it is there-
fore called the Winter Solstice.
XI. The earth at the Vernal Equinox. The earth
reaches its perihelion about the 31st of December.
It is then nearest the sun, which is therefore said
to be in perigee. The sun rises and sets each day
further and further north, and climbs up higher
in the heavens at midday. Our days gradually
increase in length, and our nights shorten in the
same proportion. On the 21st of March* the sun
reaches the equinoctial, at the vernal equinox. He
is overhead at the equator, and the days and nights
are again equal. It is our spring, but in the south
temperate zone it is autumn.
XII. The yearly path finished. The earth moves
on in its orbit through the spring and summer
months. The sun continues its northerly course,
ascending each day higher in the heavens, and its
rays becoming less and less oblique. On the 21st
of June it again reaches its furthest northern decli-
nation, and the earth is at the summer solstice. We
have thus traced the yearly path, and noticed the
course of the changing seasons, with the length of
the days and nights. The same series has been
repeated through all the ages of the past, and will
be till time shall be no more.
XIII. Distance of the earth from the sun varies.
* The precise time of the equinoxes and solstices varies each
year, but within a small limit.
THE EARTH. 117
We notice, from what we have just seen, that we. are
nearer the sun by 3,000,000 miles in winter than in
summer. The obliqueness with which the rays
strike the north temperate zone at that time pre-
vents our receiving any special benefit from this
favorable position of the earth.
XIV. Southern summer. The inhabitants of the
south temperate zone have then: summer while the
earth is in perihelion, and the sun's rays are about
^warmer than when in aphelion, our summer-time.
This will perhaps partly account for the extreme heat
of their season. Herschel tells us that he has found
the temperature of the surface soil of South Africa
159 F. Captain Sturt, in speaking of the extreme
heat of Australia, says that matches accidentally
dropped on the ground were immediately ignited.
The southern winters, for a similar reason, are
colder ; and this makes the average yearly tempera-
ture about the same as ours.
XV. Extremes of heat and cold not at the solstices.
We notice that we do not have our greatest heat at
the time of the summer solstice, nor our greatest
cold at the winter solstice. After the 21st of June,
the earth, already warmed by the genial spring
days, continues to receive more heat from the sun
by day than it radiates by night : thus its tempera-
ture still increases. On the other hand, after the
21st of December the earth continues to become
colder, because it loses more heat during the night
than it receives during the day.
118 THE SOLAR SYSTEM.
XYI. Summer longer than winter. As the sun is
not in the centre of the earth's orbit, but at one
of its foci, that portion of the orbit which the earth
passes through in going from the vernal to the
autumnal equinox comprises more than one-half the
entire ecliptic. On this account the summer is
longer than the winter. The difference is still fur-
ther enhanced by the variation in the earth's ve-
locity at aphelion and perihelion. The annexed
table gives the mean duration of the seasons :
Seasons. Days. Seasons. Days.
Spring 92.9 Autumn 89.7
Summer .93.6 Winter 89.0
The difference of time in the earth's stay in the
two portions of the ecliptic, as will be seen from the
above, is 7.8 days.
XVII. Varying velocity of the earth. We can see,
by looking at the plate, that the velocity of the
earth must vary in different portions of its orbit.
When passing from the vernal equinox to aphelion,
the attraction of the sun tends to check its speed ;
from that point to the autumnal equinox, the at-
traction is partly in the direction of its motion,
and so increases its velocity. The same principle
applies when going to and from perihelion.
XVIII. Curious appearance of the sun at the north
pole. " To a person standing at the north pole, the
sun appears to sweep horizontally around the sky
every twenty-four hours, without any perceptible
THE EABTH. 119
variation in its distance from the horizon. It is,
however, slowly rising, until, on the 21st of June, it
is twenty-three degrees and twenty-eight minutes
above the horizon, a little more than one-fourth of
the distance to the zenith. This is the highest point
it ever reaches. From this altitude it slowly de-
scends, its track being represented by a spiral or
screw with a very fine thread i and in the course of
three months it worms its way down to the horizon,
which it reaches on the 22d of September. On this
day it slowly sweeps around the sky, with its face
half hidden below the icy sea. It still continues to
descend, and after it has entirely disappeared it is
still so near the horizon that it carries a Bright
twilight around the heavens in its daily circuit. As
the sun sinks lower and lower, this twilight grows
gradually fainter, till it fades away. December 21st,
the sun is 23 28' below the horizon, and this is the
midnight of the dark polar winter. From this date
the sun begins to ascend, and after a time it is her-
alded by a faint dawn, which circles slowly around
the horizon, completing its circuit every twenty-four
hours. This dawn grows gradually brighter, and
on the 22d of March the peaks of ice are gilded
with the first level rays of the six months day. The
biinger of this long day continues to wind his spiral
way upward, till he reaches his highest place on the
21st of June, and his annual course is completed."
XIX. Results, if the axis of the earth were perpen-
dicular to the ecliptic. The sun would then always
120 THE SOLAK SYSTEM.
appear to move through the equinoctial. He would
rise and set every day at the same points on the
horizon, and pass through the same circle in the
heavens, while the days and nights would be equal
the year round. There would be near the equator a
fierce torrid heat, while north and south the climate
would melt away into temperate spring, and, lastly,
into the rigors of a perpetual winter.
XX. Results, if the equator of the earth were perpen-
dicular to the ecliptic. Were this the case; to a spec-
tator at the equator, as the earth leaves the vernal
equinox, the sun would each day pass through a
smaller circle, until at the summer solstice he would
reach the north pole, when he would halt for a time
and then slowly return in an inverse manner.
In our own latitude, the sun would make his
diurnal revolutions in the way we have just de-
scribed, his rays shining past the north pole fur-
ther and further, until we were included in the
region of perpetual day, when he would seem to
wind in a spiral course up to the north pole, and
then return in a descending curve to the equator.
PKECESSION OF THE EQUINOXES. We have spoken
of the equinoxes as if they were stationary in the
orbit of the earth. Over two thousand years ago,
Hipparchus found that they were falling back along
the ecliptic. Modern astronomers fix the rate at
about 50" of space annually. If we mark either point
in the ecliptic at which the days and nights are equal
over the earth, which is where the plane of the earth's
THE EARTH. 121
equator passes exactly through the centre of the
sun, we shall find the earth the next year comes
back to that position 50" (20 m. 20 s. of time) earlier.
This remarkable effect is called the Precession of the
Equinoxes, because the position of the equinoxes in
any year precedes that which they occupied the year
before. Since the circle of the ecliptic is divided
into 360, it follows that the time occupied by the
equinoctial points in making a complete revolution
at the rate of 50.2" per year is 25,816 years.
Results of tlie Precession of the Equinoxes. In Fig.
31, we see that the line of the equinoxes is not
at right angles to the ecliptic. In order that the
plane of the terrestrial equator should pass through
the sun's centre 50" earlier, it is necessary that the
plane itself should slightly change its place. The
axis of the earth is always perpendicular to this
plane, hence it follows that the axis is not rigorously
parallel to itself. It varies in direction, so that the
north pole describes a small circle in the starry
vault twice 23 28' in diameter. To illustrate this,
in the cut we suppose that after a series of years the
position of the earth's equator has changed from efh
to g K 1. The inclination of the axis of the earth, C P,
to CQ, the pole of the ecliptic, remains unchanged ; but
as it must turn with the equator, its position is moved
from CP to OP', and it passes slowly around through
a portion of a circle whose centre is C Q. The direc-
tion of this motion is the same as that of the hands
of a watch, or just the reverse of that of the revolution
a
122
THE SOLAR SYSTEM.
of the earth itself. The position of the north pole in
the heavens is therefore gradually but almost insen-
sibly changing. It is now distant from the north
polar star about 1J. It will continue to approach
CHANGE OF EARTH'S EQUATOR AND AXIS.
it until they are not more than half a degree apart.
In 12,000 years Lyra will be our polar star : 4,50C
years ago the polar star was the bright star in the
constellation Draco. As the right ascension of the
stars is reckoned eastward from the vernal equinox
along the equinoctial, the precession of the equinoxes
increases the E. A. of the stars 50" per year. On
this account, star maps must be accompanied by the
date of their calculations, that they may be corrected
to correspond with this annual variation. The con-
stellations are fixed in the heavens, while the signs of
THE EARTH. 123
the zodiac are not ; they are simply abstract divisions
of the ecliptic which move with the equinox. When
named, the sun was in both the sign and constellation
Aries, at the time of the vernal equinox ; but since
then the equinoxes have retrograded nearly a whole
sign, so that now while the sun is in the sign Aries
on the ecliptic, it corresponds to the constellation
Pisces in the heavens. Pisces is therefore the first
constellation in the zodiac. (See Fig. 72.)
Causes of the Precession of the Equinoxes. Before
commencing the explanation of this phenomenon, it
is necessary to impress upon the mind a few facts.
1. The earth is not a perfect sphere, but is swollen
at the equator. It is like a perfect sphere covered
with padding, which increases constantly in thick-
ness from the poles to the equator ; this gives it a
turnip-like shape. 2. The attraction of the sun is
INFLUENCE OF THE SUN ON A MOUNTAIN NEAR THE EQUATOR.
greater the nearer a body is to it. 3. The attraction
is not for the earth as a mass, but for each particle
separately. In the figure, the position of the earth
124 THE SOLAR SYSTEM.
at the time of the winter solstice is represented,
P is the north pole, a b the ecliptic, C the centre
of the earth, C Q a line perpendicular to the eclip-
tic, so that the angle QCP equals the obliquity
of the ecliptic. In this position the equatorial pad-
ding we have spoken of the ring of matter about
the equator is turned, not exactly toward the
sun, but is elevated above it. Now the attraction
of the sun pulls the part D more strongly than
the centre ; the tendency of this is to bring D
down to a. In the same way the attraction for C is
greater than for I, so it tends to draw C away from
I, and as at the same time D tends toward a, to pull
I up toward b. The tendency of this, one would
think, would be to change the inclination of the axis
C P toward C Q, and make it more nearly perpendic-
ular to the ecliptic. This would be the result if the
earth were not revolving upon its axis. Let us con-
sider the case of a mountain near the equator. This,
if the sun did not act upon it, would pass through
the curve H D E in the course of a semi-revolution of
the earth. It is nearer the sun than the centre C is ;
the attraction therefore tends to pull the mountain
downward and tilt the earth over, as we have just
described; so the mountain will pass through the
curve H/V/, and instead of crossing the ecliptic at E
it will cross at g a little- sooner than it otherwise
would. The same influence, though in a less degree,
obtains on the opposite side of the earth. The
mountain passes around the earth in a curve nearer
THE EARTH.
125
to b, and crosses the ecliptic a little earlier. The
same reasoning will apply to each mountain and tc
all the protuberant mass near the equatorial regions.
The final effect is to turn slightly the earth's equator
so that it intersects the ecliptic sooner than it would
were it not for this attraction. At the summer sol-
stice the same tilting motion is produced. At the
equinoxes the earth's equator passes directly through
the centre of the sun, and therefore there is no ten-
dency to change of position. As the axis C P must
move with the equator, it slowly revolves, keeping
its inclination unchanged, around C Q, the pole of
the ecliptic, describing, in about 26,000 years, a
small circle twice 23 28' in diameter.
Precession illustrated in the spinning of a top. This
motion of the earth's axis is most singularly illus-
trated in the spinning
of a top, and the more
remarkably because
there the forces are of
an opposite character to
those which act on the
earth, and so produce
an opposite effect. "We
have seen that if the
earth had no rotation, the
sun's attraction on the
" padding" at the equator would bring C P nearer
to C Q, but that in consequence of this rotation tho
effect really produced is that CP, the earth's axis,
SPINNING OP A TOP.
126 THE SOLAR SYSTEM.
slowly revolves around C Q, the pole of the heavens, in
a direction opposite to that of rotation.
In Fig. 34, let C P be the axis of a spinning top,
and C Q the vertical line. The direct tendency of
the earth's attraction is to bring C P further, from
C Q (or to make the top fall), and if the top were
not spinning this would be the result; but in
consequence of the rotary motion the inclination
does not sensibly alter (until the spinning is retarded
by friction), and so C P slowly revolves around C Q
in the same direction as that of rotation.
NUTATION (nutatio, a nodding). "We have noticed
the sun as producing precession ; the moon has,
however, treble its influence ; for although her mass
is not s-ff.info.TnnF P art tnat f tne sun > J et sne * s 400
times nearer and her effect correspondingly greater.
(See p. 168.) The moon's orbit does not He par-
allel to the ecliptic, but is inclined to it. Now
the sun attracts the moon, and disturbs it as he
would the path of the mountain we have just sup-
posed, and the effect is the same viz., the intersec-
tions of the moon's orbit with the ecliptic travel
backward, completing a revolution in about 18
years. During half of this time the moon's orbit is
inclined to the ecliptic in the same way as the
earth's equator ; during the other half it is inclined
in the opposite way. In the former state, the
moon's attractive tendency to tilt the earth is very
small, and the precession is slow ; in the latter, the
tendency is great, and precession goes on rapidly.
PATH OF THE NORTH POLE
THE EARTH. 127
The consequence of this is, that the pole of the
earth is irregularly shifted, so
that it travels in a slightly
curved line, giving it a kinti of
"wabbling" or " nodding" mo-
tion, as shown though greatly
exaggerated in Fig. 35. The
obliquity of the ecliptic, which
we consider 23 28', is the mean
of the irregularly curved line IN THB HEAVENS.
and is represented by the dotted circle.
Periodical change in the obliquity of the ecliptic.
Although it is sufficiently near for all general pur-
poses to consider the obliquity of the ecliptic invari-
able, yet this is not strictly the case. It is subject
to a small but appreciable variation of about 46"
per century. This is caused by a slow change of
the position of the earth's orbit, due to the attraction
of the planets. The effect of this movement is to
gradually diminish the inclination of the earth's
equator to the ecliptic (the obliquity of the ecliptic).
This will continue for a time, when the angle will as
gradually increase ; the extreme limit of change
being only 1 21'. The orbit of the earth thus
vibrates backward and forward, each oscillation
requiring a period of 10,000 years. This change
is so intimately blended, in its effect upon the
obliquity of the ecliptic, with that caused by pre-
cession and nutation, that they are only separable
in theory ; in point of fact, they all combine to
128 THE SOLAR SISTEM.
produce the waving motion we have already de-
scribed. As a consequence of this variation in the
obliquity of the ecliptic, the sun does not come as
far north nor decline as far south as at the Creation,
while the position of all the terrestrial circles
Tropic of Cancer, Capricorn, Arctic, etc. is con-
stantly but slowly changing. Besides this, it tends
to vary slightly the comparative length of the
days and nights, and, as the obliquity is now dimin-
ishing, to equalize them. As the result of this vari-
ation in the position of the orbit, some stars which
were formerly just south of the ecliptic are now
north of it, and others that were just north are now
a little further north ; thus the latitude of these
stars is gradually changing.
Change in tlie major axis (line of apsides) of the
earth's orbit. Besides all the changes in the posi-
tion of the earth in its orbit due to precession, the
line connecting the aphelion and perihelion points
of the orbit itself is slowly moving. The conse-
quence of this is a variation in the length of the
seasons at different periods of time. In the year
4089 B. c., about the supposed epoch of the crea-
tion, the earth was in perihelion at the autumnal
equinox, so that the summer and autumn seasons
were of equal length, but shorter than the winter
and spring seasons, which were also equal.* In the
* There is much discrepancy in the views held concerning the
Great Year of the astronomers, as it is often called. (See 14
Weeks in Geology, pp. 272-3, note.) The statement given in the
text is that held by Lockyer, Hind and others. The terms, it
THE EAETH. 129
year 1250 A. D., the earth was in perihelion when it
was at the winter solstice, December 21, instead of
January 1st, as now ; the spring quarter was there-
fore equal to the summer one, and the autumn
quarter to the winter one, the former being the
longer. In the year 6589 A. D., the earth will be in
perihelion when it is at the vernal equinox ; summer
will then be equal to autumn and winter to spring,
the former seasons being the longer. In the year
11928 A. D., the earth will be in perihelion when it
is at the summer solstice : finally, in 17267 A. D., the
cycle will be completed, and for the first time since
the creation of man the autumnal equinox will co-
incide with the earth's perihelion.
PEBMANENCE IN THE MIDST OF CHANGE. "We thus
see that the ecliptic is constantly modifying its ellip-
tical shape ; that the orbit of the earth slowly oscil-
lates upward and downward ; that the north pole
steadily turns its long index-finger over a dial that
marks 26,000 years ; that the earth, accurately
poised in space, yet gently nods and bows to the
attraction of sun and moon. Thus changes are con-
tinually taking place that would ultimately entirely
reverse the order of nature. But each of these has
its bounds, beyond which it cannot pass. The
promise made to man after the Deluge, is that
" while the earth remaineth, seed-time and harvest,
and cold and heat, and summer and winter, and
should be noticed, are applied to the real position of the earth
and not the apparent position of the sun. The dates are those
given by Chambers in his Descriptive Astronomy.
130
THE SOLAR SYSTEM.
day and night shall not cease." The modern dis-
coveries of astronomy prove conclusively that the
seasons are to be permanent ; that the Creator,
amid all these transitions, has ordained the means
of carrying out His promise through all time.
EEFEACTION. The atmosphere extends above the
earth about 500 miles. Near the surface it is
dense, while in the upper regions it is exceedingly
rare. The rays of light from the heavenly bodies
Fig. 36.
REFRACTION.
passing through these different layers are turned
downward toward a perpendicular more and more
as the density increases. According to a well-
known law of optics, if the ray of light from a star
were bent in fifty directions before entering the eye,
the star would nevertheless appear to be in the line
of the one nearest the eye. The effect of this is,
that the apparent place of a heavenly body is higher
THE EARTH.
131
than the true place. This is illustrated in Fig. 36.
The sun at S, were it not for the atmosphere, would
send a direct ray to L. Instead, the ray at A is
refracted downward, and would then enter the eye
at N ; passing, however, through a layer of a differ-
ent density, at B it is again bent, and meets the eye
of the observer at C. He sees the sun, not in the
direction of the curved line C B A S, but that of the
straight line CBS.
The amount of refraction varies with the tempera-
ture, moisture, and other conditions of the atmos-
phere. It is zero for a body in the zenith, and
increases gradually toward the horizon (as the thick-
ness of the intervening atmosphere increases), where
it is about 33'.
Fig. 37.
Change of place and appearance of the sun and moan.
The sun may be really below the horizon, and yet
132 THE SOLAR SYSTEM.
seem to be above it. For example, on April 20,
1837, the moon was eclipsed before the sun had
set. The mean diameter of both the sun and moon
being rather less than 33', it follows that when
we see the lower edge of either of these lumina-
ries apparently just touching the horizon, in reality
the whole disk is completely beloiu it, and would
be altogether hidden were it not for the effect
of refraction. The day is consequently materially
lengthened.
The sun and moon often appear flattened when
near the horizon. This is easily accounted for on
the principle just stated. The rays from the lower
edge pass through a denser layer of the atmosphere,
and are therefore refracted about 4' more than those
from the upper edge : the effect of this is to make
the vertical diameter appear about 4' less than the
horizontal, and so distort the figure of the disk into
an oval shape.
The sun and moon often appear larger when near
the horizon than when high in the sky. This is not
caused by refraction, but is a mere error of judg-
ment. At the horizon we compare them with va-
rious terrestrial objects which lie between them and
us, while aloft we have no association to guide us,
and we are led to underrate their size. On looking
at them through a tube, the illusion disappears.
The moon should naturally appear largest when
at a great altitude, as it is then at a less distance
from us.
THE EARTH. 133
The dim and hazy appearance of the heavenly
bodies when near the horizon is caused not only by
the rays of light having to pass through a larger
space in the atmosphere, but also by their travers-
ing the lower and denser part. The intensity of the
solar light is so greatly diminished by passing
through the lower strata, that we are enabled to
look upon the sun at that time without being daz-
zled by his brilliant beams.
Twiliylit. The glow of light after sunset and
before sunrise, which we term ttvilight, is caused by
the refraction and reflection of the sun's rays by the
atmosphere. For a time after the sun has truly set,
the refracted rays continue to reach the earth ; but
when these have ceased, he still continues to illumi-
nate the clouds and upper strata of the air, just as
he may be seen shining on the summits of lofty
mountains long after he has disappeared from the
view of the inhabitants of the plains below. The
air and clouds thus illuminated reflect back part
of the light to the earth. As the sun sinks lower,
less light reaches us until reflection ceases and
night ensues. The same thing occurs before sun-
rise, only in reverse order. The duration of twilight
is usually reckoned to last until the sun's depres-
sion below the horizon amounts to 18 ; this, how-
ever, varies with the latitude, seasons, and condi-
tion of the atmosphere. Strictly speaking, in the
latitude of Greenwich there is no true night for a
month before and after the summer solstice, but
134 THE SOLAR SYSTEM.
constant twilight from sunset to sunrise. The sun
is then near the Tropic of Cancer, and does not
descend so much as 18 below the horizon during
the entire night. The twilight is shortest at the
equator and longest toward the poles, where the
night of six months is shortened by an evening
twilight of about fifty days and a morning one of
equal length.
Diffused light. The diffused light of day is pro-
duced in the same manner as that of twilight. The
atmosphere reflects and scatters the sunlight in
every direction. "Were it not for this, no object
would be visible to us out of direct sunshine ; every
shadow of a passing cloud would be pitchy dark-
ness ; the stars would be visible all day ; no window
would admit light except as the sun shone directly
through it, and a man would require a lantern to go
around his house at noon. This is illustrated very
clearly in the rarified atmosphere of elevated re-
gions, as on Mont Blanc, where it is said the glare
of the direct sunlight is almost insupportable ; the
darkness of the shadows is deeper and denser ; all
nice shading and coloring disappear; the sky has
a blackish hue, and the stars are seen at midday.
The blue light reflected to our eyes from the atmos-
phere above us, or more probably from the vapor in
the air, produces the optical delusion we call the
sky. Were it not for this, every time we cast our
eyes upward we should feel like one gazing over a
dizzy precipice ; while now the crystal dome of blue
THE EARTH. 135
smiles down upon us so lovingly and beautifully
that we call it heaven.
ABERRATION OF LIGHT. "We have seen that the
places of the heavenly bodies are apparently changed
by refraction. Besides this, there is another change
due to the motion of light, combined with the mo-
tion of the earth in its orbit. For example : the
mean distance of the earth from the sun is ninety-
one and a half millions of miles, and since light
travels 183,000 miles per second, it follows that the
time occupied by a ray of light in reaching us from
the sun is about 8-J min. ; so that, in point of fact,
when we look at the sun (1), we do not see it as
it is, but as it was SJmin. since. If our globe
were at rest, this would be well enough, but since
the earth is in motion, when the ray enters our eye
we are at some distance in advance of the position
we occupied when it started. During the SJmin.
the earth has moved in its orbit nearly 20^", so that
(2) we never see that luminary in the place it occu-
pies at the time of observation.
Illustration. Suppose a ball let fall from a point
P, above the horizontal line A B, and a tube, of
which A is the lower extremity, placed to receive it.
If the tube were fixed, the ball would strike it on
the lower side ; but if the tube were carried forward
in the direction A B, with a velocity properly ad-
justed at every instant to that of the ball, while pre-
serving its inclination to the horizon, so that when
the ball, in its natural descent, reached B, the tube
136
THE SOLAR SYSTEM.
would have been carried into the position BQ, it is
evident that the ball throughout its whole descent
would be found in the tube ; and a spectator refer-
ring to the tube the motion of the ball, and carried
Fig. 38.
ABERRATION OP LIGHT.
along with the former, unconscious of its motion,
would fancy that the ball had been moving in an
inclined direction, and had come from Q. A very
common illustration may be seen almost any rainy
day. Choose a time when the air is still and the
drops large. Then, if you stand still, you will .see
that the drops fall vertically ; but if you walk for-
ward, you will see the drops fall as if they were
meeting you. If, however, you walk backward, you
will observe that the drops fall as if they were com-
ing from behind you. We thus see that the drops
have an apparent as well as real motion
THE EAKTH. 137
The general effect of aberration of light is to cause
each star to apparently describe a minute ellipse in
the course of a year, the central point of which is
the place the star would actually occupy were our
globe at rest.
PARALLAX. This is tlie difference in the direction of
an object as seen from two different places. For a
simple illustration of it, hold your finger before you
Fig. 39.
PARALLAX.
in front of the window. Upon looking at it with
the left eye only, you will locate your linger at some
point on the window ; on looking with the right eye
only, you will locate it at an entirely different point.
Use your eyes alternately and quickly, and you will
138 THE SOLAR SYSTEM.
be astonished at the rate with which your finger
will seem to change its place. Now, the difference
in the direction of your finger as seen from the two
eyes is parallax.
In astronomical calculations, the position of a
body as seen from the earth's surface is called its
apparent place, while that in which it would be seen
from the centre of the earth is called its true
place. Thus, in the cut, a star is seen by the ob-
server at O in the direction OP ; if it could be
viewed from the centre R, its direction would be
in the line EQ. It is therefore seen from O at a
point in the heavens beloiu its position in reference
to R. From looking at the cut, we can see (1), that
the parallax of a star near the horizon is greatest,
while it decreases gradually until it disappears alto-
gether at the zenith, since an observer at O, as wel]
as one at R, would see the star Z directly overhead ;
and (2), that the nearer a body is to the earth the
greater its parallax becomes. It has been agreed
by astronomers, for the sake of uniformity in their
calculations, to correct all observations so as to refer
them to their true places as seen from the centre of
the earth. Tables of parallax are constructed for
this purpose. The question of parallax is also one
of very great importance, because as soon as the
parallax of a body is once accurately known, its dis-
tance, diameter, etc., can be readily determined. (See
Celestial Measurements.)
Horizontal Parallax. This is the parallax of
THE MOON. 139
a body when at the horizon. It is, in fact, the
earth's semi-diameter as seen from the body. In the
figure, the parallax of the star S is the angle OSR,
which is measured by the line OK the semi-diam-
eter of the earth. The sun's horizontal parallax
(8.94") is the angle subtended (measured) by the
earth's semi-diameter as seen from that luminary.
As the moon is nearest the earth, its horizontal par-
allax is the greatest of any of the heavenly bodies.
Annual Parallax. The fixed stars are so distant
from the earth that they exhibit no change of place
when seen from different parts of the earth. The
lines OS and US are so long that they are ap-
parently parallel, and it becomes impossible to
discover the slightest inclination. Astronomers,
therefore, instead of taking the earth's semi-diam-
eter, or 4,000 miles, as the measuring tape, have
adopted the plan of observing the position of the
fixed stars at opposite points in the earth's orbit.
This gives a change in place of 183,000,000 miles.
The variation of position which the stars under-
go at these remote points is called their annual
parallax.
THE MOON.
New Moon, . First Quarter, . Full Moon, . Last Quarter, >.
ITS MOTION IN SPACE. The orbit of the moon, con-
sidering the earth as fixed, is an ellipse of which our
planet occupies one of the foci. Its distance from
140
THE SOLAR SYSTEM.
the earth therefore, varies incessantly. At perigee
it is 26,000 miles nearer than in apogee : the mean
distance is about 238,000 miles. It would require a
chain of thirty globes equal in size to the earth to
reach the moon. An express-train would take about
a year to accomplish the journey. The moon com
pletes its revolution (sidereal) around the earth in
about 27i days ; but, as the earth is constantly pass-
Fig. 40.
PATH OP MOON.
ing on in its own orbit around the sun, it requires
over two days longer before it comes into the same
position with respect to the sun and earth, thus com-
pleting its synodic revolution.
THE MOON. 141
The real path of the moon is the result of its own
proper motion and the onward movement of the
earth. The two combined produce a wave-like
curve that crosses the earth's path twice each
month ; this, owing to its small diameter com-
pared with that of the ecliptic, is always concave
toward the sun. As the moon constantly keeps
the same side turned toward us, it follows that
it must turn on its axis once each month.
DIMENSIONS. Its diameter is about 2,160 miles.
It would require fifty globes the size of the moon to
equal the earth. Its apparent size varies with its
distance ; the mean is, however, about one half a
Pig. 41.
THE SIZE OP MOON AT HORIZON AND ZENITH.
degree, the same as that of the sun. It always ap-
pears larger than it really is, on account of its
brightness. This is the effect of what is termed in
optics Irradiation. To illustrate this principle, cut
two circular pieces of the same size, one of black
THE 80LAE SYSTEM.
/the other of white paper. The white circle,
en held in a bright light, will appear much larger
than the black one. For the same reason it is often
noticed that the crescent moon seems to be a part of
a larger circle than the rest of the moon. As we
have already said, the moon appears larger on the ho-
rizon than when high up in the sky. By an examina-
tion of the cut, it is easily seen that it is 4,000 miles
nearer when on the zenith than when at the horizon.
Besides these general variations in size, the moon
varies in apparent size to different observers. Much
amusement may be had in a large party or class by
a comparison of its apparent magnitude. The esti-
mates will differ from a small saucer to a wash-tub.
LIBKATIONS (librans, swinging). "While the moon
presents the same hemisphere to us, there are three
causes which enable us to see about 576 out of the
1,000 parts of its entire surface. (1.) The axis of
the moon is inclined a little to its orbit, as also its
orbit is inclined to the earth's orbit; so when its
north pole leans alternately toward and from the
earth, we see sometimes past its north, and some-
times past its south pole. This is called libration in
latitude. (2.) The moon's rotation on its axis is al-
ways performed in the same time, while its move-
ment along its orbit is variable ; hence it happens
that we occasionally see a little further around each
limb (outer edge) than at other times. This is called
libration in longitude. (3.) The size of the earth is
so much greater than that of the moon, that an ob-
THE MOON. 143
server, by the rotation of the earth, or by going
north or south, can see further around the limbs.
LIGHT AND HEAT. If the whole sky were covered
with full moons, they would scarcely make daylight,
since the brilliancy of the moon does not exceed
sir^Tnnj- tnat f tne sun - That portion of the moon's
surface which is exposed to the sun is supposed
to be highly heated, possibly to the degree of boil-
ing water, yet its rays impart no heat to us ; indeed
Prof. Tyndall considers them rays of cold. This is
probably caused by the fact that our dense atmos-
phere absorbs all the heat, which in the higher re-
gions produces the effect of scattering the clouds.
It is a well-known fact that the nights are oftenest
clear at full moon. (Herschel.)
CENTEE OF GRAVITY. It is thought that the centre
of gravity of the moon is not exactly at its centre
of magnitude, but nearly thirty-three miles beyond,
and that the lighter half is toward us. If that be
so, this side is equivalent to a mountain of that
enormous height. We can easily see that if water
and air exist upon the moon, they cannot remain on
this hemisphere, but must be confined to the side
which is forever hidden from our view.
ATMOSPHERE OF THE MOON. The existence of an
atmosphere upon our satellite is at present an open
question. If there be any, it must be extremely
rarefied, perhaps as much so as that which is found
in the vacuum obtained in the receiver of our best
air-pumps.
144
THE SOLAR SYSTEM.
Pig. 42.
APPEARANCE OF THE EARTH TO LUNARIANS. If tlieie
be any lunar inhabitants on the side toward us, the
earth must present to them all the phases which
their world exhibits to us, only in a reverse order.
When we have a new moon, they have a futt earth,
a bright full-orbed
moon fourteen times
as large as ours. The
lunar inhabitants upon
the side opposite to us
of course never see our
earth, unless they take
a journey to the re-
gions from whence it
is visible, to behold
this wonderful spec-
tacle. Those living
near the limbs of the disk might, however, on ac-
count of the librations, get occasional glimpses of it
near their horizon.
THE EARTH-SHINE. For a few days before and
after new moon, we may distinguish the outline of
the unillumined portion of the moon. In England,
it is popularly known as " the old moon in the new
moon's arms." This reflection of the earth's rays
must serve to keep the lunar nights quite light,
even in new earth.
PHASES OF THE MOON. The phases of the moon
show conclusively that it is a dark body, which
shines only by reflecting the light it receives from
APPEARANCE OP EARTH AS SEEN FROM
MOON.
THE MOON.
145
the sun. Let us compare its various appearances
with the positions indicated in the figure.
Fig. 43.
PHASES OF MOON.
We see it (1) as a delicate crescent in the west
just after sunset, as it first emerges from the sun's
7
146 THE SOLAR SYSTEM.
rays at conjunction. It soon sets below the horizon
Half of its surface is illumined, but only a slender
edge with its horns turned from the sun is visible to
us. Each night the crescent broadens, the moon
recedes about 13 further from the sun, and sets cor-
respondingly later, until at quadrature half of the
enlightened hemisphere is turned toward us, and the
moon is said to be in her first quarter. Continuing
her eastern progress round the earth, the moon (2)
becomes gibbous* in form, and, about the fifteenth
day from new moon, reaches the point in the heavens
directly opposite to that which the sun occupies.
She is then in opposition, the whole of the illumined
side is turned toward us, and we have a full moon.
She is on the meridian at midnight, and so rises in
the east as the sun sets in the west, and vice versa.
The moon (3) passing on in her orbit from oppo-
sition, presents phases reversed from those of the sec-
ond quarter. The proportion of the illumined side
visible to us gradually decreases ; she becomes gibbous
again ; rises nearly an hour later each evening, and
in the morning lingers high in the western sky after
sunrise. She now comes into quadrature, and is in
her third quarter.
From the third quarter the moon (4) turns her en-
lightened side from us and decreases to the crescent
form again; as, however, the bright hemisphere
* (jitibw* means less than a half and more than a quarter
circle.
THE MOON. 147
constantly faces the sun, the horns are pointed
toward the west. She is now seen as a bright cres-
cent in the eastern sky just before sunrise. At last
the illumined side is completely turned from us, and
the moon herself, coming into conjunction with the
sun, is lost in his rays. To accomplish this journey
through her orbit from new moon to new moon, has
required 29J days a lunar month.
Moon runs high or low. All have, doubtless, no-
ticed that, in the long nights of winter, the full moon
is high in the heavens, and continues a long time
above the horizon; while in midsummer it is low,
and remains a much shorter time above the horizon.
This is a wise provision of Providence, which is seen
yet more clearly in the arctic regions. There the
moon; during the long summer day of six months, is
above the horizon only for her first and fourth quar-
ters, when her light is least ; but during the tedious
winter night of equal length, she is continually above
the horizon for her second and third quarters. Thus
in polar regions the moon is never full by day, but
is always full every month in the night. We can
easily understand these phenomena when we remem-
ber that the new moon is in the same quarter and
the full moon in the opposite quarter of the heavens
from the sun. Consequently, the moon always be-
comes full in the other solstice from that in which
the sun is. When, therefore, the sun sinks very
low in the southern sky the full moon rises high,
and when the sun rises high the full moon sinks low.
148 THE SOLAR SYSTEM.
HARVEST MOON. While the moon rises on the
average 50 m. later each night, the exact time va-
ries from less than half an hour to a full hour.
Near the time of autumnal equinox the moon, at
her full, rises about sunset a number of nights in
succession. This gives rise to a series of brilliant
moonlight evenings. It is the time of harvest in
England, and hence has received the name of the
Harvest Moon. Its return is celebrated as a festi-
val among the peasantry. In the following month
(October) the same occurrence takes place, and it is
then termed the Hunter's Moon. The cause of this
phenomenon lies in the fact that the moon's path is
variously inclined to the horizon at different seasons
of the year. When the equinoxes are in the hori-
zon, it makes a very small angle with the horizon ;
whereas, when the solstitial points are in the horizon,
the angle is far greater. In the former case, the
moon moving eastward each day about 13, will de-
scend but little below the horizon, and so for sev-
eral successive evenings will rise at about the
same hour. In the latter, glie will descend much
further each day and thus will rise much later each
night. The least possible variation in the hour of
rising is 17 minutes the greatest is 1 hour, 16
minutes.
In the figure, S represents the sun, E the earth,
M the moon ; C F the moon's path around the earth
\vhen the solstitial points are in the horizon E D
when the equinoxes are in the horizon ; A M B S the
THE MOON.
149
Fig. 44.
horizon ; M.d = M.b =13, the distance the moon
moves each day. When passing along the path G F,
the moon sinks below the horizon the distance al,
and when mov-
ing along the
path E D, only
the distance
cd. It is ob-
vious that be-
fore the moon j\
can rise in the
former case,
the horizon
must be de-
pressed the
distance a I,
and in the lat-
ter only cd; and the moon will rise correspondingly
later in the one and earlier in the other.
NODES. The orbit of the moon is inclined to the
ecliptic about 5, the points where her path crosses
it being termed nodes. The ascending node (&) is
the place where the moon crosses in coming above
the ecliptic or toward the north star ; the descending
node (8) is where it passes below the ecliptic. The
imaginary line connecting these two points is called
the " line of the nodes."
OCCULTATION. The moon, in the course of her
monthly journey round the earth, frequently passes
in front of the stars or planets, which disappear on
HARVEST MOON.
150 THE SOLAR SYSTEM.
one side of her disk and reappear on the other,
This is termed an occultation, and is of practical use
in determining the difference of longitude between
various places on the earth.
LUNAR SEASONS; DAY AND NIGHT, ETC. As the
moon's axis is so nearly perpendicular to her orbit,
she cannot properly be said to have any change of
seasons. During nearly fifteen of our days, the sun
pours down its rays unmitigated by any atmosphere
to temper them. To this long, torrid day succeeds a
night of equal length and polar cold. How strange
the lunar ' appearance would be to us ! The disk of
the sun seems sharp and distinct. The sky is
black and overspread with stars even at midday.
There is no twilight, for the sun bursts instantly
into day, and after a fortnight's glare, as suddenly
gives place to night; no air to conduct sound, no
clouds, no winds, no rainbow, no blue sky, no gor-
geous tinting of the heavens at sunrise and sunset,
no delicate shading, no soft blending of colors, but
only sharp outlines of sun and shade.
What a bleak waste ! A barren, voiceless desert !
The nights, however, of the visible hemisphere must
be brilliantly illuminated by the earth, while its
phases " serve well as a clock a dial all but fixed
in the same part of the heavens, like an immense
lamp, behind which the stars slowly defile along the
black sky."
TELESCOPIC FEATURES. The lunar landscape is
yet more wonderful than its other physical features
THE MOON.
Pi*. 45.
151
EAT, LANDSCAPE OF THK MOON.
152 THE SOLAR SYSTEM.
Even with the naked eye we see on its surface bright
spots the summits of lofty mountains, gilded by
the first rays of the sun and darker portions, low
plains yet lying in comparative shadow. The tele-
scope reveals to us a region torn and shattered by
fearful, though now extinct* volcanic action. Every-
where the crust is pierced by craters, whose irregu
lar edges and rents testify to the convulsions our
satellite has undergone at some past time.
Mountains. The heights of more than 1,000 of
these lunar mountains have been measured, some of
which exceed 20,000 feet. The shadows of the
mountains, as the sun's rays strike them obliquely,
are as distinctly perceived as that of an upright
staff when placed opposite the sun. Some of these
are insulated peaks that shoot up solitary and alone
from the centre of circular plains ; others are moun-
tain ranges extending hundreds of miles. Most of
the lunar elevations have received names of men
distinguished in science. Thus we find jPlato, Aris-
tarchus, Copernicus, Kepler, and Newton, associated
however with the Apennines, Carpathians, etc.
Gray plains or seas. These are analogous to our
prairies. They were formerly supposed to be sheets
of water, but have more recently been found to ex-
* Several distinguished astronomers assert, however, that the
crater Linnaeus has undergone of late certain marked changes.
Its sides seem to have fallen in, and the interior to have become
filled up, as if by a new eruption. It is said to present an ap-
pearance similar to that of the Sea of Serenity.
154 THE SOLAR SYSTEM.
hibit the uneven appearances of a plain, instead of
the regular curve of bodies of water. The former
names have been retained, and we find on lunar
maps the " Sea of Tranquillity," the " Sea of Nee-
tar," " Sea of Serenity," etc.
Rills, luminous bands. The latter are long bright
streaks, irregular in outline and extent, which radi-
ate in every direction from Tycho, Kepler, and other
mountains ; the former are similar, but are sunken,
and have sloping sides, and were at first thought to
be ancient river-beds. Their exact nature is yet a
mystery.
Craters. These constitute by far the most curious
feature of the lunar landscape. They are of volcanic
origin, and usually consist of a cup-like basin, with a
conical elevation in the centre. Some of the craters
have a diameter of over 100 miles. They are great
walled plains, sunk so far behind huge volcanic ram-
parts, that the lofty wall which surrounds an ob-
server at the centre would be beyond his horizon.
Other craters are deep and narrow, as Newton,
which is said to be about four miles in depth,
so that neither earth nor sun is ever visible from a
great part of the bottom. The appearance of these
craters is strikingly shown in the accompanying
view of the region to the southeast of Tycho. (Fig.
46.)
ECLIPSES.
155
ECLIPSES.
ECLIPSE OF THE SUN. If the moon should pass
through either node at or near the time of conjunc-
tion or neiv moon, she would necessarily come be-
tween the earth and the sun, for the three bodies
are then in the same straight line. This would cause
Fig. 47.
of &*
ECLIPSE OP SUN.
an eclipse of the sun. If the moon's orbit were in
the same plane as the ecliptic, an eclipse of the sun
would occur at every new moon ; but as the orbit is
inclined, it can occur only at or near a node.
The eclipse may be partial, total, or annular. In
Fig. 48, we see where the dark shadow (umbra) of
Fig. 48
UMBRA AND PENUMBRA.
the moon falls on the earth and obscures the entire
body of the sun. To the persons within that region
156 THE SOLAR SYSTEM.
there is a total eclipse; the breadth of this space
is not large, averaging only 140 miles. Beyond
this umbra there is a lighter shadow, penumbra
(pene, almost - umbra, a shadow), where only a
portion of the sun's disk is obscured. Within this
region there is a partial eclipse. To those persons liv-
ing north of the equator and of the umbra, the eclipse
passes over the lower limb of the sun ; to those
south of the umbra, it passes over the upper limb.*
When the eclipse occurs exactly at the node, it is said
to be central. If the eclipse takes place when the moon
is at apogee, or furthest from the earth, her apparent
diameter is less than that of the sun ; as a conse-
quence, her disk does not cover the disk of the sun,
and the visible portions of that luminary appear in
the form of a ring (annulus) ; hence there is an an-
nular eclipse in all those places comprised within the
limits of the cone of shadow prolonged to the earth.
General facts concerning a solar eclipse. The fol-
lowing data may perhaps guide in better under-
. standing the phenomena of solar eclipses.
(1.) The moon must be new.
(2.) She must be at or near a node.
(3.) When her distance from the earth is less than
the length of her shadow, the eclipse will be total
or partial.
(4.) When her distance is greater than the length
of her shadow, the eclipse will be annular or partial.
(5.) There can be no eclipse at those places where
the sun himself is invisible during the time.
* South of the equator the reverse of these phenomena would
happen.
ECLIPSES. 15V
(6.) An eclipse is not visible over the whole illu-
mined side of the earth. As the moon's diameter
is so much less than that of the earth, her cone of
shadow is too small to enshroud the entire globe, so
that the region in which it is total cannot exceed
180 miles in breadth. As, however, the earth is con-
stantly revolving on its axis during the duration of
the eclipse, the shadow may travel over a large sur-
face of territory.
(7.) If the moon's shadow fall upon the earth
when she is just nearing her ascending node, it will
Fiff. 49
SOLAR ECLIPTIC LIMIT (17).
only sweep across the south polar regions : if when
nearing her descending node, it will graze the earth
near the north pole. The nearer a node the con-
junction occurs, the nearer the equatorial regions
the shadow will strike.
(8.) At the equator, the longest possible duration
of a total solar eclipse is only about eight minutes,
and of an annular, twelve minutes. One reason of the
greater length of the latter is, that then the moon
is in apogee, when it always moves slower than
when in perigee. The duration of total obscuration
is greatest when the moon is in perigee and the sun
in apogee ; for then the apparent size of the moon
is greatest and that of the sun least. We see from
158
TilE SOLAR SYSTEM.
this that the relative situation of the moon and sun
decides the length and kind of the eclipse.
(9.) There cannot be more than five nor less
than two solar eclipses per year. A total or an an-
nular eclipse is exceedingly rare. For instance,
there has not been a total eclipse visible at London
since 1715, and previous to that, there had been
none visible for five and a half centuries.
(10.) A solar eclipse comes on the western limb
or edge of the sun and passes off on the eastern.
(11.) The disk of the sun and moon is divided into
twelve digits, and the amount of the eclipse is esti-
mated by the number of digits which it covers. Thus
an eclipse of six digits is one in which half the di-
ameter of the disk is concealed.
Curious phenomena. Various singular appearances
always attend a total eclipse. Around the sun is
seen a beautiful Fig. 50.
corona or halo
of light, like
that which paint-
ers give to the
head of the
Virgin Mary.
Flames of a
blood-red color
play around the
disk of the moon,
and when only
a mere crescent
of the sun is BottpsE OF isss
ECLIPSES.
159
Fig. 51.
visible, it seems to resolve itself into bright spots
interspersed with dark spaces, having the appear-
ance of a string
of bright beads
(Baily's Beads.)
Attendant cir-
cumstances of a
total eclipse.
These are of a
peculiarly im-
pressive charac-
ter. The dark-
ness is so intense
that the brighter
stars and planets
are seen, birds
cease their songs
and fly to their nests, flowers close, and the face of
nature assumes an unearthly cadaverous hue, while
a sudden fall of the temperature causes the air to
feel damp, and the grass wet as if from excessive
dew. Orange, yellow, and copper tints give every
object a strange appearance, and startle even the
most indifferent. The ancients regarded a total
eclipse with feelings of indescribable terror, as an
indication of the anger of an offended Deity, or the
presage of some impending calamity. Even now,
when the causes are fully understood, and the time
of the eclipse can be predicted within the fraction
of a second, the change from broad daylight to in-
ANNULAR ECLIPSE OP 183& SHOWING BAILY'd
BEADS.
1GO THE SOLAR SYSTEM.
stantaneous gloom is overwhelming, and inspires
with awe even the most careless observer.
Curious custom among the Hindoos. Among the
Hindoos a singular custom is said to exist. When,
during a solar eclipse, the black disk of our satellite
begins slowly to advance over the sun, the natives
believe that some terrific monster is gradually de-
vouring it. Thereupon they beat gongs, and rend
the air with most discordant screams of terror and
shouts of vengeance. For a time their frantic efforts
seem futile and the eclipse still progresses. At
length, however, the increasing uproar reaches the
voracious monster ; he appears to pause, and then,
like a fish rejecting a nearly swallowed bait, grad-
ually disgorges the fiery mouthful. When the sun
is quite clear of the great dragon's mouth, a shout
of joy is raised, and the poor natives disperse, ex-
tremely self-satisfied on account of having so suc-
cessfully relieved their deity from his late peril.
THE SAROS. The nodes of the moon's orbit are
constantly moving backward. They complete a rev-
olution around the ecliptic in about eighteen and
a half years. Now the moon makes 223 synodic
revolutions in 18 yr. 10 da. ; the sun makes 19 rev-
olutions with regard to the lunar nodes in about the
same time. Hence, in that period the sun and
moon and the nodes will be in nearly the same rela-
tive position. If, then, we reckon 18 yr. 10 da. from
any eclipse, we shall find the time of its repetition.
This method was discovered, it is said, by the dial-
ECLIPSES. 161
deans. The ancients were enabled, by means of it,
to predict eclipses, but it is considered too rough by
modern astronomers : eclipses are now foretold cen-
turies in advance, true to a second. In this manner
historical incidents are verified, and their exact dates
determined.
METONIC CYCLE. The Metonic Cycle (sometimes
confounded with the Saros) was not used for foretell-
ing eclipses, but for the purpose of ascertaining the
age of the moon at any given period. It consists of
nineteen tropical years,* during which time there
are exactly 235 new moons ; so that, at the end of
this period, the new moons will recur at seasons of
the year exactly corresponding to those of the pre-
ceding cycle. By registering, therefore, the exact
days of any cycle at which the new or full moons
occur, such a calendar shows on what days these
events will occur in succeeding cycles. Since the
regulation of games, feasts, and fasts has been
made very extensively, both in ancient and modern
times, according to new or full moons, such a calen-
dar becomes very convenient for finding the day on
which the new or full moon required takes place.
Thus if a festival were decreed to be held in any
given year on the day of the first full moon after
the vernal equinox : find what year it is of the
lunar cycle, then refer to the corresponding year of
* A tropical year is the interval between two successive retums
of the sun to the vernal equinox.
162 THE SOLAlt SYSTEM.
the preceding cycle, and the day will be the same aa
it was then. The Golden Number, a term still used
in our almanacs, denotes the year of the lunar cycle.
Seven is the golden number for 1868.
ECLIPSE OF THE MOON. This is caused by the
passing of the moon into the shadow of the earth,
Fig. 52.
ECLIPSE OF THE MOON.
and hence can take place only at full moon oppo-
sition. As the moon's orbit is inclined to the ecliptic,
her path is partly above and partly below the earth's
shadow ; thus an eclipse of the moon can take place
only at or near one of the nodes. In the figure, the
umbra is represented by the space between the lines
K c and I b ; outside of this is the penumbra, where the
earth cuts off the light of only a portion of the sun. The
moon enters the penumbra of the earth at a, this is
termed her first contact with the penumbra ; next she
encounters the dark shadow of the earth at b, this is
called ike first contact with the umbra ; she then emerges
from the umbra at c, which is called the second con-
tact with the umbra ; finally, she touches the outer
edge of the penumbra at d, t lie second contact with the
penumbra. Since the earth is so much larger than
ECLIPSES. 163
the moon, the eclipse can never be annular , as,
however, the eclipse may occur a little above or be-
low the node, the moon may only partly enter the
earth's shadow, either on its upper or lower limb.
From the first to last contact with the penumbra,
five hours and a half may elapse. Total eclipses of
the moon are rarer events than those of the sun,
since the lunar ecliptic limit is only about 12 ; yet
they are more frequently seen by us, (1) because each
one is visible over the entire unillumined hemisphere
of the earth, and also (2) because by the diurnal ro-
tation during the long duration of the eclipse, large
areas may be brought within its limits. So it will
happen that while the inhabitants of one district wit-
ness the eclipse throughout its continuance, those of
other regions merely see its beginning, and others
only its termination. The moon does not completely
disappear even in total eclipses. The cause of
this fact lies in the refraction of the solar rays in
traversing the lower strata of the earth's atmos-
phere ; they are analyzed, and purple our moon with
the tints of sunset. The amount of refraction and
the color depend upon the state of the air at the
time.
HISTORICAL ACCOUNTS OF ECLIPSES. The earliest
account of an eclipse on record is in the Chinese
annals ; it is thought to be the solar eclipse of Octo-
ber 13, 2127 B. c. On May 28, 584 B. c., one oc-
curred which was predicted by Thales, as wo have
before mentioned. In the writings of the early Eng-
164 THE SOLAK SYSTEM.
lish chroniclers are numerous passages relating to
eclipses. William of Malmesbury thus refers to that
of August 2, 1133, which was considered a presage
of calamity to Henry I. : " The elements manifested
their sorrows at this great man's last departure.
For the sun on that day, at the 6th hour, shrouded
his glorious face, as the poets say, in hideous
darkness, agitating the hearts of men by an eclipse ;
and on the 6th day of the week, early in the morn-
ing, there was so great an earthquake, that the
ground appeared absolutely to sink down ; an horrid
noise being first heard beneath the surface." The
same writer, speaking of the total eclipse of March
20, 1140, says : " During this year, in Lent, on the
13th of the kalends of April, at the 9th hour of the
4th day of the week, there was an eclipse, through-
out England, as I have heard. With us, indeed, and
with all our neighbours, the obscuration of the Sun
also was so remarkable, that persons sitting at table,
as it then happened almost every where, for it was
Lent, at first feared that Chaos was come again :
afterwards learning the cause, they went out and
beheld the stars around the Sun. It was thought
and said by many, not untruly, that the king [Ste-
phen] would not continue a year in the govern-
ment." Columbus made use of an eclipse of the
moon, which took place March 1, 1504, to relieve his
fleet, which was in great distress from want of sup-
plies. As a punishment to the islanders of Jamaica,
who refused to assist him, he threatened to deprive
THE TIDES. 165
them of the light of the moon. At first they were
indifferent to his threats, but " when the eclipse ac-
tually commenced, the barbarians vied with eacli
other in the production of the necessary supplies for
the Spanish fleet."
THE TIDES.
DESCKIPTION. Twice a day, at intervals of about
twelve hours and twenty-five minutes, the water be-
gins to set in from the ocean, beating the pebbles
and the foot of the rocky shore, and dashing its
spray high in air. For about six hours it climbs
far up on the beach, flooding the low lands and
transforming simple creeks into respectable rivers.
The instant of high-water or flood-tide being reached,
it begins to descend, and the ebb succeeds the flow.
The water, however, falls somewhat slower than it
rose.
CAUSE OF THE TIDES. The tides are caused by a
great wave, which, raised by the moon's attraction,
Fte. 53.
Spring Tidts
SPKINO TIDE.
follows her in her course around the earth. The
sun, also, aids somewhat in producing this effect;
but as the moon is 400 tim^s nearer the earth, her
1S6 THE SOLAR SYSTEM.
influence is far greater. As the waters are free to
yield to the attraction of the moon, she draws them
away from C and D and they become heaped up at
A. The earth, being nearer the moon than the
waters on the opposite side, is more strongly at-
tracted, and so, being drawn away from them, they
are left heaped up at B. As the result, high-water
is produced at A by the water being pulled from the
earth, and at B by the earth being pulled from the
water. The influence of the moon is not instanta-
neous, but requires a little time to produce its full
effect ; hence high- water does not occur at any place
when the moon is on the meridian, but a few hours
after. As the moon rises about fifty minutes later
each day, there is a corresponding difference in the
time of high-water. While, however, the lunar tide-
wave thus lags about fifty minutes every day, the
solar tide occurs uniformly at the same time. They
therefore steadily separate from each other. At one
time they coincide, and high-water is the sum of
lunar and solar tides ; at other times, high-water of
the solar tide and low-water of the lunar tide occur
simultaneously, and high-water is the difference
between the lunar and solar tides.
We should bear in mind tha philosophical truth,
that the tide in the open sea ioes not consist of a
progressive movement of the water itself, but only
of the form of the wave.
Causes that modify the tides. At new and full moon
(the syzygies) the sun acts with the moon (as in Fig.
THE TIDES. 167
53) in elevating the waters ; this produces the highest
or Spring tide. In quadrature (as in Fig. 54), the
sun tends to diminish the height of the water : this is
called Neap-tide. When the moon is in perigee her
attraction is stronger ; hence the flood-tide is higher
and the ebb-tide lower than at other times. This re-
Fig. 54.
Bcap Tides
NEAP-TIDE.
mark applies also to the sun. The height of the tide
also varies with the declination of the sun and moon,
the highest or equinoctial tides taking place at the
equinoxes, if, when the sun is over the equator, the
moon also happens to be very near it : the lowest
occur at the solstices. The force and direction of
the winds, the shape of the coast, and the depth of
the sea wonderfully complicate the explanation of
local tides.
Height of the tide at different places. In the open
sea the tide is hardly noticeable, the water some-
times rising not higher than a foot ; but where tho
wave breaks on the shore, or is forced up into bays
or narrow channels, it is very conspicuous. The
difference between ebb and flood neap-tide at New
York is over three feet, and that of spring tide over
168 THE SOLAR SYSTEM.
fivo feet ; while at Boston it is nearly double this
amount. A headland jutting out into the ocean will
diminish the tide ; as, for instance, off Cape Florida,
where the average height is only one and a half feet.
A deep bay opening up into the land like a funnel,
will converge the wave, as at the Bay of Fundy,
where it rolls in, a great roaring wall of water sixty
feet high, frequently overtaking and sweeping off
men and animals. The tide sets up against the
current of rivers, and often entirely changes their
character ; for example, the Avon at Bristol is a
mere shallow ditch, but at flood-tide it becomes a
deep channel navigable by the largest Indiarnen.
Differential effect. The whole attraction of the
moon is only T J-g- that of the sun : yet her influence in
producing the tides and precession is greater, because
that depends not upon the entire attraction either
exerts, but upon the difference between their attrac-
tion upon the earth's centre and upon the earth's
nearest surface. For the moon, on account of her
nearness, the proportion of the distance of these
parts is treble that of the sun, and hence her greater
effect.
MARS.
The god of war. Sign, $ , shield and spear.
DESCRIPTION. Passing outward in our survey of the
solar system, we next meet with Mars. This is the
first of the superior planets, and the one most like
the earth. It appears to the naked eye as a bright
MAES. 169
red star, rarely scintillating, and shining with a
steady light, which distinguishes it from the fixed
stars. Its ruddy appearance has led to its being
celebrated among all nations. The Jews gave it the
appellation of " blazing," and it bore in other lan-
guages a similar name. At conjunction its apparent
Fi<r. 53.
DIAMETER OP MARS AT EXTREME, LEAST, AND MEAN DISTANCES.
diameter is only about 4"; but once in two years it
comes into opposition with the sun, when its diam-
eter increases to 30". At intervals of Syr. 7 mo.
this occurs when the planet is also in perihelion
and perigee. Mars then shines with a brilliancy
rivalling that of Jupiter himself.
MOTION IN SPACE. Mars revolves about the Sun
at a mean distance of about 140,000,000 miles. Its
orbit is sufficiently flattened to bring it at perihelion
26,000,000 miles nearer that luminary than when in
aphelion. Its motion varies in different portions of
its orbit, but the average velocity is about fifteen
8
170 THE SOLAR SYSTEM.
miles per second. The Martial day is about 40 min,
longer than ours, and the year contains about 668
Martial days, equal to 687 terrestrial days (nearly
two years).
DISTANCE FROM EARTH. When in opposition, the
distance of Mars is (like that of all the superior
planets) the difference between the distance of the
planet and that of the earth from the Sun : at con-
junction it is the sum of these distances. If the
orbits were circular, these distances would be the
same at every revolution. The elliptical figure, how-
ever, occasions much variation. Thus, if it is in
perihelion while the earth is in aphelion, the dis-
tance is 126,000,000 - 93,000,000 = 33,000,000 miles.
DIMENSIONS. Its diameter is a little less than
5,000 miles. Its volume is about J that of the earth,
but as its density is only J, it follows that its mass
is only of the terrestrial mass. A stone let fall on
its surface would fall not quite five feet the first
second. It is somewhat flattened at the poles, and
bulges at the equator like our globe.
SEASONS. The light and heat of the sun at Mars
are less than one half that which we enjoy. Its axis
is inclined about 28.7, therefore its zones and sea-
sons do not differ materially from our own : its days,
also, as we have seen, are of nearly the same length
Since, however, its year is equal to neaily two of
our years, the seasons are lengthened in proportion.
There must be a considerable difference between the
temperature of its northern and southern hemi-
MAES. 171
spheres, as the former has its summer when 26,000,000
miles further from the sun than the latter : an in-
creased length of 76 days may, however, be suffi-
cient compensation. It has an atmosphere like our
own, loaded with clouds. Mars has* &o moon. Its
nights, therefore, are dark. Our own earth and
moon must present in its evening sky a very beauti-
ful pair of planets, showing all the phases which
Mercury and Yenus present to us, the two always
remaining within one half the moon's apparent di-
ameter of each other.
TELESCOPIC FEATURES. Under the telescope, Mars
exhibits slight phases, but by no means to the same
Pig. 56.
7TSW OF XARS.
extent as the inferior planets. Its surface appears
covered with dusky patches, which are believed to
be continents : these are of a dull red hue. Other
17 '2 THE SOLAR SYSTEM.
portions, of a greenish tint, are considered to be
bodies of water. The proportion of land to water
on the earth is reversed in Mars. " Here every con-
tinent is an island ; there every sea is a lake : but
these, like our own continents, are chiefly confined to
one hemisphere, so that the habitable area of the
two globes may not differ so much as the size of the
planets." The ruddy color of the planet is thought
by Herschel to be due to an ochrey tinge in the
soil ; by others it is attributed to peculiarities of the
atmosphere and clouds. Lambert suggests that it
is the color of the vegetation, which, on Mars, may
be red instead of green. There are constant
changes going on in the brightness of the disk,
owing, it is supposed, to the variation of the clouds
of vapor in its atmosphere. No mountains have yet
been discovered. In the vicinity of the poles are
brilliant white spots, which are considered to be
masses of snow. The " snow zones" apparently melt
and recede with the return of summer in each hemi-
sphere, and increase on the approach of winter. "We
can thus from the earth watch the formation of polar
ice and the fall of snow in fact, all the vicissitudes
of the seasons on the surface of a neighboring
planet.
THE MINOK PLANETS.
i
DISCOVERY. Beyond Mars there is a wide interval
which until the present century was not filled. The
bold, imaginative Kepler conjectured that there was
THE MINOR PLANETS.
173
a planet in this space. This supposition was cor-
roborated by Titius's discovery of what has since
been known as Bode's law.
Take the numbers 0, 3, 6, 12, 24, 48, 96, 192, 384,
each of which, after the second, is double the pre-
ceding one. If we add 4 to each of these numbers,
we form a new series :
4, 7, 10, 16, 28, 52, 100, 196, 388.
At the time this law was discovered, these numbers
represented very nearly the proportionate distance
from the sun of the planets then known, taking the
earth's distance as ten, except that there was a blank
opposite 28.* This naturally led to inquiry, and a
systematic effort to solve the mystery. On the 1st
day of January, 1801, the nineteenth century was
inaugurated by Piazzi's discovery of the small
planet Ceres, at almost the exact distance necessary
to fill the gap in Bode's series. This was soon fol-
lowed by the announcement of other new planets,
until (1870) there are one hundred and twelve, and a
probability of many more. Indeed, Leverrier has
calculated that there may be perhaps 150,000 in all
* PIQUETS.
True dis-
tance
from .
Distance
by Bode's
law.
PLANETS.
True dis-
tance
from .
Distance
by Bode'a
law.
Vulcan
Ceres
27 C6
28 00
Mercury
Venus
8.87
7.23
4.00
7.00
Jupiter
Saturn
62.03
95.39
52.00
10000
Earth ....
10.00
10.00
Uranus . .
191 82
19600
Mara
1523
1600
Neptune
30087
38800
174 THE SOLAR SYSTEM.
DESCRIPTION. These minor worlds, or " pocket
planets," as Herschel styled them, are extremely
diminutive. The largest of them is Pallas, whose
diameter is perhaps 600 miles. Those recently dis-
covered are so small that it is difficult to decide
which is the smallest. A French astronomer recently
remarked concerning them, that a "good walker
could easily make the tour of one in a day;" a
prairie farmer would need to pre-empt a whole one
for a flourishing cornfield. They all revolve about
the sun in regular orbits, comprising a zone about
100,000,000 miles in width. Their paths are va-
riously inclined to the ecliptic ; Massilia's 41', while
that of Pallas rises 34.
ORIGIN. One theory concerning the origin of these
small planets is, that they are the fragments of a
large planet which, in a remote antiquity, has been
shivered to pieces by some terrible catastrophe.
"One fact seems above all others to confirm the
idea of an intimate relation between these planets.
It is this: if their orbits consisted of solid rings,
they would be found so entangled that it would be
possible, by taking up any one at random, to lift
all the rest." Another theory is given under the
" Nebular Hypothesis."
Names and signs. Ceres, thjp first discovered, re-
ceived the symbol 9 , a sickle. This was appropri-
ate, since that goddess was supposed to preside over
harvests. Pallas, the second, named from the god-
dess of wisdom and scientific warfare, obtained the
JTJPITEB. 175
sign 4 , the head of a spear. To Juno, the third
planet, was assigned o , a sceptre surmounted with
a star, the emblem of the queen of heaven. An
altar with fire upon it, fi , appropriately represented
Vesta, the household goddess, whose sacred fire was
kept burning continually. In this way names of
goddesses and appropriate symbols were used to
designate the minor planets which were earliest dis-
covered. Since then a simple circle with the num-
ber inclosed has been adopted; thus (D represents
Ceres (D is the sign of Pallas.
JUPITEE.
The king of the gods. Sign y. , a hieroglyphic representation of an eagle
"the bird of Jove."
DESCRIPTION. From the smallest members of the
solar system we now pass at once to the largest
planet the colossal Jupiter. Its peculiar splendor
and brilliancy distinguish it from the fixed stars,
and vie even with the lustre of Yenus. It is one of
the five planets discovered in primitive ages. In
those early times, Jupiter was supposed to be the
cause of storm and tempest. Pliny thought that
lightning owed its origin to this planet. An old al-
manac of 1368, foretelling the harmless condition of
Jupiter for a certain month, says, " Jubit es hote
and moyste and does weel til al thynges and noyes
nothing.*'
176 THE SOLAR SYSTEM.
MOTION IN SPACE. Jupiter revolves about the sun
at a mean distance of 475,000,000 miles. His orbit
has much less eccentricity than those of the smaller
planets. Were his path very elliptical, the attrac-
tion of the sun would be insufficient to bring him
back from its extreme limit, and the huge un-
wieldy planet would plunge headlong into space.
This careful fitting, whereby the plan is always
modified to accomplish an end, is everywhere
characteristic of nature, and is a continued rev-
elation of its common Author. The revolution
of Jupiter among the fixed stars is slow and ma-
jestic, comporting well with his vast dimensions
and the dignity conferred by four attendant worlds.
He advances through the zodiac at the rate of one
constellation yearly ; so that if we locate the planet
now, a year hence we can find it equally advanced
in the next sign. Yet slowly as he seems to travel
through the heavens, he is bowling along through
space at the enormous speed of 500 miles per min-
ute. The Jovian day is only equal to about ten of
our hours, while his year is lengthened to about
12 of our years, comprising near 10,000 of his days.
DISTANCE FROM EARTH. Once in thirteen months
Jupiter is in opposition, and his distance from the
earth is measured by the difference of the distances
of the two bodies from the sun. At the expira-
tion of half this time he is in conjunction, and his
distance from us is measured by the sum of these
distances.
JUPITER.
177
Fipr. 57.
DIMENSIONS. Its diameter is about 88,000 miles,
or one-tenth of the sun. Its volume is 1,400 times
that of the earth,
and much exceeds
th at of all the other
planets combined.
Seen at the dis-
tance of the moon,
this immense
globe would em-
brace 1,200 times
the space of the
full moon. Jupi-
ter's density is
only one-fifth that
of the earth ; moreover, its rapid rotation upon its
axis, whereby a particle on the equator revolves
with a velocity of 467 miles per minute against the
earth's 17 miles per minute, must produce a power-
ful centrifugal force which materially diminishes the
weight of all objects near its equator. Consequently
a stone let fall on Jupiter would pass through but
about thirty-nine feet the first second. As a result
of this rapid rotation, the planet is one of the most
flattened of any in the solar system the equatorial
diameter exceeding the polar by about 5,000 miles.
SEASONS. As the axis of Jupiter is but slightly
inclined from a perpendicular to the plane of its
orbit, there is but little difference in the length of
its days and nights, which are each of about five
8*
178 THE SOLAR SYSTEM,
hours' duration. At the poles the sun is visible foi
nearly six years, and then remains set for the same
length of time. The seasons also are but slightly
varied. Summer reigns near the equator, while the
temperate regions enjoy perpetual spring. The light
and heat of the sun are only -fa of that which we re-
ceive; yet peculiarities of soil or atmosphere may
compensate this difference. The evening sky on
Jupiter must be inexpressibly magnificent ; besides
the glittering stars which adorn our heavens, four
moons, waxing and waning, each with its diverse
phase, illuminate its night. All the starry exhibition
sweeps through the sky in five hours.
TELESCOPIC FEATURES. Jupiter's moons. Under
the telescope Jupiter presents a beautiful Copernican
system in miniature. Four small stars moons are
seen to accompany it in its twelve-yearly revolutions.
From hour to hour their positions vary, and they
seem to oscillate from one side to the other of the
planet. At one time there will be two on each side,
and again, three on one side ; while the remaining
star is left alone. They are also frequently found
to disoppear, one, two, or even three at a time, and,
more rarely, all four at once. There are well-
authenticated instances on record of their having
been seen by the naked eye. Among others, the
following singular case is mentioned. Wrangle, the
celebrated Eussian traveller, states, that when in Si-
beria, he once met a hunter, who said, pointing to
Jupiter, " I have just seen that star swallow a small
JUPITER.
179
one and then vomit it up again." These moons are
called by the ordinal numbers, reckoning outward
from the planet. With an ordinary glass, there is
nothing to distinguish them from small stars. The
Hid, however, being the largest and brightest, will
generally be identified easiest. The 1st satellite ap-
pears to the inhabitants of the planet almost as
large as our moon to us ; the lid and Hid about
half as large. Their real size and density are in-
dicated in the following table. It will be seen that
the IVth is about the weight of cork, and the 1st
and lid are still lighter.
SATELLITES OF JUPITER.
Mean distance
from Jupiter.
Diameter.
Density.
Water as 1.
Sidereal period.
I lo
267380
2,352 m.
.114
D. H. M.
1 18 28
II. Europa
425,156
2,099 "
.171
3 13 4
HI. Ganymede
IV. Callisto.........
678,393
1,192,823
3,436 "
2,929 "
.396
.222
7 3 43
19 16 32
;t is no^iceablfe-that here are four satellites revolv-
ing 'about Jupiter, one of them larger than the planet
Mercury, and each far surpassing in size the minor
planets between Mars and Jupiter. The moons are
not only thus distinguished by their various dimen-
sions, but also by the variety of their color. The
1st and lid have a bluish tint, the Hid a yellow,
and the IVth a reddish shade. The total space oc-
cupied by this miniature system is about two and
a half million miles in diameter.
Eclipse of the moons. Jupiter, like allcelestialbodies
not self-luminous, casts into space a cone of shade.
180
THE SOLAR SYSTEM.
The 1st, lid, and nid satellites revolve in or-
bits but very little inclined to the plane of the
planet's orbit. During each revolution they pass
Fig. 58.
ECLIPSES AJTO OCCTTLTA.TION8 OF JUPITEB 8 MOONS.
between the Sun and Jupiter, producing a solai
eclipse ; and also by passing through the shadow of
JUPITER. 181
the planet itself, cause to themselves an eclipse of
the sun, and to Jupiter an eclipse of a moon. The
IVth passes through a path more inclined, and there-
fore its eclipses are less frequent : instead of being
fully eclipsed, it sometimes just grazes the shadow,
as it were, and so its light is much diminished.
Through a telescope we can distinctly watch the
disappearance or immersion of the satellites in the
planet's shadow, their reappearance or emersion, and
also their transits, as a round black dot or shadow
moving across the disk of Jupiter. In the cut, we
see represented the various positions of the moons :
the 1st is eclipsed; the lid is passing across the
disk of the planet on which its shadow is also thrown ;
the IIEd is just behind the planet, and so occulted or
concealed, while it has not yet entered the shadow;
the IVth is in view from the earth. These satellites
revolve with great rapidity, as is necessary in order
to overcome the superior attraction of the planet and
prevent being drawn to its surface. The 1st goes
through all its phases in 1| days, and the lYth in less
than twenty days. A spectator on Jupiter might
witness, during the Jovian year, 4,500 eclipses of
the moon (moons), and about the same number of
the sun.
Jupiter's lelts. These are dusky streaks of
varying breadth and number, lying more or less
parallel to the planet's equator, but terminating at a
short distance from the edges of the disk. Between
these a brighter, often rose-colored space, marks the
182 THE SOLAR SYSTEM.
equatorial regions. They are not permanent, but
change sometimes very materially in the course of
a few minutes. Occasionally only two or three
broad belts are seen ; at other times a dozen narrow
ones appear. It is supposed that the planet is en-
veloped in dense masses of cloud, and that the belts
are merely fissures, laying bare the solid body be-
neath. The parallel appearance is doubtless due to
strong equatorial currents, analogous to our trade-
winds.
VELOCITY OF LIGHT. By an attentive examination
of the eclipses of Jupiter's moons, Homer (a Danish
astronomer, in 1617) was led to discover the pro-
gressive motion of light. Before him, it had been
considered instantaneous. He noticed that the ob-
served times of the eclipses were sometimes earlier
and sometimes later than the calculated times, ac-
cording as Jupiter was nearest or furthest from the
earth. His investigations convinced him that it
requires about 16 \ min. for light to traverse the orbit
of the earth. Bomer's conclusion has since been
verified by the phenomena of aberration of light.
The velocity of light is about 183,000 miles pel
second. (See 14 Weeks in Philosophy, p. 189.)
SATUEN.
The god of time. Sign * , an ancient ecythe.
DESCRIPTION. We now reach, in our outward jour-
ney from the sun, the most remote world known to
the ancients. On account of its distance, it shines
SATURN.
183
with a feeble but steady pale yellow light, which dis-
tinguishes it from the fixed stars. Its orbit is so
vast that its movement among the constellations
may be easily traced through one's lifetime. It re-
quires two and a half years to pass through a single
sign of the zodiac ; hence, when once known, it may
be easily found again. The earth leaves it at con-
7 junction, makes a yearly revolution about the sun,
comes to its starting point, and overtakes Saturn in
about thirteen days thereafter.* On account of its
slow, dreary pace, Saturn was chosen by the ancients
as the symbol for lead. It is smaller than Jupiter,
but much more gorgeously attended. Besides a
retinue of eight satellites, it is surrounded by a sys-
tem of rings, some shining with a golden light and
others transparent a spectacle which is as wonder-
ful as it is unique.
MOTION IN
SPACE. Saturn
revolves about
the sun at a
mean distance
of 872,000,000
miles. The
eccentricity of
its orbit is a
trifle more than
that of Jupiter,
* From this the year of Saturn may be determined. As 13 : 378
days : Earth's year : Saturn's year = 30 yr. nearly
184 THE SOLAR SYSTEM.
so that while it may at perihelion come fifty mil-
lion miles nearer than its mean distance, at aphe-
lion it swings off as much beyond. We can form
some estimate of the size of its immense orbit,
when we remember that it is moving along at the
rate of 21,000 miles per hour, and yet as we look
at it from night to night, we can scarcely detect any
change of place. The Saturnian year is equal to
about thirty of ours, and comprises nearly 25,000
Saturnian days, each of which is about ten and a
half hours in length.
DISTANCE FROM EARTH. This is found in the same
manner as that of the other superior planets, being
least in opposition and greatest at conjunction. As
the earth and Saturn occupy different portions of
their orbits, the distances between them at different
times may vary 200,000,000 miles.
DIMENSIONS. Its diameter is about 72,000 miles.
Its volume is nearly 750 times that of the earth. Its
density is very low indeed, being much less than that
of water, and about the same as that of pine wood.
The Saturnian force of gravity is therefore scarcely
greater than the terrestrial, so that a stone falls
toward the surface of that immense globe only about
seventeen feet the first second.
SEASONS. The light and heat of the sun at Saturn
are only j^- that which we receive. The axis of
Saturn is inclined from a perpendicular to the
plane of its orbit about 31. The seasons there-
fore are similar to those on the earth, but on a
SATURN. 185
larger scale. The sun climbs in summer about 8
higher above the horizon, and sinks correspondingly
lower in winter. The tropics are 16 further apart,
and the arctic and antarctic circles 8 further from
the poles. Each of Saturn's seasons lasts more than
seven of our years. There is about fifteen years
interval between the autumn and spring equinoxes,
and between the summer and winter solstices. For
fifteen years the sun shines on the north pole, and a
night of the same length envelops the south pole.
The atmosphere is doubtless very dense, as the belts
would seem to indicate.
TELESCOPIC FEATURES. Saturn's Rings. Galileo
first noticed something peculiar in the shape of Sat-
urn. Through his imperfect telescope it seemed to
have on each side a small planet like a supporter,
to help old Saturn on his way. He therefore an-
nounced to his friend Kepler his curious discovery,
that "Saturn is threefold." As the planet, how-
ever, approached its equinoxes, these attendants van-
ished altogether from his simple instrument. This
was a great perplexity to Galileo, and he never
solved the mystery. When the rings were after-
ward seen, their real form was not known. They
were supposed to be a kind of handle attached to the
planet, but for what purpose was not explained.
The series consists of three rings of unequal
oreadth, surrounding the planet at the equator. The
exterior ring is separated from the middle one by a
distinct break, while the interior one seems joined
186 THE SOLAR SYSTEM.
fco the middle one. They differ in their brightness
the exterior ring is of a grayish tint ; the middle one
is the most brilliant and is more luminous than Sat-
urn itself ; the interior is dusky and has a purple
tinge. The exterior and middle rings are both
opaque and cast on the planet a distinct shadow ;
while the interior one is so transparent that it ap-
pears upon the globe of Saturn as a dark band
through which the surface of the planet is readily
seen. The dimensions of the rings are given in the
following table (Guillemin) :
Miles.
Diameter of exterior ring 173,500
Breadth of exteriorring 10,000
Diameter of middle ring 150,000
Breadth of middle ring 18,300
Distance between exterior and middle ring 1,750
Diameter of interior ring 113,400
Breadth of interiorring 9,000
Distance of interior ring from planet 10,150
Entire breadth of ring system 39,050
Thickness of rings not more than 100
The rings revolve around Saturn in about 10
hours, in the same direction as the planet revolves
on its axis. The globe of Saturn is not exactly at
the centre of the rings. This fact, combined with
the rotary motion, is essential to the stability of the
rings, preventing them from being precipitated in
an overwhelming ruin and devastation upon the
body of the planet.
Phases of the rings. The plane of the rings is in-
clined 28 to the ecliptic. In its revolution about
the sun, the axis of Saturn remaining parallel to
SATURN.
187
itself, the sun sometimes illumines the northern
and sometimes the southern face of the rings. At
Saturn's equinoxes the edge only receives the light,
and the rings are invisible to us, except with the
Fig. 60.
PHASES OF SATURN'S KINGS.
most powerful telescopes, and then only as a line of
light. The body of the planet constantly cuts off
the sun's rays from a portion of the rings, and also
serves to conceal from our view some of the lumin-
ous part. By a careful study of the cut these vari-
ous positions of the planet and rings, with the most
favorable times for observation, may be understood.
Belts. The surface of Saturn is traversed by dusky
belts of a less distinct and definite appearance than
188 THE SOLAR SYSTEM.
those upon Jupiter. The equatorial regions are
brighter than the other parts of the disk ; the poles
especially are less luminous.
SATELLITES. Saturn has eight satellites, named
1. Mimas. 3. Tethys. 5. Rhea. 7. Hyperion.
2. Enceladus. 4 Dione. 6. Titan. 8. lapetus.
lapetus is the largest of these, and in size exceeds
Mars. Enceladus and Mimas are the faintest of
twinklers, and can only be seen with a powerful
telescope, and under most favorable circumstances.
They were first detected by Herschel, "threading
like pearls the silver line of light," to which the
ring, then seen edgewise, was reduced, advancing
off it at either end, returning, and then hiding them-
selves behind the planet. The first four of these
moons are nearer to Saturn than our moon to the
earth, but lapetus is nearly ten times as distant : so
that the diameter of the Saturnian system is nearly
four and a half million miles. The movements are
extremely rapid. Mimas traverses a space equal to
the diameter of our moon in two minutes, passing
from new to full in twelve hours, a little more than
a Saturnian day.
SATURNIAN SCENERY. The grandeur and magnifi-
cence of the scenery upon Saturn undoubtedly far
surpass anything with which we are familiar. In
the cut is given an ideal view of a landscape located
upon the planet at a latitude of about 28, taken
about midnight. The rings form an immense arch,
URANUS.
189
which spans the sky and sheds a soft radiance
around; while to add to the strange beauty of the
Fig. 61.
IDEAL LANDSCAPE ON SATURN.
Saturnian night, eight moons in all their different
phases, full, new, crescent, or gibbous, light up the
starry vault.
UKANUS.
" Heaven," the most ancient of the gods. Sign JJl ; H, the initial letter of
Herschel, with a planet suspended from the cross-bar.
DESCRIPTION. On the 13th of March, 1781, between
10 and 11 P. M., Sir William Herschel was engaged
in examining with his great telescope some stars
in the constellation Gemini. One small star at-
tracted his attention, which he accordingly observed
with a higher magnifying power, when, unlike the
190 THE SOLAB SYSTEM.
effect produced on the fixed stars, its disk widened,
Watching it for several nights, he detected its mo-
tion in space, and, mistaking its true character,
announced the discovery of a new comet. A few
months' examination revealed the error, and the new
body was universally admitted to be a member of
the solar system new to us, but older perhaps than
our own world. It is now known that Uranus had
been previously observed by other astronomers.
Indeed, Le Monier at Paris had watched it for
twelve successive nights, but pronounced it a fixed
star. Since he had also seen it on previous occa-
sions, had he been an orderly observer, he would
doubtless have detected its planetary character ; but
he was extremely careless, as may be inferred from
the fact related by Arago, that he had been shown
one of Le Monier's observations of this planet writ-
ten on a paper bag which originally contained hair-
powder purchased at a perfumer's. Uranus may be
seen by a person of strong eyesight in a perfectly
dark sky, if he previously knows its exact position
among the stars. Its faintness is due to its great
distance from the earth. Were it as near as the sun,
it would appear twice as large as Jupiter.
MOTION IN SPACE. Uranus revolves about the sun
at a mean distance of 1,754,000,000 miles. Its year
exceeds eighty-four of ours.
DIMENSIONS. Its diameter is about 33,000 miles.
It is lighter than water, having a density about
equal to that of ice.
NEPTUNE. 191
SEASONS. We know little of the seasons of Uranus.
Since its axis lies in the plane of its orbit, the sun
winds in a spiral form around the whole planet. The
light and heat are only y^Vtr of that which we
receive ; the light is about the quantity which would
be afforded by three hundred full moons. The in-
habitants of Uranus can see Saturn, and perhaps
Jupiter, but none of the planets within the orbit
of the latter.
TELESCOPIC FEATURES. No spots or belts have
been discovered with any telescope yet made. The
time of rotation and other features so familiar to us
in the nearer planets, are unknown with regard to
Uranus.
Satellites. Uranus has four moons, of which
little is known except the curious fact that their
orbits are nearly perpendicular to the plane of the
planet's orbit, and that their movements are retro-
grade i. e., in the same direction as the hands of a
watch.
NEPTUNE.
The god of the sea. Sign j , his trident.
DESCRIPTION. Neptune is the far-off sentinel at
the very outposts of the solar system, being the most
distant planet of which we have any knowledge. It
is invisible to the naked eye, and appears in the tel
oscope as a star of the eighth magnitude.
DISCOVERY. For many years the motions of Ura-
nus were such as to baffle the most perfect calcula-
192 THE SOLAR SYSTEM.
tions. While far-distant Saturn came around to his
place true to the minute and second, even after his
journey of nearly thirty years, Uranus defied arith-
metic, and refused to conform to the time set down
for him on the heavenly dial.
At length it was suggested by several astronomers
that there was another planet outside of its orbit,
whose attraction produced these perturbations. So
marked was this impression with Herschel, that he
writes : " "We see it as Columbus saw America from
the shores of Spain. Its movements have been felt
trembling along the far-reaching line of our analysis
with a certainty not far inferior to ocular demonstra-
tion." Finally, two young mathematicians, Lever-
rier of Paris, and Adams of Cambridge, England,
each unknown to the other, set themselves about the
task of finding the place of this new planet. The
problem was this : Given the disturbances produced
by the attraction of the unknown planet, to find its orbit
and its place in the orbit. Adams, after assiduous
labor for nearly two years, completed his calcula-
tions and submitted them to Prof. Airy, the Astron-
omer Koyal, in October, 1845. In the summer of
1846, Leverrier laid a paper before the Academy of
Sciences in Paris, announcing the position of the
unknown planet. Prof. Airy, hearing of this, was so
impressed with the value of Adams's calculations,
that he wrote to Prof. Challis, of Cambridge, to use
his large telescope to search that quarter of the
heavens. Prof. Challis did as requested, and saw a
NEPTUNE. 193
star which afterward proved to be the planet so
anxiously sought for, although at that time he failed
to ascertain its true character. On September 23d,
of the same year, Leverrier wrote to Berlin, asking
for assistance in searching for the planet. Dr. Galle,
that same evening, turned the large telescope of the
Observatory to the place indicated, and almost im-
mediately detected a bright star not laid down in
the maps. This proved to be the predicted planet,
found within less than a degree of the spot de-
scribed by Leverrier. Such is the history of one of
the grandest achievements of the human mind. It
stands as an ever fresh and assuring proof of the
exactness of astronomical calculations, and the pow-
er of the intellect to understand the laws of the God
of Nature.
MOTION IN SPACE. Neptune revolves about the
sun at a mean distance of about 2,750,000,000 of
miles. The Neptunian year is equal to nearly 165
terrestrial ones. Its motion in its orbit is the slow-
est of any of the planets, since it is the most remote
from the sun. The velocity decreases from Mercury,
which moves at the rate of 105,000 miles per hour,
to Neptune, whose rate is only 12,000 miles.
DIMENSIONS. Its diameter is about 37,000 miles.
Its volume is nearly 100 times that of the earth. Its
density is about that of Uranus, a little less than that
of water.
SEASONS. As the inclination of its axis is un-
known, nothing can be ascertained concerning its
9
194 THE SOLAR SYSTEM.
seasons. The sun gives to Neptune but y^Vfr the
light and heat which we receive.
Though at the extreme of the solar system, 2,650
millions of miles beyond us, the same heavens bend
above, the same starry sky is seen by night the
Milky Way is no nearer to the eye, the fixed stars
shine no more brightly. The planets, however, are
all too near the sun to be seen, except Saturn and
Uranus. The Neptunian astronomers, if there be
any, are well situated for observing the orbits of
correts, and for measuring the annual parallax of
the stars, since they have an orbit of 5,500 million
miles in diameter, and hence the angle must be 30
times as great as that which the terrestrial orbit
affords.
TELESCOPIC FEATURES. On account of the recent-
ness of the discovery of this planet and its immense
distance, nothing is known of its rotation or physical
features.
Satellites. Neptune has one moon, at nearly the
same distance from it as our own moon is from the
earth. The revolution of this about the planet,
which is accomplished in about six days, has fur-
nished the materials for calculating the mass of
Neptune.
METEOKS AND SHOOTING STAES.
DESCRIPTION. All are familiar with those lumin-
ous bodies that flash through our atmosphere as if
METEORS AND SHOOTING STARS.
195
the stars were indeed falling from heaven. Differ-
ent names have been applied to them, although the
distinction is not very definite. (1) Aerolites are those
A METEOR WITH ITS TBAIN.
stony masses which fall to the earth. (2) Shooting
Stars are those evanescent brilliant points that snd-
196 THE SOLAR SYSTEM.
denly dart through the higher regions of the air,
leaving a fiery train behind. (3) Meteors are lumin-
ous bodies which have a sensible diameter and a
spherical form. They frequently pass over a great
extent of country, and are seen for some seconds of
time. Many leave behind a train of glowing sparks ;
others explode with reports like the discharge of
artillery, the pieces either continuing their course,
or falling to the earth as aerolites. Some meteors,
doubtless, after having favored us with a transient
illumination, pass on into space ; some are vapor-
ized; while others are burned and the ashes and
fragments fall to the ground.
AEROLITES. The fall of aerolites is frequently men-
tioned and well authenticated. Chinese records tell
of one as long ago as in 616 B. c., which, in its fall,
broke several chariots and killed ten men. A block
of stone, equal to a full wagon-load, fell in the Helles-
pont, B. c. 465. By the ancients, these stones were
held in great repute. The Emperor Jehangire, it is
related, had a sword forged from a mass of meteoric
iron which fell in the Punjab in 1620. In 1795, a
mass was seen, by a ploughman, to descend toward
the earth at a spot not far from where he was stand-
ing. It threw up the soil on every side, and pene-
trated some distance into the solid rock beneath,
In 1807, a shower of stones, one weighing 200 Ibs.,
fell at "Weston, Connecticut. These aerolites are
sometimes seen to plunge downward into the earth,
aiuj are found while yet glowing. A mass thus fell in
METEORS AND SHOOTING STABS. 197
South America, which was estimated to weigh fifteen
tons. When first discovered, it was so hot as to
prevent all approach. Upon its cooling, many efforts
were made, by some travellers who were present, to
detach specimens, but its hardness was too great for
any tools which they possessed. There is a mass of
meteoric iron in Yale College cabinet, weighing
1,635 Ibs.
Aerolites consist of elements which are familiar.
The analysis of these stellar masses gives us names
as commonplace as if they had known a far
less romantic origin oxygen, sulphur, phosphorus,
iron, tin, copper : in all, nineteen elements have
been found. This fact is interesting as reveal-
ing something of the chemistry of the region of
space, concerning which we otherwise know nothing.
The compounds, however, are very peculiar, so as
to distinguish an aerolite from any terrestrial sub-
stance. For example, meteoric iron, a prominent
constituent of aerolites, is an alloy that has never
been found in terrestrial minerals.
METEORS. The records of meteors are still more
wonderful. It is related that at Crema, Italy, one
day in the 15th century, the sky at noonday be-
came dark, a cloud of appalling blackness over-
spreading the heavens. Upon this cloud appeared
the semblance of a great peacock of fire flying over
the town. This suddenly changed to a huge pyramid,
that rapidly traversed the sky. Thence arose awful
lightnings and thunderings, amid which there feD
198 THE SOLAR SYSTEM.
upon the plain great rocks, some of which weighed
100 Ibs. In 1803 a brilliant fireball (meteor) was
seen traversing Normandy with great velocity, and
some moments after, frightful explosions, like the
noise of cannon or roll of musketry, were heard com-
ing from a single black cloud hanging in a clear
sky; they were prolonged for five or six minutes.
These discharges were followed by a great shower
of stones, some weighing over 24 Ibs. In 1819 a
meteor was witnessed in Massachusetts and Mary-
land, the diameter of which was estimated at half
a mile. Its height was thought to be about 25 miles.
In July, 1860, a brilliant fireball passed over the
state of New York from west to east, and was last
seen far out at sea.
SHOOTING STARS. One of the earliest accounts of
star-showers is that which relates how, in 472, the
sky at Constantinople appeared to be alive with fly-
ing stars and meteors. In some Eastern annals we
are told that in October, 1202, " the stars appeared
like waves upon the sky. They flew about like
grasshoppers, and were dispersed from left to right."
It is recorded that in the time of King William II.
there occurred in England a wonderful shower of
stars, which " seemed to fall like rain from heaven.
Aai eye-witness seeing where an aerolite fell, cast
water upon it, which was raised in steam with a
great noise of boiling." Kastel says concerning it :
" By the report of the common people in this kynge's
METEORS AND SHOOTING STABS. 199
time, diverse great wonders were seene, and there-
fore the kynge was told by diverse of his familiars,
that God was not content with his lyvyng."
In more modern times, the most remarkable ac-
counts are those of the showers of November 12th,
1799, and 1833. Humboldt, in describing the former,
says the sky was covered with innumerable fiery
trails, which incessantly traversed the sky from
north to south. From the beginning of the phenom-
enon there was not a space in the heavens three
times the diameter of the moon which was not filled
every instant with the celestial fireworks, large
meteors blending constantly their dazzling brilliancy
with the long phosphorescent paths of the shooting
stars. Tto latter shower was most brilliant on this
continent, and was visible from the lakes to the equa-
tor. The scene was one of the most imposing grand-
eur. Phosphoric lines swept over the sky like the
flakes of a sharp snow-storm. Large meteors darted
across the heavens, leaving luminous trains behind
them that were visible sometimes for half an hour :
they generally shed a soft white light ; occasionally,
however, yellow, green, and other colors varied
the scene. Irregular fireballs, almost stationary,
glared in the sky; one especially, larger than the
moon, hung in mid air over Niagara Falls and'
mingled its ghastly light with the foam and mist of
the cataract. The shower commenced near mid-
night, but was at its height about 5 A.M. In many
200 THE SOLAR SYSTEM.
sections of the country, the people were terror-
stricken by the awful spectacle, and supposed that
the end of the world had come.
An inferior shower was seen in 1831 and 1832 ;
and so also in the succeeding years, until 1839.
These did not compare in brilliancy with the re-
markable phenomenon of 1833.
There was an interval of about 33 or 34 years
between the great showers of 1799 and 1833 ; this
seemed to indicate another shower in November,
1866. The people of both hemispheres were liter-
ally awake to the subject. Newspapers aroused the
most sluggish imagination with thrilling accounts of
the scenes presented in 1799 and 1833. Extempore
observatories were founded in every convenient point.
Watchmen were stationed, and the city bells were to
be rung on the appearance of the first wandering
celestial visitor. The exact night was not definitely
known, but for fear of a mistake, the llth, 12th, and
13th were generally observed. All painfully testify
to those nights being clear and beautiful as moon-
light and starlight could make them. The anxious
vigils, the fruitless scannings of the sky, the disap-
pointment, the meteors that were dimly tJiought to
be seen all these are recorded in the memory of
the temporary astronomers of that year. While,
however, the people of America were thus disap-
pointed, there was being enacted in England a dis-
play brilliant indeed, though inferior to the one of
METEORS AND SHOOTING STAES. 201
1833. The staff at Greenwich Observatory counted
about 8,000 meteors ; other observers, however, made
a much lower estimate. Chambers, in describing the
phenomena, says : " Of the large number of descrip-
tions which came under my eye in manuscript and
in print, the following is a fair example : 'From 11^
p. M. until 2 A. M. we were much interested in watch-
ing the shooting stars ; anything so beautiful I never
saw, especially about one o'clock, when they were
most brilliant ;' and so on by the ream." In Novem-
ber, 1867, the long-expected shower was seen in this
country, but it failed to satisfy the public expecta-
tion. The sky was, however, illumined with shoot-
ing stars and meteors, some of which exceeded even
Jupiter or Yenus in brilliancy.
Number of meteors and shooting stars. In a paper
lately read by Prof. Newton, it is estimated that the
average number of meteors that traverse the atmos-
phere daily, and which are large enough to be visi-
ble to the eye on a dark clear night, is 7,500,000 ;
and if to these the telescopic meteors be added, the
number would be increased to 400,000,000. In the
space traversed by the earth there are, on the aver-
age, in each volume the size of our globe (including
its atmosphere), as many as 13,000 small bodies,
each one capable of furnishing a shooting star visi-
ble under favorable circumstances to the naked eye.
Annual periodicity of the star-showers. On almost
any clear night, from five to seven shooting stars
202 THE SOLAR SYSTEM.
may be seen per hour, but in certain months they
are much more abundant. Arago names the fol-
lowing principal dates :
April 4-11 ; 17-25. October (about) 15.
August 9-11. November 11-13.
ORIGIN. Aerolites, meteors, and falling stars all
seem to have a common origin. They are produced
by small bodies planets in miniature which are
revolving, like our earth, about the sun. Their or-
bits intersect the orbit of the earth, and if at any
time they reach the point of crossing exactly with
the earth, there is a collision. Their mass is so
small, that the earth is not jarred any more than
is a railway train by a pebble thrown against it.
These small bodies may come near the earth and
be drawn to its surface by the power of attraction ;
or they may simply sweep through the higher re-
gions of the atmosphere, and there escape its gr&sp ;
or, finally, they may, under certain conditions, be
compelled to revolve many times around the earth
as satellites. Indeed, a French astronomer esti-
mates that there is one now circling about the
earth at a distance of 5,000 miles. This companion
of our moon has a period of three hours and twenty
minutes. The average velocity of these meteoric
bodies or bolides, as they are frequently called, is
thirty-six miles per second much greater than that
of Mercury itself. As they sweep through the air,
METEORS AND SHOOTING STARS. 203
the friction partly arrests their motion, and converts
it into heat and light. The body thus becomes visi-
ble to us. Its size and direction determine its ap-
pearance. If very small, it is consumed in the upper
regions, and leaves only the luminous trail of a shoot-
ing star. If of large size, it may sweep along at a
high elevation, or plunge directly toward the ground.
Becoming highly heated in its course, it sheds a
vivid light, while, unequally expanding, it explodes,
throwing off large fragments which fall to the earth
as aerolites, or continue their separate course as
meteors. The cinders of the portion consumed rain
down on us as fine meteoric dust.
METEORIC KINGS. These little bodies, it is thought,
do not generally revolve individually about the sun,
but myriads of them are collected in several rings,
and when the earth passes through one of these
floating girdles, a star-shower follows. This would
account for their regular appearance in certain sea-
sons of the year. In the cut we see how one ring,
intersecting the earth's orbit at two points, would
account for the August and November showers.
Another ring, more inclined to the earth's path, and
crossing it nearer the aphelion point, would produce
the April showers.
Recent investigators are inclined to the view that
there are separate rings for each of the established
periods, and that they are very elliptical. The No-
vember ring seems to have its perihelion near the
204 THE SOLAR SYSTEM.
ecliptic, and its aphelion beyond the orbit of Uranus;
while the August ring extends beyond the solar sys-
tem. The day of the month in which the great No-
vember shower occurs is becoming later at each re-
Fig. 63.
METEORIC RING.
turn ; hence it is believed that the nodes of that ring
are slowly travelling eastward along the ecliptic. The
meteoric bodies are supposed to be quite uniformly
distributed through the August stream, but very un-
METEORS AND SHOOTING STARS. 205
equally thiough the November one. On this ac-
count, the former star-showers are quite regular,
while the latter vary in brilliancy through periods
of 33^ years.
RELATION BETWEEN METEORS AND COMETS. The
orbit of the November shower is found to be almost
identical with that of the comet of 1866 ; while the
August stream is in the track of the comet of 1862.
It is a popular theory that these comets are only
clusters of meteors crowded so closely together as to
be visible by the reflected light of the sun. The single
meteors are too small to be seen, except when they
plunge into the earth's atmosphere and take fire.
On the other hand, Herschel thinks that meteors are
the dissipated parts of comets torn into shreds by
the sun's attraction.
RADIANT POINT. A star (jx) in the blade of the
sickle is the point from which the stars in the Novem-
ber shower seem to radiate, while one in Perseus (7)
is the radiant point of the August shower. In the
shower of 1866, two observers, who counted the
falling stars at the rate of 2,500 per hour, saw only
five whose paths, if traced back, would not meet
in Leo.
METEOROLOGICAL EFFECT. The temperature of
August and November is said to be considerably in-
creased by this ring of meteoric bodies, which pre-
vents the heat of the earth from radiating into
space. A corresponding decrease of temperature
in February and May is caused by the stream
206 THE SOLAB SYSTEM.
or ring of meteors coming between the sun and
earth.
HEIGHT. Herschel estimates the average height
of shooting stars above the earth at 73 miles at their
appearance and 52 at their disappearance.
WEIGHT. Prof. Harkness estimates that the aver-
age weight of shooting stars does not differ much
from one grain.
COMETS.
We come now to notice a class of bodies the
most fascinating, perhaps, of any in astronomy.
The suddenness with which comets flame out in
the sky, the enormous dimensions of their fiery
trains, the swiftness of their flight, the strange and
mysterious forms they assume, their departure as
unheralded as their advent all seem to bid defiance
to law, and partake only of the marvellous. Su-
perstitious fears have always been excited by their
appearance, and they have been looked upon in
every age as
" Threatening the world with famine, plague, and war ;
To princes, death ; to kingdoms, many corses ;
To all estates, inevitable losses ;
To herdsmen, rot ; to ploughmen, hapless seasons ;
To sailors, storms ; to cities, civil treasons."
Thus the comet of 43 B.C., which appeared just
after the assassination of Julius Csesar, was looked
upon by the Komans as a celestial chariot sent to
convey his soul heavenward. An old English writer
COMETS. 207
observes : " Cometes signifie corruptions of the ayre.
They are signs of earthquakes, of warres, of chang-
yng kyngedomes, great dearthe of corn, yea, a com-
mon death of man and beast." Another remarks :
"Experience is an eminent evidence that a comet,
like a sword, portendeth war ; and a hairy comet, or a
comet with a beard, denoteth the death of kings, as
if God and nature intended by comets to ring the
knells of princes, esteeming bells in churches upon
earth not sacred enough for such illustrious and emi-
nent performances."
DESCRIPTION. The term comet signifies a hairy
body. A comet consists usually of three parts ; the
nucleus, a bright point in the centre of the head, ; the
Fig: 64. Fig. 65.
COMKT WITHOUT A NUCLEUS. COMET WITH A NUCLEUS.
coma (hair), the cloud-like mass surrounding the nu-
cleus ; and the tail, a luminous train extending gen-
erally in a direction from the sun. There are comets
without the tail, and others with several, while some
are deprived of even the nucleus. These last consist
merely of a fleecy mass, known to be comets from
208 THE SOLAR SYSTEM.
their orbits and rapid motion. Comets are not con-
fined, like the planets, to the limits of the zodiac,
but appear in every quarter of the heavens, and move
in every conceivable direction. "When first seen,
the comet resembles a faint spot of light upon the
dark background of the sky : as it approaches the
sun the brightness increases, and the tail begins to
show itself. Generally it is brightest near perihelion,
and gradually fades away as it recedes, until it is
finally lost, even to the telescope.
THE TIME OF THE GREATEST BRILLIANCY depends
somewhat on the position of the earth. If, as rep-
resented in the figure, the earth is at a when the
comet, moving toward perihelion, is at r, the comet
will appear more distinct than
when it is more distant at s, al-
though at the latter point it
is really brighter. If, how-
ever, the earth is at c or b at
the time of perihelion, the com-
et would be much more con-
spicuous. Again, if the earth
is passing from a to "b during the .time the comet is
near the sun, it will appear less brilliant than if it
were moving from c to d, as we should then be much
nearer it during its greatest illumination.
NUMBER OF COMETS. Kepler remarks that there
are as many " comets in the heavens as fish in the
sea." Arago has estimated that there are 17,500,000
within the solar system, basing his calculations on the
ORBIT OF COMET.
COMETS. 209
number known to exist between the sun and Mercury.
Of this vast number, few are visible to the naked
eve, and a still less number attract observation, ow-
ing to their inferior size and brilliancy. Many are
doubtless lost to our sight by being above the hori-
zon in the daytime. Seneca mentions that during a
total solar eclipse, a large and splendid comet sud-
denly made its appearance near the sun.
ORBITS or THE COMETS. Comets form a part of
the solar system, and are subject to the laws of grav-
itation. Like the planets, they revolve around the
sun, but they differ in the form of their orbits.
While the planets move in paths varying but little
from circular, and thus never depart so far from the
sun as to be invisible to us, the comets travel in ex-
tremely elongated (flattened) ellipses, so that they
can be observed by us only through a very small
portion of their paths. In Fig. 67 are represented the
three general classes of their orbits. A comet travel-
ling along an elliptical orbit, though it may pass far
from the sun, will yet return within a fixed time;
one pursuing either a parabolic or hyperbolic curve
cannot return, as the two sides separate from each
other more and more. Many of the comets of the
first class have been calculated, and they have re-
peatedly visited our portion of the heavens ; while
those of the other classes, having once formed part
of our system, go away forever, seeking perhaps in
the far-off space another sun, which in turn they
will abandon as they have our own.
210
THE SOLAR SYSTEM.
Fig. 67.
THREE FORMS OP COMETARY OBBITB.
CALCULATION OF A COMET'S EETUEN. As we can
observe so small a proportion of the entire orbit, it
is very difficult, indeed oftentimes impossible, to
decide whether it is an ellipse, hyperbola, or para-
bola. A few are known to move in clearly ellip-
tical paths, and their movements have been so
accurately estimated that it is possible to predict
their exact place in the starry vault on any given
COMETS. 211
day and hour. The other comets may never return,
or at least not for centuries hence. They may be
paying our sun their first visit ; or if they have swept
through the solar system before, it may have been
at so remote a time that no record is preserved,
even if it were not before the creation of man. Un-
der these circumstances it is obviously extremely
difficult to determine the times of these apparently
erratic wanderers ; yet, in spite of all these obsta-
cles, some have been tracked far into space beyond
the telescopic view. For example, the comet of
1844 is announced to pay a visit to the astronomers
of the year of our Lord 101,844. The period of the
comet of 1744, is fixed at 122,683 years.
DISTANCE FKOM THE SUN. The comets at their
perihelion sweep very near the sun. Thus the one
of 1680 came where the temperature was estimated
by Newton to be about 2,000 times that of red-hot
iron. The nearest approach known is that of the
comet of 1843, whose perihelion distance was but
about 30,000 miles from the surface of the sun ; in
fact, it doubled around that body in two hours' time.
(Guillemin.) The greatest aphelion distance yet
estimated is that of the comet of 1844, which is
over 400,000,000,000 miles. The velocity varies, of
course, with the position in the orbit. The comet of
1680 moved in perihelion at the rate of over two
hundred and seventy-seven miles per second ; while
in aphelion its velocity is only about six miles per
hour.
212 THE SOLAR SYSTEM.
DENSITY OF COMETS. The quantity of matter con-
tained in a comet is exceedingly small. Telescopic
stars even are visible through them. The comet of
1770 became entangled among Jupiter's moons, and
remained there four months without interfering with
their movements in the least; indeed, so far from
that, its own orbit was so much changed by the prox-
imity, that from a periodical return of 5J years, it
has not been seen since. The same comet came
within 1,400,000 miles of the earth without produ-
cing any sensible effect. In 1861, we have good
reason to suppose that the earth actually passed
through the tail of a comet, its presence being
indicated only by a peculiar phosphorescent mist.
So that even should our earth run full-tilt against
a comet, the shock would be quite imperceptible.*
Still, however lightly we may speak of the proba-
bility of such a collision, we must remember that
there are comets of greater solidity. Donati's, for
instance, is estimated to be about -fa the bulk of
the earth. The concussion of such a body, moving
* " However dangerous might be the shock of a comet, it might
be so slight that it would only do damage at that part of the earth
where it actually struck ; perhaps even we might cry quits, if,
while one kingdom were devastated, the rest of the earth were
to enjoy the rarities which a body coming from so far might
bring to it. Perhaps we should be very surprised to find that the
debris of these masses that we despised were formed of gold or
diamonds; but who would be the more astonished we or the
comet-dwellers who would be cast on our earth ? What strange
beings each would find the other !" Lettre sur la Combte (M
De Maupertuis.)
COMETS. 213
with the speed of a cannon-ball, would undoubtedly
produce a very sensible effect.
It is not understood whether comets shine by their
own or by reflected light. If, however, their nuclei
consist of white-hot matter, a passage through such
a furnace would be any thing but desirable or satis-
factory. After all the calculations of Astronomy, our
only safety lies in ttat Almighty Power which traces
the path and guides the course alike of planets and
comets : He, whose eye marks the fall of the spar-
row, sees as well the flight of the worlds He has
created.
VARIATIONS IN FORM AND DIMENSIONS. Comets ap-
pear to be subject to constant variations. They are
now generally thought to decrease in brilliancy at
each successive revolution about the sun. The same
comet may present itself sometimes with a tail, and
sometimes without. When the comet first appears,
there is generally no tail visible, and the light is
faint. As it approaches the sun, however, its bright-
ness increases, the tail shoots out from the coma,
and grows daily in length and splendor. Supernu-
merary tails, shorter and less distinct than the prin-
cipal one, dart out, but they generally soon disap-
pear, as if from lack of material. The tail of the
comet of 1843, just after the perihelion, increased in
length 5,000,000 miles per day. As the tail thus
extended, the nucleus was correspondingly con-
tracted, so that this comet actually " exhausted
itself in the manufacture of its own tail."
214 THE SOLAR SYSTEM.
REMARKABLE COMETS. Among the many comets
celebrated in history, we shall only notice some of
those that have appeared in the present century.
The great comet of 1811 was a magnificent spec-
tacle. The head was 112,000 miles in diameter ; the
nucleus was 400 miles ; while the tail, of a beautiful
fan-shape, stretched out 112,000,000 miles. The
aphelion distance of this comet is fourteen times
that of Neptune, or 40,000,000,000 miles. It is an-
nounced to return in thirty centuries ! To what
profound depths of space, beyond the solar system,
beyond the reach of the telescope, must such a
journey extend !
The comet of 1835 is commonly known as Halley 's
comet. This is remarkable as being the first comet
whose period of revolution was satisfactorily estab-
lished. Dr. Halley, on examining the accounts of
the great comets of 1531, 1607, and 1682, suspected
that they were only the reappearance of the same
comet, whose period he fixed at about 75 years. He
finally ventured to predict the return of the comet
about the end of 1758 or beginning of 1759. Although
Halley did not live to see his prophecy fulfilled, great
interest was felt in the result. It was not destined,
however, for a professional astronomer to be the first
to detect the comet. A peasant near Dresden saw
it on Christmas night, 1758. The history of this
comet, as it has been traced back by its period of
seventy-five years, is quite eventful. It was seen in
England in 1066, when it was looked upon with
COMETS. 215
dread as the forerunner of the victory of William of
Normandy. It was then equal to the full moon in
size. In 1456, its tail reached from the horizon to
the zenith. It was supposed to indicate the success
of Mahomet II., who had already taken Constanti-
nople, and threatened the whole Christian world.
Pope Calixtus III., therefore, ordered extra Ave
Marias to be repeated by everybody, and also the
church bells to be rung daily at noon (whence origi-
nated the custom now so universal). A prayer was
added as follows : " Lord, save us from the devil, the
Turk, and the comet." In 1223, it was considered
the precursor of the death of Philip Augustus. The
first recorded appearance of Halley's comet was
B. c. 130, when it was supposed to herald the birth of
Mithridates.
TJie comet of 1843 was so intensely brilliant that it
was visible in full daylight. It was so near the
sun as " almost to graze his surface."
Encke's comet has a period of only 3J years. A
most interesting discovery has been made from ob-
servations upon its motion. The comet returns each
time to its perihelion about 2 J hours earlier than the
most perfect calculations indicate. Hence, Prof.
Encke has been led to conjecture that space is filled
with a thin, ethereal medium capable of diminishing
the centrifugal force, and thus contracting the orbifc
of a comet.
Donates comet, which appeared in 1858, was the
subject of universal wonder. When first discovered,
216 THE SOLAR SYSTEM.
in June, it was 240,000,000 miles from the earth. In
August, traces of. a tail were noticed, which expanded
in October to about 50,000,000 miles in length. This
Fig. 68.
DONATI'8 COMET.
comet, though small, lias never been exceeded in
the brilliancy of the nucleus and the graceful cur-
vature of the tail. It will return in about 2,000
years.
ZODIACAL LIGHT.
217
ZODIACAL LJOHT.
ZODIACAL LIGHT.
DESCRIPTION. If we watch the western horizon in
March or April, just after sunset, we shall sometimes
see the short twilight of that season illuminated by
10
218 THE SOLAR SYSTEM.
a faint, nebulous light, of a conical shape, flashing
upward, often as high as the Pleiades. In September
and October, at early dawn, the same appearance
can be detected near the eastern horizon. The
light can be seen in this latitude only on the most
favorable evenings, when the sky is clear and the
moon absent. Even then, it will be frequently con-
founded with the Milky Way or auroral lights. At
the base it is of a reddish hue, where it is so bright
as very often to efface the smaller stars. In tropical
regions the zodiacal light is perpetual, and shines
with a brilliancy sufficient, says Humboldt, to cast a
sensible glow on the opposite part of the heavens.
ORIGIN. The commonly received opinion is, that
it is caused by a faint cloud-like ring, perhaps a me-
teoric zone, that surrounds the sun, and only be-
comes visible to us when the sun himself is hidden
below the horizon. Others maintain that, since it
has been seen in tropical regions in the east and
west simultaneously, it can be explained only on the
theory of a "nebulous ring that surrounds the earth
within the orbit of the moon."
the Sidereal jfetqm.
"He telleth the number of the stars; He calleth them all by
their names."
PSALM cxlvii. 4.
THE SIDEREAL SYSTEM.
THE STAKS.
IN our celestial journey we have reached Neptune,
the sentinel outpost of the solar system. "We are
now 2,750 millions of miles from our sun. Yet we
are apparently no nearer the fixed stars than when
we first started. They twinkle as serenely there in
the far-off sky as to us here on the earth. The
heavens by night, with the exception of a few
changes in the planets, look perfectly familiar.
Between them and us there is a vast chasm which
no imagination can bridge ; a distance so immense
that figures are meaningless, and we can only call
it space, so profound that to us it is limitless, though
beyond we see other worlds twinkling like distant
lights over a waste of waters.
WE NEVER SEE THE STABS. This assertion seems
almost paradoxical, yet it is strictly true. So far
are the stars removed from us, that we see only the
light they send, but not the surface of the worlds
themselves. They are merely glittering points of
222 THE SIDEREAL SYSTEM.
light. The most powerful telescope fails to produce
a sensible disk. This constitutes a marked point
of difference between a planet and a fixed star.
THE ANNUAL PARALLAX OF THE FIXED STARS. When
speaking of this subject on page 139, we said that
183,000,000 miles, or the diameter of the earth's
orbit, is taken as the unit for measuring the par-
allax of the fixed stars. Yet when the stars are
viewed from even these extreme points, they mani-
fest so very slight a change of place, that to esti-
mate it is one of the most delicate feats of astron-
omy.* At the present time, it is considered that
the star Alpha (a) Centauri in the southern heavens
is the nearest to the earth. Its parallax is judged
to be about 1". Its distance is more than 200,000
times that of the earth from the sun, or nineteen tril-
lions of miles. This is probably by no means its ex-
treme distance, but merely the limit ivithin which
it cannot be, but beyond which it must be. These
figures convey to our mind no idea of distance. Our
imagination fails to grasp the thought, or to picture
the vast void across which we are gazing. We
remember that light moves at the wonderful rate
of 183,000 miles per second. A ray at this speed
would plunge out into the abyss beyond Neptune,
in one day, six times the distance of that planet
* Prof. Airy says the star which gives the greatest parallax
of any, presents the same angle as that at which a circle six-
tenths of an inch in diameter would be seen at the distance of
a mile 1
THE STABS. 223
from the sun. Yet it must sweep on at this prodig-
ious speed, day and night, for three years and nine
months to span the gulf and reach a stopping point
at the nearest fixed star. "To a spectator standing
at a Centauri, the entire diameter of the earth's
orbit would be hidden by a thread -fa of an inch in
diameter, held at a distance of 650 feet from the
eye." That is to say, a line 183,000,000 miles long,
looked at broadside, would shrink into a mere point.
If our sun were removed to that distance, it would
shine with a light only equal to that of the north
polar star, and would take its place among the con-
stellations as a fixed star.
This, we must remember, is the distance of the
nearest fixed star. It has been estimated that the
average time required for the light of the smallest
stars which are visible to the naked eye to reach the
earth is about 125 years. What, then, shall we say
of those far-distant ones, whose faint light appears
as a mere fleecy whiteness even in the most power-
ful telescopes ? The conclusion is irresistible, that
the light we receive set out on its sidereal journey
far back in the past, perhaps before the creation of
man!
MOTION OF THE FIXED STABS. It will aid us still
further in comprehending the immense distances of
the stars, to learn that though they seem to be fixed,
yet they are moving much more swiftly than any of
the planets. Thus, Arcturus flies through space at
the astonishing rate of about 200,000 miles per hour,
224 THE SIDEREAL SYSTEM.
or nearly twice that of Mercury, and more than three
times that of the earth. Yet, through all our life-
time, we shall never be able to detect any change in
its position. It requires three centuries for it to
move over the starry vault a space equal to the
moon's apparent diameter.
THE STABS ARE SUNS. The vast distance at which
they are known to be, precludes the thought of their
shining, like the planets or the moon, by reflecting
back the light of our sun. They must be self-lumin-
ous, and are doubtless each the centre of a system
of planets and satellites.
OUR SUN A STAR. As we see only the suns of these
distant systems, so their inhabitants see only the
sun of ours, and that as a small star.
OUR SYSTEM ITSELF IN MOTION. Like all the other
stars, our sun is in motion. It is sweeping onward,
with its retinue of worlds, 150,000,000 miles per year,
toward a point in the constellation Hercules. The
Pleiades are thought to be the centre around which
this great movement is taking place, but the orbit is
so vast and the centre so remote, that nothing defi-
nite is yet known.
THE NUMBER OF THE FIXED STARS. As we look at
the heavens on a clear night, the stars seem almost
innumerable. To count them, one would think al-
most as interminable a task as to number the leaves
on the trees. It is, therefore, somewhat startling to
learn that the entire number visible to the most
piercing eyesight, does not exceed 6,000, while few
THE STARS.
225
can discern more than 4,000. This illusion may be
easily explained, when we remember how the impres-
sion of a bright light remains upon the retina, as in
the whirling of a firebrand. However, the number
Fie. 70.
A PART OF THE CONSTELLATION OF THE TWTKfl.
which may be seen with a telescope becomes alto-
gether marvellous. In the cut is shown a portion
226 THE SIDEREAL SYSTEM.
of the heavens where the naked eye sees but sis
stars. Could we examine the same region of the
sky with more powerful instruments, new constella-
tions would doubtless be descried in the infinite
depths of space.
SCINTILLATION. The twinkling of the fixed stars is
due to what is termed in Natural Philosophy " the
interference of light." The air being unequally
dense, warm, and moist in its various strata, trans-
mits very irregularly the different colors of which
white light is composed. Now one color prevails
over the rest, and now another, so that the star ap-
pears to change color incessantly. As the purity
of the air varies, the twinkling of the stars also
changes, although it is always greatest near the
horizon. Humboldt says that at Cumana, in South
America, where the air is remarkably pure and uni-
form in density, the stars cease to twinkle after they
have risen 15 above the horizon. This gives to
the celestial vault a peculiarly calm and soft appear-
ance.
MAGNITUDE OF THE STARS. As the telescope re-
veals no disk of even the nearest stars, we know
nothing of their comparative size. The finest spi-
der's web, placed at the focus of the instrument,
hides the star from the eye. When the moon passes
in front of a star, the occultation is instantaneous,
and not gradual, as in the case of the planets. Clas-
sification depends, therefore, upon their relative
brightness. The most conspicuous are termed stars
THE STABS. 227
of the first magnitude. There are about twenty of
these. The number of second magnitude stars in
the entire heavens is about sixty-five ; of the third,
about 200 ; of the fifth, 1,100 ; and of the sixth,
Fig. 71.
3,200. Few persons can see any smaller stars than
those of the fifth or sixth magnitude. The ordinary
telescope shows faint stars down to the tenth, while
the more powerful instruments reveal those as low
as the twentieth magnitude.
THE CAUSE OF THE DIFFERENCE IN THE BRIGHTNESS
OF THE STARS. This may result from a difference in
their distance, size, or intrinsic brightness. Whence
it follows that the faintest stars may not be the most
distant from the earth.
NAMES OF THE STARS. Many of the brightest stars
received proper names at an early date ; as Sirius,
Arcturus. The stars of each constellation are dis-
tinguished by the letters of the Greek alphabet ; the
brightest being usually called Alpha, the next Beta
etc., the name of the constellation, in the genitive
case, being put after each. Ex., a Arietis, fi Lyras.*
* This means a of Aries, /3 of Lyra; the genitive case in Latin
being equivalent to the preposition of.
228
THE SIDEREAL SYSTEM.
THE GREEK
ALPHABET.
A
a
Alpha
N
V
Nu
B
#
Beta
H
I
Xi
r
7
Gamma
Omicron
A
6
Delta
n
<x
Pi
E
i
Epsilon
p
P
Rho
Z
r
Zeta
2
s-
Sigma
H
>?
Eta
T
r
Tau
Theta
T
u
Upsilon
I
I
Iota
$
9
Phi
K
X
Kappa
X
X
Chi
A
X
Lambda
*
4,
Psi
M
*
Mu
ft
CO
Omega
When the Greek letters are exhausted, the Roman
alphabet is used in the same way. Star catalogues
are issued, containing the stars arranged in the
order of their Right Ascension, and numbered for
convenience of reference. Argelander's Charts have
300,000 stars marked in the northern hemisphere.
THE CONSTELLATIONS. From the earliest ages, the
stars have been arranged in constellations, for the
purpose of more readily distinguishing them. Some
of these groups were named from their supposed re-
semblance to some figures, such as perching birds,
pugnacious bulls, or contorted snakes, while others
do honor to the memory of the classic heroes of an-
tiquity.
" Thus monstrous forms, o'er heaven's nocturnal arch,
Seen by the sage, in pomp celestial march ;
THE STABS. 229
See Aries there his glittering bow unfold,
And raging Taurus toss his horns of gold ;
With bended bow the sullen Archer lowers,
And there Aquarius comes with all his showers;
Lions and Centaurs, Gorgons, Hydras rise,
And gods and heroes blaze along the skies."
With a few exceptions, the likeness is purely fan-
ciful. The heavens are much less of a menagerie
than a celestial atlas would make them appear.
The division into constellations is a mere relic of
barbarism, entirely unworthy of modern civilization.
Not only are the figures uncouth, and the origin
often frivolous, but the boundaries are not distinct.
Stars often occur under different names ; while one
constellation encroaches upon another. As Cham-
bers well remarks, " Aries should not have a horn in
Pisces and a leg in Cetus, nor should 13 Argos pass
through the Unicorn's flank into the Little Dog. 51
Camelopardali might with propriety be extracted
from the eye of Auriga, and the ribs of Aquarius re-
leased from 46 Capricorni." While, however, the
constellations are thus rude and imperfect, there
seems little hope of any change. Age gives them a
dignity that insures their perpetuation.
INVENTION OF THE CONSTELLATIONS. This goes
back into ages of which no record remains. By
some it has been ascribed to the Greeks. When the
signs of the zodiac were named, they doubtless coin-
cided with the constellations. Aries (the ram) was
so called because it rose with the sun in the spring-
time, and the Chaldean shepherds named it from
230 THE SIDEREAL SYSTEM.
their flocks, their most valued possession. Then fol-
lowed in order Taurus (the bull) and Gemini (the
twins), called from the herds, which were esteemed
next in value. At the summer solstice the sun ap-
pears to stop, and, crab-like, to crawl backward;
hence the name Cancer (the crab). When the sun
is in Leo, the brooks being dry, the lion leaves his
lurking-place and becomes a terror to all. Virgo
comes next, when the virgins glean in the summer
harvest. At the autumnal equinox the days and
nights are equally balanced, and this is beautifully
represented by Libra (the scales). The vegetation
decays in the fall, causing sickness and death ; the
Scorpion, that stings as it recedes, is suggestive oi
this Parthian warfare. Sagittarius (the archer) tells
of the hunting month. Capricornus (the goat),
which delights in climbing lofty precipices, denotes
how at the winter solstice the sun begins to climb
the sky on his return north. Aquarius (the water-
bearer) is a natural emblem of the rainy season.
Pisces (the fishes) is the month for fishing.
SIGNS AND CONSTELLATIONS DO NOT AGREE. By
the precession of the equinoxes, as we have before
described on page 121, the signs have fallen back
along the ecliptic about 30, so that those stars
which were, in the infancy of astronomy, in the sign
Aries (T) are now in Taurus (8), and those which
were in the sign Pisces ( K ) are now in Aries
* If the teacher put a pin at the centre of Fig. 72, and, drawing a sharp
kuife between the eignu and the constellations?, cause the inner part to re-
volve, the si^ns may be turned before any constellation, aud thus thie change
he clearly apprehended.
THE SIGNS.
231
The accompanying cut may illustrate this more
clearly.
Fig. 72.
S AND CONSTELLATIONS, AS THEY NOW COMPARE IN THE
HEAVENS, THE FORMER HAVING FALLEN BACK, AND THE
LATTER APPARENTLY ADVANCED, 30 EACH.
PERMANENCE OF THE CONSTELLATIONS. The figures
which the stars form, and the general appearance of
the constellations, are due to the position we occupy.
Could we cross the gulf of space beyond Neptune,
the stars now so familiar to us would look strangely
enough in their new groupings. As one in riding
through a forest sees the trees apparently increase
in size and open up to view before him, while they
232 THE SIDEREAL SYSTEM.
decrease in size and close in behind him, forming
clusters and groups which constantly change as he
passes along ; so, as our earth travels with the solar
system on its immense sidereal journey, the stars
will grow larger and brighter in front, while those
behind us will appear smaller and dimmer. Since,
in addition to this, the stars themselves are in mo-
tion with varying velocity and in different directions,
the constellations must change still more rapidly, so
as ultimately to transform entirely the appearance of
the heavens. In time, the " bands of Orion" will
be loosened, and the "Seven Sisters" will glide
apart into remote space. Such are the dibtances
however, that, although these movements have been
going on constantly, yet since the creation of man
no variation has occurred that is perceptible, save to
the watchful astronomer. Nothing in nature is as
invariable as the stars. They are the standards of
time. Myriads of years must elapse before new star-
maps will be required. We need not, then, allow any
fear of confusion to disturb us while we study the
sky as it is.
VALUE OF THE STARS IN PRACTICAL LIFE. " The
stars are the landmarks of the universe." They seem
to be placed in the heavens by the Creator, not alone
to elevate our thoughts and expand our conceptions
of the infinite and eternal, but to afford us, amid the
constant fluctuations of our own earth, something
unchangeable and abiding. Every landmark about
us is constantly changing, but over all shine the
THE STAKS. 233
"eternal stars," each with its place so accurately
marked, that to the astronomer and geographer no
deception is possible. To the mariner, the heavens
become a dial-plate, the figures on its face set with
glittering stars, along which the moon travels as a
shining hand that marks off the hours with an accu-
racy no clock can ever rival. Standing on the deck
of his vessel, far out at sea, a single observation of
the sun or stars decides his location in the waste of
waters as accurately as if he were at home, and had
caught sight of some old landmark he had known
from his boyhood. In all the intricacies of survey-
ing, the stars furnish the only immutable guide.
Our clocks vainly strive to keep time with the celes-
tial host. Thus, by a wise provision of Providence,
even in the most common affairs of life, are we com-
pelled to look for guidance from the shifting objects
of earth up to the heavens above.
THE VIEWS OF THE ANCIENTS. Standing in the light
of our present knowledge, the ideas of the ancients
seem almost incredible, and we can hardly under-
stand how they could have been seriously enter-
tained. Anaximenes (550 B. c.) thought that the stars
were for ornament, and were nailed like bright studs
into the crystalline sphere. Anaxagoras (450 B. c.)
considered that they were stones whirled up from the
earth by the rapid motion of the ether around us,
and that its inflammable properties set them on fire
and caused them to shine as stars. Many schools
of the Grecian philosophers the Stoics, Epicu-
234 THE SIDEREAL SYSTEM.
reans, etc. believed that they were celestial fires kept
alive by matter that constantly streamed up to them
from the centre of the heavens. The stars were at
one time said to feed on air ; at another, to be the
breathing holes of the universe.
THREE ZONES OF STARS. If we recall what was said
on page 104, concerning the paths of the stars and
appearance of the heavens at different seasons of
the year, we shall see that the constellations are nat-
urally divided into three zones. The first embraces
those which are visible through the entire year ; the
second, those whose orbits can be seen only in part
on any given night ; and the third, those whose paths
just graze our southern horizon, or never pass
above it.
THE CONSTELLATIONS.
NORTHERN CIRCUMPOLAR CONSTELLATIONS. These
constellations in our latitude are visible every
night. They may be easily traced by holding the
book up toward the northern sky in such a way
that Polaris and the Dipper on the map and in the
heavens agree in position, and then locating the
other constellations by comparison. As they revolve
about Polaris, their places will vary with every
successive night through the year. The cut repre-
sents them as they are seen at midnight of the win-
ter solstice. At 6 P. M. of that day the right-hand
side of the map should be held downward, and the
THE CIRCUMPOLAB CONSTELLATIONS. 235
Big Dipper will be directly below the north star.
At 6 A. M. the left-hand side should be at the bot-
tom, and the Dipper will be above Polaris. From
day to day this aspect will change, each star coming
(Map No. 1.) Fig. 73.
NORTHERN CIRCTJMPOLAR CONSTELLATIONS.
a little earlier to the meridian, or to its position on
the preceding night. The rate of this progression
is six hours, or 90, in three months.
Ursa Major is represented under the figure of a
great bear. It contains 138 stars visible to the
naked eye. The constellation has been celebrated
236 THE SIDEREAL SYSTEM.
among all nations. It is remarkable that the shep-
herds of Chaldea in Asia, and the Iroquois Indians
of America, gave to it the same name.
Principal stars. A noticeable cluster of seven
stars six of the second and one of the fourth mag-
nitude forms what is familiarly termed " The Dip*
per." In England it is styled Charles's Wain, from
a fancied resemblance to a wagon drawn by three
horses tandem. Mizar () has a minute companion,
Alcor, which Humboldt tells us could be rarely
seen in Europe. A person with good eyesight may
now readily detect it. Megrez (), at the junction of
the handle and the bowl, is to be marked particu-
larly, since it lies almost exactly in the colure passing
through the autumnal equinox. Dubhe and Merak
are termed " The Pointers" since they always point
out the polar star. The bear's right fore paw and
hinder paw are each marked by two small stars, as
shown in the cut ; a similar pair nearly in line with
these denote the left hinder paw (see , Fig. 76).
The pairs are 15 apart.
Mythological history. Diana had a very beau-
tiful attendant named Callisto. Juno, the queen of
heaven, becoming jealous of the maid, transformed
her into a bear.
The prostrate wretch lifts up her head in prayer,
Her arms grow shaggy, and deformed with hair ;
Her nails are sharpened into pointed claws,
Her hands hear half her weight and turn to paws.
Her lips, that once would tempt a god, begin
To grow distorted in an ugly grin.
THE CIRCUMPOLAR CONSTELLATIONS. 237
And lest the supplicating brute might reach
The ears of Jove, she was deprived of speech.
How did she fear to lodge in woods alone,
And haunt the fields and meadows once her own i
How often would the deep-mouthed dogs pursue,
Whilst from her hounds the frighted hunters flew.
Some time afterward, Callisto's son, Areas, being
out hunting, pursued his mother and was about to
transfix her with his uplifted spear, when Jupiter in
pity transferred them both to the heavens, and
placed them among the constellations as Ursa Ma-
jor and Ursa Minor.
Ursa Minor is represented under the figure of a
small bear. It contains twenty-four stars, of which
only three are of the third, and four of the fourth
magnitude.
Principal stars. A cluster of seven stars forms
what is termed the " Little Dipper" Three of them
are small, and are seen with difficulty. Polaris, at
the extremity of the handle, has been known from
time immemorial as the North Polar Star. Among
the Greeks it was styled Cynosure. Until the ma-
riner's compass came into use, it was the star
" Whose faithful beams conduct the wandering ship
Through the wide desert of the pathless deep."
Polaris does not mark the exact position of the
pole, since that is about 1 J toward the Pointers.
This distance will gradually diminish, until in time
it will be only J : then it will increase again, until
in the lapse of ages 12,000 years hence the bril-
238 THE SIDEREAL SYSTEM.
liant star a Lyrse will fulfil the office of polar star
for those who shall then live on the earth.
Curious fact concerning the Pyramids. Of the
nine Pyramids which are standing at Gizeh, Egypt,
six have openings facing the north. These lead to
straight passages which descend at a uniform angle
of about 26 and are parallel with the meridian. If
we suppose a person, 4000 years ago, standing at
the lower end of one of these passages, and looking
out, his eye would strike the sky near the star
Thuban, which was then the polar star. The
supposed date of the building of these Pyramids
(2123 B. c.) agrees with that epoch, and very naturally
suggests that the builders had some special design
in this peculiar construction.
The distance of Polaris is so great, that though the
star is moving through space at the rate of ninety
miles per minute, this tremendous speed is imper-
ceptible to us. It requires nearly fifty years for its
light to reach the earth ; so that when we look at Po-
laris, we know that the ray which strikes our eye
set out on its journey through space half a cen-
tury ago. We cannot state positively that the star
is now in existence, since if it were destroyed to-day
it would be fifty years before we should miss it.
Calculation of latitude from Polaris. By an ob-
server at the equator, Polaris is seen at the
horizon. If he advances north, the horizon is de-
pressed and Polaris seems to rise in the heavens.
When it has reached the height of a degree, the ob-
THE CIRCUMPOLAB CONSTELLATIONS. 239
server is said to have passed over a degree of lati-
tude on the earth's surface. As he moves further
north, the polar star continues to ascend ; its dis-
tance above the horizon denoting the latitude of
each place in succession, until at the north pole, if
one could reach that point, Polaris would be seen
directly overhead.
Draco is represented under the figure of a long
sinuous serpent, stretching between Ursa Major and
Ursa Minor, nearly encircling the latter constellation,
and finally reaching out its head almost to ;he body
of Hercules.
Principal stars. Four small stars form a quad-
rilateral figure at the head; a fifth of the fourth
magnitude which is scarcely visible, marks the
end of the nose ; several scattered groups and deli-
cate triangles of small stars, denote the position of
the various coils of the body ; thence, an irregular
line of stars traces the dragon's tail around between
Ursa Major and Ursa Minor. Thuban lying midway
between y of the Little Dipper and of the Big Dip-
per, is noted as the polar star of forty centuries ago.
Mythological history. Many accounts are given of
the origin of this constellation, as indeed there are of
almost every one in the heavens. The prevalent
opinion is, that it is the dragon which Cadmus slew.
The story is as follows. Jupiter had carried off Eu-
ropa. Agenor, her father, sent her brother Cadmus
in pursuit of his lost sister, bidding him not to re-
turn until he was successful in his search. After a
240 THE SIDEREAL SYSTEM.
time, Cadmus, weary of his wanderings, inquired of
the oracle of Apollo concerning the fate of Europa.
He was told to cease looking for his sister, to fol-
low a cow as a guide, and when she rested, there
to build a city. Hardly had Cadmus stepped out
of the temple, when he saw a cow slowly walking
along. He followed her until she came upon the
broad plains where Thebes afterward stood. Here
she stopped. Cadmus wishing to offer a sacrifice to
Jupiter in gratitude for the delightful location, sent
his servants to seek for water. In a dense grove
near by was a fountain guarded by a fierce dragon
(DRACO), and sacred to Mars. The Tyrians approach-
ing this and attempting to dip up some water, were
attacked, and many of them killed by that enormous
serpent, whose head overtopped the tallest trees.
Cadmus, becoming impatient, went in search of his
men, and on coming to the spring, saw the sad disas-
ter. He forthwith fell upon the monster, and after a
severe battle succeeded in slaying him. While stand-
ing over his conquered foe, he heard a voice from
the ground bidding him take the dragon's teeth and
sow them. He obeyed. Scarcely had he finished
ere the earth began to move and the points of spears
to prick through the surface. Next nodding plumes
shook off the clods, and the heads of armed men pro-
truded. Soon a great harvest of warriors covered
the entire plain. Cadmus, in terror at the appear-
ance of these giants, whom he termed Sparti (the
Sown), prepared to attack them, when suddenly they
THE CIECUMPOLAE CONSTELTATIONS. 241
turned upon themselves, and never ceased their war-
fare until only five of the crowd survived. These
making peace with each other, joined Cadmus and
assisted him in building the city of Thebes.
Cephetts is represented as a king in regal state,
with a crown of stars on his head, while he holds in
Ids hand a sceptre which is extended toward his
wife, Cassiopeia. The constellation contains thirty-
five stars visible to the naked eye.
Principal stars. The brightest star is Alderamin
(), in the right shoulder. Alphirk (/3), in the girdle,
is at the common vertex of several triangles, which
point out respectively the left shoulder (t), the left
knee (7), and the right foot. The head, which lies
in the Milky Way, is marked by a delicate little
triangle of three stars. This forms, with , /3, and *,
quite a regular quadrilateral figure. A bright little
star of the fifth magnitude, close to Polaris, points
out the left foot.
Cassiopeia* is represented as a queen seated on
her throne. On her right is the king, on her left
Perseus, her son-in-law, 1 and above her is Androme-
da, her daughter. The constellation contains fifty-
five stars visible to the naked eye.
Principal stars. A line drawn from Megrez (5), in
Ursa Major, through Polaris and continued an equal
distance beyond, will strike Caph ((3) in Cassiopeia.
This star is noticeable as marking, with the others
* For mythological history, see Perseus and Andromeda.
U
242 THE SIDEREAL SYSTEM.
named, the equinoctial colure, and as being on the
same side of the true pole as Polaris. The principal
stars form the figure of an inverted chair, which is
very striking and may be easily traced.
EQUATORIAL CONSTELLATIONS.
The constellations we shall now describe lie south
of the circumpolar groups. Only a portion of their
paths is above our horizon. In using the maps, tho
observer is supposed to stand with his back toward
Polaris, and to be looking directly south. Com-
mencing with the constellation Perseus, so intimately
connected with the other members of the royal fam-
ily just described, we pass eastward in our survey
and notice the various constellations as they slowly
defile in silent march across the sky. The first map
represents the constellations on or near the meridian
at nine o'clock in the evening of the winter solstice.
On the evening of the autumnal equinox, the left-
hand side of the map should be turned downward
toward the eastern horizon. On the evening of the
vernal equinox, the right-hand side should be turned
to the western horizon. At these different times, the
stars, though preserving their relative positions, will
be diversely inclined to the horizon. As the stars
apparently move westward at the rate of 15 per
hour, the time of the evening determines what stars
\\ill be visible, anx] also their distances above the
honzon,
EQUATORIAL CONSTELLATIONS. 248
(Map No. 2) Fig. 74.
Perseus is represented as brandishing an enor-
mous sword in his right hand, while in his left he
holds the head of Medusa. The constellation com-
prises eighty-one stars visible to the naked eye.
Principal stars. The most prominent figure is
called the segment of Perseus. It consists of several
stars arranged in a line curving toward Ursa Major.
Algenib (), the brightest of .these, is of the second
magnitude. Algol, in the midst of a group of small
stars, marks the head of Medusa. Between the
bright stars of Perseus and Cassiopeia is a beautiful
star-cluster visible to the naked eye.
Mythological history. Perseus, from whom this
constellation was named, was the son of Jupiter and
Danae. His grandfather, Acrisius, having been in-
formed by the oracle that his grandson would be the
2J4 THE SIDEREAL SYSTEM.
instrument of Lis death, put the mother and child in
a coffer and set them adrift on the sea. Fortunately,
they floated near the island Seriphus, where they
were rescued and kindly treated by a brother of Pol-
ydectes, king of the country. When Perseus had
grown up, he was ordered by Polydectes to bring
him, as a marriage gift, the head of Medusa. Now
Medusa was once a beautiful maiden, who dared to
compare her ringlets with those of Minerva ; where-
upon the goddess changed her locks into hissing
serpents, and made her features so hideous, that she
turned to stone every living object upon which she
fixed her Gorgon gaze. Perseus was at first quite
overpowered at the thought of undertaking this en-
terprise, but was visited by Mercury, who promised
to be his guide, and to furnish him with his winged
shoes. Minerva loaned him her wonderful shield,
that was bright as a mirror. The Nymphs gave him,
in addition, Pluto's helmet, which made the bearer
invisible. Thus equipped, Perseus mounted into the
air and flew to the ocean, where he found the three
Gorgons, of whom Medusa was one, asleep. Fear-
ing to gaze in her face, he looked upon the image
reflected in Minerva's shield, and with his sword
severed Medusa's head from her body. The blood
gushed forth, and with it the winged steed PEGASUS.
Grasping the head, Perseus flew away. The other
Gorgons awaking, pursued him, but he escaped their
search by means of Pluto's helmet. Flying over the
wilds of Libya, in his aerial route, drops dripping
EQUATORIAL CONSTELLATIONS. 245
from the gory head of the monster produced the in-
numerable serpents for which that country was after-
ward celebrated.
Andromeda is represented as a beautiful
maiden chained to a rock.
Principal stars. Algenib and Algol in Perseus?
form, with Almaach (7) in the left foot of Androme-
da, a right-angled triangle opening toward Cassio-
peia. This figure is so perfect, that the stars may
be easily recognized. The girdle is pointed out bj
Merach ((3), and two other stars which form a line
slightly curving toward the right foot. The breast is
denoted by a very delicate triangle composed of
three stars, 8 of the fourth magnitude, another of the
fifth magnitude just south, and an exceedingly minute
star a little at the west. Alpheratz (a), in the head
of Andromeda, belongs also to PEGASUS. This star,
with three others, all of the second magnitude, con-
stitute the " Great Square of Pegasus." Their names
are Algenib (y), Markab (a), and Scheat (|3). The
brightest stars of these two constellations form a
figure strikingly like the Big Dipper. Algenib and
Alpheratz lie in the equinoctial colure which passes
through Caph.
. Mythological history. Cassiopeia had boasted that
her daughter Andromeda was fairer than the Sea-
nymphs. They appealed, in great indignation, to
Neptune, who sent a sea-monster (CETUS) to devas-
tate the coast of Ethiopia. To appease the deities,
her father Cepheus was directed by the oracle to
246 THE SIDEREAL SYSTEM.
bind his daughter to a rock, to be devoured by Cetus.
Perseus returning from the destruction of Medusa,
saw Andromeda in her forlorn condition. Struck by
her beauty and tears, he offered to liberate her
at the price of her hand. Her parents consented
joyfully, and, in addition, offered a royal dowei.
Perseus slew the terrible monster, and freeing An-
dromeda, restored her to her parents. All the promi-
nent actors in this scene were honored with seats
among the constellations. The Sea-nymphs, it is
said, in petty spite of Cassiopeia, prevailed that she
should be placed where for half of the time she
hangs with her head downward a fit lesson of hu-
mility. Cepheus, her husband, shares in her pun-
ishment.
Aries, the ram, was anciently the first constella-
tion of the zodiac. It is now the first sign, but the
second constellation. On account of the precession of
the equinoxes, the constellation Pisces occupies the
first sign.
Principal stars. The most noted star is a Arietis
(Alpha of Aries, more commonly called simply Arie-
tis), in the right horn. This lies near the path of the
moon and is one of the stars from which longitude is
reckoned. A line drawn from Almaach to Arietis
will pass through a beautiful figure of three stars
called the THE TRIANGLES.
Mythological history. Phryxus and Helle were the
children of Athamas, king of Thessaly. Being per-
secuted by Ino, their step-mother, they were com-
EQUATORIAL CONSTELLATIONS. 247
pelled to flee for safety. Mercury provided them a
rani which bore a golden fleece. The children were
no sooner placed on his back than he vaulted into
the heavens. In their aerial journey Helle becom-
ing dizzy fell off into the sea, which was afterward
called the Hellespont, now the Dardanelles. Phryx-
us coming in safety to Colchis, on the eastern shore
of the Black Sea, offered the ram in sacrifice to Ju-
piter, and gave the golden fleece to Aetes, his pro-
tector. The Argonautic expedition in pursuit of this
golden fleece, by Jason and his followers, is one of
the most romantic of mythological stories. It is,
undoubtedly, a fanciful account of the first impor-
tant maritime expedition. Rich spoils were the
prizes to be secured.
Taurus consists only of the head and shoulders
of a lull, which is represented im the act of plunging
at Orion.
Principal stars. The Hyades, a beautiful cluster
in the head, forms a distinct Y. TJhe brightest of
these is Aldebaran, a fiery red star of the first mag-
nitude. The Pleiades* or the " Seven Sisters," as
it is sometimes termed, is the most conspicuous
group in the heavens. It contains a large* number of
stars, six of which are visible to the naked eye.
There were said to have been anciently seven, but
Electra left her place that she might not behold the
ruin of Troy, which was founded by her son Dar-
* Job. xxxyiii. 31 ; Amos, v. 8.
;448 THE SIDEREAL SYSTEM.
danus. Others say that the " lost Pleiad" was Mero-
pe, who married a mortal. Alcyone is the most dis-
tinctly seen. El Nath (#) and point out the horns
of Taurus.
Mythological history. This is the animal whose
form Jupiter assumed when he bore off Europa. The
Pleiades were the daughters of Atlas, arid Nymphs
of Diana's train. They were distinguished for their
unblemished virtue and mutual affection. The hunt-
er OnioN having pursued them one day, they prayed
to the gods in their distress. Jupiter in pity trans-
ferred them to the heavens.
A.uvi(/ci, the Charioteer or Wagoner, is represented
as a man resting one foot on a horn of Taurus, and
holding a goat and kids in his left hand and a bridle
in his right.
The principal stars are arranged in an irregular
five-sided figure, which is very noticeable. Capella,
the goat-star, is of the first magnitude. It travels
in its orbit 1,800 miles per minute; and it takes
seventy-two years, or a man's lifetime, for its light
to reach the earth. Near by is a delicate triangle
formed of three small stars, called tlte Kids. Men-
kalini (/3) is in the right shoulder, 6 in the right
hand, /3 (common to Auriga and Taurus) the right
foot and t> the left foot. Capella, /3 ?> and ? (a star in
the head) form a triangle. The origin of this con-
stellation is unknown.
Pisces, the fakes, is represented by two fishes
tied together by a long ribbon. It consists of small
EQUATORIAL CONSTELLATIONS.
249
stars, which can be traced only upon a cle/ir night,
and in the absence of the moon.
Cetus, the wJiale, is a huge sea-monster, slowly
ploughing his way westward, midway between the
horizon and the zenith. It may easily be found, on
a clear night, by means of the numerous figures
given in the map.
(Map No. 3) Fig. 75.
Gemini, the Twins t represents the twin brothers
Castor and Pollux.
The principal stars are Castor and Pollux, which
are of the first and second magnitudes. The latter
is also one of the stars from which longitude is reck-
oned by means of the Nautical Almanac. The con-
stellation is clearly distinguished by means of two
nearly parallel rows of stars, which by a slight effort
It*
250 THE SIDEKEAL SYSTEM.
of the imagination may be extended into the constel-
lations Taurus and Orion.
Mythological history. Castor and Pollux were no-
ted the former for his skill in training horses, the
latter for boxing. They were tenderly attached to
each . other, and were inseparable in all their adven-
tures. They accompanied Jason on the Argonautic
expedition. A storm having arisen on this voyage,
Orpheus played on his wonderful lyre and prayed to
the gods ; whereupon the tempest was stilled, and
star-like flames shone upon the heads of the twin-
brothers. Sailors, therefore, considered them as pa-
tron deities,* and the balls of electric flame seen on
masts and shrouds, now called St. Elmo's fire, were
named after them. Afterward, Castor was slain.
Pollux being inconsolable, Jupiter offered to take
him up to Olympus, or to let him share his immor-
tality with his brother. Pollux preferred the latter,
and so the brothers pass alternately one day under
the earth, and the next in the Elysian Fields. Not
only did sailors thus think them to watch over navi-
gation, but they were believed to return, mounted on
snow-white steeds and clad in rare armor, to take
part in the hard-fought battle-fields of the Komans.
" Back comes the chief in triumph,
Who in the hour of fight
Hath seen the great Twin Brethren,
In harness on his right.
Acts, xxviii. 11.
EQUATORIAL CONSTELLATIONS. 251
Safe comes the ship to haveii.
Through billows and through gales,
If once the great Twin Brethren
Sit shining on the sails.' 1 Lays of Ancient Home.
Orion is represented under the figure of a hunter
assaulting Taurus. He has a sword in his belt, a
club in his right hand, and the skin of a lion in his
left. This is one of the most clearly defined and
conspicuous constellations in the heavens.
Principal stars. Four brilliant stars, in the form of
a parallelogram, mark the outlines of Orion. Betel-
geuse, a beautiful ruddy star of the first magnitude,
is in the right shoulder ; Bellatrix (7), of the second
magnitude, is in the left shoulder ; Eigel, of the first
magnitude, is in the left foot ; and Saiph (x), of the
third magnitude, is in the right knee. Two small
stars near X form with it a small triangle, which is
itself the vertex of a larger triangle composed of \
y, and Betelgeuse. Near the centre of the parallel-
ogram are three stars forming " the Belt of Orion"
called also the " Bands of Orion" (Job, xxxviii. 31),
Jacob's rod. but more commonly the " Ell and Yard."
They received the last name because they form a
line just 3 long, divided in equal parts by a star
in the centre. These divisions are useful for meas-
uring the distances of the stars. Kunning from the
belt southward, is an irregular line of stars which
marks the sword ; and west of Bellatrix is a curved
line denoting the lion's skin. South of Orion are four
stars forming a beautiful figure styled the HARE.
252 THE SIDEREAL SYSTEM.
Mythological History. Orion was a famous hunter.
Becoming enamored of Merope, he desired to mar-
ry her. (Enopion, her father, opposing the choice,
took a favorable opportunity and put out the eyes of
the unwelcome suitor. The blinded hero followed
the sound of a Cy clop's hammer until he came to Vul-
can's forge. He, taking pity, instructed Kedalion to
conduct him to the abode of the sun. Placing his
guide on his shoulder, Orion proceeded to the east,
and at a favorable place
" Climbing up a narrow gorge,
Fixed his blank eyes upon the sun."
The healing beams restored him to sight. As a pun-
ishment for having profanely bpasted that he was
able to conquer any animal the earth could produce,
he was bitten in the heel by a scorpion. Afterward,
Diana placed him among the stars ; where SIRIUS
and PROCYON, his dogs, follow him, the PLEIADES fly
before him, and far remote is the SCORPION, by whose
bite he perished.
Canis Major and Cants Minor contain each a
single star of the first magnitude, Sirius and Procyon.
These two, with Betelgeuse, Phaet in the Dove, and
Naos in the Ship, form a huge figure known as
the Egyptian X. Sirius, the dog-star, is the most
brilliant star in the heavens. It travels at the rate
of 840 miles per minute. Twenty-two years are
required for its light to reach the earth ; its distance
being estimated at 1,375,000 times that of the sun
from us. 1! : ts intrinsic brilliancy be the same as
EQUATORIAL CONSTELLATIONS. 253
that of our sun, its diameter at that distance must be
fifteen times as great, or 12,000,000 miles. Prob-
ably these estimates fall far below the reality of this
magnificent orb.
(Map No. 4)- Fi#. 76.
Leo is represented as a rampant lion. It is one of
the most beautiful constellations in the zodiac.
The principal stars are arranged in the form of a
sickle. Kegulus, in the handle, is a brilliant star of
the first magnitude. It is one of the stars from which
longitude is reckoned. It is almost exactly in the
ecliptic. Zosma (5) lies in the back of the lion, in
254 THE SIDEREAL SYSTEM.
the thigh, and Denebola, a star of the second mag-
nitude, in the brush of the tail.
Cancer includes the stars which lie irregularly
scattered between Gemini, Head of Hydra, Procyon,
and Leo. In the midst of these is a luminous spot,
called Presepe or the Beehive, which an ordinary
glass will resolve into stars.
Virgo is represented as a beautiful maiden with
folded wings, bearing in her left hand an ear of
corn.
The principal star is Spica Virginis, in the ear of
corn. It is of the first magnitude, and is used for
determining longitude at sea. Denebola, Cor Caroli,
(a), Arcturus (Map No. 5), and Spica form a figure
about 50 in length from north to south, called the
Diamond of Virgo. The other stars may be easily
traced by means of the map.
Mythological History. Virgo was the goddess As-
trsea. According to the poets, the early history of
man was the golden age. It was a time of inno-
cence and truth. The gods dwelt among men, and
perpetual Spring delighted the earth. Next came
the silver age, less tranquil and serene, but still the
gods lingered and happiness prevailed. Then fol-
lowed the brazen and iron ages, when wickedness
reigned supreme. The earth was wet with slaughter
The gods left the abodes of men one by one, As-
trnea alone remaining ; until finally she too, last of all
the immortals, bade the earth farewell. Jupiter
thereupon placed her among the constellations.
EQUATORIAL CONSTELLATIONS. 255
Hydra is a long straggling serpent having its head
near Procyon and extending its tail beyond Virgo,
a total distance of more than 100.
The principal star is Cor Hydrae, of the second
magnitude. It is a lone star, and may be easily found
by a line drawn from y Leonis through Regulus,
and continued about 23. The head is marked by a
rhomboidal figure of four stars of the fourth magni-
tude lying near Procyon. Several delicate triangles
may be formed of them and other small stars lying
near. The Crater or Cup is a beautiful and very
striking semicircle of six stars of the fourth magni-
tude directly south of 6 Leonis. Corvus, the raven,
lios 15 east of the Cup. e Corvi is in the equinoctial
colure.
Mythological history. Hydra was a fearful serpent
which in ancient times infested the lake Lerna. Its
destruction constituted one of the twelve labors of
Hercules. The Crow was formerly white, it is said,
but was changed to its raven tint on account of its
proneness to tale-bearing.
Cor Caroli (a) is marked by a line passing from
Benetnasch (*]) through Berenice's Hair to Denebola
W).
Berenice's Hair is a beautiful cluster midway
between Cor Caroli and Denebola. Nearby is a single
bright star of the fourth magnitude.
Mythological history. Berenice was the wife of
Ptolemy. Her husband going upon a dangerous ex-
pedition, she promised to consecrate her beautiful
256
THE SIDEREAL SYSTEM.
tresses to Venus if he should return in safety. Soon
after the fulfilment of this vow the hair disappeared
from the temple where it had been deposited
Berenice being much disquieted at this loss, Conon,
the astronomer, announced that the locks had been
transferred to the heavens. In proof of which, he
pointed out this cluster of hitherto unnamed stars.
All parties were satisfied with this happy termina-
tion of the difficulty.
(Map No. 5)-Fig. 77.
Bootes, the bear-driver, is represented as a hunts-
man grasping a club in his right hand, while in his
left he holds by the leash his two greyhounds, with
which he is pursuing the Great Bear continually
around the north pole.
Principal stars. Arctnrua,* a magnificent star
* Job, ix. 9.
EQUATORIAL CONSTELLATIONS. 257
of the first magnitude, is in the left knee. It forms
a triangle with Denebola and Spica, and also one
with. Denebola and Cor Caroli. It travels in its orbit
fifty-four miles per second, or more than three times
as fast as the earth. Its light reaches the earth in
about twenty-six years. Mirac (s) lies in tlje girdle,
S in the right shoulder, Alkaturops (M-) in the club, /3
in the head, and Seginus (y) in the left shoulder.
Seginus forms with Oor Caroli and Arcturus a tri-
angle, right-angled at Seginus. Three small stars
in the left hand of Bootes lie near Benetnasch.
Mythological history. Bootes is supposed to have
been Areas, the son of Callisto. (See Ursa Major.)
Hercules is represented as a warrior clad in the
skin of the Nemsean lion, holding a club in his right
hand and the dog Cerberus in his left. His foot is
near the head of Draco, while his head lies 38 south,
and his club reaches 10 degrees beyond.
The principal star is Has Algethi ( of Hercules
and % of Serpentarius). This forms a triangle with
|3 and S. A peculiar figure of four stars (*, nj, , e),
north of these, marks the body. (See Maps, Nos.
5, 7, and 7.) The left knee is pointed out by 6, and
the left foot by y.
Mythological history. This constellation immor-
talizes the name of one of the greatest heroes of
antiquity. Hercules was the son of Jupiter and
Alcmena. While he was yet lying in his cradle,
Juno, in her jealousy, sent two serpents to destroy
him. The precocious infant, however, strangled
258 THE SIDEREAL SYSTEM.
them with his hands. By the canning artifice of
Juno, Hercules was made subject to Eurystheus, his
elder half-brother, and compelled to perform all his
commands. Eurystheus enjoined upon him a series
of the most difficult and dangerous enterprises which
could be conceived. These are termed the " Twelve
Labors of Hercules." Having completed these
tasks, he afterward achieved others equally cele-
brated. Near the close of his life he killed the cen-
taur Nessus. The dying monster charged Dejanira,
the wife of Hercules, to preserve a portion of his
blood as a charm to use in case the love of her hus-
band should ever fail her. In time, Dejanira thought
she needed the potion, and Hercules having sent for
a white robe to wear at a sacrifice, she steeped the
garment in the blood of Nessus. No sooner had
Hercules put on the fatal robe than the venom stung
his bones and boiled through his veins. He at-
tempted to tear it off, but in vain. It stuck to his
flesh, and tore off great pieces of his body. The
hero finding he must die, ascended Mount (Eta,
where he erected a funeral pyre, spread out the skin
of the Nema3an lion, and laid himself down upon
it. Philoctetes applied the torch. With perfect se-
renity of countenance Hercules awaited approaching
death
" Till the god, the earthly part forsaken,
From the man in flames asunder taken,
Drank the heavenly ether's purer breath.
Joyous in the new unwonted lightness
Soared he upward to celestial brightness,
Earth's dark, heavy burden lost in death."
SCHILLER.
EQUATORIAL CONSTELLATIONS.
(Map No. 6) Fig. 78.
259
Corona consists of six stars arranged in a semi-
circular form. The brightest of these is Alphacca.
This makes a triangle, with Mirac (e) and d in Bootes.
It forms a similar figure with Mirac and Arcturus.
Serpentarius, or Ophiuchus, the serpent-
bearer, is represented under the figure of a man
grasping in both hands a prodigious serpent, which
is writhing in his grasp.
Principal stars. Eas Alhague (a), in the head, is
of the second magnitude. It is about 5 from Eas
Algethi. They form a pair of stars conspicuous like
the pairs in Gemini, Canis Minor, Canis Major, etc.
Q marks the right shoulder, and x the left. There is
260 THE SIDEREAL SYSTEM.
a small cluster near ft, called TAUEUS PONIATOWSKII.
An irregular square of four stars, near / Herculis,
denotes the head of the serpent.
Mythological history. This constellation perpetu-
ates the memory of 2Esculapius, the father of medi-
cine. He was so skilful that he restored several to
life; whereupon Pluto complained to Jupiter that
his kingdom was in danger of being depopulated.
Therefore Jupiter struck him with a thunderbolt,
but afterward placed him among the constellations.
Serpents were sacred to .ZEsculapius, because of the
superstitious idea that they have the power of re-
newing their youth by changing their skin.
Libra represents the scales of Astraea (Virgo), the
goddess of justice. It may be recognized by the
quadrilateral figure formed by its four principal
stars.
Scorpio is represented under the figure of a huge
scorpion, stretching through 25. It is a most in-
teresting constellation.
Principal stars. Antares (a) is a fiery red star of the
first magnitude. It marks the heart of the Scor-
pion. The head is indicated by several stars, the
most prominent of which is /3, arranged in a line
slightly curved. The tail may be easily traced by a
series of stars which wind around through the
Milky Way in a very beautiful manner.
Mythological history. This is the scorpion that
sprang out of the earth at the command of Juno,
and stung Orion. Scorpio and Orion are so placed
EQUATORIAL CONSTELLATIONS. 261
among the constellations that they never appear in
the heavens together.
Sagittarius, the archer, is represented as a cen-
taur with his bow bent, as if about to let fly an
arrow at Scorpio.
Principal stars. A row of stars from /x to (3 marks
the bow : another from 7 eastward points out the
arrow and the right arm drawn back in bending the
bow. North of r, two stars of the fourth magnitude
denote the head of the centaur. The " Milk Dipper"
so called because the handle lies in the Milky Way,
is a very striking figure.
Mythological history. This constellation is named
in honor of Chiron, one of the centaurs. These
monsters were represented as men from the head to,
the loins, while the remainder of the body was that
of a horse of which animal the ancients had so high
an opinion that this union was not considered in the
least degrading. Chiron was renowned for his skill
in music, medicine, hunting, and the art of prophecy.
The most distinguished heroes of mythology were
among his pupils. He taught 2Esculapius physic,
ApoUo music, and Hercules astronomy. At his
death, the centaur furnished Dejanira with the in-
formation which proved so fatal to Hercules.
Capricornus contains no very conspicuous stars.
The SOUTHERN FISH (No. 6) has one star of the first
magnitude, Fomalhaut (a, No. 7), which on a clear
summer evening may be seen in the south mid-
way to the zenith. ANTINOUS AND THE EAGLE is a
262
THE SIDEREAL SYSTEM.
double constellation. It contains a beautiful star
of the first magnitude, Altair. This is conspicuous,
as being the centre one in a row of three bright stars.
A similar row, the first star of which is named '(, de-
notes the tail of the eagle, the last star lying in Cerberus.
The DOLPHIN is a beautiful little cluster in the form
of a diamond. It is sojnetimes called " Job's Coffin."
(Map No. 7) Fig. 79.
Cygnus, the swan, is a remarkable group of stars,
the principal ones being so arranged as to form a
large and beautiful cross. The upright piece lies
along the Milky Way. It is composed of four stars,
three of which, Deneb (a), 7, and /3, are bright, while
the fourth is a variable star. In this constellation,
No. 61, a minute star, scarcely visible to the naked
eye, is noted as being the nearest to the earth i f any
of the fixed stars in the northern hemisphere.
THE SOUTHERN CONSTELLATIONS.
263
Lyra, the harp, contains one brilliant blue star,
Vega. Close by it is a parallelogram of four smaller
stars, by which it may be easily recognized. This is
the celestial lyre upon which Orpheus discoursed
such ravishing music that wild beasts forgot their
fierceness and gathered about him to listen, while
the rivers ceased to flow, and the very rocks and
trees stood entranced.
THE SOUTHEKN CONSTELLATIONS
fMao No. 8) Fte. 80.
We now imagine ourselves viewing the stars visible
only to a person south of the equator. The constel-
lations are reversed with reference to the horizon.
The two stars which, in the northern hemisphere.
264
THE SIDEREAL SYSTEM.
compose the base of the parallelogram in Orion,
form here the upper side. Sirius is above Orion.
All the northern circumpolar constellations are
hidden from view. At the southern pole there is no
conspicuous star, but the richness and number of
the neighboring stars compensate this deficiency,
and give to the heavens an incomparable splendor.
Here is the magnificent constellation Argo, in which
we find Canopus, looked upon in ancient times as
(Map No. 9) Fig. 81.
next to Sirius in brilliancy : ?j, a variable star, now
surpasses it in brightness.
Nearly at the height of the south pole blazes the
SOUTHERN CROSS ; below is the CENTAUR, containing
two stars of the first magnitude and five of the
second ; and above is Hydrus, where shines Achernar,
anoiher beautiful star of the first magnitude.
DOUBLE STABS. 265
DOUBLE STAES, COLOEED STAES,
NEBULAE, ETC.
DOUBLE STAHS. To the naked eye all the stars
appear single. With the telescope, over 6,000 have
been found to be double. Thus, Polaris consists of
two stars about 18" apart, Eigel has a companion
about 10" from it, and Sirias one distant 7". A good
opera-glass will separate s Lyrse into two compo-
nents. In case two stars happen to He in the same
straight line from us, though at immense distances
from each other, their light will blend. They will be
seen by the naked eye as a single star, and by the
telescope as a double star. They are called optical
double stars. Over 650, however, of the double stars
have been found to be physically connected. Each
double star of this class forms a binary system of two
suns revolving in an elliptical orbit about their com-
mon centre of gravity, like the planets in the solar sys-
tem, in accordance with Newton's law of gravitation.
In a few instances there are combinations of triple,
quadruple, and even septuple stars. Thus e Lyrse is a
double-double star, while 6 Orionis is a system of seven
suns. The components of a double star commonly dif-
fer in brightness ; so that frequently the fainter one
is nearly lost in the brilliancy of its companion sun.
The periods of some of these systems have been
ascertained. Thus, | Ursse is a double star, and the
two stars of which it is composed have performed
an entire revolution about each other sinoe they were
H
266 THE SIDEREAL SYSTEM.
known to be connected. There are only eight
binary stars whose periods are less than a century,
while 325 have periods which seem to extend one
thousand years.
Orlits. It is not possible to estimate the dimen-
sions of the orbits of the double stars, until their dis-
tances from us are known. Taking the estimated dis-
tance of 61 Cygni (550,000 times the sun's mean distance
from the earth) as a basis, the companions of that
system cannot cultivate a very intimate acquaintance,
since they must be over a billion miles apart. From
these data, astronomers have even attempted to cal-
culate the mass of some of the double stars. 61
Cygni, although scarcely visible to the naked eye,
and known to be the second nearest to us of any of
the fixed stars, is yet estimated to weigh one-third
as much as our sun.
COLORED STARS. We have already noticed that the
stars are of various colors. Sirius is white, Antares
red, and Capella yellow ; while Lyra has a blue tint,
and Castor a green one. In the pure transparent at-
mosphere of tropical regions, the colors are far more
brilliant. There, oftentimes, the nocturnal sky is a
blaze of jewels, the stars glittering with the green
of the emerald, the blue of the amethyst, and the red
of the topaz. In our latitudes, there are no stars
visible to the naked eye which are decidedly blue or
green. In the double and multiple stars, every
color is presented in all its richness and beauty.
We find also combinations of colors complementary
to each other. Here is a green star with a blood-
VAKIABLE STABS. 267
red companion : here an orange and blue sun- there
a yellow and purple one. The triple star y Andro-
medse, is formed of an orange-red sun and two others
of an emerald green. Every tint that blooms in the
flowers of summer, flames out in the stars at night.
" The rainbow flowers of the footstool and the starry
flowers of the throne," proclaim their common
Author ; while rainbow, flower, and star alike evince
the same Divine love of the beautiful.
As to the effects produced in a system having col-
ored suns we can hardly conceive. Take a planet re-
volving about 4* Cassiopeise for instance. This is il-
luminated by a red, a blue, and a green sun. Some-
times, by the succession of these suns, a cheerful
green day would present a charming relief to a
fiery red one ; and that might be still farther sub-
dued by a gentle blue one. The odd contrasts of
color and the vicissitudes of extreme heat and cold
which obtain on such a world, present a picture
which our fancy can sketch better than words can
paint. The colors of the stars change. Sirius was
anciently red. It is now unmistakably white.
There are two double stars which were described by
Herschel as white ; they are each now composed of
a golden-yellow and a greenish star.
VARIABLE STAKS. These are stars which have pe-
riodic changes of brilliancy. There are many of this
class, of which the following are most conspicuous.
ALGOL, in the head of Medusa, is a star of the second
magnitude for about two and a half days, when it
suddenly decreases, and in three and a half hours
268 THE SIDEREAL SYSTEM.
descends to the fourth magnitude. It then rekindles,
and in three and a half hours again is as brilliant aa
ever. MIRA, the ivonderful, a star in the Whale, has
a period of eleven months. Its irregularities are
very curious and fickle. It is ordinarily of the
second magnitude for about fifteen days. It then
decreases for three months, until it is reduced to
the 9th magnitude. This period of darkness lasts
five months ; it then rebrightens for three months,
until it regains its former lustre. Occasionally,
however, it fails to brighten at all beyond the fourth
magnitude, while on one occasion its light was
almost equal to that of Aldebaran. Sometimes no
perceptible change takes place for a month ; then
again, there is a sensible alteration in a few days.
The reason of this variability is not understood.
It has been suggested, in the case of Mira, that it
may be a globe revolving on its axis, and that dif-
ferent portions of its surface, illuminated to different
degrees of intensity, are thus presented to us.
Others have conceived that there may be satellites
revolving about these suns, and that when their dark
bodies interpose between* the stars and our earth,
they eclipse their light wholly or in part.
TEMPORARY STARS. These are stars which sud-
denly blaze out in the heavens, and then gradually
fade away. The most celebrated one of this class
burst forth in Cassiopeia, in the year 1572. Tycho
Brahe says : " One night as I was examining the ce-
lestial vault, I saw with unspeakable astonishment a
TEMPORARY STARS. 269
star of extraordinary brightness in Cassiopeia
Struck with surprise, I could scarcely believe my
eyes. To convince myself that there was no illusion,
I called the workmen of my laboratory and the
passers-by, and asked them if they saw the star
which had so suddenly made its appearance." It waa
more brilliant than Sirius or Jupiter even, and could
be compared only with Venus at her quadrature, ex-
cept that it twinkled wonderfully. It was seen
distinctly at midday. Its color was at first white,
then yellow, and finally red. Its brightness decreased
gradually until the spring of 1574, when the star dis-
appeared from view and has not since been seen.
As two brilliant stars had previously appeared in
Cassiopeia, at intervals of about three centuries,
they have been thought, by some, to be identical,
and that it is only a variable star of long period.
Since the discovery of Tycho Brahe, numerous in-
stances are recorded of stars which have suddenly
burst forth, and then either faded out entirely, or re-
mained only as faint telescopic objects. In the latter
case they are termed new stars. One of this kind
appeared in Corona Borealis, in 1866. At first it was
of the second magnitude, but in a week changed to
the fourth, and hi a month diminished to the 9th.
Strangely, too, some stars have disappeared from
the heavens, and are styled lost stars. These changes
which are thus constantly taking place are calculated
to make the term " eternal stars" seem a very in-
definite phrase.
270 THE SIDEREAL SYSTEM.
Explanation. These phenomena are as yet little
understood. A revolution about the axis would fail
to explain the changes in color, besides being in it-
self a very unaccountable supposition. Some think
that these stars revolve in enormous orbits of such
eccentricity that at their most distant points they
fade out of sight. Arago has shown, in reply to this,
that for a star to decrease in brightness from the first
magnitude to the second by simply moving directly
from us, would require six years, even if it should
speed away with the velocity of light. As we have
just seen, the star of 1866 underwent this change in
brilliancy in a week.
The mind cannot help wondering if they are not
instances of enormous conflagrations in which a
world is overwhelmed in ruin ! The investigations
of spectrum analysis indicate that the star of 1866
consisted of burning hydrogen gas. We can suppose
that this was evolved by some convulsion, and taking
fire, wrapped in flames the entire globe. This need
not involve the idea of destruction, but only a change
of form. In this manner a dark star may become
luminous, or a bright one may be extinguished.
Thus do we see that the process of apparent crea-
tion and destruction is going on in the heavens imme-
diately before the eye of the astronomer. New
stars flash into light, old stars are lost, worlds burst
into flame, and their glowing embers fade into dark-
ness. Are they re-created into new worlds? We
know not. We only perceive that the same Al-
STAR CLUSTERS. 271
mighty power which fitted up this earth for our
home is yet at work among the worlds about us, and
we are thus witnesses of His eternal presence.
STAR CLUSTERS. These are groups of stars so
massed together as to present a hazy, cloud-like ap-
pearance. Several of them have been already
named the Pleiades, the Beehive in Cancer, Bere-
nice's Hair, the Hyades, and the group in the sword-
handle of Perseus. The stars of which they are
composed can generally be easily distinguished by
Fig. 82.
STAR-CLUSTER IN TOUCAN.
the naked eye, although by the use of a small opera
or spy glass the number is largely increased. In
the southern sky there are clusters still more re-
markable. In the Cross is a group of 110 stars of
272 THE SIDEREAL SYSTEM.
various colors, red, blue, and green, so that looking
on it, says Herschel, is "like gazing into a casket
of precious gems." A cluster in Toucan is compact at
the centre, where it is of an orange-red color ; the
exterior is composed of pure white stars, making a
border of exquisite contrast. It is generally conceded
that there is some close physical relation existing
between the stars composing such an " archipelago of
worlds," but its nature is a mystery. They seem
generally crowded together toward the centre, blend-
ing into a continuous blaze of light. Yet, although
they appear so densely compacted, it is probable
that if we could change our stand-point, penetrating
one of these groups of suns we should find it open-
ing up and spreading out before us on our approach,
until, in the midst, the suns would shine down upon
us from the heavens as the stars do in our own sky.
NEBULAE. These are faint misty objects like specks
of luminous clouds. They are generally either round
or oval, and brightest at the centre. They differ
from "clusters" in not being resolvable into stars
when viewed through the largest telescopes. With
the constant improvement made in these instru-
ments, however, many nebulae have been resolved,
and thus the number of clusters increased, while new
nebulae are being discovered to take their places.
Until of late, it was thought that all nebulae were
simply groups of stars, which would be ultimately
discerned in the more powerful telescopes yet to
be made. Spectrum analysis shows, however, that
NEBULJL
273
many of these luminous clouds are gaseous, and not
solid. They cannot, therefore, be suns. Since they
maintain the same position with respect to the stars,
their distance must be inconceivably great, and in
order to be visible to us, their magnitude must be pro-
portionately vast. They are most abundant at the
two poles of the Milky Way, but are more uniformly
distributed over the heavens lying near the south
pole. Those portions of the sky which are poorest
in stars, are richest in nebulae. Herschel was ac-
customed to say to his secretary, whenever for a
brief time he saw no star passing the field of his
telescope, as in the diurnal revolution the heavens
swept by it, " Prepare to write ; nebulae are about
to arrive."
Nebulas are divided, according to their form, into
six classes elliptic, annular, spiral, planetary, irregu-
lar nebulce, and nebulous stars.
The elliptic, or merely oval nebulae, are the most
abundant. Under this head is commonly classe'd the
" great nebula in Andromeda," which was discov-
ered over a thousand years
ago. It is visible to the naked
eye. Prof. Bond, of the Cam-
bridge Observatory, has part-
ly resolved it into stars. He
has distinctly counted 1500,
although its nebulous appear-
ance is still retained. Under
the telescope it is one of the
12*
NKBULA IN ANDROMEDA.
274 THE SIDEREAL SYSTEM.
most glorious objects in the heavens. " If we sup-
pose this nebula to be one continuous bed of stars
of different sizes for its entire extent, it must
comprise the enormous number of 30,000,000." The
distance of such nebulae from the earth entirely passes
our comprehension. Some astronomers have estima-
ted that a ray of light would require 800,000 years to
span the gulf that intervenes. Imagination wearies*
itself in the attempt to understand these figures.
They only teach us something of the limitless ex-
panses of that space in which God is working the
mysterious problem of creation.
The annular nebulce have the form of a ring.
There are but four of these "ring universes." In
Pig. 84.
NEBULA IN LYRA.
the cut is a representation of one in Lyra first as
seen by Herschel, and having in the centre a nebu-
lous film like a "bit of gauze stretched over a hoop ; "
second, as .shown in Lord Kosse's great telescope,
which resolves the filmy parts of the nebula into ex-
cessively minute stars, and reveals a fringe of stars
CLUSTER IN CANBS VEXATICT.
276 THE SIDEREAL SYSTEM.
along the edge. Though apparently so small, its
dimensions must be enormous. If no further from
the earth than 61 Cygni, the diameter would be
2,000,000,000 miles. It is probably immensely further
distant.
The spiral or " whirlpool nebulae " are exceedingly
curious in their appearance. The most remarkable
one is that in Canes Venatici. It consists of brilliant
spirals sweeping outward from a central nucleus,
and all overspread with a multitude of stars. One
is lost in attempting to imagine the distance of such
a mass, and the forces which produce such a " tre-
mendous hurricane of matter perhaps of suns."
Planetary nebulae, by their circular form and pale
uniform light, resemble the disks of the most dis-
tant planets of our system. Their edges are gener-
ally Avell defined, though some-
times slightly furred. Three-
fourths of them are in the
southern hemisphere. Several
have a blue tinge. There is
one in Ursa Major, which if lo-
cated at the distance named
before that of 61 Cygni
would fill a space equal to
. PLANETARY NEBULA.
three times the entire orbit of
Neptune. About twenty-five of these "island uni-
verses" have been found scattered through the
ocean of space. Columbus discovered a new conti-
nent, and so immortalized his name ; what shall we
NEBULA. 277
say of the astronomer who discovers a universe of
worlds ?
Irregular nebulae are those which have no definite
form. Many of them present all the irregularities
of clouds torn and FIg 87
rent by the tem-
pest. Some of the
likenesses which
may be traced by
the fancy are
strangely fantas-
tic : for example,
the " dumb-bell
nebula" in the
constellation Vul-
pecula, and the
"crab nebula"
near the southern
horn of TaurUS. DUMB-BELL NEBULA.
There is also one known as " the great nebula in the
sword-handle of Orion,"^ in which may be seen a
faint resemblance to the wings of a bird.
Nebulous stars are so called because they are en-
veloped by a faint nebula, usually of a circular
form. The star is generally seen at the centre, al-
though some which are elliptical surround two stars,
one in each focus. It is thought that these may
be suns possessing immense atmospheres, which are
rendered visible somewhat as that of our sun is in
the zodiacal light ; and that in like manner our sun
278
THE SIDEREAL SYSTEM.
Fig. 88.
CRAB NEBULA.
itself to those in space presents the appearance of
a nebulous star. The luminous atmosphere of the
star in Cygnus, if located at the distance of a Cen-
tauri, is of an extent equal to " fifteen times the
distance of Neptune from the sun."
Variable nebulw. Certain changes take place among
the nebulfc which can be accounted for only under
NEBUL2E. 279
the supposition that they, like some of the stars, are
variable. Mr. Hind tells us of one in Taurus which
was distinctly visible with a good telescope in 1852,
but in 1862 it had vanished entirely out of the reach
of a much more powerful instrument. It seems to
have disappeared altogether. The great nebula in
Argo, when observed by Herschel in 1838, had in
the centre a vacant space containing a star of the
first magnitude completely enshrouded by nebulous
matter. In 1863, the nebulous matter had disap-
peared, and the star was only of the sixth magni-
tude. These facts as yet defy explanation. They
only illustrate the vast and wonderful changes con-
stantly taking place in the heavens.
Double ncbulce. There seems to be a physical con-
nection existing between some of the nebulae, similar
to that already noticed in respect to certain stars.
In the case of the latter, this inter-relation has been
proved, since their movements even at their distances
can yet be traced in the lapse of years. " But owing
to the almost infinite depths in the abyss of the
heavens at which these nebula) exist, thousands of
years, perhaps thousands of centuries, would be
necessary to reveal any movement." (Guillemin.)
MAGELLANIC CLOUDS. Not far from the southern
pole of the heavens there are two cloud-like masses,
distinctly visible to the naked eye, known to naviga-
tors as " Cape Clouds." Sir John Herschel describes
them as consisting of swarms of stars, clusters, and
nebulae, seemingly grouped together in the wildest
280 THE SIDEREAL SYSTEM.
confusion. In the larger, he found 582 single stars,
46 clusters, and 291 nebulae.
THE MILKY WAY Via Lactea or Galaxy, as it is
variously termed is that luminous, cloud-like band
that stretches across the heavens in a great circle.
It is inclined to the celestial equator about 63, and
intersects it in the constellations Cetus and Virgo.
This stream of suns is divided into two branches
from a Centauri to Cygnus. To the naked eye it
presents merely a diffused light ; but with a power-
ful telescope it is found to consist of myriads of stars
densely crowded together. These stars are not uni-
formly distributed through its entire extent. In
some regions, within the space of a single square
degree we can discern as many as can be seen with
the naked eye in the entire heavens. In other parts
there are broad open spaces. A remarkable instance
of this occurs near the Southern Cross. There is a
dark pear-shaped vacancy with a single bright star
at the centre, glittering on the blue background of
the sky. In viewing it, one is said to be impressed
with the idea that he is looking through an opening
into the starless depths beyond the Milky "Way.
The number of stars in the galaxy which may be
seen by Herschel's great reflector is estimated at
twenty-one and a half .millions. With the more
powerful instruments now being made it is probable
the number will be largely increased. The northern
galactic pole is situated near Coma Berenices, and
the southern in Cetus. Advancing from either pole
THE MILKY WAY. 281
toward the Milky Way, the number of stars increases,
at first slowly and then more rapidly, until the pro-
portion at the galaxy itself is thirty-fold.
HerscheVs theory. Sir W. Herschel has conjec-
tured that the stars are not indifferently scattered
through space, but are collected in a stratum some-
thing like that shown in the cut, and that our sun
Fig. 89.
HERSCHEL'B THEORY OF THE MILKY WAY.
occupies a place at S, near where the stream branches.
A and E are the galactic poles. It is evident that,
to an eye viewing the stratum of stars in the direc-
tion SB, SO, or SD, they would seem much denser
than in the direction SA or SE. Thus are we to
think of our own sun as a star of the second or third
magnitude, and our little solar system as plunged
far into the midst of this vortex of worlds, a mere
atom along that
" Broad and ample road
Whose dust is gold and parement stare."
282 THE SIDEREAL SYSTEM.
NEBULAR HYPOTHESIS. This is a theory which was
advanced by Laplace, to show how the solar system
was formed. In the "beginning," all the matter
which now composes the sun and the various planets,
with their moons, was in a gaseous and highly heated
state. It filled all the space now occupied by the
system, and extended far beyond the orbit of Nep-
tune. In other words, the solar system was simply
an immense nebula. The heat, which is the repel-
lant force, overcame the attraction of gravitation
Gradually the mass cooled by radiation. As centu-
ries passed, the repellent force becoming weaker, the
attractive force drew the matter and condensed it
toward one or more centres. The nebula then
presented the appearance of a nebulous star a
nucleus enveloped to a great distance by a gaseous
atmosphere. According to a well-known law in
philosophy, seen in every-day life, in a whirlpool,
a whirlwind, or even in water poured into a funnel,
wherever matter seeks a centre, a rotary motion is
established. As this rotary motion increased, the
centrifugal force finally overcame at the exterior the
attraction of gravitation, and so threw off a ring of
condensed vapor. Centuries elapsed, and again, un-
der the same conditions, a second ring was detached.
Thus, one by one, concentric rings were separated
from the parent nebula, all revolving in the same
plane and in the same direction. These different
rings, becoming gradually consolidated, formed the
planets, generally however, in this process, while
NEBULAR HYPOTHESIS. 283
still in the vaporous state and slowly condensing,
themselves throwing off rings which were in turn
consolidated into satellites. In the case of Saturn,
several of these secondary rings did not break up,
and so condense into globes, but still remain as
rings which revolve about the planet.* Mitchell
naively remarks, "Saturn's rings were left un-
finished to show us how the world was made."
The ring which formed the minor planets broke up
into small fragments, none large enough to attract
the rest and thus form a single globe. The central
mass of vapor finally condensed itself into the sun,
which remains the largest member of the system.
According to this theory, the sun may yet give off
a few more planets, whose orbits will not exceed its
present diameter. After a time its heat will have all
been radiated into space, its fire will become extinct,
and life on the planets will cease. We know not
when this remote event may occur. We cannot
fathom the purpose of God in creating and main-
taining this system of worlds, nor foretell how soon it
may complete its mission. We are assured, however,
" That nothing walks with aimless feet,
That not one life shall be destroyed,
Or cast as rubbish to the void,
When God hath made the pile complete."
In Memoriam.
* It is possible that these rings may yet break up and form
new satellites for that planet. Indeed, some hold that one at
least of the rings has thus been resolved into small meteorites.
These may be attracted, and so picked up, one by one, by the larger
in succession, until they form another moon, which will continue
to revolve about the planet as the ring does now.
284
THE SIDEREAL SYSTEM.
Fig. 90.
CELESTIAL CHEMISTEY.
SPECTRUM ANALYSIS. The rainbow that child of
the sun and shower is familiar to all. The brilliant
band of colors, seen when the sunbeam is passed
through a prism, is scarcely less beautiful. The ray
of light containing the primary colors is spread out
fan-like, and each tint reveals itself. This variously
colored band is called in philosophy a spectrum (plu-
ral, spectra). There are three different kinds of
spectra
1st. When the light of a solid or liquid body, as
CELESTIAL CHEMISTRY. 285
iron white-hot, is passed through a prism, the spec-
trum is continuous, and consists of a series of distinct
colors, varying from red on one side to violet on the
other.
2d. If the light of a burning gas containing any
volatilized substance be passed through a prism, the
spectrum is not continuous, but is ornamented by
bright-colored lines sodium giving two yellow
lines, strontia a red one, silver two beautiful green
ones. Each element produces a definite series
which can be readily recognized as its test.
3d. If a light of the first kind be passed through
one of the second, the spectrum will be found to be
crossed by dark lines. Thus, if the white light of a
burning match be passed through a flame containing
sodium, instead of the vivid yellow lines so charac-
teristic of that metal, two black lines will exactly
occupy their place. A gaseous flame absorbs the rays
of the same color that it emits.
THE SPECTROSCOPE. This instrument consists of
two small telescopes, with a prism mounted between
their object-glasses, in the manner shown in the cut.
The rays of light enter through a narrow slit at A
and are rendered parallel by the object-glass. They
then pass through the prisms at C, are separated into
the different colors, and entering the second telescope
at D, fall upon the eye at B. A third telescope is
sometimes attached, which contains a minutely accu-
rate scale for measuring the distances of the lines. In
addition, a mirror may throw in a ray of sunlight or
286 THE SIDEREAL SYSTEM.
starlight at one side of the slit, and so we can com-
pare the spectrum of the sunbeam with that of any
flame we desire.
Vis. 91
A SPECTROSCOPE.
Revelations of the spectroscope concerning the sun.
The spectrum of the sunbeam is not continuous, but
is crossed by a large number of dark lines, called,
from their discoverer, Fraunhofer's lines. It is there-
fore concluded that the sun's light is of the third
class just named, and that it is produced by the vivid
light of a highly heated body shining through a
flame full of volatilized substances. But not only
does spectrum analysis thus shed light on the phys-
ical constitution of the sun, but these lines are so
distinctive, so marked and varied, that the very ele-
ments of which the sun is composed may be dis-
covered. Thus, for example, iron gives a spectrum
of some 70 lines, differing in intensity and relative
length. These are bright when iron vapor is burn-
CELESTIAL CHEMISTRY. 287
ing, and dark when white light is passed through
such burning vapor. In the solar spectrum we have
the perfect coincidence of 70 dark lines, line for line
and strength for strength. The conclusion is irre-
sistible that iron is contained in the sun's atmos-
phere. The following include all the elements that
are now known to exist in it :
Sodium, Iron, Strontium
Calcium, Chromium, Cadmium,
Barium, Nickel, Cobalt,
Magnesium, Zinc, Hydrogen.
STARS ARE SUNS. The same method of analysis
has been apph'ed to the stars. Their spectra also
are marked by dark lines. Their constitution is
therefore like our sun ; they contain also the same
familiar elements. Aldebaran seems the most like
our earth. It has at least nine elements known to
chemists :
Sodium, Iron, Magnesium,
Hydrogen, Bismuth, Antimony,
Tellurium, Mercury, Calcium.
Betelgeuse contains many elements known to us,
but no hydrogen. What a world that must be with-
out water ! Arcturus, Kutherford says, closely re-
sembles our sun.
We thus trace in the faintest star that trembles in
the measureless depths of space the same elements
that compose the food we eat and the water \ve
drink. We know that we are akin to nature every-
where that we are a part of a system vast as the
universe.
288 THE SIDEREAL SYSTEM.
SPECTRA OF NEBUKE. Instead of being marked
with dark lines, as are the spectra of the stars, many
of these exhibit bright lines. Their spectra are of the
2d kind. This proves the nebula to consist, not, like
the stars, of an intensely heated solid body shining
through aluminous atmosphere, but of a glowing mass
of gas. Out of 60 nebulae examined by Mr. Huggins,
20 exhibited the bright lines belonging to the gases,
and all contained nitrogen.
It is possible in this manner even to decide the
relative brightness of the different nebulae. The
dumb-bell nebula was found to emit a light only
about one twenty-thousandth part that of a common
wax-candle. If this matter be a "sun-germ," how
immensely must it become condensed before its
rushlight glimmering can rival the dazzling brilliancy
of even our own sun!
THE SOLAR FLAMES, which before were seen only
at an eclipse, can now be examined at any time.
The sun is a sea of fire. Flames travel over its sur-
face faster than the earth in its orbit : one shot out
80,000 miles and disappeared in ten minutes. Such
tremendous convulsions surpass all terrestrial phe-
nomena.
TIME.
SIDEREAL TIME. A sidereal day is the exact in-
terval of time in which the earth revolves on its axis.
It is found by marking two successive passages of a
star across the meridian of any place. This is so
TIME. 289
absolutely uniform, that the length of the sidereal
day has not varied T |^ of a second in 2,000 years.
The sidereal day is divided into twenty-four equal
portions, which are called sidereal hours, and each
of these into sixty portions, termed sidereal min-
utes, etc.
Astronomical docks are regulated to keep sidereal
time. The day commences when the vernal equinox
is on the meridian. Therefore, the time by the si-
dereal clock does not in any way point out the hour
of the ordinary day. It only indicates how long it
is since the vernal equinox crossed the meridian, and
thus always shows the right ascension of any star
which may happen to be on the meridian at that
moment. The hours of the clock are easily reduced
to degrees (see p. 38). The astronomer always
reckons the hours of the day consecutively up to
twenty-four.
SOLAR TIME. A solar day is the interval between
two successive passages of the sun across the me-
ridian of any place. If the earth were stationary in
its orbit, the solar day would be of the same length
as the sidereal > but while the earth is turning around
on its axis, it is going forward at the rate o - : 360 in
a year, or about 1 per day. When the earth has
made a complete revolution, it must therefore per-
form a part of another revolution through this ad-
ditional degree, in order to bring the same meridian
vertically under the sun. One degree of diurnal
revolution is about equal to four minutes of time,
13
290 THE SIDEREAL SYSTEM.
H
Hence the solar day is about four minutes longer
than the sidereal day. For the convenience of so-
ciety, it is customary to call the solar day 24 hours
long, and make the sidereal day only 23 hr. 56 min.
4 sec, in length, expressed in mean solar time. A
sidereal day being shorter than a solar one, the si-
dereal hours, minutes, etc., are shorter than the
solar ; 24 hours of mean solar time being equal to
24 hr. 3 min. 56 sec. of sidereal time.
From what has been said, it follows that the earth
makes 366 revolutions around its axis in 365 solar
days.
MEAN SOLAR TIME. The solar days are of unequal
length. To obviate this difficulty, astronomers sup-
pose a mean sun moving through the equator of the
heavens (which is a circle and not an ellipse) with a
perfectly uniform motion. When this mean sun
passes the meridian of any place, it is mean noon ;
and when the true sun is in the same position, it is
apparent noon. This day is the average length of all
the solar days in the year. The clocks in common
use are regulated to keep mean time. When, there-
fore, it is twelve by the clock, the sun may be either
a little i ast or a little behind the meridian. The
difference between the sun-time (apparent solar-
time) and the clock-time (mean time), is called the
" equation of lime" This is the greatest about the
first of November, when the sun is sixteen and a
quarter minutes in advance of the clock. The sun
is the slowest about February 10th, when it is about
TIME. 291
fourteen and a half minutes behind mean time.
Mean and apparent time coincide four times in the
year namely, April 15th, June 15th, September 1st,
and December 24th. On those days the noon-mark
on the sun-dial coincides with twelve o'clock. In
France, until 1816, apparent time was used ; and the
confusion was so great, that Arago relates how the
town clocks would differ thirty minutes in striking the
same hour. As the time varied every day, no watch-
maker could regulate a watch or clock to keep it.
THE SUN-DIAL The apparent time of the dial may
be readily changed to mean time, by adding or sub-
tracting the number of minutes given in the almanac
for each day in the year, under the heading " sun
slow" or "sun fast." As a noon-mark is thus a
very convenient method of regulating a timepiece,
especially in the country, the following manner of ob-
taining one without a transit instrument may be
useful.
Select a level hard surface which is exposed to the
sun from about 9 A. M. to 3 p. M. Upon this carefully
describe, with compasses, a circle of eight or ten
inches in diameter. Take a piece of heavy wire, six
or eight inches in length, one end of which is
sharpened. Drive this perpendicularly into the cen-
tre of the circle, leaving it just high enough to allow
the extreme end of its shadow to fall upon the circle
about 9 J or 10 A. M. Mark this point, and also the place
where the shadow touches the circle in the afternoon.
Take a point half-way between the two, and drawing
-
292
THE SIDEREAL SYSTEM.
a line from that to the centre of the circle, it will
be the meridian line or noon-mark.
WHY THE SOLAR DAYS ARE OF UNEQUAL LENGTH.
There are two reasons for this the unequal orbital
motion of the earth and the obliquity of the ecliptic.
First : the orbit of the earth is an ellipse ; and thus
I lie apparent yearly motion of the sun along the
ecliptic is variable. In perihelion, in January, the
sun appears to move eastward daily 1 1' 9.9" ; while
at aphelion, in July, only 57' 11.5". As the earth
in its diurnal motion revolves uniformly from west to
east, and the sun passes eastward irregularly, this
must produce a corresponding variation in the
length of the solar day. The sun, therefore, comes
to the meridian sometimes earlier and sometimes
later than the mean noon, and they agree only at
perihelion and aphelion.
Second : as we have just seen, the mean sun is sup-
posed to move in a circle and not an ellipse. This
would make
the motion
along the
ecliptic uni-
form, but the
obliquity of
the ecliptic
would still
cause an ir-
N M L K
regularity in the length of the day. The mean sun
is therefore supposed to pass along the equinoctial,
TIME. 293
which is perpendicular to the earth's axis ; while the
ecliptic is inclined to it 23 28'. Let A represent the
vernal equinox, I the autumnal, AEI the ecliptic,
AI the equinoctial, PK, PL, PM, etc., meridians.
Let the distances AB, BC, CD, etc., be equal arcs of
the ecliptic, which are passed over by the sun in
equal times. Next, mark off on the equinoctial dis-
tances Aa, db t &c, etc., equal to AB, BO, etc. These
are equal arcs of right ascension, or hour-circles,
through which the earth, revolving from west to east,
passes in equal times. Now, meridians drawn through
these divisions, would not agree with those drawn
through equal divisions on the ecliptic. Hence, a sun
moving along the ecliptic, which is inclined, would not
make equal days, even though the ecliptic were a per-
fect circle. Let us see how the mean and apparent
solar days would compare. Let the real sun pass in
its eastward course from A to B in a certain time, the
mean sun moving the same distance would reach the
point a, since the latter travels on the base and tho
former the hypothenuse of a triangle. The earth, re-
volving from west to east, would cause the real sun
to cross any meridian earlier than the mean sun ;
hence, apparent time would be faster than clock-time.
By holding the figure up above us toward the
heavens, we can see how a westerly sun would cross
the meridian earlier than an easterly one. Follow-
ing the same reasoning, we can see that at the sol-
stice, solar and mean time would agree; while
beyond that point the mean time would be faster.
294 THE SIDEREAL SYSTEM.
THE CIVIL DAY. This is the .mean solar day of
which we have spoken. It extends from midnight
to midnight. The present method of dividing the
day into two portions of twelve hours each, was
adopted by Hipparchus, 150 years B. c., and is now
in general use over the civilized world. Until re-
cently, however, very many nations terminated one
day and commenced the next at sunset. Under this
plan, 10 o'clock on one day would not mean the same
as 10 o'clock on another day. The Puritans com-
menced the day at 6 P. M. The Babylonians, Per-
sians, and modern Greeks begin the day at sunrise.
The names of the days now in use are derived as
follows :
1. Dies Solis ( Latin ) . . . . Sun's day.
2. Dies Lunae ( " ).... Moon's day.
8. Tius daeg (Saxon) Tius's day.
4. Wodnes daeg. . .( " ) . . . . Woden's day.
6. Thames daeg . . ( " ) Thor's day.
6. Friges daeg ( " ) Friga's day.
7. Dies Saturni . . . ( Latin ) . . . . Saturn's day.
THE TEAR. The sidereal year is the interval of a
complete revolution of the earth about the sun, meas-
ured by a fixed star. It comprises 365 d., 6hrs.,
9 min., 9.6 sec. of mean solar time. The mean solar
year (tropical year) is the interval between two suc-
cessive passages of the sun through the vernal equi-
nox. It comprises 365 d., 5hrs., 48 min., 49.7 sec.
If the equinoxes were stationary, there would be no
difference between the sidereal and tropical year.
As the equinoxes retrograde along the ecliptic 50" of
space annually, the former is 20 min., 20 sec. longer.
TIME. 295
The anomalistic year is the interval between two
successive passages of the earth through its perihe-
lion. It is 4 min., 40 sec. longer than the sidereal
year.
THE ANCIENT YEAR. The ancients ascertained
the length of the year by means of the gnomon. This
was a perpendicular rod standing on a smooth plane
on which was a meridian line. "When the shadow
cast on this line was the shortest, it indicated the
summer solstice ; and when it was the longest, the
winter solstice. The number of days required for
the sun to pass from one solstice back to it again de-
termined the length of the year. This they found
to be 365 days. As that is nearly six hours less than
the true solar year, dates were soon thrown into con-
fusion. If, at a certain date the summer solstice oc-
curred on the 20th June, in four years it would fall
on the 21st ; and thus it would gain one day every
four years, until in time the summer solstice would
happen in the winter months.
JULIAN CALENDAR. Julius Caesar first attempted
to make the calendar year coincide with the motions
of the sun. By the aid of Sosigenes, an Egyptian
istronomer, he devised a plan of introducing every
fourth year a leap-year, which should contain an
sxtra day. This was termed a bissextile year, since
'iie sixth (sextilis) day before the kalends (first day)
Of March was then counted twice.
GREGORIAN CALENDAR. Though the Julian calen-
dar was nearly perfect, it was yet somewhat defec-
296 THE SIDEREAL SYSTEM.
tive. It considered the year to consist of 365J days,
which is 11 min. in excess. This accumulated year
by year, until in 1582 the difference amounted to
ten days. In that year, the vernal equinox occurred
on the llth of March, instead of the 21st. Pope
Gregory undertook to reform the anomaly, by drop-
ping ten days from the calendar and ordering that
thereafter only centennial years which are divisible
by 400 should be leap-years. The Gregorian calen-
dar was generally adopted in all Catholic countries.
Protestant England did not accept the change until
1752. The difference had then amounted to 11 days.
These were suppressed and the 3d of September
was styled the 14th.
Dates reckoned according to the Julian calendar
are termed Old Style (O. S.), and those according to
the Gregorian calendar New Style (N. S.) This
sweeping change was received in England with great
dissatisfaction. Prof. De Morgan narrates the fol-
lowing. "A worthy couple in a country town, scandal-
ized by the change of the calendar, continued for
many years to attempt the observance of Good Fri-
day on the old day. To this end they walked seri-
ously and in full dress to the church door, on which
the gentleman rapped with his stick. On finding no
admittance, they walked as seriously back again and
read the service at home. There was a wide-spread
superstition that, when Christmas day began, the
cattle fell on their knees in their stables. It was as-
serted that, refusing to change, they continued their
TIME. 297
prostrations according to the Old Style. In Eng-
land, the members of the government were mobbed
in ihd streets by the crowd, which demanded
the eleven days of which they had been illegally
depiived."
COMMENCEMENT or THE TEAK. The Jews began
thoir civil year with the autumnal equinox, but their
ecclesiastical with the vernal. When Caesar revised
the calendar, among the Romans the year com-
menced with the winter solstice (Dec. 22), and it is
probable he did not intend to change it materially.
He, however, ordered it to date from January 1st, in
order that the first year of his new calendar should
begin with the day of the new moon immediately
succeeding the winter solstice.
THE EARTH OUR TIMEPIECE. The measure of time
is, as we have just seen, the length of the mean
day. That is estimated from the length of the si-
dereal day. Hence the standard for time is the rev-
olution of the earth on its axis. All weights and
measures are based on time. An ounce is the weight
of a given bulk of distilled water. This is measured
by cubic inches. The inch is a definite part of the
length of a pendulum which vibrates seconds in the
latitude of London. Arago remarks, a man would
be considered a maniac who should speak of the in-
fluence of Jupiter's moons on the cotton trade. Yet
there is a connection between these incongruous
ideas. The navigator, travelling the waste of waters
where there are no paths and no guide-boards, may
13*
298 THE SIDEREAL SYSTEM.
reckon his longitude by the eclipses of Jupiter's
moons, and so decide the fate of his voyage. We
can easily see how the revolution of the earth on its
axis influences the cost of a cup of tea.
CELESTIAL MEASUEEMENTS.
Many persons read the enormous figures which
indicate the distances and dimensions of the heaven-
ly bodies with an indefinite idea, which conveys no
such feeling of certainty as is experienced when
they read of the distance between two cities, or the
number of square miles in a certain State. Many,
*oo, imagine that celestial measurements are so mys-
terious in themselves that no common mind can
hope to grasp the methods. Let us attempt the so-
lution of a few of these problems.
1st. TO FIND THE DISTANCES OF THE PLANETS FROM
THE SUN. In the figure, E represents the earth, ES
the earth's distance from Pig. 93.
the sun, V the planet Ve-
nus, and YES the angle of
elongation (a right-angled
triangle). It is clear, that
as Yenus swings apparent-
ly east and west of the sun,
this angle may be easily
measured ; also, that it will
be the greatest when Yenus
COMPARATIVE DISTANCE OF VEKU9
is in aphelion and the earth ANB THE EARTH -
CELESTIAL MEASUBEMENTS. 299
in perihelion at the same time, for then VS will be
the longest and VE the shortest. Now in every
right-angled triangle the proportion between the
h jpothenuse, ES, and the side opposite, VS, changes
as the angle at E varies, but with the same angle re-
mains the same whatever may be the length of the
lines themselves. This proportion between the hy-
pothenuse and the side opposite any angle is termed
the sine of that angle. Tables are published which
contain the sines for all angles. In this way, the
mean distance of Yenus is found to be $* that of
the earth, Mars f times, Jupiter 5 times, etc.
The same result would be obtained by the use of
Kepler's third law; and on page 29, we saw how
the distances of the planets themselves could be de-
termined by the periodic times, if the distance of
the earth from the sun is first known. So that
when we have accurately determined the sun's dis-
tance from us, we can then decide by either of the
methods named the distance of all the planets. In-
deed that is, as already remarked, the " foot-rule"
for measuring all celestial distances.
2d. TO MEASURE THE MOON'S DISTANCE FROM THE
EARTH. (1.) The ancient method. As the moon's dis-
tance is so much less than that of the other heavenly
bodies, it is measured by the earth's semi-diameter.
* If the pupil has studied Trigonometry, he may apply here
the simple proportion
ES : VS : : Radius : Sine of 47* 15" = greatest elongation of Venus.
300 THE SIDEREAL SYSTEM.
The method, an extremely rough one, which was in
use among the ancients, was something like the fol-
lowing. In an eclipse of the moon, that body passes
through the earth's shadow in about four hours. If,
then, the moon travels along its orbit in four hours
a distance equal to the diameter of the earth, in
twenty-four hours it would pass over six times, and
in a lunar month (about thirty days) one hundred
and eighty times, that distance. The circumference
of the lunar orbit must be then one hundred and
eighty times the diameter of the earth. The ancients
supposed the heavenly orbits to be circles, and as
the diameter of a circle is about J of the circum-
ference, they deduced directly the diameter of the
moon's orbit as 120 times, and the distance of the
the moon from the earth as 60 times the semi-diam-
eter of the earth.
(2.) Modern method by ihe, lunar parallax. Under
the head of parallax we saw how, in common life,
we obtain a correct idea of the distance of an object
by means of our two eyes. We proved that one eye
alone gives no notion of distance. Just, then, as we
use two eyes to find how far from us an object is, so
the astronomer uses two astronomical eyes or obser-
vatories, located as far apart as possible, to find the
parallax of a heavenly body. In the figure, M rep-
resents the moon/ G an observatory at Greenwich,
and C another at the Cape of Good Hope. At the
former, the distance from the north pole to the
centre of the moon, measured on a meridian of the
CELESTIAL MEASUREMENTS.
301
celestial sphere, is found to be 108. At the latter
station, the distance from the south pole to the
moon's centre is measured in the same way, and
found to be 73J. The sum of these angles is 181^.
Now, the entire distance from the north pole around
to the south pole, measured on a meridian, can be
only half a great circle, or 180. This difference of
Pig. 94.
P' Z'
MEASURING MOON'S DISTANCE FROM THE EARTH.
1J must be the difference in the position of the
moon, as seen from the two observatories. For the
observer at the former station will see the moon
projected on the celestial sphere at G', and in meas-
uring its distance from the north pole will measure
an arc bG' further than if he were located at E, the
centre of' the earth. The observer at the latter sta-
tion will see the moon projected on the celestial
sphere at C', and in measuring its distance from the
302 THE SIDEREAL SYSTEM.
south pole will measure an arc bC' more than if he
were located at E, the centre of the earth. The sum
of bG' and bC'= G'C' is the difference in the position
of the moon as seen from the two stations. In other
words, it is the moon's parallax. The arc G'C'
measures the angle C'MG'; that angle is equal to
the opposite angle GMC = 1J. Now, in the four-
sided figure GECM, the sides GE and CE are each
equal radii of the earth = 3956 miles ; while the dis-
tance from G to C is the difference in the latitude of
the two places. The angles ZGM and Z'CM, being
the zenith distances of the moon, are known, and so
the angles MGE and MCE are easily found. EM,
the moon's distance from the centre of the earth, is
thus readily computed by a simple trigonometrical
formula.
(3.) The horizontal paraUax of the moon is most com-
monly found by estimating its distance, not from the
north and south poles, as just explained under the
general meaning of the term parallax, but from a
fixed star. The moon's horizontal parallax is now
estimated at 57', which makes its distance about
sixty times the earth's semi-diameter.*
To FIND THE SUN'S DISTANCE FROM THE EARTH.
This might be estimated by obtaining the solar
* In figure 95, let S represent the moon, sun, or any other
heavenly body, AB the semi-diameter of the earth, and ASB the
" horizontal parallax" of the body. Then, by the following trig-
on ometrical formula, the distance from the earth may be easily
calculated
AS : AB : : Radius : Sin of ABB.
CELESTIAL MEASUREMENTS. 303
parallax in the same manner as the lunar parallax.
It would be only necessary to take the sun's distance
from the north and south poles respectively at
Greenwich and the Cape of Good Hope, and then
subtracting 180 from the sum of the two angular
distances, the remainder would be the solar parallax.
The difficulty in this method lies in the fact that
when the sun shines the air is full of tremulous mo-
tion. This increases refraction that plague of all
astronomical calculations to such an extent that it
becomes impossible to calculate so small an angle
with any accuracy. Neither can the parallax be
estimated, as in the case of the moon, by measuring
Pig. 85.
the distance from a fixed star, since when the sun
shines the stars near by are invisible even in a tele-
scope. Astronomers have therefore been compelled
to resort to other methods.
(1.) Calculation of solar paraUax by observation of
the planet Mars. We have already seen that the dis-
tance of Mars from the sun is f that of the earth
from the sun. If, therefore, we can find Mars' dis-
tance from the earth, we can multiply it by three,
304 THE SIDEREAL SYSTEM.
and so obtain the distance of the sun from the earth.
In 1862, when Mars was in opposition, it came very
near us, for it was in perihelion while the earth was
in aphelion, so that its distance (as since ascertained)
was only 126,300,000 - 93,000,000 = 33,300,000 miles.
Observers at Greenwich and the Cape, and at various
American and European observatories, calculated
the distance of the planet from the north and south
poles, as well as from several fixed stars, in precisely
the manner just explained for obtaining the lunar
parallax. The result of these observations fixed the
solar parallax at 8.94".*
(2.) Calculation of solar paraUax ty observation of
the transit of Femes. In the figure, let A and B rep-
resent the positions of two observers stationed at
Fig. 96.
TRANSIT OP VENU8.
opposite sides of the earth. At the time of the
transit, the one at A will see the planet Venus as a
round black spot at V" on the sun's disk, while the
one at B will see it at V. The distance V'V" is the
* By the formula on page 302, we have
AS : AB : : Radius : Sin 8.94".
CELESTIAL MEASUREMENTS. 305
difference in the position of Venus as seen from the
two stations on the earth. The distance AB is the
diameter of the earth. The distance VT" is as much
greater than AB as VV" is greater than VA. The
distance of Venus from the sun is known, by Prob. L,
to be .72 that of the earth. The distance of Venus
from the earth must be, then, 1.00 .72 = .28.
Hence, W", the distance from the sun to Venus, =
.72 -4- .28=2.5 times the length of AV, the distance
of Venus from the earth. Therefore, V'V" is equal
to 2J times AB, the earth's diameter, or 5 times
the solar parallax. Knowing the hourly motion of
Venus, it is only necessary for each observer to find
when the planet's disk enters upon and leaves the
sun's disk to determine the length of the path (chord)
it traces. A comparison of the length and direction
of these chords will give the length of V V" in
seconds of space.
The advantage of this method is, that as the dis-
tance V V" is two and a half times that of AB, an
error in measuring that chord affects the solar par-
allax less than one-fifth.
Time of a transit of Venus. This is an event of rare
occurrence. It happens only at intervals of 8, 105^ ;
8, 121J, years, &c. Were the planet's orbit in the same
plane as the ecliptic, a transit would take place dur-
ing each synodic revolution ; but as it is inclined
about 3, the transit can occur only when the earth
is at or near one of the nodes at the same time with
the planet, when in inferior conjunction. As the nodes
306 THE SIDEREAL SYSTEM.
of Yenus fall in that part of the earth's orbit which
we pass in the beginning of June and December
transits always occur in those months.
The transit of June 3d, 1769, excited great interest.
King George III. fitted out an expedition to Tahiti,
under the command of the celebrated navigator Capt.
James Cook. In order to make the angle as great
as possible, and so increase the length of the chords,
or paths of the planet across the sun, astronomers
were sent to all the most favorable points of obser-
vation St. Petersburg, Pekin, Lapland, California,
etc. The result of these calculations fixed the solar
parallax at 8.58". This was considered accurate un-
til lately, but has now ceased to have any value.
The next transits will happen,
December 8 ... ... 1874.
June 7 2004.
The first transit ever seen was witnessed by Hor-
rox, a young amateur astronomer residing near Liv-
erpool. His calculations fixed upon Sunday, Nov.
24, 1639 (O. S.)
He however commenced his watch of the sun on
Saturday preceding. On the following day he re-
sumed his observation at sunrise. The hour for
church arriving, Jie repaired to service as usual. Re-
turning to his labor immediately afterward, he says :
" At this time an opening in the clouds, which ren-
dered the sun distinctly visible, seemed as if Divine
Providence encouraged my aspirations; when oh
CELESTIAL MEASUREMENTS. 307
most gratifying spectacle! the object of so many
earnest wishes I perceived a new spot of perfectly
round form that had just entered upon the left limb
of the sun."
The transits of Mercury are more frequent ; but
owing to the nearness of the planet to the sun,
they are of little value in determining the solar
parallax.
The difficulty of determining the solar parallax accu-
rately will be seen, when one is told that the correc-
tion from the old value of 8.58" to the new one of
8.94", is a change in the angle equal to that which
the breadth of a human hair would make when seen
at a distance of 125 feet. Yet this reduces the esti-
mated distance of the sun from 95,293,000 miles, to
91,430,000 miles.
4. TO FIND THE LONGITUDE OF A PLACE. (1.) The
solar method. If the sailor can see the sun, he
watches it closely with his sextant; and when it
ceases to rise any higher in the heavens it is appa-
rent noon. By adding or subtracting the equation
of time (as given in his almanac), he obtains the true
or mean noon. He then compares the local time thus
obtained, with the Greenwich time as kept by the
ship's chronometer. The difference in time reduced
to degrees, etc., gives the longitude.
(2.) The lunar method. On account of the difficulty
in obtaining a watch which will keep the exact
Greenwich time through a long voyage, the moon is
more generally relied upon than the chronometer.
308 THE SIDEREAL SYSTEM.
The Nautical Almanac* is always published, for the
benefit of sailors, three years in advance. It gives
the distance of the moon from the principal fixed
stars which lie along its path, at every hour in the
night. The sailor has only to determine with his
sextant the moon's distance from any fixed star, and
then by referring to his almanac find the correspond-
ing Greenwich time. By comparing this with the
local time, and reducing the difference to degrees,
etc., he obtains the longitude.
5. TO FIND THE LATITUDE OF A PLACE. (1.) By
means of the sextant find the elevation of the pole
above the horizon, and this gives the latitude di-
rectly. (2.) In the same manner, determine the
height of the sun above the horizon at noon. The
sun's declination for that day (as laid down in the
almanac), added to or subtracted from this gives the
height of the equinoctial above the horizon. Sub-
tract this from 90, and the remainder is the lati-
tude.
* It is pleasant to notice that the astronomer can predict with
the utmost precision. He announces that on such a year, month,
day, hour, and second, a celestial body will occupy a certain posi-
tion in the heavens. At the tune indicated we point our telescope
to the place, and at the instant, true beyond the accuracy of any
timepiece, the orb sweeps into view ! A prediction of the Nauti-
cal Almanac is received with as much confidence as if it were a
fact contained in a book of history. " On the trackless ocean,
this book is the mariner's trusted friend and counsellor; daily and
nightly its revelations bring safety to ships in all parts of the
world. It is something more than a mere book. It is an ever-
present manifestation of the order and harmony of the universe.**
CELESTIAL MEASUREMENTS. 309
6. TO FIND THE CIRCUMFERENCE OF THE EARTH. If
the earth were a perfect sphere, it is obvious that
degrees of latitude would be of the same length wher-
ever measured on its surface. Each would be -^
of the entire circumference. If, however, a person
sets out from the equator, and travels along a me-
ridian toward either pole, and when the polar star
has risen in the heavens one degree above the ho-
rizon, he marks the spot, and then continues his
journey, marking each degree in succession, he will
find that the degrees are not of equal length, but
increase gradually from the equator to the pole. If
now the length of a degree be measured at different
places, the rate of variation can be found, and then
the average length be estimated. Measurements for
this purpose have been made in Peru (almost exactly
at the earth's equator), Lapland, England, France,
India, Russia, etc. So great accuracy has been at-
tained, that Airy and Bessel, who have solved the
problem independently, differ in their estimate of
the equatorial diameter but 77 yards, or only yff^
of a mile.
7. To FIND THE RELATIVE SIZE OF THE PLANETS.
The volumes of two globes are proportional to the
cubes of their like dimensions. The diameter of Mer-
cury is 2,962 miles, and that of the earth 7,925 ; then,
The volume of Mercury : the volume of the earth : : 2962' : 7925 s .
The same principle applied to the volume or bulk
of the sun gives
The bulk of the sun : bulk of earth : : 852584' : 7925*.
310 THE SIDEREAL SYSTEM.
8. TO FIND THE DIAMETER OP THE SUN. (1.) A Very
simple method is to hold up a circular piece of paper
before the eye at such a distance as to exactly hide
the entire disk of the sun. Then we have the pro-
portion,
As dist. of paper disk : dist. of sun's disk :: diam. of paper d. : diam. sun's d.
(2.) The apparent diameter of the sun, as seen
from the earth, is about 32' : the apparent diameter
of the earth, as seen from the sun, is twice the solar
parallax, or 17.88". Thence, the
Ap. diam. of earth : ap. diam. of sun : : real diam. of earth : real diam. of sun.
(3.) Knowing the apparent diameter of the sun,
and its distance from the earth, the real diameter is
found by Trigonometry. In figure 95, let S repre-
sent the earth, AB the radius of the sun, and ASB
half the apparent diameter of the sun. We shall
then have the proportion,
AS : AB : : radius : sin. 16' (half mean diam. of sun).
By a similar method the diameters of the planets
are obtained.
04 se
APPENDIX.
TABLE ILLUSTRATING KEPLER'S THIRD LAW. (CHAMBERS.)
IN the first column are the relative distances of
the planets from the sun ; in the second, the periodic
times of the planets ; and in the third, the squares
of the periodic times divided by the cubes of the
mean distances. The decimal points are omitted in
the third column for convenience of comparison.
The want of exact uniformity is doubtless due to
errors in the observations.
Vulcan ?
.143
19.7
132 716
Mercury
.38710
87969
133 421
Venus
72333
224 701
133413
Earth
1
365 256
133408
Mars *.. .
1.52369
686.979
133410
Jupiter.. ...
5.20277
4 332 585
133294
Saturn
9 53878
10 759 220
133401
Uranus
19.18239
30,686.821
133 422
Neptune
30.03680
60,126.710
133405
Arago, speaking of Kepler's Laws, says: "These interesting laws, tested
for every planet, have been found so perfectly exact, that we do not hesitate
to infer the distances of the planets from the sun from the duration of their
sidereal periods ; and it is obvious that this method possesses considerable
advantages in point of exactness."
MEASUREMENTS OF THE EARTH'S DIAMETER.
Airy.
Bessel.
Polar diameter
7899.17
7899.11
Equatorial diameter .
7925.64
7925.60
Compression
26.47
26.49
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III
ll
fi S
w
II
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7 = ?
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IPS
9 K SS S
fi 03 t^ 10 10
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Saturn...
Uranus...
Neptune .
-fp )U3J
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QUESTIONS.
THESE are the questions which the author has used in his
own classes for review and examination. In the historical
portion, he has required his pupils to write articles upon the
character and life of the various persons named, gathering
materials from every attainable source. He has also intro-
duced whatever problems the class could master, taking topics
from the article on Celestial Measurements and the various
mathematical treatises.
INTRODUCTION. Define Astronomy. Is the earth a planet ?
What is the difference in the appearance of a fixed star and
a planet? What is the Milky Way? HISTORY. What can
you say of the antiquity of astronomy? How far back do
the Chinese records extend ? Name some astronomical phe-
nomena they contain.
17. Why should the Chaldeans have become versed in this
study? How ancient are their records? What discoveries
did they make ? What Grecian philosopher early acquired a
reputation in this science ? What other discovery did Thales
make (Phil., p. 261)? What did -he teach? What memora-
ble eclipse did he predict ? What were the names of two of
his pupils ? What did Anaximander teach ?
IB. Anaxagoras? What was his fate? In what century
did Pythagoras live ? What was his characteristic trait ? Did
he have any proof of his system ? Explain his theory. How
does it differ from ours ? What strange views did he hold ?
What theory did Eudoxus advance ?
19. What is the theory of the crystalline spheres? What
has Hipparchus been styled? What addition did he make
to astronomical knowledge ? How many stars in our present
catalogue (p. 228) ? How did Egypt rank in science at an
early day? What preparation did the Grecian philosophers
make to fit themselves for teachers ? How long did Pythag-
oras travel for this purpose ? What can you say of the school
at Alexandria? What great work did Ptolemy write there?
What theory did he expound ?
316 QUESTIONS IN ASTRONOMY.
20. Was it original ? What discovery did Eratosthenes
make? Describe that method (p. 309). Show how the
movements of the planets puzzled the ancients. What was
the theory of " cycles and epicycles?"
21. Did the ancients believe in the reality of this cumbrous
machinery? Did this theory possess any accuracy? Could
they adapt it to explain any new motion ?
22. What was the remark of Alphonso ? When did astron-
omy cease to be cultivated as a science ? In what century ?
Why did Caesar import an astronomer ? Why did he attempt
to revise the Calendar ? What change did he make (p. 295) ?
State something of the repute in which astrology was held.
23. Tell what you can of the system. What use did it sub-
serve? What theory displaced the Ptolemaic? When?
Was the system of Copernicus original ? What credit is due
him ? Describe his idea of apparent motion. How did he
apply this to the heavenly bodies ?
24. What crudity did he retain ? Who was Tycho Brahe ?
What was his theory? How did it differ from Ptolemy's and
Copernicus's ?
25. What good did he accomplish? Could he generalize
his f facts ? Had he a telescope ? How did Kepler differ from
Brahe ? What were the two prominent characteristics of Kep-
ler ? Give his three laws. Tell how he discovered the first.
The second. The third (p. 313). Describe the ellipse. De-
fine focus, perihelion, and aphelion. What remarkable state-
ment did Kepler make ?
29. When did Galileo live ? What discoveries did he make
in Natural Philosophy? .In Astronomy? What advantage
did he have over his predecessors ?
30. Give an account of his observations on the moon. On
Jupiter's moons.
31. Why did this settle the controversy between the Ptole-
maic and the Copernican system? How were Galileo's dis-
coveries received ? Give some of Sizzi's ponderous arguments.
33. Who discovered the law of gravitation ? Repeat it.
How was this idea suggested ? What familiar laws of motion
aided Newton ? How did he apply these to the motion of the
moon ? Repeat the story of his patient triumph.
35. What is the celestial sphere? Give the two illustrations
which show its vast distance from the earth.
36. Why can we not see the stars by day, as by night?
What portion of the sphere is visible to us ? Name the three
systems of circles.
37-41. Name and define (i) the principal circle, (2) the
QUESTIONS IN ASTRONOMY. 317
secondary circles, (3) the points, and (4) the measurements
of each system. Define, especially, because in common use,
zenith, nadir, azimuth, altitude, equinoctial, right ascension,
declination, equinox, ecliptic, colure, and solstice. What is N
or S in the heavens ? What is the Zodiac ?
42. How wide? How ancient? How divided? Give the
names and signs. State the meaning of each (p. 229).
II. THE SOLAR SYSTEM.
Of what is the solar system composed ? Describe how we
are to picture it to ourselves.
THE SUN. Its sign. Its distance from us ? Illustrate.
47. How are celestial distances measured ? To what is the
sun's light equal ? To how many full moons ? Its heat? Illus-
trate. What proportion of the sun's heat reaches the earth ?
48-50. Its apparent size ? How does this vary ? Its dimen-
sions (i) diameter illustrate, (2) volume, (3) mass, (4)
weight, (5) density. How large did Pythagoras think the sun
is ? Tell something about the force of gravity in the sun.
How much would you weigh if carried to its surface? (This
can be calculated from the table in Appendix.) How does the
sun appear to the naked eye ? How can we see the spots ?
What were formerly the views of astronomers with regard to
the sun's face ? When were the spots discovered ?
52. Tell something about the number of the spots. Their
location. Size.
53. Describe the parts of which they are composed. The
motion of the spots.
54-5. How do they change in form as they pass across the
disk ? What does this prove ? What is the length of a solar
axial revolution ? Explain a sidereal and a synodic revolution.
56-7. Why do not the spots move in straight lines? Show
how they curve. Tell what you can about the irregular move-
ments of the spots. Tell how suddenly they change.
58. What can you say about their periodicity? Who dis-
covered this ? Is there any connection between the solar spots
and the aurora? Tell the influence of the planets on the spots.
Explain.
59. Do the spots affect the fruitfulness of the season ? Does
the temperature of the spots differ from that of the rest of the
sun ? Are they depressions in the sun ? How much darker
are they than the adjacent surface ?
60. Is the sun brighter than the Drummond light? Ans.
The sun gives out as much light as one hundred and forty-six
318 QUESTIONS IN ASTRONOMY.
lime-lights would do, if each were as large as the sun and
were burning all over. What are the faculae ? Describe the
mottled appearance of the sun.
61. What is the shape of the bright masses? What is a
pore?
62. Describe the constitution of the sun according to Wil-
son's theory. How are the spots produced ? The faculae ?
63. The penumbra? The umbra?
64. What is KirchhofFs theory? How are the spots pro-
duced? The umbra? The penumbra? Upon what does
this theory depend (p. 286) ? What is the cause of the
heat of the sun ? Will the heat ever cease ? *
THE PLANETS. Name the six characteristics common to
all the planets.
67. Compare the two groups of the major planets.
68. Draw an ellipse, and name the various parts. Define
the ecliptic, f The ascending node. The descending node.
Line of the nodes. Longitude of the node. Tell what you
can with regard to the comparative size of the planets.
71. What is a conjunction ? Name the earliest that are re-
corded.
72. Tell what you can concerning the planets being in-
habited.
74. What about the conditions of life on the different
planets ? What are the two divisions of the planets ?
75. What causes the apparently irregular movements of
the planets ? Define heliocentric and geocentric place. Il-
lustrate. In what part of the sky is an inferior planet always
seen ? Define inferior and superior conjunction.
76. Greatest elongation. Quadrature. Why is a star at
one time " evening" and at another " morning star?"
77. What is a transit ? Explain the retrograde motion of
an inferior planet. (This motion, it will be remembered, was
one that sorely puzzled the ancients. )
*If we accept the Nebular hypothesis (p. 283), we must suppose that
the heat is produced by the condensation of the nebulous matter and con-
sequent chemical changes. The sun is radiating its heat constantly, and,
after a time, will go out, in turn, as the earth and all the planets have be-
fore it.
j- Lockyer beautifully says : "We may imagine the earth floating around
the sun on a boundless ocean, both sun and earth being half immersed in it.
This level, this plane, the plane of the ecliptic (because all eclipses occur
in it), is used by astronomers as we use the sea-level. We say a moun-
tain is so far above the level of the sea. The astronomer says a star is so
high above the level of the ecliptic."
QUESTIONS IN ASTRONOMY. 319
78. Describe the phases of an inferior planet. Why does
an inferior planet have phases ? Define gibbous.
79. Explain the opposition and conjunction of a superior
planet. Its retrograde motion. Must a superior planet al-
ways be seen in the same part of the sky as the sun ?
80. Which retrogrades more, a near or a distant planet?
Define a sidereal and a synodic revolution of an inferior and a
superior planet, and tell what you can about each. In what
case would there be no difference between a sidereal and a
synodic revolution ? Why is a planet invisible when in con-
junction ?
82. When is a planet evening, and when morning star ?
Tell what you can about the supposed discovery of a planet
interior to Mercury.
83. MERCURY. Definition and sign ? Describe the appear-
ance of Mercury, and where seen.
84. What was the opinion of the ancients ? The astrolo-
gists ? Chemists ? Why is it difficult to see it ? When can
we see it best ?
85. What is the peculiarity of its orbit ? Its distance from
the sun? Velocity? Length of its day? Year? Difference
between its sidereal and synodic revolution ? why ? Its dis-
tance from the earth ?
86. Show why its greatest and least distances vary so much.
What is its diameter ? Volume ? Density ? Force of
gravity? Specific gravity ? How much would you weigh on
Mercury? Describe its seasons. (If the pupil does not un-
derstand pretty well the subject of the terrestrial seasons, it
would be well here to read carefully page no, et seq.)
88. Its temperature ? Appearance of the sun ? Has it any
moon? What is the appearance of the planet through a
telescope ? What do these phases prove ? What do we know
of its mountains and valleys ?
89. VENUS. Definition and sign ? Ancient names ? Ap-
pearance to us ?
90. When brightest? Can Venus be seen by day? Il-
lustrate.
91. Describe the orbit. What is the distance of Venus
from the sun ? Velocity? Length of the year? Day? Dif-
ference between the sidereal and synodic revolution? Dis-
tance from the earth ?
92. How does the apparent size vary ? When is Venus the
brightest? What is the diameter ? Volume? Density?
93. Force of gravity? Does the force of gravity increase
320 QUESTIONS IN ASTRONOMY.
or decrease with the mass or volume of the body ? Describe
the seasons.
94. Describe the telescopic appearance. Who discovered
the phases of Venus ? What was Copernicus's idea ?
95. What proof have we of an atmosphere? Of clouds?
Has Venus any moon ?
96. EARTH. Sign ? What is the appearance of the earth
from the other planets? Do we, then, live on a star? Is it
probable that the earth was always dark and dull as it now
seems to us ? * How does the size of the earth compare with
that of the other planets ? Form of the earth ? Exact diam-
eter ? Is the equator a perfect circle ?
98. Circumference ? Density ? Weight ? What can you
say of its inequalities ? How do you prove the rotundity of
the earth ?
99. Why can we see further from the top of a hill than
from its base ? Why is the horizon a circle ?
100. Give some illustrations of apparent motion.
101. Explain the cause of the rising and setting of the sun
and stars. Who first explained it in this manner ? What do
you say of its simplicity ?
1 02. Cause of day and night? Do all places on the earth
revolve with equal velocity ? Illustrate. At what rate do we
move?
103. Why do we not perceive our motion ? What would
be the effect if the earth were to stop ?
104-5. Is there any danger of this catastrophe ? Draw the
figure, and show how the stars move daily through unequal
orbits and with unequal velocities. Describe the appearance
of the stars at the N. Pole.
1 06. At the Equator. S. Pole. Describe the path of the
earth about the sun. Define eccentricity. Is this stable ?
107. Do we see the same stars at different seasons of the
year? Why not? If we should watch from 6 P. M. to 6 A. M.,
what portion of the sphere could we see? What do we
mean by the yearly motion of the sun among the stars? How
can we see it ?
109. What is the cause? What is the ecliptic? Why so
called ? What are the equinoxes ? What do we understand
* Probably not. The earth was doubtless once a glowing star, like the
sun. Its crust is only the ashes and cinders of that fearful conflagration.
The rocks are all burnt bodies. The atmosphere is only the gas left over
after the fuel was all consumed. Every organic object has been rescued by
plants and the sunbeam from the grasp of oxygen.
QUESTIONS IN ASTRONOMY. 321
when we see in the almanac "the earth is in Aries?" "The
sun is in Sagittarius ?"
1 10. How many apparent motions has the sun ? Name
them, and give the cause and effects of each. Has the sun any
real motions (pp. 54 and 224) ? Describe the apparent mo-
tion of the sun, N. and S. How is it that the sun in summer
shines on the north side of some houses both at rising and
setting, but in winter never does? Define the obliquity of the
ecliptic. The parallelism of the earth's axis. What do you
say of its permanence ?
112. Why will a top stand while spinning, but will fall as soon
as it ceases ? Show how the rays of the sun strike the various
parts of the earth at different angles at the same time. Show
how the angles vary at different times. Is the sun really hotter
in summer than in winter ? Why does it seem to be ?
113. Explain the cause of equal day and night at the
Equinoxes. Why are our days and nights of unequal length
at all other times ? Why do they vary at different seasons of
the year ? How do the seasons, &c. , in the N. Temperate
Zone compare with those in the S. Temperate Zone ? De-
scribe the yearly path of the earth about the sun ( i ) at the
summer solstice ; (2) at the autumnal equinox; (3) at the
winter solstice ; (4) at the vernal equinox ; (5) the yearly path
finished back to the starting-point. Is the division of the
earth's surface into zones an artificial or a natural distinction ?
Who invented it ?
117. How much nearer are we to the sun in the winter?
Why is it not the warmest at that time ? How is it in the
South Temperate Zone ? When do the extremes of heat and
cold occur ? Why not exactly at the solstices ?
1 1 8. Why is summer longer than winter? Does the earth
move with the same velocity in all parts of its orbit ? Describe
the curious appearance of the sun at the North Pole. In
Greenland, at what part of the year will the midnight sun be
seen due north ? What is the length of the days and nights
at the Equator ?
119. Describe the results if the axis of the earth were per
pendicular to the ecliptic.
120. If the equator were perpendicular to the ecliptic. De-
fine precession of the equinoxes. Who discovered this ? At
what rate does this movement proceed ? What is the amount
at present ?
121. What are the results? What star was formerly the
Pole star ?
123. Explain the cause of precession.
322 QUESTIONS IN ASTRONOMY.
125. How does the spinning of a top illustrate this subject?
126. What is Nutation? Cause? How does the moon's
influence compare with that of the sun ?
127. What is the real path of the N. Pole through the
heavens ? Is the obliquity of the ecliptic invariable ? What
is the limit ? What is the effect of this variation ?
128. Are the solstices and equinoxes stationary? What is
the result of this change on the seasons ? When will the
cycle be completed ? When is the sun in perigee ?
129. What do you say of the provisions made to secure
permanence, so that slight changes themselves prevent greater
changes ?
130. What is refraction? Its effect?
131. How does it vary?
132. Are the sun and moon ever where they seem to be ?
Is the real day longer or shorter than the apparent one ?
Why do the sun and moon appear flattened when near the
horizon ? Why not when they are high in the heavens ?
Why do they appear smaller in the latter case ?
133. What causes the hazy appearance of the heavenly
bodies near the horizon? What is the cause of twilight?
How long does it last ? Is it the same at all seasons of the
year?
134. At all parts of the earth? Where is it longest?
Shortest ? What is diffused light ? What would be the effect
if the atmosphere did not act in this way ? r Is there really any
sky in the heavens ? Cause of the appearance ?
135. What is aberration of light ? Illustrate. Give two
reasons why we never see the sun where it really is.
137. The general effect of aberration ? Define parallax.
Illustrate.
138. Define true and apparent place. How does parallax
vary ? What is the practical importance of this subject (p.
300, etseq.)?
139. Define horizontal parallax. What is the sun's hori-
zontal parallax ? What is the annual parallax ?
THE MOON. Signs ? Describe its orbit.
140. Its distance from the earth ? Illustrate. Difference
between its sidereal and synodic revolution ?
141. What is the real path of the moon? (Imagine a pen-
cil fastened to the spoke of a wheel, and the wheel rolled by
the side of a wall on which the pencil is constantly marking. )
How often does it turn on its axis ? What is the moon's di-
ameter ? Volume ? How does its apparent size vary ? Why
does it appear larger than it really is ?
QUESTIONS IN ASTRONOMY. 323
142. Why does the crescent moon appear larger than the
dark body of the moon ? When ought the moon to appear
the largest ? Do all persons think the moon of the same ap-
parent size ? Explain the three librations of the moon.
143. How does moonlight compare with sunlight ? Is there
any heat in moonlight ? Why is it generally clear at full
moon ? Does the centre of gravity in the moon coincide with
that of magnitude ? Has the moon any atmosphere ? What
proof have we of this? Ans. (i) We see but slightly if any
appearance of twilight in the moon. (2) When the moon
passes between us and a star, it does not refract the light of
the star, so that the atmosphere cannot be sufficient to sup-
port more than TOTT of an inch of the mercurial column.
144. How does the earth appear from the moon ? What is
the earth-shine ? How is it caused? What is it called in
England ? Describe the path of the moon around the earth,
and the consequent phases. Why is new moon seen in the
west and full moon in the east ? Why can we sometimes see
the moon in the west after the sun rises, and in the east before
the sun sets ?
147. Length of a lunar month ? What do we mean by the
moon's running high or low ? Cause ? Use ?
148. What is harvest moon? Hunter's moon? Cause?
149. What are nodes ? How much is the moon's orbit in-
clined to the ecliptic our ideal sea-level ? What is an oc-
cultation? Use?
150. Describe the seasons, heat, &c., on the moon.
152. Telescopic appearance of the moon ? Are the mount-
ains the light or dark portions ? What can you say about
them ? The gray plains ? The rills ? The craters ? What
are the peculiar features, then, of the lunar landscapes ? Are
the lunar volcanoes extinct ?
ECLIPSES. When can an eclipse of the sun occur? Show
how a solar eclipse may be total, partial, or annular.
156. Define umbra. Penumbra. Central eclipse. State
the general principles of a solar eclipse.
158. What curious phenomena attend a total eclipse?
159. Describe the effect of a total eclipse?
1 60. What curious custom prevails among the Hindoos?
What is the Saros ? Cause ?
161. Is it now of any value? What is the metonic cycle?
Explain its use.
162. What is the golden number? Cause of a lunar
eclipse ? Draw the figure and describe it. Why are lunar
eclipses seen oTtener than solar ones ?
324 QUESTIONS IN ASTBONOMY.
163. What is the earliest account of an eclipse ? How were
eclipses formerly regarded ?
164. What story is told of Columbus ?
THE TIDES.* Define ebb. Flow. How often does the
tide happen ? Explain the cause.
1 66. Why does the tide occur fifty minutes later each
day ? Why is there a tide on the side opposite the moon ?
The sun is much larger than the moon ; why does it not pro-
duce the larger tide ? Why is not the tide felt out at sea ?
167. What is spring-tide? Neap-tide? Causes? Why
does the tide differ so much in various localities ? Tell about
the height of the tide at different points.
1 68. Why is there no tide on a lake ?
MARS. Definition and sign ?
169. Describe its appearance. When is it brightest ? Its
distance from the sun ? Velocity ? Day ? Year ?
170. Distance from the earth? Peculiarity of its orbit?
Diameter? Volume? Density? Mass? Force of gravity?
Figure ? Describe its seasons.
171. Has it any atmosphere? Moon? Appearance of
our earth ? Telescopic features. (The land and sea features
have been so well decided that they have been named, and a
Mars's globe made.)
172. Cause of its ruddy color ? What are the snow-zones?
Can we watch the change of its seasons ?
MINOR PLANETS (ASTEROIDS). Give Bode's law. Tell
how the first of these planets was discovered. How many are
now known? Ans. There are (Sept. 21,1870)112. Are they
probably all discovered ?
174. Describe these "pocket planets." Are they all found
within the Zodiac? What is their origin? Ans. According
to the Nebular hypothesis, the ring of matter broke up into
numberless small bodies instead of aggregating into one large
planet. Give some of the names and signs.
JUPITER. Definition and sign ? Describe its appearance.
Ancient views. Describe its orbit. What is its distance from
the sun? Velocity? (1869. n is in r). Day? Year? Dis-
tance from the earth ?
177. Diameter? Volume? Density? Centrifugal force?
*. As the tidal wave does not move as rapidly as the earth does, the
water has an apparent backward motion. It has been suggested that this
acts as a ^reak on the earth's diurnal revolution. It has been shown that
the moon's true place can be best calculated if we suppose that the sidereal
day is shortening, by tidal action, at the rate of % of a second in 2,500
years.
QUESTIONS IN ASTRONOMY. 325
Force of gravity ? Figure ? Describe its seasons. Upon what
does the change of seasons in any planet depend ?
178. The appearance of the sky ? The telescopic features?
Are Jupiter's moons visible to the naked eye ?
179. How named? What is their size? What space do
they occupy ?
1 80. Describe the eclipse of the moons.
181. Define immersion, emersion, and transit. How rapid-
ly do the satellites revolve ? What can you say of the fre-
quency of eclipses on Jupiter ? Describe the belts. Why are
they parallel to its equator ?
182. How was the velocity of light discovered ?
SATURN. Definition and sign ? Describe its appearance.
How rapidly does it move through the sky? (1869. is in m).
Its distance from the sun ? Peculiarity of its orbit ?
184. Velocity? Year? Day? Distance from the earth?
Diameter? Volume? Density? Force of gravity? De-
scribe its seasons.
185. Has it any atmosphere? Who discovered the rings
of Saturn ? Describe them.
1 86. Are they stationary? Explain their phases.
187. Describe Saturn's belts.
1 88. Describe Saturn's moons. The scenery on Saturn.
URANUS. Definition and sign ? How was it discovered?
Tell of its previous discovery by Le Monnier. Is Uranus
visible to the naked eye ? (1869. Jjt is in o). Distance from
the sun? Year? Diameter? Density?
191. Describe its seasons. Telescopic features. Satellites
Peculiarity of its moons.
NEPTUNE. Definition and sign ? Appearance in the sky?
Give an account of its wonderful discovery.
193. What is its distance from the sun ? Year ? Velocity ?
Diameter? Volume? Density? Do we know anything of
the seasons ? Why not ? Intensity of the light ?
194. Appearance of the heavens ? What are the telescopic
features ? Has Neptune any moon ? What advantage have
the Neptunian astronomers?
METEORS, AEROLITES, AND SHOOTING-STARS. Define an
aerolite. A shooting-star. A meteor. Give some account
of the fall of meteors (aerolites).
197. What elements are found in aerolites? How can an
aerolite be distinguished ? Give an account of wonderful
meteors.
198. Of shooting-stars.
199. Describe the showers of 1799 and 1833.
326 QUESTIONS IN ASTRONOMY.
200. The shower of 1866. At what intervals did these showers
occur? Why was not the shower of 1866 seen in this country t
Am. Our side of the earth was not turned toward the meteors.
201. What is the average number of meteors and shooting-
stars daily ? Why do we not see more of them ?
202. In what months are they most abundant? Describe
the origin of meteors and shooting-stars. What is their
velocity ? What causes the light ? The explosion often
heard ? What is said of a companion to our moon ?
203. What is the theory of meteoric rings ? What is their
shape ? How do these account for the showers at regular in
tervals ?
204. What is the period of the November ring ? Why is
the August shower so uniform, while the November one is only
periodic ?
205. What is the relation between meteors and comets?
What do you mean by the radiant point ? What effect do
meteors have on the weather ?
206. What is their height ? Weight ?
COMETS. How were they looked upon by the ancients ? Il-
lustrate. Define the term comet. What is the tail ? The
nucleus ? The head ? The coma ? Does each comet neces-
sarily possess all these parts ? How would a mere round,
fleecy mass be known to be a comet ? What mistake did
Herschel make in looking, as he supposed, at one of this
kind (p. 189)?
208. Where do comets appear ? In what direction do they
move ? . How does a comet look when first seen ? Upon what
does the time of greatest brilliancy depend ? What do you say
of the number of the comets ? What was Kepler's remark ?
209. Why do we not see them oftener ? Where did Seneca
see one? Describe the orbits of comets. Which class has
been calculated ? Which classes never return ?
210. Describe the difficulty of calculating a comet's orbit.
211. Name the periods of some. What has been the dis-
tance from the sun of some noted comets ? Velocity ?
212. What do you say of the density of a comet ? Illustrate.
Is there any danger of our running against a comet?
213. Do comets shine by their own or by reflected light?
Tell what you can of their variation in form and dimensions.
214. Give some account of the comets of 1811, 1835, and
1843. For what is Encke's comet noted ? What is its period?
Give some description of Donati's comet.
ZODIACAL LIGHT. Where can this be seen? What is its
appearance ? Where is it brightest ? What is its origin ?
QUESTIONS IN ASTRONOMY. 327
III. THE SIDEREAL SYSTEM.
Tell something of the appearance of the heavens at Nep-
tune's distance from the sun our starting-point? Do we
ever see the stars ? What do we see, then ?
222. Which star is nearest the earth ? What is its paral-
lax? Its distance ? What is Prof. Airy's remark?
223. How long would it take light to reach the nearest star ?
How would the earth's orbit appear at that distance ? Our
sun ? How long does it take for the light of the smaller stars
to reach the earth ? What can you say of the motion of the
fixed stars? Illustrate.
224. What proof have we that the stars are suns ? ("If
Sirius shines as brightly as our sun, at its distance, it must be
three thousand times larger." LOCKYER.) That our sun is
only a small star ? Describe the motion of the solar system.
What is the centre ? How many stars can we see with the
naked eye ? With a telescope ? Have all the stars been dis-
covered ?
226. What is the cause of the twinkling of the stars ? Do
the stars twinkle in tropical regions ? Why not ? What do
you say of the magnitude of the stars ? Name four points
of difference between a planet and a fixed star.
227. What do you mean by a star of the first magnitude ?
How many are there ? Of the second magnitude ? How
many sizes may one see with the naked eye ? With a tele-
scope ? What is the cause of the difference in the brightness
of the stars ? What can you say of the names of the stars ?
228. What can you say with regard to the division of the
stars into constellations ? Is there any real likeness to the
mythological figures ? Name any figure which seems to you
well founded.
229. Are the boundaries distinct ? Who invented the sys-
tem ? Give the meaning of the signs of the Zodiac and their
origin.
230. Explain why the signs and constellations of the Zodiac
do not agree.
231. What causes the appearance of the constellations?
Would they appear as they now do, if we should go out into
space among them ?
232. Are the present forms permanent? State the value of
the stars in practical life.
233. What were the views of the ancients with regard to
the stars?
328 QUESTIONS IN ASTRONOMY.
234. Describe the division of the stars into three zones, and
name them.
THE CONSTELLATIONS. The questions on these are uni-
formly : (i) description, (2) principal stars, and (3) mythologi-
cal history. They need not therefore be repeated with each
constellation. What are the pointers? Does Polaris mark
the exact position of the North Pole ? How many times per
day is Polaris on the meridian of any place ? Explain how
this applies in navigation or surveying. State how the amount
of the variation from the true north will change through the
ages. What star will ultimately become the pole-star ? What
curious facts are stated concerning the Pyramids ? What do
you say of the distance of Polaris ? How may latitude be
calculated by means of Polaris ?
DOUBLE STARS, ETC. Does any star appear double to the
naked eye ? How many have been found by the use of the
telescope ? What is an optical double star ? Are all double
stars of this class ? Describe the revolution of a binary sys-
tem. What other combinations have been discovered ? Their
periods ?
266. Orbits ? Mass ? Are these companion stars as close
to each other as they seem ? What can you say of the colored
stars ? Do their colors ever change ? Which colors would in-
dicate the hottest star ?
267. What is the probable effect in a system having colored
suns ? What are variable stars ? Describe the changes of
Algol.
268. Of Mira. What is the cause ? What are temporary
stars ? Describe the one seen in Cassiopeia.
269. The one in Corona Borealis, in 1866. What are lost
stars ?
270. Can you give any explanation ? Of what did the star
of 1866 consist? Are these stars destroyed? Is the process of
creation now complete ?
271. What are star clusters ? Name several.
272. Is such a grouping a mere optical effect ? Are they
probably as closely compacted as they seem to be ? What
are nebulas ? How do they differ from clusters ? Is it proba-
ble that all nebulas will be resolved into clusters ? What has
spectrum analysis proved some of the nebulas to be ?
273. Are they suns? Where are they most abundant?
What can you say about their distances ? Into how many
classes are they divided ? Describe and illustrate the elliptic
nebulae. What is said of the distance of the great nebula in
Andromeda ? The number of stars it contains ? Describe
QUESTIONS IN ASTRONOMY. 329
the annular nebulae. What is said of the " ring universe"
in Lyra ?
276. Its diameter? Describe the spiral nebula in Canes
Venatici. Describe the planetary nebulas. What is said of
the number and size of these "island universes?"
277. Describe the fantastic appearance of the irregular
nebulae. What are nebulous stars ? What is the cause ?
278. What is said of the size of the one in Cygnus ? What
are variable nebulae ?
279. Give instances. What is said of double nebulae ? Is
anything definite known with regard to them ? What are the
Magellanic clouds ?
280. Describe the Milky-way. What can you say of the
number of stars in the Galaxy ? Are the stars uniformly dis-
tributed ?
281. What is HerschePs theory of the constitution of the
universe ? If this theory be true, what is our sun ?
282. Give an account of the Nebular hypothesis. What is
said of Saturn's rings ? May they ultimately disappear ?
284. What is spectrum analysis ? Name the three kinds of
spectra.
285. What colored rays will a flame absorb ? Describe the
spectroscope.
286. What are Fraunhofer's lines ? What is known of the
constitution of the sun ? What proof have we that iron exists
in the sun ?
287. What elements have been found in the sun ? What
proof have we that the stars are suns ? What can you say of
the similarity existing between the stars and our earth ?
288. What has been discovered with regard to the constitu-
tion of the Nebulae ? Of their relative brightness ?
TIME. What two methods of measuring time ? What is a
sidereal day ?
289. What are astronomical clocks? Tell how they are
used. Why do astronomers use sidereal time ? What is a
solar day ? What causes the difference between a sidereal and
a solar day ? To how much time is a degree of space equal ?
290. Which is taken as the unit, the solar or the sidereal
day ? How long is a solar day ? A sidereal day ? A solar
day equals how many sidereal hours ? A sidereal day equals
how many solar hours ? Describe mean solar time. What is
apparent noon ? Mean noon ? The equation of time ? When
is this greatest ? When least ?
291. When do mean and apparent time coincide? Can a
watch keep apparent time ? How may apparent time be kept?
330 QUESTIONS IN ASTRONOMY.
How can it be changed into mean time ? Tell how to erect a
sun-dial. When will a sidereal and a mean-time clock co-
incide ? A mean-time clock and the sun-dial ?
292. Give the two reasons why the solar days are of unequal
length.
294. What is the civil day ? Who invented the present
division ? Describe the customs of various nations. What
is the origin of the names of the days ?* What is the sidereal
year ? The mean solar year ? What causes the difference ?
295. What is the anomalistic year ? How did the ancients
find the length of the year ? What error did they make ?
What was the result ? Give an account of the Julian calendar.
The Gregorian calendar. What is the meaning of the terms
O. S. and N. S. ? What country now uses O. S. ? When
was the change adopted in England ? How was it received ?
How could a child be eight years old before a return of its
birthday ?
297. When do the Jews begin their year ? Why does our
year begin January ist ? Show how the earth is our timepiece.
What influence has Jupiter's moons on the cotton trade?
CELESTIAL MEASUREMENTS. These problems are to be
used throughout the study. They require no questions but
the formal statement of the problem requiring solution.
* It is said that the Egyptians named the seven days from the seven
celestial bodies then known. The order was continued by the Romans.
Tuesday they called Dies Mortis ; Wednesday, Dies Mercurii , Thursday,
Dies Jovis ; Friday, Dies f^eneris. In the Saxon mythology, Tius, Wo-
den, Thor, and Friga are equivalent to Mars, Mercury, Jupiter, and
Venus. Hence we see the origin of our English names.
GUIDE TO THE CONSTELLATIONS.
THE following is a description of the appearance of the heavens on or about
the first day of each month in the year.
January. (7 p. M.) ~ In the North, Cassiopeia and Per-
seus are above Polaris, Cepheus and Draco west, Ursa Minor
below, and Ursa Major below and to the east. In the East,
Cancer is just rising, Canis Minor (Procyon) has just risen.
Along the Ecliptic, Gemini is well up, then Taurus, Aries
reaches to the meridian, next Pisces, Aquarius (letter Y) and
Capricornus just setting. In the Southeast, Orion and the
Hare are well up. In the South, Cetus swims his huge bulk
far to the east and west. In the Southwest is Piscis Australis
(Fomalhaut). North of the Ecliptic the Triangles are nearly
in the zenith, Perseus is just east, below is Auriga, Androme-
da lies just west of the meridian, and Pegasus is midway, while
Delphinus (the Dolphin, Job's Coffin), Aquila (Altair), and
Lyra (Vega) are fast sinking to the western horizon.
February. (7 p. M.) In the North, Ursa Major lies
east of Polaris, Ursa Minor and Draco below, Cepheus west,
Cassiopeia above and to the west. In the East, Regulus and
Cor Hydrae are just rising. Along the Ecliptic, Leo (Regulus,
the sickle) just rising, Cancer well up, Gemini midway, Taurus
on the meridian, Aries (the scalene triangle) past, Pisces
next, and lastly Aquarius just setting. In the Southeast,
Canis Minor, Canis Major (Sirius), and Orion are conspicuous.
In the Southwest, Cetus covers nearly the whole sky. North
of the Ecliptic, Perseus is on the meridian, while Auriga is a
little east of it ; west of Perseus is Andromeda, while the great
square of Pegasus is fast approaching the horizon.
march. (7 p. M.) In the North, Ursa Major lies east
of Polaris, Draco and Ursa Minor below, Cepheus below and
to the west, and Cassiopeia west. In the East, Cor Caroli
(the Greyhound) is well up, and Coma Berenices is rising.
Along the Ecliptic, Leo is fully risen, next Cancer, Gemini
reaches to the meridian, Taurus is past, Aries midway, and
lastly Pisces is just beginning to set. In the Southeast, Cor
332 GUIDE TO THE CONSTELLATIONS.
Hydrae, Canis Minor and Canis Major are conspicuous. In (he
South, Orion blazes brilliantly. In the Southwest, Cetus is
hiding below the horizon. North of the Ecliptic, Auriga is in
the zenith ; west are Perseus and Andromeda, while Pegasus
is just beginning to sink out of sight.
April. (7 p. M.) In the North, Ursa Major is above and
to the east of Polaris ; opposite and to the west is Perseus,
Draco below and to the east, Cepheus below and to the west,
Cassiopeia west. In the East, Bootes ( Arcturus) not quite fully
risen. Along the Ecliptic, Virgo (Spica) rising, Leo midway,
Cancer reaches to the meridian, Gemini past, next Taurus,
then Aries, and lastly Pisces just setting. In the Southeast is
the Crater (the Cup), and Hydra stretches its long neck to the
meridian. In the South, Canis Minor. In the Southwest,
Sirius and Orion. North of the Ecliptic, and in the northeast,
are Coma Berenices and Cor Caroli ; above Gemini and Taurus
is Auriga, while Andromeda is just setting in the northwest.
May. (8 P. M.) In the North, Ursa Major is above Polaris,
Ursa Minor and Draco east, Cepheus and Cassiopeia below,
and Perseus west. In the East, Lyra is just rising, and Her-
cules is just up. Along the Ecliptic, Libra is just rising, Virgo
is midway, Leo is on the meridian, Cancer is past, next Gemini,
and lastly Taurus just setting. In the South, stretching east
and west of the meridian, is Hydra, with the Crater and Cor-
vus a little east. In the Southwest, is Cor Hydras, Canis Major,
and Canis Minor, while Orion is just setting in the west. North
of the Ecliptic, in the east, above Hercules, are Corona Bore-
alis (The Northern Crown), Bootes (Arcturus), Coma Bere-
nices, and Cor Caroli, which stretch nearly to the meridian. In
the Northwest, above Taurus and Perseus, is Auriga.
June. (8 P. M.) In the North, Ursa Major is above Po-
laris, Draco and Ursa Minor to the east, Cepheus below and
to the east, and Cassiopeia directly below. In the East, Cyg-
nus and Aquila are just rising, Lyra and Taurus Poniatowskii
are well up. Along the Ecliptic, Scorpio is rising, Libra is mid-
way, Virgo on the meridian, Leo past, Cancer midway,
Gemini next, and Taurus just setting. In the South are Cor-
vus and the Crater, a little past the meridian. In the South-
west is Cor Hydras, and in the west Canis Minor approaching
the horizon. North of the Ecliptic, in the east, above Scorpio,
is Hercules ; then Corona and Bootes, and near the meridian,
Cor Caroli and Coma Berenices. In the Northwest is Auriga,
just coming to the horizon.
July. (9 p. M.) In the North, Draco and Ursa Minor
GUIDE TO THE CONSTELLATIONS. 333
above Polaris, Ursa Major west, Cepheus east, and Cassi-
opeia below to the east. In the East, the Dolphin (Job's
Coffin) is row well up, Cygnus is almost midway to the me-
ridian, and Lyra is still higher. Along the Ecliptic, Capri-
cornus is rising, Sagittarius (the Archer) is next, Scorpio, with
its long tail swinging along the horizon, is directly south,
Libra is past the meridian, Virgo midway, and Leo has almost
reached the horizon. In the Southwest, the Crater is setting,
and Corv-us is just above. North of the Ecliptic, above Scorpio
and east of the meridian, are Serpentarius, Hercules, and
Taurus Poniatowskii ; Corona is almost on the meridian, to
the west of which lie Bootes, Cor Caroli, and Coma Berenices.
August. (9 P. M.) In the North, Draco and Ursa Minor
are above Polaris, Cepheus above and to the east, Cassiopeia
east, and Ursa Major west. In the Northeast, Perseus is just
rising, while south of it Andromeda and Pegasus are fairly
up. Along the Ecliptic, Aquarius is risen, next Capricornus,
Sagittarius reaches to the meridian, Scorpio is just past, Libra
next, and Virgo (Spica) just touches the horizon. North of
the Ecliptic, Taurus Poniatowskii is on and Lyra is just east of
the meridian ; the Swan and Dolphin are east of Lyra, Ser-
pentarius and Hercules are above Scorpio, and just west of
the meridian ; thence west are Corona and Bootes, while far
in the northwest are Coma Berenices and Cor Caroli.
September. (8 p. M.) Draco is above and to the west
of Polaris, Cepheus above and to the east, Cassiopeia east,
Ursa Major is below and'to the west. In the Northeast, Per-
seus is just rising. In the East, Andromeda is fairly up, Peg-
asus is nearly midway to the meridian. Along the Ecliptic,
Pisces is just rising, next Aquarius, Capricornus in the south-
west, Sagittarius on the meridian in the south, next Scorpio
in the southwest, Libra, and lastly Virgo just setting. North
vfthe Ecliptic, Lyra is on the meridian, Cygnus, the Dolphin,
and Aquila just to the east, while to the west are Taurus
Poniatowskii and Serpentarius; north of these latter are Her-
cules, Corona, Bootes, Cor Caroli, and Coma Berenices.
October. (7 p. M.) In the North, Cepheus and Draco
are above Polaris, Ursa Minor west, Cassiopeia east, and Ursa
Major below and west. In the Northeast, Perseus is fairly
risen. In the East, Andromeda is nearly midway to the ze-
nith. Along the Ecliptic, Aries is just rising, Pisces well- up,
Aquarius and Capricornus in the southeast, Sagittarius in
the south, Scorpio far down in the southwest, and Libra just
/ settin g. North of the Ecliptic, Cygnus and Aquila are on the
834 GUIDE TO THE CONSTELLATIONS.
meridian, the Dolphin just east of it, and far south ; Lyra is
west of the meridian, Taurus Poniatowskii lower down and to
the south, Serpentarius is just above Scorpio ; next, in line
with it and Polaris, is Hercules ; Corona and Bootes are toward
the northwest, where Coma Berenices is just setting.
November. (7 p. M.) In the North, Ursa Major is below
Polaris, Ursa Minor and Draco are to the west, Cepheus
above, and Cassiopeia above and to the east. In the North-
east, Auriga is just rising, and Perseus is above, nearly mid-
way to the meridian. Along the Ecliptic, Taurus is just rising,
next Aries and Pisces ; Aquarius is on the meridian, south ;
then Capricornus, and lastly Sagittarius, in the southwest.
North of the Ecliptic, Pegasus and Andromeda lie east of the
meridian, the Swan, Dolphin, Eagle, Taurus Poniatowskii, and
Lyra west. In the Northwest are Hercules and Corona.
December. (7 p. M.) In the North, Cassiopeia is above
Polaris, Cepheus above and to the west, Perseus above and
to the east, Draco west, and Ursa Major below. In the
Northeast, below Perseus, is Auriga. In the East, Orion is
rising. Along the Ecliptic, Gemini is just rising, Taurus is
nearly midway, next Aries, Pisces is on the meridian, then
Aquarius, and lastly Capricornus, far in the southwest. In the
South, east of the meridian, is Cetus, and west is Fomalhaut.
North of the Ecliptic, Andromeda is nearly on the meridian,
and Pegasus west of it; Cygnus, Delphinus, Lyra, and Aquila
are about midway, while Taurus Poniatowskii is just sinking to
the horizon. In the Northwest, Hercules is just setting.
NOTE. It should be borne in mind that a month makes a variation of
about two hours (30) in the rise of a star : hence, in the foregoing " Guide,"
the "January Sky 1 ' of 9 p. M. would be about the same as the "February
Sky" of 7 P. M. ; the "January Sky" of 11 P. M. would be about the same as
the "March Sky" of 7 P. M., &c. In this way the "Guide" may be used for
any hour in the night. The pupil will see that in the " Guide" the prominent
figures and stars in each constellation are given in parentheses. Examples :
the " Y" in Aquarius, the " scalene triangle" in Aries. " Job's coffin" iu the
Dolphin, " Procyon" in Canis Minor, &c. These aid in identifying the con-
stellation.
INDEX.
PAGE
Aberration 136
Aerolites 195
Algol 243
Aldebaran 247
Amplitude 37
Antinous 261
Anaxagoras 17
Andromeda 245
Antares 260
Apsides 128
Apparent motion 99
Arcturus 256
Argo 264
Arcturus 256
Aries 246
Auriga 248
Azimuth 37
Astrology 22
Daily's Beads 159
Bellatrix 251
Betelgeuse 251
Bode'sLaw _ 173
Bolides 196
Bootes 256
Berenice's Hair 255
Cassiopeia 241
Cams Major, Canis Minor 252
Cancer 254
Capricornus 261
Castor and Pollux 250
Celestial Sphere 35
" Pole 38
" Measurements 38
" Chemistry 284
Centanr 264
Cepheus 241
Cetus 249
Chinese 26
Chaldeans 17
Colures 40
Conjunctions 71, 75
CorCaroli 255
Corona. 259
Comets 206
Constellations 234
Copernican System 23
Cross 264
Crystalline Spheres 18
Cygnus 262
Declination
Dipper
Diurnal Motion.
Dolphin.
Draco
100
Earth 96
Earth-shine 144
Eclipses 155
Ecliptic 40, 109
r ' Potesof . 41
Ecliptic, Obliquity of. 110
Egyptians 19
Ellipse 68, 26
Elongation 76
(Measurements; 298
Emersion 181
Equinoxes- 113
" Precession of 121
Equinoctial 38
Evening Stars 82
Falling Stars . 195
Fixed Stars 222
44 Names of 227
" Distance of..... .. 223
" Motion of 223
" Size of. 226
44 Parallaxof 223
Galileo.... 29
Galaxy 280
Gemini 249
Geocentric 75
Gibbous 146
Golden Number 162
Greek Alphabet 228
Grecians 17
Gravitation 34
Harvest Moon 148
Hare 251
Hercules 257
Herschel's Theory 281
Heliocentric 75
Horizon 37
Hour Circles 38
Hyades 247
Hydra 255
Immersion '. 181
Irradiation 141
Job's Coffin.... .. 252
Jupiter 175
Kepler's Laws * 25
KirchofiTs Theory 61
Latitude ... .41
LeMonnier 190
Le Verrier 193
Leo 253
Libra 260
Linniens 152
Librations : 142
Lyra 263
Mars . 168
Meteors 194
Mean day 293
Mercury 83
Metonic Cycle 161
Milky War 280
336
INDEX.
FAGS
Minor Planets 172
Moon 139
" Eclipseof. 162
Na<Hr 37
Naos 252
Newton 31
Nebular Hypothesis 282
Nebube 272
Neptune 191
Noon-mark 291
North PolarStar. 237
Nodes 69,149
11 Longitude 69
' Line of. 69
Orbits of Planets 66
" Stars 104
Occultntion 149
Orion 251
Parallax... ,. 137
ofstars 222
Penumbra 155
PerseuK 243
Pegasus 245
Pisces 248
Phases 78
Planet* 65
Pleiades 247
Polaris 237
PolarSiar 237
" Stars, South 56,106
" (L stance 39
Procyon 252
Precession 120
Ptolemaic Theory 20
Pythagoras 18
Quadrature ,
76
Refraction 130
Retrograde motion 77. 79
Reprulus 253
Right ascension 39
Saros 160
Saturn 182
Sagittarius 261
Scorpio 260
Scintillation 226
Signs of Zodiac 42, 230
Seobcoa . 110
Serpentarins 2. r 9
Shooting Stars 194
Sirius 252
Sidereal Revolution 55, 80
Southern Fish 261
Solstices 41, 114
Solar time 289
Solar System < 45
Spectrum Analysis 2S4
Spica 254
Sun 43
" Pathof 108
" Change in form and place of. 131
" Spots 5C
Stars 221
" Numberof. 224
" Size 226
" Distance 223
" Colored 266
" Variable .. 267
Temporary,
auble
Double 265
Syzygies 166
Synodic 55, 80
Taurus 247
" Poniatowskii 860
Tides 165
Time 288
Transit 77
Triangles 246
Tycho Brahe 24
Twilight ; 133
Umbra 155
Uranus 189
Ursa Major 235
" Minor. 237
.. 262
Vega
Venus
Vertical Circle 37
Velocity of Light 182
Virgo 254
Vnlcan 82
Whale 249
Wilson's Theory 62
Zenith 87
Zodiac 41
Zodiacal Light 217
14
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