POPULAR GUIDE 
 
LIBRARY 
 
 OF THK 
 
 UNIVERSITY OF CALIFORNIA. 
 
 Class 
 
A POPULAR GUIDE 
 
 TO THE 
 
 HEAVENS. 
 
POPULAR GUIDE 
 
 TO 
 
 THE H EAVENS 
 
 A SERIES OF EIGHTY-THREE PLATES, 
 
 WITH EXPLANATORY TEXT & INDEX. 
 
 BY 
 
 SIR ROBERT STAWELL BALL, LL.D., F.R.S., 
 
 \ 
 
 LOWNDEAN PROFESSOR OF ASTRONOMY AND GEOMETRY IN THE UNIVERSITY OF CAMBRIDGE. 
 
 OF THE 
 
 DIVERSITY 
 
 D. VAN NOSTRAND COMPANY, 
 
 23 MURRAY AND 27 WARREN STREETS, 
 NEW YORK. 
 

 
 GENERAL 
 
PREFACE. 
 
 THE object of the present work is to provide a popular guide to the study of the sky 
 by furnishing a summary of our present knowledge of the Solar system, a guide to 
 the positions of the planets for the first half of the present century, a series of star 
 maps, some examples of the finest achievements in the art of drawing and photographing 
 celestial objects, and a list of interesting objects which may be observed with small 
 telescopes. 
 
 In the text will be found a descriptive account of the plates, and of the methods 
 of using the maps and tables. It is, however, desirable to draw attention in this place 
 to certain characteristics of the work, and to make my acknowledgment to the 
 friends who have kindly assisted me. 
 
 In 1892 I edited an atlas of the celestial bodies which has long been out of print. 
 Though this atlas bore my name yet as explained in the preface it was largely due 
 to my friend Dr. Rarnbaut. The question of a new issue of the work having arisen, 
 it was deemed better to recast the book completely, and the present volume is the 
 result. 
 
 The star maps carefully drawn by Dr. Rarnbaut having been corrected for the 
 changes obviously required by the lapse of 12 years have been retained, so have also 
 the maps of the Moon, drawn by the late Mr. Elger. 
 
 But the advance of Astronomical portraiture has rendered it necessary to 
 supersede most of the remaining plates by new material. This has involved so many 
 changes in the text that the book is substantially a new one, and is now arranged in 
 such a manner as may, I hope, entitle the book to be called a Popular Guide to the 
 Heavens. 
 
 The map of Mars is reduced from the large map made by Mr. A. E. Douglass, 
 published in Volume II. of the Annals of the Lowell Observatory. 
 
 The drawings of Jupiter on plate 9 have been copied from Dr. O. Lohse's obser- 
 vations, in the third volume of the Astrophysiklische Observatoriuin at Potsdam. The 
 drawings of Jupiter's satellite are from a paper by Professor Barnard, published in 
 the Monthly Notices of the Royal Astronomical Society. The drawing of Saturn, plate 
 10, by Professor Barnard, is reproduced from a drawing also published in the Monthly 
 Notices. 
 
 179892 
 
vi. PEEFACE. 
 
 The photograph of the great sunspot of 1898 September is reproduced from a 
 photograph taken at the Royal Observatory, Greenwich, for which I am indebted to 
 the kindness of the Astronomer Royal. 
 
 The drawings of the Solar Prominences on plate 12 are from a paper by Herr 
 Fenyi, in the Aslrophysical Journal ; the picture of the Solar Prominence photographed 
 by Professor Barnard is from the report of the Yerkes Observatory Eclipse Expedition 
 to Wadesboro', U.S.A., published in the same journal. 
 
 The map of the paths of Solar Eclipses, 1901-1950, has been prepared from the 
 series of maps in Dr. Oppolzer's great work, Canon der Finsternisse. 
 
 The photographs of typical Solar Coronae on plate 16 are selected from the 
 series of Eclipse photographs brought together by the Royal Astronomical Society. 
 
 Plate 17, the drawing of Donati's Comet, by the late Professor Bond, is from the 
 splendid volume of observations of that comet in the Annals of the Harvard College 
 Observatory. 
 
 I am indebted to Professor Barnard for the use of the comet photographs in plate 
 18, which are selected from the series of his photographs published by the Royal 
 Astronomical Society. I owe to him also the photograph of a region of the Milky Way 
 in plate 81, taken from the same series. 
 
 For the permission to reproduce the two comet photographs of plate 19, I must 
 thank the Astronomer Royal of England and the Astronomer Royal at the Cape, 
 respectively. 
 
 I am greatly indebted to Professor Hale, Director of the Yerkes Observatory 
 of the Uuiversity of Chicago, and to Mr. Ritchey, Astronomer at that observatory, 
 who took the photographs, for permission to use the three photographs of the Moon, 
 plates 20, 21, 22 ; the photographs of the nebulae in Orion and Andromeda, plates 73 
 and 47, and the drawings of the nebulae round Nova Persei. The photographs of that 
 star and of the region in which it appeared I owe to Mr. Stanley Williams, of Brighton. 
 
 My friend Mr. W. E. Wilson kindly allows me to use the photographs of the 
 Cluster in Hercules, and of the nebula in Cygnus, forming plate 75, which were taken 
 by him at his observatory at Daramona, county Westmeath. To Professor Campbell, 
 Director of the Lick Observatory, I owe permission to reproduce the three photo- 
 graphs of the spiral nebula in Canes Venatici, the Ring nebula in Lyra, and the Dumb- 
 bell nebula in Vulpecula, made with the Crossley Reflector by his lamented pre- 
 decessor, Professor J. E. Keeler. 
 
 Plate 80, of the Pleiades Cluster, is taken from a photograph by the brothers 
 Henry, published in a report of the Paris Observatory ; and for the photograph of the 
 nebulae in that cluster I am indebted to the late Dr. Isaac Roberts, of Crowborough. 
 Sussex. 
 
 Plate 83, illustrating the adoption of Standard Time, and the line where the 
 date changes, has been made from information kindly furnished by the Hydrographer 
 to the Admiralty, 
 
PREFACE. Vll. 
 
 The work involved has been very onerous, and I could not have undertaken it 
 had I not been so fortunate as to have had the aid of Mr. Arthur Hinks, M.A., Chief 
 Assistant at the Cambridge Observatory. To Mr. Hinks I am indebted for the 
 selection of the new plates, as well as for the preparation of the text which 
 accompanies them. I would like to record my thanks to him for all his skill 
 and zeal. 
 
 CAMBRIDGE, ROBERT S. BALL. 
 
 November, 1904. 
 
CONTENTS. 
 
 PAGE 
 
 PREFACE v. vii. 
 
 CHAPTER I. 
 THE CELESTIAL SPHERE AND THE SOLAR. SYSTEM. 
 
 The Celestial Sphere The Seasons The Horizon and the Zenith Refraction 
 ~Diurnal Parallax Annual Parallax Apparent Daily R-otation^of the Heavensj 
 J&ging andJSfittijioj. The Signs of the 2odiac^-TIie~ Orbits of the Inner Planets- 
 The OrrTits of the Outer Planets Bode's Law ' ... 1-6 
 
 CHAPTER II. 
 THE PLANETS AND SATELLITES. 
 
 The Size of the Planets Phases of the Planets and of Saturn's Rings Systems of 
 Satellites Map of Mars Jupiter and Satellite I. Saturn 7-13 
 
 CHAPTER III. 
 THE SUN; ECLIPSES OF THE SUN AND MOON. 
 
 The Sun Paths of Spots Across the Sun's Disc Phases of the Moon Lunar and 
 Solar Eclipses-Paths of Total Eclipses of the Sun 1901-1950 Typical Solar Corouse 15-19 
 
 CHAPTER IV. 
 COMETS. 
 
 Donati's Comet Holmes' Cornet and the Andromeda Nebula Comet a 1893 IV. 
 (Brooks) Comet 1901 I. Comet b 1902 III. (Perrine) 21-23 
 
 CHAPTER V. 
 
 THE MOON. 
 
 The Moon Place of the Moon The Lunar Charts Catalogue of Lunar Objects ... 25-33 
 
* CONTENTS. 
 
 CHAPTER VI. 
 
 THE SKY MONTH BY MONTH AND THE INDEX 
 TO THE PLANETS. 
 
 The Monthly Maps Table to find the Aspect of the Heavens at any given Month 
 and Hour of Night Table of Planetary Phenomena Mercury Venus Index to 
 Venus Mars Index to Mars Jupiter Index to Jupiter Saturn Index to 
 Saturn The Naming of an Unknown Planet 35-48 
 
 CHAPTER VII. 
 THE STAR MAPS. 
 
 The Maps Variable Stars Algol Variables Short Period Variables Irregularly 
 Variable Stars Temporary or "New" Stars Meteor Showers Precession ... 49-58 
 
 CHAPTER VIII. 
 STAR CLUSTERS AND NEBULA. 
 
 The Great Nebula in Orion The Great Nebula in Andromeda The Great Star-Cluster 
 in Hercules and a Nebula in Cygnus The Spiral Nebula in Canes Venatici The 
 Dumb-Bell Nebula The Ring Nebula in Lyra The Pleiades The Milky Way 
 around the Star Cluster Messier 11 Nova Persei and the Nebula in Motion ... 59-64 
 
 CHAPTER IX. 
 SELECT LIST OF TELESCOPIC OBJECTS. 
 
 Distance of the Stars Distance of Star in Light Years Velocity of Star at Right 
 Angles to the Line of Sight Brightness of Stars compared with the Sun Masses 
 of the Stars compared with the Sun Spectroscopy Spectroscopic Binaries Cata- 
 logue and description of objects 65-81 
 
 APPENDIX Standard Time 82 
 
 INDEX. 
 
LIST OF ILLUSTRATIONS. 
 
 PLATE 
 
 1. THE CELESTIAL SPHERE 
 
 2. THE SEASONS AND THE TIDES 
 
 3. THE INNER PLANETS 
 
 4. THE OUTER PLANETS 
 
 5. THE SIZE OF THE PLANETS 
 
 6. PHASES OF THE PLANETS AND OF THE RINGS OF SATURN 
 
 7. SYSTEMS OF SATELLITES 
 
 8. MAP OF MARS 1896-97. A. E. DOUGLASS, LOWELL OBSERVATORY 
 
 9. JUPITER AND SATELLITE I. 0. LOHSE ; E. E. BARNARD - 
 
 10. SATURN, JULY 2ND, 1894. E. E. BARNARD - 
 
 11. A GUEAT SUN SPOT, 1898, SEPT. HTH. ROYAL OBSERVATORY, GREENWICH - 
 
 12. (a.) SOLAU PROMINENCES DRAWN WITH THE SPECTROSCOPE BY J. FENYI, 1895, 
 
 JULY 15TH 
 
 (6.) SOLAR PROMINENCES PHOTOGRAPHED BY E. E. BARNARD DURING THE 
 TOTAL ECLIPSE OF THE SUN, 1900 MAY 23RD 
 
 13. PATHS OF SPOTS ACROSS THE SUN'S Disc 
 
 14. ECLIPSES, AND PHASES OF THE MOON 
 
 15. PATHS OF TOTAL SOLAR ECLIPSES, 1901-1950 - 
 
 16. THE SOLAR CORONA. PHOTOGRAPHED DURING TOTAL ECLIPSES OF THE SUN : 
 
 (1) 1871, DEC. 12TH (2) 1882, MAY UTH (3) 1893, APRIL 16TH (4) 1878, 
 JULY 29tH-(5) 1889, JAN. IST (6) 1900, MAY 23RD - 
 
 17. COMET OF DONATI, OCT. STH, 1858. G. P. BOND, HARVARD COLLEGE OBSERVATORY 
 
 18. HOLMES' COMET AND THE ANDROMEDA NEBULA BROOKS' COMET, 1893, IV. 
 
 OCT. 20TH AND 21ST. E. E. BARNARD - " 
 
 19. PERRINE'S COMET, 1902, III. 30m. REFLECTOR, ROYAL OBSERVATORY, GREENWICH 
 GREAT COMET OF 1901, MAY 4TH, MCCLEAN TELESCOPE, ROYAL OBSERVATORY, 
 
 CAPE OF GOOD HOPE 
 
 20. THE MOON, REGION OF THE MARE SERENITATIS, G. W. RITCHEY, 40-iN. 
 
 REFRACTOR, YERK.ES OBSERVATORY 
 20A. KEY MAP TO DITTO - 
 
 21. THE MOON. REGION OF CLAVIUS AND TYCHO, G. W. RITCHEY, 40-iN. 
 
 REFRACTOR, YERKES OBSERVATORY 
 2lA. KEY MAP TO DITTO 
 
 22. THE MOON. REGION OF COPERNICUS, G. W. RITCHEY, 40-m. REFRACTOR, 
 
 YERKES OBSERVATORY 
 
 To follow page 6 
 
 To follow page 14. 
 
 To follow page 20. 
 
 To follow page 24 
 
 To follow page 34 
 
Xll 
 
 LIST OF ILLUSTRATIONS. 
 
 22A. KEY MAP TO DITTO 
 
 23. CHART OF THE MOON, FIRST QUADRANT 
 
 24. ,, ,, SECOND - 
 
 25 - . THIRD J-To follow page 34 
 
 26. t ,, ,, FOURTH ,, 
 
 27-38. THE MOON, SRD DAY TO 14TH DAY 
 
 27A-38A. KEY MAPS TO DITTO 
 
 39-50. MONTHLY STAR MAPS, JANUARY TO DECEMBER To follow page 48 
 
 51-70. GENERAL STAR MAPS, SECTIONS 1-20 - - ~| 
 
 71. NORTHERN INDEX MAP - - \-To follow page 53 
 
 72. SOUTHERN ,, ,, 
 
 73. THE GREAT NEBULA IN ORION, G. W. RITCHEY, 2-FT. REFLECTOR, YERKES 
 
 OBSERVATORY 
 
 74. THE GREAT NEBULA IN ANDROMEDA (M. 31), G. \V. RITCHEY, 2 FT. REFLECTOR, 
 
 YERKES OBSERVATORY 
 
 75. PHOTOGRAPHS TAKEN WITH 24 IN. REFLECTOR, W. E. WILSON, DARAMONA, 
 
 IRELAND : (1) THE GLOBULAR CLUSTER IN HERCULES (2) AN IRREGULAR 
 NEBULA IN CYGNUS 
 
 76. SPIRAL NEBULA IN CANES VENATICI (M. 51), J. E. KEELER, CROSSLEY REFLECTOR, 
 
 LICK OBSERVATORY 
 
 77. THE RING NEBULA IN LYRA (M. 57), J. E. KEELER, CUOSSLEY REFLECTOR, LICK 
 
 OBSERVATORY 
 
 78. THE DUMB-BELL NEBULA IN VULPECULA, J. E. KEELER, CROSSLEY REFLECTOR, 
 
 LICK OBSERVATORY - To follow page 64 
 
 79. THE NERJJL.E IN THE PLEIADES, ISAAC ROBERTS, 20-iN. REFLECTOR, CROW- 
 
 BOROUGH, SUSSEX - 
 
 80. THE PLEIADES, FROM PHOTOGRAPH BY P. AND P. HENRY, PARIS OBSERVATORY 
 80A. KEY PLATE, TO DITTO - 
 
 81. THE MILKY WAY AROUND THE STAR CLUSTER, MESSIER 11, E. E. BARNARD, 
 
 6-iN. PORTRAIT LENS, LICK OBSERVATORY - 
 
 82. NOVAPERSEI PHOTOGRAPHS BY A. STANLEY WILLIAMS, BRIGHTON. (1) BEFORE 
 
 THE APPEARANCE OP THE NOVA ; (2) THE NOVA TUB MOVING NEBULA SUR- 
 ROUNDING NOVA PERSEI. DRAWN BY G. W. RITCHEY FROM PHOTOGRAPHS 
 
 TAKEN WITH 24-IN. REFLECTOR, YBliKES OBSERVATORY : (3) 1901, SEPTEMBER 
 
 20TH ; (4) 1901, NOVEMBER 13TH 
 
 83. STANDARD TIME . - - - - - To follow page 82 
 
CHAPTER 1. 
 
 PLATES 1 <fe 2. 
 THE CELESTIAL SPHERE, THE SEASONS, &c. 
 
 Our first plate is an attempt to represent in a diagram what cannot properly be figured, 
 save in the imagination of the student, the relation of the terrestrial sphere to the celestial. 
 The celestial sphere must be imar/ined of infinite diameter ; in our figure it has to be 
 represented as only twice the diameter of the orbit of the Earth about the Sun. 
 
 The centre of the Earth describes an ellipse, very nearly a circle, in a plane which passes 
 through the centre of the Sun. If this plane is produced all ways to infinity it cuts the 
 celestial sphere in a great circle the Ecliptic. Could the Sun be viewed among the stars from 
 the centre of the Earth, it would be seen to lie always upon this great circle. 
 
 The axis of rotation of the Earth makes a constant angle with the plane of the ecliptic, 
 and points constantly in the same direction. (We are neglecting here the very slow effects of 
 precession). Consequently the plane of the Earth's equator, produced all ways to infinity, 
 cuts the celestial sphere in a fixed great circle which is the celestial equator, and the axis of 
 rotation of the Earth, similarly produced to infinity, cuts the celestial sphere, in two points 
 which are the poles of the celestial equator, more commonly called the poles of the sky. 
 
 It is now easy to see that at northern midwinter the north pole of the Earth is turned 
 away from the Sun, which is at the winter solstice, the point where the ecliptic is farthest 
 south of the celestial equator. As spring advances, the Sun, apparently moving along the 
 ecliptic, approaches the celestial equator, and enters it at the vernal equinox, otherwise 
 known as the " first point of Aries." At northern midsummer the north pole of the Earth 
 is turned towards the Sun, which then appears farthest north of the celestial equator, and 
 thence forward begins to dip again towards the autumnal equinox. 
 
 It is found convenient to refer the places of all stars on the celestial sphere to the 
 celestial pole and equator. Distance north or south of the equator is called north or south 
 declination, and corresponds to north or south latitude of a place on Earth. This provides 
 for one co-ordinate. The other, called Eight Ascension in the sky, corresponds to longitude on 
 Earth ; and as the longitude of a place is measured from a meridian on the Earth, which passes 
 through the terrestrial poles and through an arbitrary point, namely Greenwich Observatory, 
 so Right Ascension in the sky is measured from a meridian passing through the poles of the 
 celestial equator and a point, the vernal equinox, the point where the ecliptic cuts the 
 equator and the Sun crosses from south to north. 
 
 Right Ascension is commonly expressed in hours, minutes, and seconds of time, because it 
 is measured as the time which elapses between the passage over the meridian of any place of 
 
POPULAR GUIDE TO THE HEAVENS. 
 
 the first point of Aries and of the object whose position is to be defined. Declination is 
 expressed in degrees of arc, because it is usually measured by graduated circles so divided on 
 the instrument. 
 
 For further account of the subject of the measurement of positions on the celestial sphere, 
 the student must be referred to the text books of spherical astronomy. 
 
 THE HORIZON AND THE ZENITH, 
 
 An observer upon the Earth is debarred by the Earth itself from seeing more than one 
 half the sky at once. The plane which touches the Earth at the point where he stands, 
 produced all ways to meet the celestial sphere, cuts it in the great circle which is his celestial 
 horizon. When the observer is looking over the sea, his visible horizon is, owing to the 
 spherical shape of the Earth, depressed below the above defined celestial horizon by an 
 amount which depends on the height of the observer above sea level. This depression is 
 called the "dip of the horizon," and must be taken into account when altitudes of a heavenly 
 body are measured from the visible sea horizon. In other words, the celestial horizon is 90 
 from the zenith, the point vertically above the observer ; the visible sea horizon is more than 
 90, and the observer can by this amount see more than half the sky. 
 
 REFRACTION. 
 
 The effect of the layers of air through which light must pass on its way from a star to 
 the observer upon the Earth is to raise the star apparently above its real position. The effect 
 of refraction is sometimes very obvious when either the Sun or Moon is close to the horizon, 
 in a flattening of the solar or lunar disc. The closer a body to the horizon, the more it is 
 raised by refraction ; the lower limb of the Sun is consequently raised more than the upper, 
 with the result that the Sun appears no longer round, but flattened. 
 
 On the horizon a body is apparently raised 34' of an arc. 
 At an elevation of 1 
 3 
 
 5 
 
 10 
 
 20 
 
 30 
 40 
 
 Above 40 of elevation the refraction is measured by seconds of arc alone, and becomes 
 less and less till it vanishes at the zenith. 
 
 DIURNAL PARALLAX. 
 
 It is clear that when a celestial body is viewed from a point on the Earth's surface, it 
 cannot appear precisely in the same direction as when it is viewed from the centre. The 
 difference is named Diurnal Parallax. Owing to the small size of the Earth, and the vast 
 distance of the stars, the Diurnal Parallax of stars is absolutely insensible. With the Sun 
 and planets, however, the case is different. The nearer the body to the Earth, and the 
 nearer to the horizon of the observer, the greater the effect. Upon the Moon the effect is 
 quite large : when the Moon is just rising it appears lower among the stars than it would do 
 from the centre of the Earth, by nearly a degree, or about two diameters of the Moon. 
 
PARALLA.X. 3 
 
 Owing to this large displacement in the position of the Moon as seen from different parts of 
 the Earth, a star which is occulted by the Moon at one place may be completely clear of it at 
 another, and, similarly, while at one place a total eclipse of the Sun is seen, at another the 
 eclipse may not even be partial. 
 
 ANNUAL PARALLAX. 
 
 It is equally clear from the figure that a star will not be seen exactly in the same 
 direction at different times of year. By far the greater number of stars are so far away that 
 not even the displacement of the Earth by 186,000,000 miles produces any sensible effect. 
 But upon a certain number of nearer stars the effect is just measurable. They shift their 
 positions relative to the more distant stars very slightly during the year ; and this effect is 
 called Annual Parallax. 
 
 APPARENT DAILY ROTATION OF THE HEAVENS: 
 RISING AND SETTING. 
 
 In consequence of the actual rotation of the Earth, from W. to E., an observer upon it 
 sees the heavens apparently rotating about an axis directed to the pole of the sky. Every 
 celestial body therefore apparently describes once a day a circle round the pole. The pole is 
 elevated above the horizon by an amount equal to the latitude of the observer. Suppose this 
 is 50. A star nearer the pole than 50 describes the whole of its circle above the horizon ; 
 it never sets, and is called circumpolar. A star further than 50 from the pole will not be 
 circumpolar ; part of its daily circle will be below the horizon, and a greater part the farther 
 the star is from the pole, until for a star 180 50, i.e., 130 from the pole, the whole circle is 
 permanently below the horizon ; and in lat. 50 N. this star will never rise at all. 
 
 The figure in Plate 2, " apparent diurnal paths of the Sun," illustrates this principle in 
 the case of the Sun, and shows why the days are longer in summer than in winter : the sun 
 is nearer the north pole of the sky in summer than in winter, for we have seen that the 
 ecliptic cuts the equator at a considerable angle (23 27'). 
 
 Tides. The figure in the lower part of Plate 2 illustrates the fact that when a body like 
 the Earth, covered with an ocean, is rotating, the attraction of the Sun or Moon produces 
 disturbances in the level of the ocean, which are called tides. Though these protuberances 
 are caused by the attraction of the tide producing body they are not necessarily, nor indeed 
 generally, in line with it. On an earth whose ocean is much broken up by continents the 
 tidal waves are much broken up and disturbed, and the theory of the tides becomes 
 exceedingly complex. Owing to its relative nearness more than counter-balancing its 
 smallness, the Moon is a much more efficient tide producing agent than the Sun. 
 
 The figure at the top of the Plate is to explain the expressions spring and neap tides. 
 At New Moon and Full Moon the tides raised separately by the Sun and Moon conspire, and 
 an exceptionally high tide is produced, which is called a spring tide. At first or last quarter 
 of the Moon, the Sun tends to produce low water when and where the Moon tends to 
 produce high water, and the result is a small or neap tide. 
 
 THE SIGNS OF THE ZODIAC. 
 
 The region of the heavens along the ecliptic, or the zodiac, was divided by the ancients 
 into twelve parts, or signs, each 30 in length, which took their names from the principal 
 
POPULAR GUIDE TO THE HEAVENS. 
 
 constellations along the zodiac. Thus, starting from the Vernal Equinox, the first sign was 
 called Aries, the second Taurus, and so on. The gradual change in the position of the 
 Equator and Equinox, due to precession, has thrown back the Equinox into the constellation 
 Pisces, and displaced all the signs of the zodiac from the constellations whose names they 
 bear. Nevertheless the old names are retained, and the student must be warned against 
 possible confusion. When the Almanac says " Sun enters Aries ; spring commences," a 
 reference to the star maps will show that the Sun is still in Pisces, and will .be for a month 
 We must distinguish, therefore, the names of the constellations from the same names applied 
 to the signs of the zodiac. 
 
 The Signs of the Zodiac, with their symbols, are given in the following table. Counting 
 from the Vernal Equinox we have 
 
 to 30 ... 0. T Aries. 180 to 210 ... VI. =& Libra. 
 
 30 to 60 ... I. Taurus. 210 to 240 ... VII. m. Scorpio. 
 
 60 to 90 ... II. n Gemini. 240 to 270' ...VIII. J Sagittarius. 
 
 90 to 120 ... III. 55 Cancer. 270 to 300 ... IX. >y Capricornus. 
 
 20 to 150 ... IV. Si Leo. 300 to 330 ... X. ^ Aquarius. 
 
 50 to 180 ... V. "B Virgo. 330 to 360 ... XL X Pisces. 
 
 PLATE 3. 
 
 THE ORBITS OF THE INNER PLANETS. 
 
 In the attempt to represent the orbits of celestial bodies on maps or charts, it must 
 always be remembered that, except in the case of orbits which happen to lie in the same plane 
 it is impossible to depict on any drawing the veritable position of more than one. We are 
 obliged to resort to some process of a more or less artificial character. For instance, we take 
 the plane of the Ecliptic, that is, the Earth's orbit, as the plane of the paper, and then we 
 simply lay down on it the orbits of the other bodies, notwithstanding that their planes are 
 inclined to the Ecliptic. The points in which the real orbit passes through the plane of 
 representation are called the Nodes, the ascending node being that at which the planet passes 
 from the southerly to the northerly side of the plane. Each orbit may be conceived to be 
 turned around its line of nodes till its plane coincides with the Ecliptic. It is thus tha 
 Plate III. is produced. 
 
 The path which every planet 
 describes is an ellipse, and the 
 Sun is situated in one of the two 
 foci of the ellipse, S or H. The 
 longest diameter of the ellipse, 
 P A, which passes through the 
 two foci, is called the major 
 axis; the diameter X Y, at 
 right angles to it, is the minor 
 axis, and the two intersect in 
 the centre, 0, of the ellipse. 
 The points A and P are the 
 Apsides of the ellipse. We will 
 suppose the Sun is in the focus 
 
 Y 
 
 TEE ELLIPSH. 
 
THE CEBITS OF THE INNER PLANETS. 5 
 
 S in the figure, and that a planet is describing, under its attraction, the ellipse. 
 The ellipse is called its orbit. The point P, nearest to the Sun, is the Perihelion 
 of the orbit ; the point A, farthest away, is the Aphelion. The half major axis, P, which 
 is also equal to the distance S X, is called the mean distance. The ratio of O S to O P is the 
 eccentricity of the orbit ; the smaller this ratio is, the more does the ellipse resemble a circle. 
 The orbits of the more important planets all have small eccentricities. 
 
 It will be convenient to give here the symbols which are in use for the Sun, Moon, and 
 Planets, and certain other signs used occasionally in this work. 
 
 Explanation of Astronomical Symbols and Abbreviations. 
 
 O The Sun. 
 <i The Moon. 
 Mercury. 
 9 Venus, 
 ffi or 6 The Earth. 
 
 h Hours. 
 
 m Minutes of Time. 
 
 8 Seconds of Time. 
 
 cS Mars. 
 
 H Jupiter, 
 
 h Saturn, 
 
 y Uranus. 
 
 *f Neptune. 
 
 Decrees. 
 
 Minutes of Arc. 
 Seconds of Arc. 
 
 6 Conjunction. 
 
 O. Quadrature. 
 
 <? Opposition. 
 
 ft Ascending Node. 
 
 y Descending Node. 
 
 N. North. S. South. 
 E. East. W. West. 
 
 The orbits of the planets Mercury, Venus, Earth, Eros, and Mars are represented in this 
 Plate, and for illustrating the use of it we take the orbit of Mercury. The point A is the 
 Aphelion where the planet is most distant from the Sun. The next point marked is the 
 Ascending Node ft, where the orbit comes through the plane of the paper, the inclination 
 being 7" 0', as given in the table in the upper right hand corner of the map. P is the 
 Perihelion, where Mercury is nearest the Sun. For a complete revolution this planet requires 
 a period of 87 '969 days. Similar remarks apply to the other orbits. Thus, for instance 
 Mars, the outermost of the four planets shown in this figure, revolves in the period of 686'951 
 days. Its Perihelion is marked P, and Aphelion A, the Ascending Node is Si, and the 
 inclination is 1 51'. The inclinations of the cometary orbits are given in the right hand 
 lower corner of the Plate. The orbits of the three following comets are drawn, Biela's Comet, 
 Comet I. 1866, and Comet III, 1862. These have been chosen because they possess the 
 additional interest of being the paths of the three chief meteor swarms. The famous showers 
 of " Leonids," which used to appear about November 13th, in magnificent displays every 33 
 years, move in the track of Comet I. 1866. The " Andromedids," or meteors of November 
 27th, have the same orbit as Biela's Comet, and the " Perseids " pursue the course of Comet 
 III. 1862. In the case of each of the cometary orbits the Descending Node has been marked 
 on the Plate, as it is at this Node that the Earth meets the associated meteor swarm. 
 
 The planet Eros is a recently discovered small planet, whose orbit is of a remarkable 
 character. It is very eccentric, and considerably inclined to the ecliptic ; and on favourable 
 occasions the planet may be within about 13,000,000 miles of the Earth, nearer to us than 
 any celestial body except our own Satellite. 
 
 PLATE 4. 
 THE ORBITS OF THE OUTER PLANETS, 
 
 The innermost orbit on this Plate is that of Mars, for those belonging to planets still 
 closer to the Sun would be too small to be shown in a figure of the scale necessary for the 
 outer planets. 
 
POPULAR GUIDE TO THE HEAVENS. 
 
 Next to Mars comes the zone of minor planets, of which more than 500 are now known, 
 while some twenty or thirty new ones are discovered by photography yearly. Their orbits 
 are tangled in a way impossible to represent otherwise than conventionally in a figure of 
 small size. They exhibit great diversity of eccentricity and inclination to the ecliptic. And 
 the task of keeping up the computation of the places of this fast growing family of tiny 
 planets is becoming almost beyond reasonable possibility. In our figure the innermost repre- 
 sented is Medusa, with a period of 312 years ; the outermost Hilda, with a period of V90. A 
 later discovery, Adalberta, lies closer to the Sun than Medusa, with a period of 3'01 years ; 
 and Thule, with a period of 8'86 years, lies considerably farther out than Hilda. 
 
 Beyond the zone of minor planets lie the major planets Jupiter, Saturn, Uranus, and 
 Neptune. 
 
 On this Plate are also represented the orbits of several interesting comets belonging to the 
 Solar System. The Comet of Encke has the smallest orbit of any known comet, and it is 
 especially interesting because of the somewhat irregular and unexplained acceleration to which 
 it is subject. There is room on this Plate to show the orbit of Biela's Comet, part of which 
 was shown on the preceeding Plate. 
 
 Halley's Comet is the only periodic comet which makes a splendid appearance ; the 
 others are all small, many of them almost insignificant objects. But Halley's Comet on its 
 last return had a nucleus as bright as a first magnitude star, and a tail twenty-five degrees 
 long ; and its next return in 1910 will be awaited with very great interest. 
 
 A portion of the orbit of the Comet of 1882 is shown on account of its remarkable nature. 
 The comet passed so close to the Sun that it almost grazed, and it swung round 180 of its 
 orbit in the space of three hours. 
 
 A remarkable relation, hitherto unexplained, connects the distances of the various planets 
 from the Sun. 
 
 If we write down the series of numbers 
 
 3 6 12 24 48 96 192 384, 
 and add 4 to each, we have 
 
 4 7 10 16 28 52 100 196 388. 
 
 The first four are very nearly in the proportion of the distances from the Sun of Mercury, 
 Venus, the Earth, and Mars ; 52 and 100 represent equally well the distances of Jupiter and 
 Saturn ; the intermediate No. 28, which stands for the average minor planet, actually suggested 
 the search for them ; when Uranus was discovered, it was found to fit 196 ; and when 
 there was a suspicion of a planet beyond Uranus, it was assumed that its distance would be 
 nearly represented by 388. But it is not ; 300 is the real number, and here the rule, which 
 is called Bode's law, breaks down completely. 
 
. 
 
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 CHAPTER II. 
 
 PLATE 5. 
 THE SIZE OF THE PLANETS. 
 
 Plate 5 has been drawn to show the relation and actual sizes of the different planets and 
 of the rings of Saturn. The determination of the size of a planet in miles is by no means a 
 simple matter. Firstly, it is necessary to measure the angular size of the planets, as seen from 
 the Earth, in seconds of arc, and this is affected by the phenomenon of irradiation by which 
 a bright object against a dark background looks larger than it really is. Also the planets 
 Uranus and Neptune are so far away and look so small that it is hard to measure them, and 
 it is still quite uncertain which is really the larger. We have therefore shown them equal. 
 When the angular diameters at a given distance have been found, we next require a knowledge 
 of the Solar Parallax, that is, of the angular radius of the Earth as seen from the Sun ; the 
 adopted value of this quantity is 8"80. And, finally, we require the diameter of the Earth in 
 miles ; for this we adopt Col. Clarke's latest value, 7926'6 miles. 
 
 We can then calculate the diameters of the planets given below, and shown to scale upon 
 the Plate. The times of axial rotation and the inclination of the planets' equator to the 
 Ecliptic are given when they are known. 
 
 
 
 Diameter 
 
 
 
 in miles. 
 
 Mercury 
 
 
 3,000 
 
 Venus 
 
 
 7,700 
 
 Earth 
 
 
 7,926 
 
 Mars 
 
 
 4,300 
 
 Jupiter 
 
 / Equatorial 
 \ Polar 
 
 90,000 
 84,000 
 
 Saturn 
 
 i Equatorial 
 \ Polar 
 
 76,000 
 70,000 
 
 Uranus 
 
 
 31,000 
 
 Neptune 
 
 
 31,000 
 
 Time of Rotation. 
 
 Unknown 
 Unknown 
 
 23 h - 
 
 24 
 9 
 
 37 
 
 4"- 
 23 
 
 10 14 
 
 Unknown 
 Unknown 
 
 Inclination of Equator 
 to Ecliptic. 
 
 Unknown 
 Unknown 
 23* 27' 
 26 21 
 3 5 
 
 28 10 
 
 Unknown 
 Unknown 
 
 Dimensions of Saturn's rings : 
 
 Outer radius of outer ring ... ... ... 86,000 miles. 
 
 Inner radius of outer ring ... ... ... 75,000 
 
 Outer radius of inner ring - ... ... ... 73,000 
 
 Inner radius of inner ring ... ... ... 55,000 
 
 Inner radius of dusky ring ... ... ... 44,000 
 
 All these dimensions are based upon a careful comparison of the most recent measures 
 made with the great telescopes at Lick, Yerkes, Washington, and Greenwich Observatories. 
 The time of rotation and position of the equator of Mercury, Venus, Uranus, and Neptune 
 are unknown because of the want of definite markings on those planets. There is consider- 
 able reason to suppose that the periods of rotation of Mercury and Venus are the same as 
 their periods of revolution round the Sun, namely 88*0 and 224'7 days. In that case they 
 would always turn the same face towards the Sun. If we assume, which is probably true, 
 that the satellites of Uranus and Neptune move nearly in the planes of the planets' equators, 
 then we may add to the last column for those planets, 101 and 145, the inclinations being 
 given greater than 90 to conform to the fact that the satellites, unlike any other bodies 
 in the Solar System, move in a retrograde direction. 
 
POPULAR GUIDE TO THE HEAVENS. 
 
 Recent measures have given the following diameters for the four principal minor planets 
 Ceres ... ... ... 480 miles. 
 
 Pallas ... ... ... 300 
 
 Juno ... ... ... 120 
 
 Vesta 240 
 
 PLATE 6. 
 PHASES OF THE PLANETS AND OF SATURN'S RINGS. 
 
 This Plate exhibits the appearances of the planets Mars, Venus, and Saturn when 
 occupying different parts of their orbits. A reference to Plate 3 makes it clear that the distance 
 between the Earth and Mars must vary considerably at different dates, according to the positions 
 which the bodies occupy in their paths around the Sun. Of course, if the orbits were both 
 circular, it is clear that the greatest possible separation between the two bodies would be 
 attained at every conjunction ; that is to say, whenever the Earth, Sun, and Planet are in a 
 straight line (at least, in their projected orbits), the Earth and Planet being at opposite sides 
 of the Sun. The same diagram makes it plain that the least distance apart would occur at 
 every opposition; that is, whenever the three bodies, as represented in their projected orbits, 
 were in a straight line, with the Earth in the middle. 
 
 The eccentricity of the orbit of Mars considerably modifies the circumstances. It will be 
 seen, by referring to Plate 3, that an opposition occurring in the latter half of the year will 
 generally be more i'avourable (i.e., bring the two bodies closer together) than one in the first 
 half of the year, and that the most favourable opposition happens when the Earth and Planet 
 are situated in about 333 longitude On the other hand, an opposition occurring in 
 longitude 153 will be as unfavourable as possible. The Earth's longitude on August 26th is 
 333, and on February 22nd it is 153 ; hence the most favourable opposition of Mars will 
 occur on August 26th, and the closer to that date the opposition happens the better. The most 
 unsuitable oppositions are about February 22nd. 
 
 The greatest distance at which the two planets can possibly be separated is attained 
 when the Earth's longitude is 333, and that of Mars 153 ; that is to say, when conjunction 
 occurs about August 26th. 
 
 Figures 1, 4, and 5, in the upper part of the left-hand portion of Plate 6, show the 
 relative apparent sizes of the planet at most favourable opposition (August 26th), at least 
 favourable opposition (February 22nd), and at its greatest possible distance. These views 
 illustrate the advantage of an opposition occurring somewhere near the end of August, when 
 the appearance of the planet is to be studied. 
 
 When the lines from the Sun to the Earth and the Sun to the Planet are at right angles, 
 the Planet is said to be in quadrature. A very distinct phase is then perceptible in Mars, by 
 which about a quarter of its diameter is cut off. The appearances of the planet at western 
 and eastern quadrature, as shown in an inverting telescope, and the apparent size of the 
 planet on the same scale as the other figures, is also given. For the topography of the planet, 
 the reader may refer to Plate 8. As to the times and seasons for observing Mars in its vary 
 ing aspects, reference may be made to the Index to Planets, see pages 38 and 42. 
 
 Since the orbit of Venus lies inside that of the Earth, the appearances of this planet 
 differ considerably from those of an exterior planet like Mars. It is obvious that the nearest 
 approach of the two bodies will occur at inferior conjunction, or when Venus and the Earth 
 
PHASES OF THE PLANETS AND OF SATURN'S RINGS. 9 
 
 are on the same side of the Sun ; and that the greatest distance between them will occur at 
 superior conjunction, or when the two bodies are at opposite sides of the Sun. It might, at 
 first sight, therefore, be supposed that at inferior conjunction the planet would be seen best, 
 being then apparently largest ; and that it would be least favourably placed at superior con- 
 junction. The relative apparent sizes of this planet just before inferior, and at superior, con- 
 junction are shown in the lower part of the left-hand portion of this plate ; but since, in the 
 former configuration, the illuminated part of the globe is reduced to a very thin crescent, and 
 since in both cases the planet Is enveloped in the Sun's rays, in neither of these phases is it 
 suitably situated for observation. 
 
 Venus attains its greatest brightness as an evening star about a month after its greatest 
 elongation east. The greatest brightness of the same planet as a morning star precedes by 
 about a month its greatest elongation west. 
 
 The second figure has been drawn to represent the size and shape of Venus when most 
 brilliant. The third figure exhibits the appearance of Venus when situated at a distance of 40 
 from the Sun in the further part of its orbit. In this position it presents a gibbous form. 
 It will be seen, however, that the diminution of light caused by its increased distance from the 
 Earth, more than compensates for the larger proportion of the illuminated surface visible, so 
 that, on the whole, the amount of light received from the planet is less than when it is in the 
 position corresponding to Figure 2. In the Index to Planets, p. 39, the method of finding the 
 position of Venus for any date up to 1950 is explained. 
 
 For the general details of the planet Saturn reference may be made to Plate 11. In this 
 place we discuss only the varying appearances of the rings. The right-hand portion of Plate 6 
 contains twelve figures depicting the different aspects which the ringed planet presents 
 according to the position it happens to occupy in its orbit. In connection with the Table of 
 Planetary Phenomena, p. 38, this plate will enable the reader to determine with considerable 
 accuracy the appearance of the rings at any time. If the opposition of Saturn occurs in the 
 middle cf January in any year, it will be found that Fig. 1 represents the system. The rings 
 are then opened nearly to their full extent, and the upper portion of the ball just extends be- 
 yond the outer margin of the rings. If the opposition occurs in February, the rings will be 
 found to have closed up somewhat, and to appear as shown in Fig. 2. If the opposition 
 occurs in March, the rings will shrink almost to a straight line, as in Fig. 3. At oppositions 
 occurring in April, May, and June, the appearances will be as in Figs. 4, 5, and 6, the rings 
 appearing the more open the more nearly the date of opposition approaches June. 
 Figs. 7 12, in a similar way, show the changes which this system will undergo at oppositions 
 occurring in the latter six months of the year. 
 
 It must, of course, be understood that the appearance here depicted for any month will not 
 recur every year in that month, but will only be seen in those years in which the opposition of 
 the planet occurs during the month in question, and then only with accuracy at the date of 
 opposition. But, as Saturn takes a period of no less than 29| years to accomplish its revolution, 
 the alteration in its appearance will vary very little for several months before and after opposi- 
 tion, so that the figure for any month may be taken to represent the appearance of the system 
 during the year in which opposition occurs in that month. Thus, in the year 1921, the Table 
 of Planetary Phenomena tells us that the opposition of Saturn takes place in March, whence 
 we learn that during this year the rings will be almost edgewise towards us. Again, in the 
 year 1928, opposition occurs in June, from which we infer that during that year the rings will 
 be open to their fullest extent, and most favourably situated for observations 
 
10 POPULAR GUIDE TO THE HEAVENS. 
 
 These pictures have, as usual, been drawn to represent the planet as seen in an astiunomical 
 telescope, which always inverts the object, so that Figs. 3 8 exhibit the appearance of the 
 system when the northern face of the ring is tilted towards us so as to become visible, while 
 in Figs 1 and 2, and 9 12, it is the southern side of the rings which is seen. 
 
 To facilitate reference, a column has been added to the Table of Planetary Phenomena, 
 p. 38, to show which of the phases are presented in the corresponding opposition. For 
 example, if the opposition is in October, the column alluded to gives the number 10, which 
 means that during the year in question the planet Saturn will present, when visible at all, a 
 phase resembling that shown in Fig. 10 on Plate 8. 
 
 At the times when the ring is seen edgewise the sequence of appearances may be very 
 
 complicated. The ring may become quite or very nearly invisible from any one of three causes ; 
 
 (1.) The plane of the ring may pass through the Earth, in which case the ring is seen 
 
 exactly edgewise. And as the ring is very thin, its illuminated edge is not bright 
 
 enough to be seen, and the ring disappears completely in all telescopes. 
 
 (2.) The plane of the ring may pass between the Earth and the Sun, in which case the 
 
 Sun is shining on the opposite side of the ring to that which is presented, very 
 
 obliquely, to the Earth ; and in this case the ring is almost invisible, even in great 
 
 telescopes. 
 
 (3.) The plane of the ring may pass through the Sun, in which case neither side of the 
 
 ring is effectively illuminated, and again it almost disappears. 
 
 It is sometimes a matter of discussion how big a planet looks in a telescope of a given 
 magnifying power. By means of this Plate the question may be answered. The Plate is 
 drawn to such a scale that if it is placed ten feet from the eye the figures of the planetary 
 discs subtend the same angle as the planets' images themselves, at the corresponding phases 
 would do when seen in a telescope which gives a magnifying power of 80 diameters. 
 
 PLATE 7. 
 SYSTEMS OF SATELLITES. 
 
 This Plate exhibits the relative dimensions of the orbits of the systems of satellites 
 attending certain of the planets. With the exception of the system surrounding Mars, which 
 is on a scale twenty times as large as the rest, the orbits are all laid down on a uniform scale of 
 half a million miles to the inch. The periods of revolution of the satellites around their 
 primaries are also marked on the orbits approximately. More complete numerical information 
 than it has been found convenient to represent on the map is given in the following tables. 
 
 THE SATELLITE OF THE EARTH : THE MOON. 
 
 Mean distance from the centre of the Earth : 239,000 miles. 
 Periodic time : 27 days, 7 hrs. 43 mins. 11 sees. 
 
 m n -. r Mean distance from Periodic Time. 
 
 THE SATELLITES OF MARS : Centre of Planet. Days hrs. mins. sees : 
 
 Phobos 5,850 miles 7 39 14 
 
 Deimos 14,650 1 6 17 55 
 
 THE SATELLITES OF JUPITER : 
 
 V. (Nameless) ... 112,500 11 57 23 
 
 I. (lo) 261,000 
 
 II. (Europa) 415,000 
 
 III. (Ganymede) ... 664,000 
 
 IV. (Callisto) 1,167,000 
 
 1 18 27 34 
 
 3 13 13 42 
 
 7 3 42 33 
 
 16 16 32 11 
 
SYSTEMS OP SATELLITES. 
 
 THE SATELLITES OF SATURN: 
 
 Mimas. 117,000 22 37 5 
 
 P^nceladus 150,000 
 
 Tethys 186,000 
 
 Dione 238,000 
 
 Rhea 332,000 
 
 Titan 771,000 
 
 Hyperion 934,000 
 
 lapetus 2,225,000 
 
 1 8 53 7 
 
 1 21 18 26 
 
 2 17 41 10 
 4 12 25 12 
 
 15 22 41 27 
 
 21 6 38 24 
 
 79 7 56 23 
 
 p. , In ' ^ U J>> 190 f- Pro E- C. Pickering announced the confirmation of the discovery of a ninth satellite of Saturn, 
 nailer ' ' n P hot S ra P hs m ls99 - Its period is about 1 years, and its distance from Saturn about 8,000,000 
 
 THE SATELLITES OF UKANUS : 
 
 Mean distance from Periodic Time. 
 
 Centre of Planet. Days hrs. mins. sees. 
 
 Ariel 120,000 miles 2 12 29 21 
 
 Umbriel 167,000 4 3 27 37 
 
 Titania 273,000 8 16 56 30 
 
 Oberon 365,000 13 11 7 6 
 
 THI: SATELLITK OF NEPTUNE : 
 
 (Nameless) 221,500 5 21 2 38 
 
 The satellites of Mars are a remarkable pair. The inner, Phobos, is the only satellite 
 that revolves faster than its primary rotates. In consequence of this, it must rise in the 
 west, and set in the east. The outer satellite, Deimos, revolves in a period so little greater 
 than that of the planet that it goes through all its phases twice between the times of rising 
 and setting. 
 
 The four well known satellites of Jupiter are almost always called by their numbers ; 
 their names, which have almost fallen into disuse, are therefore placed in brackets. The fifth 
 satellite, discovered by Barnard in 1892, still remains without a name. 
 
 Recent measures have given the following values for the diameter of the four large 
 satellites of Jupiter, and of Titan, the largest of the satellites of Saturn. 
 
 I. 2,500 miles. III. 3,600 miles. 
 
 II. 2,200 IV. 3,300 
 
 Titan ... 2,900 miles. 
 
 But it is very probable that, on account of the effect of irradiation, these diameters may 
 be several hundred miles too large. 
 
 The diameters of the other satellites of our system are, for the present, beyond the reach 
 of measurement. If we measure the amount of light they reflect from the sun, and make 
 some assumption as to their albedo, or light reflecting power, we can estimate roughly the 
 probable diameters of the others. One finds that the Phobos and Deimos are probably about 
 10 and 30 miles in diameter, the fifth satellite of Jupiter, 100. 
 
 PLATE 8. 
 MAP OF MARS. 
 
 The selection for this work of a representation of the surface of the planet Mars is a 
 matter of great difficulty. Observers of Mars are divided into two camps those who see the 
 canals and those who do not. The former are in the strong position that they are perfectly 
 
12 POPULAR GUIDE TO THE HEAVENS. 
 
 sure that they see what they represent in their drawings ; the latter declare that under the 
 finest possible conditions of observation, and with the most perfect instruments, they can see 
 nothing resembling the straight markings which are known as canals. And further, they 
 bring forward experiments which make it clear that irregularly disposed markings imperfectly 
 seen, give the effect of straight streaks, by an optical illusion. The interest which has been 
 excited by the speculations based upon the drawings of these apparently artificial markings 
 makes it impossible to present a chart of Mars in which the canals are omitted. We give, 
 therefore, a reproduction of the chart of Mars made at the Lowell Observatory, Flagstaff, 
 Arizona, by Mr. A. E. Douglass, from a study of all the drawings made there by various 
 observers during the opposition of 1896-97. At the same time it is necessary to give the 
 caution that some of the very best observers deny altogether the truth of this representation 
 of the planet. 
 
 Our difficulty is increased by the fact that there are two rival systems of nomenclature for 
 the features of Mars an earlier system in which the so-called lands and seas are named 
 after modern Astronomers Herschel, Leverrier, Dawes, &c., and a later, in which the names 
 are taken from classical geography and mythology. The later system seems likely to 
 prevail, and we have adopted it in the present work. It is useless to give a catalogue of some 
 400 names of markings whose very existence is in dispute. We confine ourselves therefore to 
 naming some of the more prominent features, to which a number is affixed in the plate. 
 
 1. Fastigium Aryn. 13. Mare Tyrrhenium. 
 
 2. Margaritifer Sinus. 14. Syrtis Minor. 
 
 3. Mare Erythraeum. 15. Syrtis Major. 
 
 4. Aurorae Sinus. 16. Cerberus (Canal). 
 
 5. Ganges (Canal). 17. Marc Icarium. 
 
 6. Lunae lacus. 18. Edom promontorium. 
 
 7. Solis lacus. 19. Hellas. 
 
 8. Sirenius lacus. 20. Ausonia. 
 
 9. Mare Sirenum. 21. Trivium Charontis 
 
 10. Eumenides (Canal). 22. Orcus (Canal). 
 
 11. Mare Cimmerium. 23. Pyriphlegethon. 
 
 12. Charontis lacus. 24. Mare Chronium. 
 
 It should be understood that in the unsteady air of England it is almost hopeless to 
 expect to see many of the finer details. Not even in the most favourable climates are they 
 to be seen always, or all at once. And much training of the eye is required before it is fit to 
 decide for or against the existence of these details on the very verge of invisibility. 
 
 PLATU 9. 
 JUPITER AND SATELLITE I. 
 
 Owing to the absence of permanent features on Jupiter it is not possible to give a map 
 of the planet. From year to year the position and breadth of the belts change, the tints of 
 the surface change, and the shape and character of the spots change. Under these circum- 
 stances the best that can be done is to present drawingsof the planet which are typical, yet possess 
 features of more than average interest. We therefore select a set of drawings covering the 
 period when the '' great red spot " was most conspicuous. It was first seen in July 1878, and 
 
JUPITER. 13 
 
 in the following year it was the most conspicuous feature on the planet (Figs. 4, 5, 6). In 
 1880 and 1881 it changed but little (Figs. 7, 8, 9, 12), but after that began, to fade ; and at the 
 present time it is visible only as an indentation or scar on the southern equatorial belt. It 
 was evident almost from the first that its period of rotation was not the same as that of the 
 average spot in the belt near it. These gained 22 sees, upon it at each rotation. And though 
 the spot is more or less permanent its own time of rotation has changed by 6 s , and for these 
 facts no satisfactory theory has been suggested. 
 
 The satellites of Jupiter were the first discoveries made with the telescope, and they 
 remain the most beautiful and interesting objects that a small telescope can show. Their 
 eclipses and occupations and transits over the planet's disc are predicted in the Nautical 
 Almanac year by year, to which reference may be made also for the configuration of the 
 satellites each night. 
 
 With a very powerful telescope the phenomenon of the transit of satellite I. is very 
 curiously varied. The figures are from drawings made by Prof. Barnard at the Lick Observa- 
 tory. It had been noticed that when Satellite I. was crossing the disc of the planet, is 
 sometimes appeared double and sometimes very elongated. The drawings supply the 
 explanation. The satellite, not unlike its primary, has a bright equatorial region and darker 
 poles. When it is projected upon a dark belt of a planet the former alone is seen ; when upon 
 a bright belt the latter. The drawing made November 19, 1893, shows the phenomena most 
 completely. The satellite was seen against the boundary separating a bright from a dark 
 belt ; and it was also partly superposed upon its own shadow. It is scarcely necessary to add 
 that, since the whole apparent diameter of the satellite is little more than a second of arc, it 
 requires the finest telescope and skill to see what is here shown. 
 
 PLATE 10. 
 SATURN. 
 
 We are indebted again to Professor Barnard and the Lick telescope for the drawing which 
 has been chosen to illustrate the appearance of the planet Saturn. Although spots are 
 sometimes seen upon the planet, they are uncommon, and the surface markings are usually 
 no more than a few vague dusky belts ; the interest lies in the rings. 
 
 In looking at the plate we must imagine the sun behind us and a little to the left. The 
 shadow of the ball is seen upon the rings (at the right hand limb) and the shadow of the rings 
 is seen upon the ball (above). The Cassini division was plainly visible all round, but the 
 Encke division in the outer ring was not visible at the time ; it seems to be a thin place in 
 the ring rather than an actual division. The dusky, or crape ring, showed steely blue against 
 the sky, and at its inner edge was so transparent that the planet could be seen through it. 
 Where it joins the inner ring there is no division, but the two rings merge rapidly the one into 
 the other. The brightest part of the whole is the outer edge of the inner bright ring. 
 
 Since this drawing was made the rings have opened out to their fullest extent, and are 
 now (1903) closing in again as the planet approaches the interesting point in its orbit where 
 the rings are seen edgewise. 
 
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 CHAPTER III. 
 
 PLATES 11 & 12. 
 THE SUN. 
 
 A very important branch of the work of the Royal Observatory, Greenwich, is the daily 
 record, by photography, of the number and size of the spots which appear upon the Sun's 
 surface. To fill the gaps caused by cloudy weather in England photographs are taken also 
 in India and Mauritius, and are sent home to Greenwich, so that there are very few days in 
 the year for which there is no record. The purpose of this continuous survey of the Sun is 
 to determine the laws which govern the changes in the area and position of the spots. It is 
 well-known that the number of spots reaches a maximum about every eleven years ; that at 
 the beginning of each new period the spots are found in higher solar latitudes than at the end ; 
 and that there is an unmistakable, but unexplained, connection between the frequency of Sun 
 spots, of displays of the Aurora Borealis, and of terrestrial magnetic storms. One of the 
 finest Sun-spot photographs ever taken at Greenwich is reproduced, by permission of the 
 Astronomer Royal, in Plate 11. The structure of the group is very complex. Every large 
 spot is accompanied by a crowd of smaller spots, which change comparatively quickly. A 
 large regular spot consists of two well-defined portions the black central -umbra and the 
 surrounding grey penumbra. In the latter, the bright granules which form the photosphere 
 of the Sun are elongated and drawn in towards the centre of the spot, making the structure 
 of the photosphere somewhat like thatch. Very frequently bright bridges are thrown across 
 from one side to the other, and this is generally the prelude to the filling up of the spot. 
 
 Sun spots are the seat of tremendous activity in the layers of glowing gas lying above the 
 photosphere. The most remarkable of the gaseous prominences, which stand out above the 
 limb of the Sun when it is totally eclipsed, are almost always associated with spots lying 
 beneath them. The lower part of Plate 12 is the reproduction of a photograph taken by 
 Prof. Barnard and Mr. Ritchey during the total eclipse of 1900 May 28th. These 
 prominences are outbursts of hydrogen, calcium, and occasionally of other metallic vapours, 
 which are often thrown up from the surface of the Sun with enormous velocities. The 
 prominences are conspicuously seen during a total eclipse because the glare in our atmosphere, 
 which ordinarily surrounds the Sun, is then for the moment removed. The application of a 
 spectroscopic method now enables us to abolish the effect of this glare at any time, and it is 
 possible to make a daily record of the prominences. 
 
 The upper part of Plate 12 is a reproduction of a set of drawings of a single prominence 
 made in this manner by Herr Fenyi, at Kalocsa in Hungary, on 1895, July 15. His des- 
 cription is as follows. At 7.10 a.m., Greenwich M.T., a very delicately formed prominence 
 stood precisely on the place where a considerable group of Sun spots was passing out of sight 
 round the limb (Fig. 1). When Fig. 2 was drawn at 7.40, the form of the prominence was 
 
16 POPULAR GUIDE TO THK HEAVENS. 
 
 changing with extraordinary rapidity. Determinations of the velocity with which parts of 
 the prominence were moving gave results up to 500 miles per second. Fig. 3 was drawn at 
 8.7 ; Fig. 4 at 8.30, when the prominence had reached its greatest height of about 100,000 
 miles. At 8.45 its shape had changed very much, and at 9.35, when Fig. 6 was drawn, the 
 great protuberances had completely gone, and the prominence had returned to nearly its 
 appearance of 2i hours before. 
 
 PLATE 13. 
 PATHS OF SPOTS ACROSS THE SUN'S DISC. 
 
 By the rotation of the Sun on its axis, the spots appear to be carried across the disc, 
 along paths parallel to its equator. 
 
 The axis, around which the Sun rotates, is inclined to the ecliptic at an angle of 82 45'. 
 The inclination of the Sun's equatorial plane to the ecliptic is therefore 7 15'. 
 
 The ascending node of the Sun's equator is the point at which a spot on the equator of the 
 Sun would be carried by the Sun's rotation from the southern to the northern side of the 
 ecliptic, and the longitude of the node is the angle which the direction of this point makes 
 with the direction of the First Point of Aries as seen from the Sun's centre. The actual 
 value of the longitude of the ascending node is 74. Its position is marked on Plate 2. 
 
 Plate 13 shows the paths along which the spots appear to travel at different dates. They 
 are here represented as actually on the face of the Sun, and not as seen through the inverting 
 telescope that the astronomer ordinarily uses. 
 
 On December 6th, the Earth is in the line of nodes, and, consequently, in the plane of the 
 Sun's equator, and the paths pursued by the spots will therefore appear projected into straight 
 lines. Again, on June 5th, when the Earth is in the opposite point of its orbit, it will be 
 again in the plane of the Sun's equator, and the paths of the spots will again appear projected 
 into straight lines. 
 
 On March 4th, the Earth, being then 90 from the node, will be depressed below the Sun's 
 equator by an angle of 7 Q 15', and the paths of the spots will appear as ellipses of considerable 
 curvature, with their convexities towards the north ; while, on September 6th, from the op- 
 posite point of the orbit, the same curves will reappear, only that they will now be convex 
 towards the south. From March till June, and from September till December, the curvature 
 is decreasing, while in the intervening periods corresponding changes take place in the opposite 
 direction. We may describe these changes in a somewhat different way by saying that on 
 June 5th and December 6th both poles of the Sun are visible just on the edge of its disc ; 
 from June to December the north pole only is visible j and from December to June the south 
 pole only can be seen. 
 
 By the " position angle of the Sun's axis," is meant the angle which the projection of the 
 northern half of the Sun's axis on its apparent disc makes with the meridian passing through 
 the Sun's centre, reckoned positive towards the eastern, and negative towards the western 
 side of the disc. If the observation is made at noon, it is the angle which the direction of the 
 axis makes with the vertical, when the image is viewed projected on a sheet of paper placed 
 behind the eyepiece of an inverting telescope. If the observer's back be turned towards the 
 
THE SUN. 17 
 
 Sun, the position angle will be positive when the upper half of the axis leans towards the 
 right, and negative when it leans towards the left. On such a projection the cardinal points, 
 N., S., E., W., lie just as they do in an ordinary terrestrial atlas. On January 5th and 
 July 6th, the position angle of the Sun's axis is Zero ; from July 6th it gradually increases in 
 a positive direction until it reaches its greatest value, viz. : + 26 20', on October 10th. From 
 this date it gradually diminishes till January 5th, alter which it becomes negative, reaching 
 its greatest negative value, viz. : - 26 20', on April 5th, and returning once more to Zero on 
 July 6th. 
 
 PLATE 14. 
 PHASES OF THE MOON: LUNAR AND SOLAR ECLIPSES. 
 
 Phases of the Moon. The hemisphere of the Moon that is turned towards the Sun is, 
 of course, brilliantly lighted ; the other hemisphere is dark. As the Moon moves in its 
 orbit round the Earth, the illuminated side is turned towards us in varying proportions; and 
 the relation between the phases thus produced and the relative positions of Sun, Earth, and 
 Moon is shown in the upper part of the plate. 
 
 When the Moon is but a few days old, and appears as a thin crescent, it frequently 
 happens that part of the Moon which is not lit directly by the Sun is seen faintly 
 shining by the reflected " Earth-light," an appearance known as " the old Moon in the new 
 Moon's arms." 
 
 Eclipses of the Moon. The Sim throws behind the Earth a dark cone of shadow, 
 which reaches a long way beyond the path of the Moon, and if it had happened that the path 
 of the Moon lay precisely in the ecliptic, then, at every full Moon, she would pass through 
 this shadow, and be totally eclipsed. Since, however, the Moon's path makes a small angle 
 with the ecliptic, she usually passes a little above or below the cone of shadow, and escapes 
 eclipse. But, from time to time, the Moon is crossing the ecliptic just about the time of full, 
 and then a partial or total eclipse occurs, and is visible over the whole of that hemisphere of 
 the Earth which is at the moment turned away from the Sun and towards the Moon. It 
 lollows that a total eclipse of the Moon being visible, whenever it occurs, over at least half 
 the Earth is not a very uncommon spectacle. 
 
 Eclipses of the Sun. The Sun also throws behind the Moon a dark cone of shadow ; 
 smaller than that thrown behind the Earth, because the Moon is smaller ; but just long 
 enough, on the average, to reach the Earth. When the Moon is nearest the Earth, the cone 
 of shadow may cover a space about 170 miles broad ; and, with the motion of the Moon, this 
 shanow-patch sweeps quickly over the Earth. Within the shadow-belt, for a few minutes, 
 the Sun is just a little more than completely obscured by the Moon, and there is a total 
 eclipse of the Sun. When the Moon is iarthest from the' Earth, the shadow-cone does not 
 reach the Earth, so that from no point can the Sun be seen completely obscured ; at best, 
 there is a ring of Sun showing all round the Moon, and the eclipse is annular, At points 
 lying outside the belt of totality, or of annularity, the Sun may be partially obscured by the 
 Moon, and there is a partial eclipse. But the limits within which any eclipse at all is 
 visible are far within the boundary of the whole hemisphere of the Earth which is turned 
 towards the Sun, and consequently eclipses of the Sun of any kind are much more rarely 
 seen at any one place than are eclipses of the Moon. 
 
18 POPULAR GUIDE TO THE HEAVENS. 
 
 PLATE 15. 
 PATHS OF TOTAL ECLIPSES OF THE SUN, 1901-1950. 
 
 In his great work, "Canon der Finsternisse," Prof. Oppolzer has given maps of the paths 
 of the Moon's shadow over the surface of the Earth for all the total and annular eclipses of 
 the Sun between the years 1207 B.C. and 2162 A.D. From this work Plate 15 has been 
 prepared, showing the tracks of the total eclipses visible between 1901 and 1950 A.D. At 
 the western end of each line the eclipse begins at sunrise ; the point in the middle of each 
 line, where the eclipse is at noon, is marked by a circle ; and at the eastern end of the line 
 the eclipse begins at sunset. 
 
 An examination of these curves will show in a striking way the repetition of eclipses in 
 a period of about eighteen years and eleven days, which period, known to the Chaldeans, is 
 called the Saros. Take, as an example, the Great Eclipse of 1901 May 18th, occuring at 
 inid-day in long. 97 E., lat. 2 5'. We have on our Plate three eclipses of this series, viz. : 
 
 Lat. Long. 
 
 1901 May 18 ... Eclipse at mid-day in 97 E. 2 S. 
 1919 29 ... 18 W. 4 N. 
 
 1937 June 8 ... 131 W. 10 N. 
 
 And later eclipses of the same series are : 
 
 1955 June 20 ... Eclipse at mid-day in 117 E. 15 N. 
 
 1973 30 ... 6 W. 19 N. 
 
 1991 July 11 ... 105 W. 22 N. 
 
 The centre of the track of the eclipse is gradually moving north, and is at each repetition 
 about seven hours, or 105, farther west in longitude. 
 
 Let us take as another example the history of the eclipse which will be total in England 
 in June, 1927. The dates of the three eclipses of this series represented on our Plate are : 
 1909 June 17. | 1927 June 29. | 1945 July 9. 
 
 The first begins in Siberia, crosses close to the North Pole, and runs down the west 
 coast of Greenland. The second begins in the Atlantic, south-west of Ireland, crosses Great 
 Britain, runs up Norway, through the Arctic Ocean, and ends south of Behring Straits. The 
 third begins in Canada, crosses Greenland and northern Norway, and ends in Central Asia. 
 
 It will be seen that the circumstances of the path of an eclipse are very complex, 
 especially when its centre is in high latitudes, and the reason for this may be readily under- 
 stood if one looks at a globe, tilted with respect to the Sun, according to the time of the year 
 of the eclipse, and considers how the shadow of a body, the Moon, passing between the Sun 
 and the globe would cut across the tilted lines of latitude and longitude. 
 
 PLATE 16. 
 TYPICAL SOLAR CORONAE. 
 
 By far the most beautiful feature of the totally-eclipsed Sun is the corona of pale white 
 light which Hashes out as soon as the dazzling photosphere is completely covered by the 
 
TYPICAL SOLAR COR01OE. 19 
 
 Moon. In the three or four minutes which is the average duration of totality it is almost 
 impossible to draw or describe the very complex structure of this appendage of the Sun. 
 But, for the last twenty-five or thirty years, almost every eclipse has been successfully 
 photographed. A reference to Plate 15 will show the arduous character of the journeys 
 which are often involved in eclipse-observation. The six photographs which are reproduced 
 in Plate 16 were taken as follows : 
 
 1. 1871. Dec. 12. H. Davis. Baikul, India. 
 
 2. 1882. May 17. Abney aud Schuster. Egypt. 
 
 3. 1893. April 16. J. Kearney. Fundium, W. Africa. 
 
 4. 1878. July 29. W. Harkness. Wyoming. 
 
 5. 1889. Jan. 1. W. H. Pickering. California. 
 
 6. 1900. May 28. E. E. Barnard. Wadesborough, N. Carolina. 
 
 The photographs have been arranged in two sets, in which it will be seen that the corona 
 is of distinctly different types. In the first set 1871, 1882, 1893 the corona is fairly equally 
 distributed right round the limb of the Sun ; in the second set 1878, 1889, 1900 the 
 corona has large equatorial extensions, aud at the poles it is broken up into short, distinct 
 streamers. Further, it will be noticed that the interval between successive photographs in 
 each set is about eleven years the sun-spot period; the first set fall near the times of 
 sun-spot maximum, the second near times of sun-spot minimum. 
 
 Not very much is known of the nature of the corona. The streamers shine largely, if 
 not entirely, by reflected light from the Sun, and must, therefore, be composed of small 
 particles. Diffused amongst them, but probably not sharing in their radial structure, is an 
 unknown gas called, for convenience, " coronium." That some of the detailed structure of 
 the corona is connected with underlying sun-spots and prominences is certain. But the most 
 significant fact is the evident dependence of the forces which determine the form of the 
 corona upon the same cause, whatever it may be, which produces the periodicity of the sun- 
 spots, disturbance of the magnet, and aurorae. 
 
 The corona and prominences alike are ordinarily invisible to us, because they are not 
 nearly so bright as the flare in our atmosphere which seems to surround the Sun. The 
 spectroscope has made it possible to observe the prominences continuously ; but, up to the 
 present, no method has been found of viewing the corona except during the rare minutes of a 
 total eclipse. 
 
Plate 12. 
 
 BALL'S POPULAR GUIDE TO THE HEAVENS. 
 
 SOLAR PROMINENCES. Drawn with the 
 spectroscope by J. FENYI, 1895, July 15th. 
 
 SOLAR PROMINENCES. PhotoHraohed by E. E. BARNARD durina the Total Eclipse of the Sun. 1900, May 28th. 
 
> x\>^ i: ' 
 
 x^ 
 
 'UNIVERSITY 
 
 of 
 
BALL'S POPULAR GUIDE TO THE HEAVENS. 
 
 Plate 16. 
 
(21) 
 
 CHAPTER IV. 
 
 PLATE 17. 
 DONATI'S COMET. 
 
 This, the most famous comet of the 19th Century, was discovered by Donati at Florence, 
 on June 2nd, 1858, as a small telescopic object approaching the Sun. Not for nearly three 
 months did it become visible to the naked eye, but thence, right up to the time of its 
 perihelion passage, at the end of September, it grew rapidly in brightness until its starlike 
 nucleus was as bright as the Pole star. During September its tail was directed nearly 
 towards the Earth, and, though bright, was seen so much foreshortened that its effect was 
 greatly marred ; but as the comet passed perihelion and began to recede from the Sun, its 
 path, by good fortune, was most favourably placed. The splendid plumed tail then lay almost 
 at right angles to the line of sight, and its whole length was for the first time displayed. 
 Other comets have had longer tails, though this was more than forty million miles long, but 
 none have surpassed Donati's comet in beauty. The main tail, the curved plume, was of the 
 type shown afterwards by the spectroscope to consist of hydrocarbons ; the thin straight 
 streamers are of the hydrogen type. Evaporated, apparently, from the nucleus of the comet 
 by the heat of the Sun, the particles of the tail are repelled from the Sun by some force 
 whose nature is still problematical, and driven backwards from it with a speed which must be 
 comparable with that of the speed of light itself. 
 
 On the evening of October 5th, Donati's comet was at its best, when its motion involved 
 the bright star Arcturus in the brightest part of its tail, through which the star shone 
 imdimmed. Our plate, which was drawn by Prof. Bond, at the Harvard College Observatory, 
 shows Arcturus close to the comet's head, while its tail sweeps up between the Great Bear 
 and the Northern Crown. 
 
 PLATE 18. 
 
 No. 1. 
 HOLMES' COMET AND THE ANDROMEDA NEBULA. 
 
 On Nov. 6, 1892, Mr. Edwin Holmes discovered in London a comet which was in many 
 ways remarkable. When found it was close to the great nebula in Andromeda, and its 
 motion was so slow that, throughout the month of November, it could be photographed on 
 the same plate with the nebula. Plate 18 is a reproduction of a photograph taken at the 
 Lick Observatory, on November 10th, by Professor Barnard, who describes the comet as 
 
22 POPULAR GUIDE TO, THE HEAVENS. 
 
 "round, and sharply defined like a planetary nebula, with a symmetrical, nebulous 
 atmosphere surrounding it for some distance." 
 
 The after-history of this comet is very curious. By the middle of December, it had 
 grown so exceedingly faint and ill-defined that scarcely any telescope could show it. But, in 
 the middle of January, it suddenly brightened up, and condensed into a small, hazy, star-like 
 object, after which it again became diffuse, and finally vanished. 
 
 The comet's orbit was equally remarkable. It lay entirely between Mars and Jupiter, in 
 the zone of the minor planets ; and it has even been suggested that the comet was not a 
 comet at all, but the result of some celestial accident such as a collision which had befallen 
 an asteroid. 
 
 Nos. 2 AND 3. 
 COMET a 1893, IV. (BROOKS.) 
 
 
 
 This comet, though small and, as a visual object, insignificant was, in some ways, the 
 most remarkable comet that has yet been studied by photography. The plate is a reproduc- 
 tion of part of a series of photographs taken by Professor Barnard at the Lick Observatory. 
 The motion of the comet was towards the north-east, the left-hand top corner of the picture. 
 On 1893, Oct. 20th, the tail was straight, but gradually widening towards the end ; on the 
 next day, the date of the second picture, it had been completely transformed. The tail is very 
 much distorted, as if the matter of which it is formed had encountered some resistance. On 
 the following day, October 22nd, the tail was completely wrecked, and large portions of it 
 were detached. In our ignorance of the way in which a comet's tail is produced and main- 
 tained, it is scarcely possible to say anything definite by way of explanation of these changes. 
 That the comet had encountered some resisting medium is a plausible conjecture, but nothing 
 more. 
 
 PLATE 19. 
 COMET 1901. I. 
 
 The Great Comet of 1901, visible in the Southern Hemisphere, was by far the finest 
 comet that had been seen for twenty years. It appeared very suddenly on April 24th, and 
 was discovered independently by several persons in South Africa and Australia. It was then 
 at perihelion, and visible only just before sunrise, but during the succeeding days it passed, 
 apparently, still closer to the Sun, and was lost in the daylight. By May 3rd it was 
 sufficiently clear of the Sun to be visible in the evening twilight, and on May 4th the 
 photograph, from which Plate 19 is made, was taken at the Royal Observatory, Cape of Good 
 Hope, with the Victoria telescope, in twilight. The tail is noticeably unsymmetrical, 
 streaming from each side of the nucleus, but much more strongly on the south-west side. 
 About this time there appeared on the same side a long, straight, faint tail, making an angle 
 of about 30 with the axis of the main tail, and as the comet got away from the Sun into 
 darker sky, this tail could be traced for about 25, the extreme length of the main tail being 
 about 7. 
 
COMETS. 23 
 
 COMET b 1902. III. (PERRINE.) 
 
 This was an excellent example of the kind of comet which raises false hopes when it is 
 reported in the papers as " visible to the naked eye." At its brightest it was little more 
 conspicuous than the Andromeda nebula, witli which few people are familiar as a naked-eye 
 object. ; in the telescope, it was an almost formless patch of light, with a vague tail. The 
 photograph taken at the Royal Observatory, Greenwich, on Sept. 29, 1902 shows the tail 
 strongly cleft. Six divisions can be counted in the original from which the plate was made. 
 
 This photograph was made with an exposure of 62m. The comet was in rapid motion 
 amongst the stars, and the telescope with which the photograph was made was kept pointed 
 precisely to it ; in consequence of this, the stars appear as trails, and give a precise idea of 
 the amount by which the comet had moved during the hour which was needed to secure this 
 picture. 
 

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 < f- 
 
 z < 
 
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 < a: 
 m u 
 
 LJ OQ 
 
 J u 
 
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 2 c 
 
 be v 
 
 ^ 1 
 
 S 5 
 
ft 
 
 O < 
 
 uj a: 
 
 5 UJ 
 
 ^ o 
 
 O ca 
 
 O O 
 
 uj >: 
 
 * o 
 o 
 
 X 
 y 
 
 
 
 z 
 
 UJ 
 
 UJ 
 
 C 
 
 - O 
 
 <N 
 
 O >- 
 
 O* { 
 
 \l 
 
 O a: 
 U uj 
 
 c/l 
 
 trt OD 
 Lj O 
 
 Z j 
 
 a: < 
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 uj o 
 
 Du o 
 
(25) 
 
 CHAPTER V.THE MOON. 
 
 PLATES 20, 21 & 22. 
 
 The three photographs here reproduced were taken at the Yerkes Observatory with the 
 great telescope, temporarily converted into a photographic telescope by the device of photo- 
 graphing through a screen of yellow glass in contact with the plate. 
 
 Plate 20 shows the region of the Mare Serenitatis and the Apennines. The Mare is 
 more than 400 miles across, and is singularly free from Craters. The appearance in the 
 photograph of the curious serpentine ridge towards its western border is a good example of 
 the importance of selecting the right moment for studying any particular lunar object. 
 When the photograph was taken this ridge was conspicuous : had it been taken a few hours 
 later the ridge would have disappeared. It is really very low, so that it soon loses its shadow, 
 and as soon as that happens it is no longer distinguishable. 
 
 The bright, white spot Linn has a long history. It was drawn by old observers as a 
 deep crater. For many years it has been merely a bright spot, with scarcely any depression 
 at all. Opinions differ widely as to the reality of any change ; perhaps, on the whole, the 
 evidence is in favour of something having happened. But the doubt as to the trustworthiness 
 of the old observations emphasises the value of photographs such as these, which could 
 scarcely give a wrong verdict on such a point. 
 
 Craters differ much in their brightness ; Alfraganus and Dionysius have exceptionally 
 brilliant walls ; Julius Csesar and Boscovich are very dark. 
 
 The boundary of Julius Csesar towards Sosigenes has a broken down and denuded 
 appearance ; the deep valley alongside it has probably been formed by the fusion of several 
 craters, which are frequently found three or four in a row close together. 
 
 The Apennines and the Caucasus of the Moon are mountainous regions much more 
 resembling those of the Earth than do the lunar mountains in general. The peaks run up to 
 18,000 and 20,000 feet, and the N.E. boundary of the Apennines is a very steep cliff, not well 
 shown in the photograph, which shows it under a setting sun. 
 
 There is a curious contrast between the craters Archimedes and Aristillus. The former, 
 though 50 miles in diameter, has its crater floor only some 600 feet below the plain outside. 
 Its walls, about 5,000 feet high, look broken and denuded, and the crater has the appearance 
 of having been filled up nearly to the brim by an outflow of lava. In Aristillus, on the 
 contrary, the depth from brim to floor is 11,000 feet ; the central peak and terraces are 
 preserved, and the plain all round is covered as if with the debris of relatively late eruptions. 
 
 In Plate 21 we have a picture of the most rugged and broken part of the Moon's surface. 
 The crater Tycho at sunrise, as shown here, is relatively undistinguished, though of such size 
 that Mont Blanc would stand on its floor, and from its summit it would not be possible to see 
 over the crater wall. But as the Moon gets toward full, while most of the other craters 
 become hard to see Clavius, for example, almost entirely disappears under the perpendicular 
 illumination Tycho stands out conspicuously brilliant, the centre of a system of radiating 
 bright streaks, whose nature is a mystery. They go straight across mountains and plains ; 
 there is only one well-marked case, Saussure, in which the streak seems to turn aside to avoid 
 a mountain. 
 
26 POPULAR GUIDE TO THE HEAVENS. 
 
 It is curious that in the district around Clavius the western walls of the craters are 
 generally higher than the eastern. In Clavius itself, a peak of the western wall stands 
 17,000 feet above the floor, and the deepest of the smaller craters within is 6,000 feet deep. 
 
 At the extreme bottom of the picture, below and to the left of Pitatus, is the Straight 
 Wall, recognised only by its shadow. The wall is almost perfectly straight, 60 miles long, 
 and about 1,000 feet high. It is much steeper on the east than on the west side, and is, 
 perhaps, better called a cliff than a wall. 
 
 PLATE 22. In Copernicus and the region around it we find lunar scenery on the grandest 
 scale. The crater itself is about 60 miles in diameter ; the highest peak is more than 12,000 
 feet above the floor ; the central mountain above 2,000 feet high. The successive terraces of 
 the wall are said to resemble those of the crater of Teneriffe : the ridges running down on to 
 the plain suggest outpourings of lava. To the north is Mt. Carpathus with an enormous c'eft. 
 To the west the whole plain is riddled like a sieve with small craters. The line of these 
 small craters running north and south, and becoming at the north end a deep cleft, suggests 
 the question : Are these small craters formed along a pre-existing cleft, or is the cleft, as we 
 see it, formed by the amalgamation of a number of small craters in a line ? 
 
 PLACE OF THE MOON. 
 
 From the monthly maps, 39 50, the positions of the Moon at different periods in the 
 lunation can be learned. In the first place, it is to be noted that our Satellite lies always in 
 or close to that part of the sky marked as the " Track of the Planets." When it is full the 
 Moon is in opposition, and comes on the meridian at midnight, and hence we have the 
 following rule : 
 
 Look out the monthly map for the month in question, then the full Moon lies in that 
 part of the heavens where the " Track of the Planets " crosses the central meridian, already 
 defined to be the line drawn on the map from the North point to the South point. 
 
 Example 1. In what Constellation does the full Moon appear in September 1 
 
 Solution. The answer is given by Plate 47, where the " Track of the Planets " crosses 
 the central meridian in Pisces, which indicates the required position. 
 
 Example 2. When is the full Moon near the Pleiades ? 
 
 Solution. Plate 49 shows the Pleiades on the central meridian, and accordingly 
 November is the answer to the question. 
 
 To find the position of the Moon at the time of the first quarter, the following is the 
 method. 
 
 Look out the monthly map for three months preceding the given date, then the 
 constellation in or near which the Moon lies at the first quarter is shown at the intersection 
 of the " Track of the Planets " with the central meridian. 
 
 Example. In what constellation does the first quarter Moon appear in June ? 
 
 Solution. The map three months earlier is Plate 41 for March. This shows the inter- 
 section of the " Track of the Planets " and the central meridian in Virgo, which is 
 accordingly the answer required. 
 
 To find the position of the Moon at the time of the last quarter, the following is the method. 
 
 Look out the monthly map for three months following the given date, then the 
 Constellation in or near which the Moon lies at the last quarter is shown at the intersection 
 of the " Track of the Planets " with the central meridian. 
 
THE MOON. 
 
 27 
 
 Example. In what constellation does the last quarter Moon appear in July 1 
 
 Solution. The map three months later is Plate 48, which shows that the constellation 
 is Aries. 
 
 It ought to be observed that, on account of the rapid motion of the Moon, only a rough 
 indication of its place can be expected from the process here given, and that the accuracy will 
 be greater the nearer the phase in question happens to the middle of the month. 
 
 The foregoing problems can also be solved by the more general method now to be 
 described. The Table of Moon Age shows the position in the heavens which the Moon 
 occupies at any age in any month. The use of this Table is as follows. 
 
 Enter the table in the verticle column bearing the name of the month. Then take the 
 age in that column nearest the given age, and the figure at the left on the same row gives the 
 number of the monthly map in which the region where the Moon is situated lies on the 
 " central meridian " where the " Track of the Planets " crosses it. 
 
 THE TABLE OF MOON AGE. 
 
 Map. 
 
 Jan. 
 
 Feb. 
 
 March. 
 
 April. 
 
 May. 
 
 June. 
 
 July. 
 
 Aug. 
 
 Sept. 
 
 Oct. 
 
 Nov. 
 
 Dec. 
 
 39 
 
 14 
 
 12 
 
 10 
 
 7 
 
 5 
 
 3 
 
 29 
 
 25 
 
 23 
 
 20 
 
 18 
 
 16 
 
 40 
 
 17 
 
 14 
 
 12 
 
 10 
 
 7 
 
 5 
 
 3 
 
 27 
 
 25 
 
 23 
 
 21 
 
 19 
 
 41 
 
 19 
 
 16 
 
 15 
 
 12 
 
 10 
 
 8 
 
 5 
 
 2 
 
 28 
 
 25 
 
 23 
 
 21 
 
 42 
 
 22 
 
 19 
 
 17 
 
 14 
 
 12 
 
 10 
 
 8 
 
 5 
 
 1 
 
 
 
 26 
 
 24 
 
 43 
 
 25 
 
 22 
 
 21 
 
 16 
 
 14 
 
 12 
 
 10 
 
 7 
 
 4 
 
 2 
 
 28 
 
 26 
 
 44 
 
 27 
 
 25 
 
 23 
 
 18 
 
 16 
 
 14 
 
 11 
 
 9 
 
 7 
 
 4 
 
 2 
 
 29 
 
 45 
 
 29 
 
 27 
 
 25 
 
 20 
 
 18 
 
 16 
 
 14 
 
 11 
 
 9 
 
 7 
 
 5 
 
 2 
 
 46 
 
 2 
 
 
 
 27 
 
 25 
 
 21 
 
 18 
 
 16 
 
 14 
 
 11 
 
 9 
 
 7 
 
 4 
 
 47 
 
 5 
 
 2 
 
 29 
 
 27 
 
 24 
 
 20 
 
 18 
 
 16 
 
 14 
 
 11 
 
 10 
 
 7 
 
 48 
 
 7 
 
 4 
 
 3 
 
 
 
 27 
 
 23 
 
 20 
 
 18 
 
 16 
 
 14 
 
 12 
 
 9 
 
 49 
 
 10 
 
 7 
 
 5 
 
 3 
 
 
 
 27 
 
 23 
 
 20 
 
 18 
 
 16 
 
 14 
 
 11 
 
 50 
 
 12 
 
 9 
 
 8 
 
 5 
 
 2 
 
 
 
 27 
 
 23 
 
 20 
 
 18 
 
 16 
 
 14 
 
 Example 1. Where does the Moon lie when four days old in October ? 
 
 Solution. The October column in the Table of Moon Age being referred to, the 
 sixth figure from the top gives 4, the age of the Moon, and the figure at the end 
 of that row on the left is 44. This monthly map shows that the Moon must 
 then be in or near Sagittarius. 
 
 Example 2. What will be the age of the Moon when on the meridian at 10 P.M. in 
 August ? 
 
 Solution. At 10 P.M. in August, the heavens will be as in Plate 45. Therefore we 
 refer to the row for Map 45 in the Table of Moon Age, which shows, under the 
 column August, that the moon must then be about 11 days old. 
 
 Example 3. Determine when the Moon, at the first quarter, has a specially high 
 altitude. 
 
 Solution. The heavens must be as in Plate 49, which refers us to the last row but 
 one of the Table. For the Moon to be 7 days old we look under the column 
 February, in which month the heavens are as in Plate 49 about 6 P.M. 
 
POPULAR GUIDE TO THE HEAVENS. 
 
 PLATES 23 TO 38. 
 
 THE LUNAR OBJECTS. 
 
 TERMINOLOGY OF LUNAR QUADRANTS. 
 
 Moon in Inverting Telescope. 
 
 For the study of the Lunar formations, Plates 23 to 38 have been specially drawn. 
 
 As the astronomical telescope shows 
 the Moon turned upside down, and with 
 right and left interchanged, the maps of 
 our Satellite are represented accord- 
 ingly. The four quadrants (Plates 23, 
 24, 25, 26) are designated in the manner 
 shown in the annexed figure. For ob- 
 servations of theMoon, the "terminator"' 
 or boundary between light and shade, 
 is the place where the objects are best 
 seen, and Plates 23 38 of the present 
 Atlas have been arranged to facilitate 
 observation of the Lunar formations on 
 the terminator at various ages, from new 
 to full. The terminators for each day 
 of a lunation are marked on the quad- 
 rants; the morning terminator being 
 that when the Sun is rising on the ob- 
 ject in question. The quadrants also 
 enable the latitudes and longitudes of 
 Lunar objects to be found. 
 
 As the Moon is so much more con- 
 veniently observed from new to full, 
 than from full to new, it is the former 
 series of changes that have been more 
 particularly provided for. The tele- 
 scopic view of the Crescent Moon, 3 days 
 old, is shown in Plate 27. On the oppo- 
 site page an index outline is given on 
 
 which each of the formations receives a special number or letter. The name of the formation 
 may be found by looking out the number or letter in the Catalogue of Lunar formations ; but 
 for greater convenience in reference, the names of the chief objects visible in each phase are set 
 out on the Index outline as well. As the Moon grows day by day, the terminator changes, and 
 an ever varying series of objects is presented. A special Plate is therefore given for each day 
 of the Moon's age, from the 3rd up to the 14th, when the Moon is full. Before the third day 
 the Moon is so close to the Sun that observations cannot be made with advantage. 
 
 Suppose, for instance, that the Moon is 9 days old. The observer then refers to Plate 
 33. On the terminator, a little below the middle, he notes a fine crater, and desires to learn 
 its name. The Index outline assigns the Number 380, and the list on the margin shows that 
 this feature is named " Copernicus." The observer will be able to trace the same object with 
 lessening detail up to the time of Full Moon. See Plates 34 to 38. From the comparison 
 of any one of these Plates with the figure on this page, it appears that Copernicus must lie 
 
THE MOON. 29 
 
 in the " Second Quadrant" or on Plate 24, where the great crater will be found again as No. 380, 
 a conspicuous object at 20 East longitude, and 10 North latitude. Along the top of Plate 
 24 are shown the positions of the terminators at corresponding ages of the Moon. It will be 
 noted that the morning terminator on the 9th day passes through Copernicus. So also does 
 the evening terminator on the 24th, so that if the observer desires to study Copernicus when 
 illuminated by the sunlight from the opposite side, he may repeat his observation 15 days later. 
 As another illustration, let us suppose the Moon to be 4 days old, and that after com- 
 paring the Moon with Plate 28 we desire to know the name of that large round dark patch, 
 a little below the centre, which lies midway between the limb and the terminator. The Index 
 outline shews it marked A, and from the reference to the margin or to the Catalogue the 
 object is identified as the Mare Crisium. It is represented in Plate 23 as A. near the top at 
 the left. 
 
 To show the mode of representing the ranges of Lunar mountains, we may suppose the stu- 
 dent to be looking at the Moon a little after the first quarter, say on the eighth day, as on Plate 
 32. He notices a remarkable formation a little below the centre. The Index outline labels 
 this object c, and the margin shows that we are looking at the lunar Apennines. Plate 24 
 exhibits the Apennines pointing towards Copernicus. 
 
 Suppose that a view of some particular formation of known name be specially desired, the 
 process is as follows. Look it out in the Index at the end of this volume, the first reference 
 is to the quadrant, and the next is to the plate where the object is represented on the 
 terminator. 
 
 Thus, for instance, to find the position of Plato. The Index shows first of all that it lies 
 on Plate 24, that is, in the Second Quadrant. The next reference is to Plate 32, which shows 
 the object lying near the terminator when the Moon is 8 days old. There are further references 
 to 33, 34, and 35, where the object is also visible. The evening terminator on Plate 24 shows 
 that when this object is suitably placed for observations with the opposite illumination, the 
 Moon is about 23 days old. The subsequent references in the Index are to those pages of the 
 Introduction in which the object is mentioned. 
 
 The beginner should, however, be apprised that even with the assistance which it is hoped 
 that these maps will afford him, considerable pains are often required to identify the lunar 
 objects. In the first place, various causes produce what are known as librations of the Moon, 
 whose effect is that the Moon does not always turn precisely the same face toward us. 
 The maps are accommodated to a state of mean libration, and the student must not be 
 surprised if he finds an object sometimes higher and sometimes lower than its position in the 
 map would have led him to expect. These changes often produce considerable variations in the 
 appearance of the lunar formations. It must also be remembered that the age of the Moon 
 cannot be always exactly that of the map which comes nearest to it. This will often involve 
 considerable alterations in the appearance of the lunar formations from those which they present 
 at the exact phase which the map depicts. The elucidation of the several points which thus 
 arise will afford much interesting occupation, and will, it is hoped, lead the student to a close 
 acquaintance with the beautiful scenery of our Satellite. 
 
30 
 
 POPULAR GUIDE TO THE HEAVENS. 
 
 CATALOGUE OF LUNAR OBJECTS. 
 
 Figures refer to the Number of the Crater or similar formation, capital letters refer to the so-called " Seas," and 
 small letters refer to the Mountain Ranges and isolated Mountains. 
 
 1 Langrenus. 
 
 2 Kastner. 
 
 3 Vendelinus. 
 
 4 Maclaurin. 
 
 5 Hecataeus. 
 
 6 Ansgarius. 
 
 7 Petavius. 
 
 8 Wrpttesley. 
 
 9 Palitzsch. 
 
 10 Ease. 
 
 11 Lerendre. 
 
 12 Wilhelra Humboldt. 
 
 13 Phillips. 
 
 14 Furnerius. 
 
 15 Stevinus. 
 
 16 Snellius. 
 
 17 Adams. 
 
 18 Marinus. 
 
 19 Fraunhofer. 
 
 20 Oken. 
 
 21 Vega. 
 
 22 Pontecoulant. 
 
 23 Biela. 
 
 24 Hagecius. 
 
 25 Boussingault. 
 
 26 Boguslawsky. 
 
 27 Schomberger. 
 
 28 Webb. 
 
 29 Messier. 
 
 30 Lubbock. 
 
 31 Godenius. 
 
 32 Guttemberg. 
 
 33 Magelhaens. 
 
 34 Colombo. 
 
 35 Cook. 
 
 36 Santbech. 
 
 37 McClure. 
 
 38 Crozier. 
 
 39 Bellot. 
 
 40 Borda. 
 
 41 Reichenbach. 
 
 42 Rheita. 
 
 43 Neander. 
 
 44 Metius. 
 
 45 Fabricius. 
 
 46 Janssen. 
 
 47 Steinheil. 
 
 48 Vlacq. 
 
 49 Rosen berger. 
 
 50 Nearchus. 
 
 51 Hommel. 
 
 52 Pitiscus. 
 
 53 Mutus. 
 
 54 Manzinus. 
 
 55 Censorinus. 
 
 56 Torricelli. 
 
 57 Capella. 
 
 58 Isidorus. 
 
 59 Madler. 
 
 60 Bolmenberger. 
 
 61 Rosse. 
 
 62 Fracastorius. 
 
 63 Piccolomini. 
 
 64 Stiborius. 
 
 65 Riccius. 
 
 66 Rabbi Levi. 
 
 67 Zagut. 
 
 68 Lindenau. 
 
 69 Nicolai. 
 
 70 Biisching. 
 
 71 Buch. 
 
 72 Hypatia. 
 
 73 Delambre. 
 
 74 Tlieon Senr. 
 
 75 TlieonJunr. 
 
 76 Taylor. 
 
 77 Alfraganus. 
 
 78 Kant. 
 
 79 Theophilus. 
 
 80 Cyrillus. 
 
 81 Catharina. 
 
 82 Tacitus. 
 
 83 Beaumont. 
 
 84 Descartes. 
 
 85 Abulfeda. 
 
 86 Almanon. 
 
 87 Geber. 
 
 88 Abenezra. 
 
 89 Azophi. 
 
 90 Sacrobosco. 
 
 91 Fermat. 
 
 92 Polybius. 
 
 93 Pons. 
 
 94 Pontanus. 
 
 95 Gemma Frisius. 
 
 96 Poisson. 
 
 97 Aliacensis. 
 
 98 Werner. 
 
 99 Apianus. 
 
 100 Playfair. 
 
 101 Blanchinus. 
 
 102 La Caille. 
 
 103 Delaunay. 
 
 104 Faye. 
 
 105 Donati. 
 
 106 Airy. 
 
 107 Argelander. 
 
 108 Parrot. 
 
 109 Albategnius. 
 
 110 Hipparchus. 
 
 111 Ilalley. 
 
 112 Hind. 
 
 113 Horrocks. 
 
 114 Rhseticus. 
 
 115 Reaumur. 
 
 116 Walter. 
 
 117 Nonius. 
 
 118 Fernelius. 
 
 119 Stotler. 
 
 120 Faraday. 
 
 121 Maurolycus. 
 
 122 Barocius. 
 
 123 Clairaut. 
 
 124 Licetus. 
 
 125 Cuvier. 
 
 126 Bacon. 
 
 127 Jacobi. 
 
 128 Lilius. 
 
 129 Zach. 
 
 130 Kinau. 
 
 131 Pentland. 
 
 132 Curtius. 
 
 133 Simpelius. 
 
 134 Miller. 
 
 135 Schubert. 
 
 136 Apollonius. 
 
 137 Firmicus. 
 
 138 Azout. 
 
THE MOON. 
 
 31 
 
 CATALOGUE OF LUNAR OBJECTS continued. 
 
 139 Ne ;er. 
 
 140 C- aid ncet. 
 
 141 Belmim. 
 
 142 La Peyrouse. 
 
 143 Hanno. 
 
 144 Le Gentil 
 
 145 Tannerus. 
 
 146 lluggms. 
 
 147 Timoleou. 
 
 148 Zeno. 
 
 149 Schwabe. 
 
 150 Ilunsen. 
 
 151 Alhazen. 
 
 152 Picard. 
 
 153 Pierce. 
 
 154 Tarun tins. 
 
 155 Secchi. 
 
 156 Proclus. 
 
 157 Maskelyne. 
 
 158 Jansen. 
 
 159 Vitruviiis. 
 
 160 Maraldi. 
 
 161 Cauchy. 
 
 162 Eininart. 
 
 163 Oriani. 
 
 164 Plutarch. 
 Ki5 Seneca. 
 
 166 Macrobius. 
 
 167 Cleomedes. 
 
 168 Tralles. 
 
 169 Burckhardt. 
 
 170 Hahn. 
 
 171 Berosus. 
 
 172 Gauss. 
 
 173 Geuiinus. 
 
 174 Bernouilli. 
 
 175 Messala. 
 
 176 Berzelius. 
 
 177 Hooke. 
 
 178 Schumacher. 
 
 179 Struve. 
 
 180 Mercurius. 
 
 181 Franklin. 
 
 182 Cepheus. 
 
 183 Oersted. 
 
 184 Shuckburgh. 
 
 185 Chevallier. 
 
 186 Atlas. 
 
 187 Hercules. 
 
 188 Endynrion. 
 
 189 De la Rue. 
 
 239 Conon. 
 
 190 Strabo. 
 
 240 Mauilius. 
 
 191 Thales. 
 
 241 Ukert. 
 
 192 Gartner. 
 
 242 Triesnecker. 
 
 193 Deiuocritus- 
 
 243 Hyginus. 
 
 194 Arnold. 
 
 244 Agrippa. 
 
 195 Moigno. 
 
 245 Godin. 
 
 196 Peters. 
 
 246 Ritter. 
 
 197 Meton. 
 
 247 Sabine. 
 
 198 Euctemou. 
 
 248 Dionysius. 
 
 199 Challis. 
 
 249 Manners. 
 
 200 Main. 
 
 250 Arago. 
 
 201 Gioja. 
 
 251 Ariadseus. 
 
 202 Scoresby. 
 
 252 Silberschlag. 
 
 203 Barrow. 
 
 253 De Morgan. 
 
 204 W. C. Bond. 
 
 254 Cayley. 
 
 205 Christian Mayer. 
 
 255 W he well. 
 
 206 Archytas. 
 
 256 Calippus. 
 
 207 Aristoteles. 
 
 257 Thesetetus. 
 
 208 Eudoxus. 
 
 258 Cassini. 
 
 209 Alexander. 
 
 259 Aristillus. 
 
 210 Egede. 
 
 260 Autolycus 
 
 211 Great Alpine Valley. 
 
 261 Hosting. 
 
 212 Grove. 
 
 262 Lalande. 
 
 213 Mason. 
 
 263 Herschel. 
 
 214 Plana. 
 
 264 Ptolemanis. 
 
 215 Burg. 
 
 265 Alphonsus. 
 
 216 Baily. 
 
 266 Arzachel. 
 
 217 Daniell. 
 
 267 Alpetragius. 
 
 218 Posidomus. 
 
 268 Lassell. 
 
 2l9 Chacornac. 
 
 269 Davy. 
 
 220 Le Monnier. 
 
 270 Guerike. 
 
 221 Roeiner. 
 
 271 Parry. 
 
 222 Bond. 
 
 272 Bonpland. 
 
 223 Maury. 
 
 273 Fra Mauro. 
 
 224 Littrow. 
 
 274 Thebit. 
 
 225 Newcoinb. \ 
 
 275 Straight Wall. 
 
 226 Dawes. 
 
 276 Birt. 
 
 227 Plinius. 
 
 277 Purbach. 
 
 228 Ross. 
 
 278 Regiomontanus. 
 
 229 Maclear. 
 
 279 Hell. 
 
 230 Sosigenes. 
 
 280 Pitatus. 
 
 231 Julius Caesar. 
 
 281 Hesiodus. 
 
 232 Boscovich. 
 
 282 Gauricus. 
 
 233 Taquet. 
 
 283 Wurzelbauer. 
 
 234 Menelaus. 
 
 284 Sasserides. 
 
 235 Sulpicius Gallus. 
 
 285 Ball. 
 
 236 Bessel. 
 
 286 Lexell. 
 
 237 Linue. 
 
 287 Nasireddin. 
 
 238 Aratus. 
 
 288 Orontius. 
 
32 
 
 POPULAR GUIDE TO THE HEAVENS. 
 
 CATALOGUE OF LUNAR OBJECTS continued. 
 
 289 Pictet. 
 
 290 Saussure. 
 
 291 Tycho. 
 
 292 Heinsius. 
 
 293 Wilhelin I. 
 
 294 Longomontanus. 
 
 295 Street. 
 
 296 Maginus. 
 
 297 Deluc. 
 
 298 Clavius. 
 
 299 Cysatus. 
 
 300 Moretus. 
 
 301 Short. 
 
 302 Newton. 
 
 303 Gruemberger. 
 
 304 Cabeus. 
 
 305 Casatus. 
 
 306 Klaproth. 
 
 307 Wilson. 
 
 308 Kircher. 
 
 309 Bettinus. 
 
 310 Zuchius. 
 
 311 Segner. 
 
 312 Blancanus. 
 
 313 Schemer. 
 
 314 Weigel. 
 
 315 Rost. 
 
 316 Bailly. 
 
 317 Schiller. 
 
 318 Bayer. 
 
 319 Pingre. 
 
 320 Hausen. 
 
 321 Phocylides. 
 
 322 Wargentin. 
 
 323 Schickard. 
 
 324 Drebbel. 
 
 325 Inghirami. 
 
 326 Hainzel. 
 
 327 Lehmann. 
 
 328 Lacroix. 
 
 329 Piazzi. 
 
 330 Lagrange. 
 
 331 Fourier. 
 
 332 Vieta. 
 
 333 Doppelmayer. 
 
 334 Lee. 
 
 335 Vitello. 
 
 336 Clausius. 
 
 337 Capuanus. 
 
 338 Cichus. 
 
 339 Mercator. 
 
 340 Campanus. 
 
 341 Kies. 
 
 342 Bullialdus. 
 
 343 Lubiniezky. 
 
 344 Nicollet. 
 
 345 Hippalus. 
 
 346 Agatharchides. 
 
 347 Gassendi. 
 
 348 Herigonius. 
 
 349 Letronne. 
 
 350 Mersenius. 
 
 351 Cavendish. 
 
 352 Byrgius. 
 
 353 Eichstadt. 
 
 354 De Viccr. 
 
 355 Ramsden. 
 35b Billy. 
 
 357 Hansteen. 
 
 358 Sirsalis. 
 
 359 Fontana. 
 
 360 Zupus. 
 
 361 Cruger. 
 
 362 Rocca. 
 
 363 Grimaldi. 
 
 364 Damoiseau. 
 
 365 Riccioli. 
 
 366 Lohrmann. 
 
 367 Hermann. 
 
 368 Flamsteed. 
 
 369 Wichmann. 
 
 370 Euclides. 
 
 371 Landsberg. 
 
 372 Gambart. 
 
 373 Sommering. 
 
 374 Schroter. 
 
 375 Pallas. 
 
 376 Bode. 
 
 377 Reinhold. 
 
 378 Hortensius. 
 
 379 Milichius. 
 
 380 Copernicus. 
 
 381 Stadius. 
 
 382 Eratosthenes. 
 
 383 Gay Lussac. 
 
 384 Tobias Mayer. 
 
 385 Kunowsky. 
 
 386 Encke. 
 
 387 Kepler. 
 
 388 Bessarion. 
 
 389 Reiner. 
 
 390 Marius. 
 
 391 Hevel. 
 
 392 Cavalerius. 
 
 393 Gibers. 
 
 394 Cardanus. 
 
 395 Kraftt. 
 
 396 Vasco de Gania. 
 
 397 Seleucus. 
 
 398 Marco Polo. 
 
 399 Archimedes. 
 
 400 Beer. 
 
 401 Timocharis. 
 
 402 Lambert. 
 
 403 Pytheas. 
 
 404 Euler. 
 
 405 Diophantus. 
 
 406 Delisle. 
 
 407 Caroline Herschel. 
 
 408 Carlini. 
 
 409 Leverrier. 
 
 410 Helicon. 
 
 411 Kirch. 
 
 412 Piazzi Smyth. 
 
 413 Plato. 
 
 414 Tinmis. 
 
 415 Birmingham. 
 
 416 Epigenes. 
 
 417 Goldschmidt. 
 
 418 Anaxagoras. 
 
 419 Fontenelle. 
 
 420 Philolaus. 
 
 421 Anaximenes. 
 
 422 J. J. Cassini. 
 
 423 Condamine. 
 
 424 Maupertuis. 
 
 425 Bianchini. 
 
 426 Sharp. 
 
 427 Mairan. 
 
 428 Foucault. 
 
 429 Harpalus. 
 
 430 J. F. W. HerscheL 
 
 431 Anaximander. 
 
 432 Pythagoras. 
 
 433 South. 
 
 434 Babbage. 
 
 435 (Enopides. 
 
 436 Robinson. 
 
 437 Cleostratus. 
 
 438 Xenophanes. 
 
THE MOON. 
 
 33 
 
 CATALOGUE OF LUNAR OBJECTS continued. 
 
 439 Repsold. 
 
 440 Harding. 
 
 441 Gerard. 
 
 442 Lavoisier. 
 
 443 UlughBeigh. 
 
 444 Lichtenberg. 
 
 445 Briggs. 
 
 446 Otto Struve. 
 
 447 Aristarchus. 
 
 448 Herodotus. 
 
 449 Wollaston. 
 
 450 Schiaparelli. 
 
 451 Gruithuisen. 
 
 452 Brayley. 
 
 453 Galileo. 
 
 454 Horrebow. 
 
 MOUNTAIN RANGES AND ISOLATED MOUNTAINS. 
 
 a Alps. 
 b Caucasus. 
 c Apennines. 
 d Carpathians. 
 
 e Sinus Iridum Highlands. 
 
 / Hsemus. 
 
 g Pyrenees. 
 
 h Altai Mountains. 
 
 t Riphsean Mountains. 
 
 j La Hire. 
 
 'k Mt. Taurus. 
 
 I TeneriS'e Range. 
 
 Mountains near the Limb : 
 
 D'Alembert Mts. on the east limb, extending from S. lat. 19 to N. lat. 12. 
 The Cordilleras near the east limb, extending from S. lat. 23 to S. lat. 8. 
 The Rook Mountains on the east limb, extending from S. lat. 39 to S. lat. 16. 
 The Doerfel Mountains on the south-east limb, extending from S. lat. 80 to S. lat. 57 
 The Leibnitz Mountains extend from S. lat. 70 on the west limb to S. lat. 80 on the 
 
 east limb. 
 Humboldt Mountains on the west limb, extending from N. lat. 72 to N. lat. 53. 
 
 m Straight Range. 
 n Percy Mountains. 
 o Harbinger Mountains. 
 
 Hercynian Mountains. 
 
 Pico. 
 
 Piton. 
 
 Mt. Argaeus. 
 
 Mt. Hadley. 
 
 Laplace Promontory. 
 
 Mt. Huygens. 
 
 Mt. Bradley. 
 
 MARIA or SEAS 
 
 A Mare Crisium. 
 
 B , Fcecunditatis. 
 
 C , Australe. 
 
 D , Humboldtianum. 
 
 E , Tranquillitatis. 
 
 F , Nectaris. 
 
 G Lacus Somniorum. 
 
 H Mortis. 
 
 J Mare Serenitatis. 
 
 K Frigoris. 
 
 L Imbrium. 
 
 M Vaporum. 
 
 N Sinus JEstuum. 
 
 P MediL 
 
 Q Mare Nubium. 
 
 R Sinus Iridum. 
 
 S Oceanus Procellarurn. 
 
 T Mare Humorum. 
 
 V Palus Somnii. 
 
 W Sinus Roris. 
 
 X Palus Nebularum. 
 
 Y Mare Smythii. 
 
 Z Palus Putredinis. 
 
BALLS POPULAR GUIDE TO THE HEAVENS 
 
 Key to Plate 20 
 
 AJfraganus 
 
 Taylor 
 
 Sabine, 
 
 O Tkeon. Jim. 
 ZTuwn, Sv 
 
 Bitter 
 O O Dionysiu* 
 
 Arago 
 
 ( JGodin, 
 Agrtppa, 
 
 Sosigeries ^J ( 
 
 p 
 
 Janten. 
 
 
 
 Boscoviah, 
 
 
 
 O 
 
 SERENITATIS 
 
 Cononi 
 
 M 
 
 . <v 
 - '*<? 
 
 PosZoLora 
 
 Archimedes 
 
 UtotxCOS J- '-v 
 
 AristMiLS 
 
 
tit's POPULAR GUIDE TO THE HEAVENS. 
 
 Plate 20. 
 
 ' > 
 
 ,> . 
 
 Pf ^K***** 
 

BALL'S POPULAR GUIDE TO THE HEAVENS 
 
 I 
 
 Mo i 
 "<^_ 
 
 X 
 Cysati. 
 
 o 
 
 'o 
 
 SCLUSSUJV 
 
 (9. 
 
 \ WtUiebn 
 
 V 
 oO, 
 
 O 
 
 O 
 
 O o 
 
 Wurz eii> cajucr 
 
 Key to Plate 21 
 
 -Merfajtor 
 J 
 
Plate 21. 
 
 .V-H W*& 
 
 THE MOON. REGION OF CLAVIUS AND TYCHO. G. W. RITCHEY, 40-in. Refractor. YERKES OBSERVATORY. 
 


Key Map. 
 
 THE MOON 3rd Day. 
 
 To face Plate 27. 
 
 25. Bovssingault. 
 22. Ponttcoulant. 
 19. Fraunhofer. 
 
 14. Furnerius. 
 12. W. Humboldt. 
 7. Petavius. 
 
 3 rd Day 
 
 A Mare Crisium. 
 
 B ,, Facunditatis. 
 
 C ,, Australe. 
 
 D ,, Hvmboldtianum . 
 
 1 1. Legendre. 
 
 5. Hecataus. 
 
 3. Vendelinus. 
 
 I. Langrenus, 
 
 z. Kastner. 
 
 136. Apollonius. 
 
 137. Firmicus. 
 
 139. Neper. 
 
 140. Condor cet. 
 
 152. Picard. 
 151. AiAaten. 
 
 153. Peirce. 
 167. Cleomedes. 
 169. Burckhardt. 
 173. Geminus. 
 172. Gauss. 
 
 175. Messala. 
 
 180. Mercurius. 
 
 188. Endymion. 
 
BALL'S POPULAR GUIDE TO THE HEAVENS. 3*? DAY. 
 
 Plate 27. 
 
Key Map. 
 
 THE MOON 4th Day. 
 
 To face Plate 28. 
 
 26. Boguslawsky. 
 25. Bovssingault. 
 22. Pontlcoulant. 
 
 49. Rosenberger. 
 46. Janssen. 
 45. Fabricivs. 
 
 A Mare Crisium. 
 
 B ,, Faecunditatis. 
 
 C ,i Australe. 
 
 D i> Humboldtianum. 
 
 44. Metius. 
 
 14. Furnerivs. 
 
 15. Stevinui. 
 43. Neander. 
 41. Reichenbach. 
 1 6. Snellius. 
 
 7. Petavius. 
 
 36. Santbech. 
 
 34. Colombo. 
 
 3. Venddinuf. 
 
 31. Godenius. 
 
 32. Guttcmberg. 
 i. Langrenvs. 
 
 30. Lubbock. 
 
 29. Messier. 
 
 155. Secchi, 
 136. Apollonius. 
 154. Taruntius. 
 
 152. Picard. 
 
 153. /V*r. 
 
 156. Proclus. 
 
 1 66. Macrobius. 
 
 167. Cleomedes. 
 
 169. Burckhardt. 
 
 173. Gauss. 
 
 176. Beruelius. 
 
 175. Messala. 
 
 181. Franklin. 
 
 185. Chevaliier. 
 
 186. yi//aj. 
 180. Mercurius. 
 188. Endymion. 
 189. 
 
 V /'a/aj Somnii. 
 
 g. Pyrenees Mis. 
 
BALL'S POPULAR GUIDE TO THE HEAVENS. 4-T? DAY. 
 
 Plate 28. 
 
 George Ph-dip A Son.,L*? 
 
Key Map. 
 
 THE MOON 5th Day. 
 
 To face Plate 29. 
 
 27. Schombcrger. 
 54 Manzinus, 
 53. Mittus. 
 
 49. Rosenberger. 
 48. Vlacq. 
 52. Pitiscus. 
 
 A Mare Crisium. 
 
 B ,, Ftecunditatis. 
 
 E ,, Tranquillitatis. 
 
 F ,, Nectans. 
 
 D Mzr* Hvmboldtianum. 
 G Locus Somniorvm. 
 H Mortis. 
 
 46. Janssen. 
 45. Fabricius. 
 44. Metius. 
 14. Fumtrius. 
 64. StiboHus. 
 63. Piccolomini, 
 62. Fracastorius. 
 36. Santbech. 
 
 7. Petavius. 
 
 3. Vendelinui. 
 
 31. Godenius. 
 
 32. Guttemberg. 
 I. Langrenvs. 
 
 58. Isidorus. 
 
 57. Capella. 
 
 29. Messier. 
 
 159. Vitruvius. 
 
 220. Z> Monnier. 
 
 221. Roemer. 
 219. Chacornac. 
 224. Littrow. 
 218. Posidonius. 
 214. Plana. 
 
 187. Hercules. 
 186. ^4//aj. 
 
 188. Endymion. 
 
 189. Z>* Za ^a^. 
 198. Euctemon, 
 
 g. TA^ Pyrenees. 
 k. Taurus Mts. 
 
BALL'S POPULAR GUIDE TO THE HEAVENS. 
 
 TV DAY. 
 
 Plate 29. 
 
UNIVERSITY 
 
 OF 
 
Key Map. 
 
 THE MOON 6th Day. 
 
 To face Plate 30. 
 
 126. Bacon. 
 121. Maurolycus. 
 
 71. Buck. 
 
 64. Stiborius. 
 
 65, Riceius. 
 
 A jl/ar Crisium. 
 
 B ,, Fcecunditatis. 
 
 D ,, Humloldtianvm. 
 
 E ,, Tranquillitatis. 
 
 F A/are Nectaris. 
 
 G Locus Somniorum. 
 H Mortis. 
 
 J Mare Serenitatis. 
 
 66. 
 
 67. 
 
 63- 
 
 93- 
 
 62. 
 
 90. 
 
 91. 
 
 81. 
 
 82. 
 
 80. 
 
 59- 
 
 79- 
 
 72. 
 247. 
 246. 
 250. 
 229. 
 228. 
 227. 
 226. 
 236- 
 220. 
 219. 
 218. 
 208. 
 207. 
 197. 
 202. 
 
 Rabbi Levi. 
 
 Zagvt. 
 
 Piccolomini . 
 
 Pans. 
 
 Fracastorius. 
 
 Sacrobosco. 
 
 Per mat. 
 
 Catharina. 
 
 Tacitus, 
 
 Cyrillus. 
 
 Madler. 
 
 Theophilus. 
 
 Hypatia, 
 
 Sabine. 
 
 Ritter. 
 
 Arago. 
 
 Maclear. 
 
 Ross. 
 
 Plinius. 
 
 Dawes. 
 
 Bessel. 
 
 Le Monnier. 
 
 Chacornac. 
 
 Posidonius. 
 
 Eudoxus. 
 
 Aristoteles. 
 
 Meton. 
 
 Scoresby. 
 
 g. The Pyrenees. 
 h. Altai Mts. 
 k. Taurus Mts. 
 8. Mt. Argaeus. 
 
BALL'S POPULAR GUIDE TO THE HEAVENS. 6T? DAY. 
 
 Plate 30. 
 
 GeargeP/uhp & Son.L' 
 

Key Map. 
 
 THE MOON 7th Day. 
 
 To face Plate 3l. 
 
 132. Curtius. 
 129. Zach. 
 128. Lilivs, 
 
 124. . Licetus. 
 123. Clairaut. 
 121. Maurolycus. 
 
 A A/a^-tf Crisium. 
 
 B ,, Fcecunditatis. 
 
 E Tranqttillitatis. 
 
 G acj Somniorum. 
 
 F A/artf Nfctaris. 
 K Frigoris, 
 M Vaporum* 
 J ,, Strenitatis. 
 
 119. StSfler. 
 118. Fernelius. 
 
 97. Atiacensis. 
 
 98. Werner. 
 
 99. Apianus. 
 100. Playfair. 
 xoi. Blancfiinus. 
 
 105. Donati. 
 
 106. ^/y. 
 
 86. Almanon* 
 85. Abulfeda. 
 
 109. 
 
 ita. 
 
 in. Halley. 
 
 no. Hipparckus. 
 
 113. HorrocJu. 
 
 114. Rhaelicus. 
 245. Godin. 
 244. Agrippa. 
 242. Triesnecker. 
 
 232. Boscovich. 
 231. Julius -Caesar. 
 240. Manilius. 
 
 233. Taquet. 
 
 234. Menelaus. 
 
 236. 5wjtf/. 
 
 237. Linnet. 
 257. Thecetetu*. 
 256. Calippus. 
 209. Alexander. 
 208. Eudoxus. 
 207. Aristotetes. 
 
 H Locus Mortis. 
 
 X /Wwj Nebularum, 
 
 M A/ar Vaporum. 
 
 b 7/i* Caucasus, 
 
 f. The Heemus Mts. 
 
 k. rAr Tizaraj J//j. 
 
BALLS POPULAR GUIDE TO THE HEAVENS. 7T? DAY. 
 
 Plate 31. 
 
 Tiden GwgraphicailrisUtate. . 
 

Key Hap. 
 
 THE MOON 8th Day. 
 
 To face Plate 32. 
 
 300. Moretus. 
 297. Deluc. 
 296. Maginus. 
 
 290. Saussure. 
 116. Walter. 
 285. Ball. 
 
 P Sinus Medii. 
 
 M ,, sEstuum. 
 
 J A/ar Serenitatis. 
 
 L ,, Imbrium, 
 
 X /Witf Nebularum. 
 2. ,, Putredinis. 
 K A/r Frigoris. 
 
 278. Regiomontanus. 
 277. Purbach. 
 274. 7"A<rfoV. 
 
 266. Arzachel. 
 
 267. Alpetragius. 
 265. Alpkonsus. 
 264. PtolemcBt'.s. 
 263. Herschel. 
 261. Masting. 
 
 373. Sbmmering. 
 
 374. Schroter. 
 376. 2?<Mfe. 
 260. Autolycus. 
 399. Archimedes. 
 
 257. Tkecetetus. 
 259. Aristillus. 
 
 258. Cassini. 
 
 211. Great Alpine Valley. 
 
 413. P/afe. 
 
 414. Timaus, 
 
 416. E pi genes. 
 
 417. Goldschmidt. 
 
 b. T'A* Caucasus. 
 
 c. 7Vi< Apennines. 
 
BALL'S POPULAR GUIDE TO THE HEAVENS. 8TV DAY. 
 
 Plate 32. 
 
 Georyeffuiy 6tSon,L'? 
 
 TTnLondon, Geographical. Institute 
 
" 
 
 OF THE 
 
 OF 
 
 
 
Key Map. 
 
 THE MOON 9th Day. 
 
 To face Plate 33. 
 
 300. Moreius. 
 299. Cysatus. 
 298. Clavius. 
 
 296. Maginus. 
 
 294- Longomontanus. 
 
 291. Tycho. 
 
 Dav 
 
 K Afare Frigoris. 
 
 L Imtrium. 
 N 
 
 P Sinus A/edit. 
 Q J/ore NvHum, 
 
 293. 
 
 292. Heinsiui. 
 282. Gauricus. 
 
 2^3. Wurtelbauer. 
 
 280. Sasscridcs. 
 
 281. Hcsiodus. 
 275. Straight Wall. 
 344. Nicollft, 
 
 274. Thebit. 
 
 266. Artacht:. 
 
 267. Alfetragiiu. 
 265. Alpkoitsus. 
 264, Ptolcmtfus. 
 
 270. Guerike. 
 
 271. Parry. 
 2/3. Bonpland.^ 
 262. Lalande. 
 273. /> Mauro. 
 372. Gambart. 
 377. Reinhold. 
 
 381. Stadius. 
 380. Copernicus. 
 
 382. Eratosthenes. 
 
 383. Cox LMSSOC. 
 403. Pytheas. 
 
 401. Titnocharis. 
 
 402. Lambert. 
 399. Archimedes. 
 413. /'^fe. 
 
 419. Fcmienelle. 
 
 417. Goidschmidt. 
 
 418 Anaxagoras. 
 
 a. 
 
 b. 7*^ Caucasus Mta. 
 
 c. The Apennines. 
 
BALL'S POPULAR GUIDE TO THE HEAVENS. 
 
 T? DAY. 
 
 Plate 33. 
 
 Tfi&Lnndon G&ographi-cai Institute 
 
Key Map. 
 
 THE MOON 10th Day. 
 
 To face Plate 34. 
 
 302. Newton. 
 
 312. Bla.ncan.us. 
 
 313. Sckeiner. 
 
 K Mare Frigoris. 
 L , , Imbrium, 
 
 P Sinus Medii. 
 
 Q *Mare Nubium. 
 
 R Sinus Jridum, 
 
 298. Clavius. 2 g I 
 
 Tycho. 
 
 315. Host. 293 . 
 
 Wilhelm I. 
 
 294. Longomonianus. 292. 
 
 Heinsius. 
 
 326. 
 
 Hainsel. 
 
 338. 
 r r '7SS^ 337- 
 
 Cichus. 
 
 Capuanus. 
 
 O z *\ 355 ' 
 
 Ramsden. 
 
 231 <^>2.9A\ 339- 
 
 (T) , o r , 2C 
 340. 
 
 Merc a tor. 
 Campanus. 
 
 Q Q 333 (\3^ 34 1 ' 
 
 Kies. 
 
 fcu. 
 
 ^ ^ > *-^> J35 Ci ^ OTW 
 
 Hippalus. 
 
 342. 
 
 O^^iV \ ^4^' 
 P) M 
 
 /TO ^ 370. 
 
 Bullialdus. 
 Lubiniezky. 
 Euclides. 
 
 ty N 371- 
 U Occx ^ 7 , 3 , /7 _ 
 
 380. 
 
 Landsberg. 
 Rcinhold. 
 Copernicus. 
 
 (^ p 3 8 4 
 
 Tobias Mayer. 
 
 V ^ ^"? 383- 
 
 X // 
 / o O 580 403- 
 
 < Q / o^ * 84 1 402- 
 
 Gay Lussac. 
 Pytheas. 
 Lambert. 
 
 /^" ** d 1 404. 
 
 Euler. 
 
 40i. 
 
 Timocharis. 
 
 , O^<92. *^ / --^ 
 c-> T ( yw 
 
 r\ *" f** 
 
 Archimedes. 
 
 407. 
 
 Caroline Herschel, 
 
 409. 
 
 Leverrier. 
 
 4 a90/J 4 20 
 V. , w /l ~J 
 
 Helicon. 
 
 ^--'^^~~^~ S~^) ^^' 
 
 Plato. 
 
 433- 
 
 Condamirte. 
 
 419. 
 
 Fontenelle. 
 
 420. 
 
 Philolaus. 
 
 a. The Alps. 
 
 
 b. The Caucasus. r. / 
 
 
 c. The Apennines. U. / 
 
 >rom. Laplace. 
 
 d. The Carpathians. 
 
 q- 
 
BALL'S POPULAR GUIDE TO THE HEAVENS. IOT" DAY. 
 
 Plate 34. 
 
 Tke,Londoru Geographical, fasUln 
 
Key Map. 
 
 THE MOON llth Da 5 
 
 To face Plate 35. 
 
 305. Casatus. 
 
 306. Klaproth. 
 
 307. Wilson. 
 
 309- Bettinus. 
 311. Segner. 
 313. Scheiner. 
 
 L Mare Imbrium. 
 
 K ,, Frigoris. 
 
 Q Nubium. 
 
 R Sinus Iridum. 
 
 S Oceanus Procellarum. 
 
 T .d/are Humorum. 
 
 b. TA* Caucasus. 
 
 c. 7^<? Apennines. 
 
 d. 7"A Carpathians. 
 
 e. 7"Ag Sinus Iridum 
 
 Highlands. 
 
 298. Clavius. 
 315. AW. 
 
 317. Schiller. 
 
 318. Bayer. 
 326. Hainzel. 
 337. Capuanus. 
 355. Ramsden. 
 335- Vitello. 
 334. <*. 
 
 333. Doppelmayer. 
 
 345. Hippalus. 
 
 346. Agatharchides. 
 
 347. Gassendi. 
 
 348. Herigonius. 
 
 349. Letronne. 
 
 370. Euclides. 
 369. Wichmann. 
 368. Flamsteed. 
 
 371. Landsberg. 
 
 385. Kunowsky, 
 
 377. Reinhold. 
 
 386. Encke. 
 
 378. Hortensius. 
 
 387. Kepler. 
 380. Copernicus. 
 
 379. Milichius. 
 384. Tobias Mayer. 
 383. Gaj Lussac. 
 
 404. Euler. 
 4 2 - Lambert. 
 401. Timocharis. 
 399. Archimedes. 
 
 405. Diophantus. 
 
 406. Delisie. 
 451. Gruithuisen. 
 427. Mairan. 
 426. Sharp. 
 
 425- Bianchini. 
 
 423. Condamine. 
 
 413- / > /a/^. 
 
 429. Harpalus. 
 
 43. /. -F. IF. Herschel. 
 
 420. Phitolaus. 
 
 421- Anaximenes. 
 
 i. Riphaan Mis. 
 
 q. /'jVo. 
 
 r. Piton Mountain. 
 
 U. Prom. Laplace. 
 
BALL'S PbPULAft GUIDE TO THE HEAVENS. MT? DAY. 
 
 Plate 35. 
 
 ffeoryefhdtf Sr Son,!,'? 
 
Key Map. 
 
 THE MOON 12th Day. 
 
 To face Plate 36. 
 
 317. Schiller, 
 
 318. Bayer. 
 321. Phocylidei. 
 
 323. Schickard. 
 327. Lthmann. 
 332. Vieta. 
 
 Day 
 
 351. Cavendish. 
 350. Mersenius. 
 347. Gassendi. 
 359. Fontana. 
 
 356. 5*Y/y. 
 
 357. Hansteen. 
 349. Letronne. 
 368. Flamsteed. 
 386. .&;. 
 389 Reiner. 
 387 .r/A?r. 
 390. Marius. 
 
 447. Aristarchus . 
 
 448. Herodotus. 
 404. Euler. 
 
 449. Wollaston. 
 427. Mairan. 
 426. Sharp. 
 425. Bia.nch.ini. 
 423. Condamine, 
 
 419. Fonteneile. 
 431. Anaximander. 
 
 420. Philolaus. 
 
 421. Anaximenes. 
 
 K Mare Frigoris. 
 L Imbrium. 
 Q Nubium. 
 
 S Oceanus Procellariim. 
 T Mare Humor-urn. 
 
 e. The Sinus Iridum 
 
 Highlands. 
 H. Prom. Laplace. 
 
BALL'S POPULAR GUIDE TO THE HEAVENS. I2T. H DAY. 
 
 Plate 36. 
 
 ThzLoncLan. Gs^yraphiccdhsUtate 
 

 
Key Map. 
 
 THE MOON 13th Day 
 
 To face Plate 37. 
 
 321. PkocyKdes. ^ Schickard. 332. 
 
 Plfte, 
 
 322. Wargentin. 3 3 9 . />,<,,-. 35*- 
 
 Cavendish. 
 
 325. Inghirami. 33O La grange . 35. 
 
 Merseniui. 
 
 raatn 3S9- 
 73 ,, Da\ 
 
 361- 
 
 Fontana. 
 Criiger. 
 
 362. 
 
 Rocca, 
 
 363- 
 
 Grimalai. 
 
 366. 
 V S?^f aj 
 
 Lohrmann. 
 
 391- 
 
 " ^ \ 392. 
 [ toy.9 
 
 1 397- 
 
 Hevel. 
 Cavalerius. 
 Seleucus. 
 
 V (} K -* /-7 \ 44-8. 
 1 ^ \ ^ \ 
 
 Herodotus. 
 
 447- 
 445- 
 
 rj ^ \ r* 432. 
 
 Aristarchus. 
 Briggs. 
 Pythagoras. 
 
 L Mare Imbrivm. 
 Q ., Nttbium. 
 R Sinus Iridum. 
 
 S Oceanus Procellarttm. 
 T Mare Humorum, 
 W 5mj Roris. 
 
 6. TA/ 5rwJ Iridum 
 
 Highlands. 
 u. Prom. Laplace. 
 
BALL'S POPULAR GUIDE TO THE HEAVENS. 13- DAY 
 
 Plate 37. 
 
Key Map. 
 
 THE MOON ,14th Day. 
 
 To face Plate 38. 
 
 316. Bailly. 
 
 321. Pkocylides. 
 
 322. Wargentin. 
 
 K A/rtre Frigoris. 
 L Afar<? Imbrium. 
 R 5*'j Iridum. 
 
 3 2 S- Inghirami. 
 323. Schickard. 
 329. Piazzi. 
 
 S Oceanus Procellarum. 
 T A/ar ffumorum. 
 W 5j Roris. 
 
 330. Lagrange. 
 353. Eiekstadt. 
 
 362, Rocca. 
 
 363. Grimaldi. 
 
 365. Riccioli. 
 
 366. Lohrmann. 
 
 391. Hevel. 
 
 392. Cavalerius. 
 393- 0/forj. 
 394. Cardanus. 
 395- Kraft. 
 448. Herodotus. 
 447- Aristarchus. 
 397- Seieucus. 
 445- Briggs. 
 446. 0#0 Struve. 
 439. Repsold. 
 43 8 - Xenophancs. 
 437- Cleostratus, 
 432. Pythagoras. 
 
BALL'S POPULAR GUIDE TO THE HEAVENS. 
 
 Plate 38. 
 
 GtergePhdif & Son^L'f 
 
 ThiLomion, GtoanwhicaL Institute 
 
UNIVERSITY 
 
 or 
 
(35) 
 
 CHAPTER VI. THE SKY MONTH BY MONTH, AND THE 
 INDEX TO THE PLANETS. 
 
 PLATES 3950. 
 THE MONTHLY MAPS. 
 
 The diurnal rotation of the earth gives rise to an apparent revolution of the celestial 
 sphere in a period of one sidereal day. In consequence of this movement the appearance of 
 the sky is continually changing, so that to the beginner it is often a matter of considerable 
 difficulty to know where to look for any particular star or constellation. 
 
 As the sidereal day is about 4 minutes shorter than the ordinary mean solar day, the effect 
 produced is a gradual shifting of the stars from east to west, a star which occupies a certain 
 position one night, reaches the same position 4 minutes earlier the next night, so that at the 
 end of a month this position is attained 2 hours earlier than at the beginning. 
 
 In order to render these changes easier to follow, and to enable the student to identify 
 the principal constellations without difficulty, and to know where any particular star or 
 group of stars is to be found at any time, Plates 39 50 are used. They represent the positions 
 of the principal stars down to the 4th magnitude at intervals of 2 sidereal hours. The first 
 shows the aspect of the heavens at midnight on January 15th, the sidereal time then being 7h. 
 37m. This map will also represent the appearance of the visible hemisphere at the times 
 shown in the corners at the top. Thus we find that the first of the monthly maps may be used 
 in February at 10 P.M., in March at 8 P.M. From April to September inclusive, the stars will 
 occupy the positions here indicated during the daylight hours, when they will be invisible ; but 
 in October this aspect of the sky may again be seen at 6 A.M., in November at 4 A.M., and in 
 December at 2 A.M. To find the right map for any month and hour we can make use of the 
 following Table. 
 
 TABLE TO FIND THE ASPECT OF THE HEAVENS AT ANY GIVEN 
 MONTH AND HOUR OF NIGHT. 
 
 
 P.M. 
 4h. 
 
 P.M. 
 
 6h. 
 
 P.M. 
 
 8h. 
 
 P.M. 
 
 10h. 
 
 Mid- 
 night. 
 12h. 
 
 A.M. 
 
 2h. 
 
 A.M. 
 
 4h. 
 
 A.M. 
 
 oh. 
 
 A.M. 
 
 8h. 
 
 January.... 
 February . . 
 March 
 
 47 
 
 48 
 49 
 50 
 
 49 
 50 
 39 
 
 50 
 39 
 
 40 
 
 39 
 
 40 
 41 
 
 40 
 41 
 42 
 
 41 
 42 
 43 
 
 42 
 43 
 44 
 
 43 
 
 April 
 May 
 
 
 
 40 
 41 
 
 41 
 42 
 
 42 
 43 
 
 43 
 
 44 
 
 44 
 45 
 
 
 
 June 
 
 
 
 42 
 
 43 
 
 44 
 
 45 
 
 46 
 
 
 
 
 
 
 
 
 
 
 
 
 
 July 
 
 
 
 43 
 
 44 
 
 45 
 
 46 
 
 47 
 
 
 
 August .... 
 September. 
 
 
 44 
 
 44 
 45 
 
 45 
 46 
 
 46 
 
 47 
 
 47 
 48 
 
 48 
 49 
 
 50 
 
 
 October 
 November- 
 December. . 
 
 45 
 46 
 
 45 
 46 
 
 47 
 
 46 
 
 47 
 48 
 
 47 
 48 
 49 
 
 48 
 49 
 50 
 
 49 
 50 
 39 
 
 50 
 39 
 40 
 
 39 
 
 40 
 41 
 
 41 
 42 
 
36 POPULAR GUIDE TO THE HEAVENS. 
 
 EXAMPLES OF THE USE OF THIS TABLE : 
 
 I. To find the map suitable for 10 P.M. in March. Take the third row, and under 10 P.M 
 
 is found 40. This means Plate 40. 
 
 II. What map should be used at 7-30 P.M. in November ? On the eleventh row we find 
 
 47 under 8 P.M., and as 7-30 is nearer to 8 than to 6, we accordingly choose Plate 47. 
 
 It will of course be understood that the maps have been designed to represent the appear- 
 ance of the sky on the 15th of each month, at the hours mentioned. The changes are, however, 
 so slow, that for most purposes they will be found sufficiently applicable to the whole month. 
 If, however, greater precision is desired, it can be obtained by subtracting half-an-hour from 
 the time given on the map for each week after, or adding half-an-hour for each week before 
 the middle of the month. Plate 39 is thus quite accurate at 11 P.M. on the 30th of January, 
 or at 8-30 P.M. on March 8th ; similarly Plate 41 is correct at 5 A.M. on the 30th December, or 
 at 1 1 P.M. on the 1st April. 
 
 These maps have been constructed for the latitude 53 23' N. They will thus be suitable 
 for all parts of the British Isles. The bounding circle represents the horizon, and the small 
 cross at the centre marks the position of the zenith. The projection used is. such that the 
 distance of each star from the centre of the map is proportional to the star's zenith distance. 
 The angle which the line joining a star to the zenith makes with the central meridian is the 
 azimuth of the star. 
 
 As the celestial sphere is viewed from the inside, the cardinal points are not disposed on 
 these maps as in a terrestrial atlas. In the present case, when the north is at the top, the west 
 will be on the right, and the east on the left. 
 
 If we wish to compare any region of the sky with the map, we suppose a radius drawn 
 through the middle of this region, and the point where it cuts the circumference of the 
 map gives us the azimuth. Turning our face towards this point of the compass, we hold 
 the map so that the corresponding point of the circumference is lowest, and, remembering 
 that the centre of the circle represents the zenith, we have on the map a picture of the corres- 
 ponding position of the sky. For instance, if we wish to find the constellation Leo at midnight, 
 in the middle of March, we find from Map 41 that the radius drawn through the middle of it 
 cuts the circumference at about fths of the way from south towards west. We accordingly turn 
 to that point of the horizon, and we can readily find this constellation. The brightest star, 
 Regulus, will be then almost exactly half-way between the zenith and horizon, or at an altitude 
 of 45, while the " Sickle," which forms the fore-part of this constellation, will be found tilted 
 over towards the west. If we turn a little further towards the west, we shall find the two 
 bright stars, Castor and Pollux, a little lower in the sky, the line joining them being nearly 
 horizontal. Again, if in October, at 10 P.M., we wish to examine " The Plough," as the group 
 formed by the principal stars in Ursa Major are called, we go to Plate 47 and find this group 
 almost due north. We have accordingly to turn the map upside down, so as to bring the north 
 point lowest, and we then see this figure stretching across the sky in a horizontal direction, at 
 an altitude of about 20. If we turn to the north-east, we again find Castor and Pollux just 
 above the horizon, but this time the line joining them is very nearly vertical. 
 
 The names of the constellations have been printed on the maps, so that when the maps 
 are held in the proper position for any constellation its name may be erect. 
 
 As the student becomes more familiar with the stars, he will probably wish to identify 
 many fainter groups that do not appear on these plates. In order to enable this to be done 
 
THE SKY MONTH BY MONTH. 37 
 
 with facility, the faint dotted lines have been inserted which mark the boundaries of the 
 regions which each of the plates, 51 70, of the general Atlas, cover on the sky. These lines 
 appear everywhere in pairs, the spaces between the pairs being the areas by which the 
 maps overlap each other. The numbers within the regions thus marked out are those of the 
 corresponding plates in this volume, where more detailed maps of the same part of the sky 
 will be found. Thus in Plate 40 we find the constellation Leo almost wholly contained in 
 the space corresponding to Plate 60, and some of its principal stars in the space common to 
 Plates 54, 55, and 60. If we turn to Plate 60 we shall find the whole group on a much larger 
 scale, while 54 and 55 show the more northern parts of this constellation. 
 
 THE INDEX TO THE PLANETS. 
 
 It is a special object of this work to indicate from month to month and from year to 
 year the positions in the sky of the principal planets. Let it be once for all understood that 
 those who want exact positions must seek for them elsewhere in the Nautical Almanac for 
 example. What is here given is an in flex to the planets sufficient for the following 
 purposes : 
 
 (1) To find the place in the heavens which each principal planet occupies in each month 
 of the years 19011950. 
 
 (2) To find when any principal planet rises, or souths, or sets. 
 
 (3) To determine thence the best season of any year for the observation of the planet. 
 
 (4) To find the name of a planet when the time and place of its appearance are known. 
 
 The following table gives the dates of the Planetary Phenomena described at the head 
 of each column. 
 
PLANETARY PHENOMENA. 
 
 1 
 
 2 
 
 3 
 
 4 
 
 5 
 
 6 
 
 7 
 
 8 
 
 9 
 
 
 MERCURY. 
 
 Vesus. 
 
 
 
 
 Phase 
 
 
 
 Greatest Elongation. 
 
 liars 
 
 Jupiter 
 
 Saturn 
 
 of 
 
 A.D. 
 
 
 
 
 
 in 
 
 in 
 
 in 
 
 Saturn 
 
 
 Evening Star. 
 
 Morning Star. 
 
 Evening. 
 
 Morning. 
 
 Opposition. 
 
 Opposition. 
 
 Opposition. 
 
 Plate 8 
 
 1901 
 
 Feb. 1623 
 
 July 29 Aug. 5 
 
 December 
 
 
 February 
 
 June 
 
 July 
 
 7 
 
 1902 
 
 Jan. 30 Feb. 6 
 
 Oct. 31 Nov. 7 
 
 
 
 April 
 
 
 
 August 
 
 July 
 
 7 
 
 1903 
 
 May 512 
 
 Oct. 1522 
 
 July 
 
 November 
 
 March 
 
 September 
 
 July 
 
 8 
 
 1904 
 
 Apr. 1825 
 
 Sept. 28 Oct. 5 
 
 
 
 
 
 
 October 
 
 August 
 
 8 
 
 1905 
 
 Mar. 30 Apr. 6 
 
 Sept. 11 18 
 
 February 
 
 July 
 
 May 
 
 November 
 
 August 
 
 8 
 
 1906 
 
 Mar. 1421 
 
 Aug. 26 Sept. 2 
 
 September 
 
 
 
 
 
 December 
 
 September 
 
 9 
 
 1907 
 
 Feb. 26 Mar. 5 
 
 Aug. 916 
 
 
 
 February 
 
 June 
 
 
 
 September 
 
 9 
 
 1908 
 
 Feb. 916 
 
 Nov. 1017 
 
 April 
 
 September 
 
 
 
 January 
 
 September 
 
 9 
 
 1909 
 
 Jan. 2229 
 
 Oct. 25 Nov. 1 
 
 December 
 
 
 September 
 
 February 
 
 October 
 
 10 
 
 1910 
 
 Apr. 28 May 5 
 
 Oct. 815 
 
 
 
 April 
 
 
 
 March 
 
 October 
 
 10 
 
 1911 
 
 Apr. 1118 
 
 Sept. 2128 
 
 July 
 
 November 
 
 November 
 
 May 
 
 November 
 
 11 
 
 1912 
 
 Mar. 25 Apr. 1 
 
 Sept. 5-12 
 
 
 
 
 
 
 
 June 
 
 November 
 
 11 
 
 1913 
 
 Mar. 815 
 
 Aug. 1926 
 
 February 
 
 July 
 
 
 
 July 
 
 December 
 
 12 
 
 1914 
 
 Feb. 1926 
 
 Aug. 18 
 
 September 
 
 
 January 
 
 August 
 
 December 
 
 12 
 
 1915 
 
 Feb. 29 
 
 Nov. 310 
 
 
 
 February 
 
 
 
 September 
 
 December 
 
 12 
 
 1916 
 
 May 916 
 
 Oct. 1825 
 
 April 
 
 September 
 
 February 
 
 October 
 
 
 
 I 
 
 1917 
 
 Apr. 2128 
 
 Oct. 18 
 
 November 
 
 
 
 
 
 November 
 
 January 
 
 1 
 
 1918 
 
 Apr. 310 
 
 Sept. 1421 
 
 
 April 
 
 March 
 
 
 
 January 
 
 1 
 
 1919 
 
 Mar. 1724 
 
 Aug. 29 Sept. 
 
 July 
 
 November 
 
 
 
 January 
 
 February 
 
 o 
 
 1920 
 
 Mar. 1--8 
 
 Aug. 1219 
 
 
 
 
 
 April 
 
 February 
 
 February 
 
 2 
 
 1921 
 
 Feb. 1219 
 
 Nov. 1320 
 
 February 
 
 July 
 
 
 
 March 
 
 March 
 
 3 
 
 1922 
 
 Jan. 25 Feb. 1 
 
 Oct. 28 Nov. 4 
 
 September 
 
 
 
 June 
 
 April 
 
 March 
 
 3 
 
 1923 
 
 May 18 
 
 Oct. 1118 
 
 
 February 
 
 
 
 May 
 
 April 
 
 4 
 
 1924 
 
 Apr. 14 -21 
 
 Sept. 24 Oct. ] 
 
 April 
 
 September 
 
 August 
 
 June 
 
 April 
 
 4 
 
 1925 
 
 Mar. 28 Apr. 4 
 
 Sept. 815 
 
 November 
 
 
 
 
 
 July 
 
 April 
 
 4 
 
 1926 
 
 Mar. 1118 
 
 Aug. 2229 
 
 ^_ 
 
 April 
 
 October 
 
 August 
 
 May 
 
 5 
 
 1927 
 
 Feb. 22 Mar. 1 
 
 Aug. 411 
 
 July 
 
 November 
 
 
 
 September 
 
 May 
 
 5 
 
 1928 
 
 Feb. 512 
 
 Nov. 613. 
 
 
 
 
 
 December 
 
 October 
 
 June 
 
 6 
 
 1929 
 
 May 1219 
 
 Oct. 21 -28 
 
 February 
 
 June 
 
 
 
 December 
 
 June 
 
 6 
 
 1930 
 
 Apr. 24 May 1 
 
 Oct. 411 
 
 September 
 
 
 
 
 
 
 
 June 
 
 6 
 
 1931 
 
 Apr. 613 
 
 Sept. 1724 
 
 
 
 February 
 
 January 
 
 January 
 
 July 
 
 7 
 
 1932 
 
 Mar. 2027 
 
 Sept. 18 
 
 April 
 
 September 
 
 
 
 February 
 
 July 
 
 7 
 
 1933 
 
 Mar. 411 
 
 Aug. 1522 
 
 November 
 
 
 
 March 
 
 March 
 
 August 
 
 8 
 
 1934 
 
 Feb. 1522 
 
 July 29 Aug. 5 
 
 
 April 
 
 
 
 April 
 
 August 
 
 8 
 
 1935 
 
 Jan. 28 Feb. 4 
 
 Oct. 31 Nov. 7 
 
 July 
 
 November 
 
 April 
 
 May 
 
 August 
 
 8 
 
 1936 
 
 May 411 
 
 Oct. 1421 
 
 
 
 
 
 
 
 June 
 
 September 
 
 9 
 
 1937 
 
 Apr. 1724 
 
 Sept. 27 Oct. 4 
 
 February 
 
 June 
 
 May 
 
 July 
 
 September 
 
 9 
 
 1938 
 
 Mar. 31 Apr. 7 
 
 Sept. 11 18 
 
 September 
 
 
 
 
 
 August 
 
 October 
 
 10 
 
 1939 
 
 Mar. 1421 
 
 Aug. 25 Sept. 1 
 
 
 
 February 
 
 July 
 
 September 
 
 October 
 
 10 
 
 1940 
 
 Feb. 25 Mar. 3 
 
 Aug. 714 
 
 April 
 
 September 
 
 
 
 November 
 
 November 
 
 11 
 
 1941 
 
 Feb. 815 
 
 Nov. 916 
 
 November 
 
 
 
 September 
 
 December 
 
 November 
 
 11 
 
 1942 
 
 Jan. 2229 
 
 Oct. 2431 
 
 
 
 April 
 
 
 
 
 
 November 
 
 11 
 
 1943 
 
 Apr. 27 May 4 
 
 Oct. 714 
 
 June 
 
 November 
 
 December 
 
 January 
 
 December 
 
 12 
 
 1944 
 
 Apr. 916 
 
 Sept. 2027 
 
 
 
 
 
 
 
 February 
 
 December 
 
 12 
 
 1945 
 
 Mar. 2330 
 
 Sept. 41 1 
 
 February 
 
 June 
 
 
 
 March 
 
 
 
 1 
 
 1946 
 
 Mar. 714 
 
 Aug. 18-25 
 
 September 
 
 
 
 January 
 
 April 
 
 January 
 
 1 
 
 1947 
 
 Feb. 1825 
 
 Aug. 18 
 
 
 
 January 
 
 
 
 May 
 
 January 
 
 1 
 
 1948 
 
 x Feb. 18 
 
 Nov. 310 
 
 April 
 
 September 
 
 February 
 
 June 
 
 February 
 
 2 
 
 1949 
 
 May 714 
 
 Oct. 1724 
 
 November 
 
 _ 
 
 
 
 July 
 
 February 
 
 2 
 
 1950 
 
 Apr. 2027 
 
 Sept. 30 Oct. 7 
 
 
 
 April 
 
 March 
 
 August 
 
 March 
 
 3 
 
THE INDEX TO THE PLANETS. 39 
 
 Since Mercury and Venus move in orbits lying between the Earth and the Sun, they 
 appear from the Earth to be always comparatively near the Sun, and are visible consequently 
 only in the hours succeeding sunset or preceding sunrise. On the average they are most 
 favourably seen at the times when their angular distance from the Sun is greatest the times 
 of greatest elongation. But the circumstances are greatly modified by the season of the year 
 at which these times fall. The planets move nearly in the Ecliptic. In the spring, even in 
 latitudes as far north as England, at sunset the Ecliptic rises steeply above the western 
 horizon, and the planets are correspondingly high for a given elongation from the Sun. In 
 autumn, at sunset, the Ecliptic lies low along the south-western horizon, and the planets are 
 correspondingly low. 
 
 MERCURY. 
 
 It follows from what has just been said that Mercury is best seen after sunset, when it 
 comes to greatest elongation east of the Sun in the spring, and best before sunrise when it 
 comes to greatest elongation west in the autumn. We have given, therefore, in the table of 
 Planetary Phenomena for Mercury, the week about the dates of greatest elongations east and 
 west, which come respectively in spring and autumn ; and these are in general the most 
 iavourable times of year for finding the planet. Owing, however, to the considerable inclina- 
 tion, 7, of the planet's orbit, some spring and autumn elongations are much more favourable 
 than others, and exact details for each year must be obtained from the Nautical Almanac. 
 
 Mercury moves so quickly among the stars, completing a circuit from conjunction to 
 conjunction in 116 days, that it is not possible within the limits of this work to give an index 
 to Mercury, as is done for the other principal planets. 
 
 VENUS. 
 
 The fourth and fifth columns of the Table of Planetary Phenomena give the month in 
 which Venus attains her greatest elongation east and west of the Sun. At these times she is 
 at her greatest angular distance from the Sun, and there is then on the average the greatest 
 chance of seeing her well. But the advantages in this respect of different elongations are 
 profoundly modified by the time of year at which they occur. For some months before 
 the time of greatest eastern elongation Venus is well to the east of the Sun, and if it happens 
 that the time of year is spring when the Ecliptic rises steeply above the western horizon, she 
 will be a long way north as well as east of the Sun, will set all the later in consequence, and 
 will be seen under more favourable conditions, though not so bright as when she reaches 
 greatest elongation, a month before she is most brilliant. Taking everything into account, in 
 northern latitudes Venus is at her best as an evening star when she comes to greatest elon- 
 gation east in June or July. She is then conspicuous after sunset all through the spring 
 months, but is low and not so well seen by the time she reaches greatest brightness. If, on 
 the other hand, she comes to greatest elongation east in February, and to greatest brightness 
 in March, she makes a less prolonged but more splendid appearance. Bearing in mind that 
 the factors to be taken into account are (1) elongation, (2) distance north of the Sun, 
 (3) brightness (greatest a month before western elongation), it will not be difficult to frame 
 similar rules for her appearances as a morning star. 
 
40 POPULAR GUIDE TO THE HEAVENS. 
 
 The Index to Venus, by which title we have designated the following table, enables the 
 approximate position of the planet to be readily ascertained for any month up to the end of 
 1950. At the top of the index the names of the months are given in a horizontal row. The 
 first column gives the year. Corresponding to each month of each year the index shows a 
 number, which is the number of one of the monthly maps, 39 50. The planet will be found 
 in the region of the sky where the central meridian of the map cuts the "Track of the Planets." 
 
 It must be remembered that, as the unit of time adopted in this index, as well as in those 
 of the other planets, is a month, and as the locality can only be indicated by dividing the 
 "Track of the Planets," around the heavens into twelve portions, no close precision need be 
 looked for. No doubt in the great majority of cases the map named in the index will be that 
 where the central meridian lies nearest the planet. In other words, the place of the planet is 
 given to within an hour. It may, however, happen in extreme conditions that the map 
 indicated is not the best one, but in such cases the right map always lies next to that to which 
 the index refers. Even when this happens, the purposes of the index are not frustrated, for 
 the planet will lie so near to the position in question, that its identification will be unmistak- 
 able, unless on the rare occasions when two planets happen to lie close together. 
 
 EXAMPLES TO ILLUSTRATE THE USE OF THE INDEX TO VENUS. 
 Example 1. What will be the aspect of Venus in March, 1908 1 
 Solution. The index given for March, 1908, the number 49. On this Plate the 
 central meridian cuts the " Track of the Planets " in Taurus. This is the region 
 of the sky required. The next question is, when is this region above the horizon 
 in England 1 The Table at the top of Plate 49 shows that it is on the meridian 
 about 4 p.m. in March. It will be well above the western horizon, therefore, at 
 sunset, and Venus will be splendidly conspicuous. 
 
 Example 2. Where will Venus be when brightest as an evening star in 1943 1 
 Solution. The Table of Planetary Phenomena shows that in 1943 Venus is at 
 greatest elongation east in June. She will, therefore, be brightest in July. The 
 index gives for 1943, July, the number 40, and the corresponding chart shows 
 that Venus is in Leo. Turning forward to plates 43 and 44 we see that at 
 about 10 p.m. in July, Venus will be setting in the N.W., and as the twilight 
 will be strong the planet will not appear to great advantage. 
 
(41) 
 INDEX TO VENUS. 
 
 A.D. 
 
 Jan. 
 
 Feb. 
 
 March 
 
 April 
 
 May 
 
 June 
 
 July 
 
 August 
 
 Sept. 
 
 Oct. 
 
 Nov. 
 
 Dec. 
 
 1901 
 
 44 
 
 46 
 
 47 
 
 48 
 
 49 
 
 39 
 
 40 
 
 41 
 
 42 
 
 43 
 
 45 
 
 46 
 
 1902 
 
 46 
 
 - 46 
 
 46 
 
 47 
 
 48 
 
 49 
 
 50 
 
 39 
 
 40 
 
 41 
 
 43 
 
 44 
 
 1903 
 
 45 
 
 47 
 
 48 
 
 49 
 
 50 
 
 40 
 
 41 
 
 41 
 
 41 
 
 41 
 
 41 
 
 42 
 
 1904 
 
 44 
 
 45 
 
 46 
 
 47 
 
 49 
 
 50 
 
 39 
 
 40 
 
 42 
 
 43 
 
 44 
 
 45 
 
 1905 
 
 47 
 
 48 
 
 48 
 
 49 
 
 48 
 
 49 
 
 49 
 
 39 
 
 40 
 
 41 
 
 42 
 
 43 
 
 1906 
 
 45 
 
 46 
 
 47 
 
 49 
 
 50 
 
 39 
 
 40 
 
 42 
 
 43 
 
 43 
 
 43 
 
 43 
 
 1907 
 
 44 
 
 45 
 
 4ti 
 
 47 
 
 48 
 
 49 
 
 50 
 
 40 
 
 41 
 
 42 
 
 44 
 
 45 
 
 1908 
 
 46 
 
 47 
 
 49 
 
 50 
 
 50 
 
 50 
 
 50 
 
 39 
 
 40 
 
 41 
 
 42 
 
 43 
 
 1909 
 
 44 
 
 46 
 
 47 
 
 48 
 
 49 
 
 39 
 
 40 
 
 41 
 
 42 
 
 43 
 
 45 
 
 46 
 
 1910 
 
 46 
 
 46 
 
 46 
 
 47 
 
 48 
 
 49 
 
 50 
 
 39 
 
 40 
 
 41 
 
 43 
 
 44 
 
 1911 
 
 45 
 
 47 
 
 48 
 
 49 
 
 50 
 
 40 
 
 41 
 
 41 
 
 41 
 
 41 
 
 41 
 
 42 
 
 1912 
 
 44 
 
 45 
 
 46 
 
 47 
 
 49 
 
 50 
 
 39 
 
 40 
 
 42 
 
 43 
 
 44 
 
 45 
 
 1913 
 
 47 
 
 48 
 
 48 
 
 49 
 
 48 
 
 49 
 
 49 
 
 39 
 
 40 
 
 41 
 
 42 
 
 43 
 
 1914 
 
 45 
 
 46 
 
 47 
 
 49 
 
 50 
 
 39 
 
 40 
 
 42 
 
 43 
 
 43 
 
 43 
 
 43 
 
 1915 
 
 44 
 
 45 
 
 46 
 
 47 
 
 48 
 
 49 
 
 50 
 
 40 
 
 41 
 
 42 
 
 44 
 
 45 
 
 1916 
 
 46 
 
 47 
 
 49 
 
 50 
 
 50 
 
 50 
 
 50 
 
 39 
 
 40 
 
 41 
 
 42 
 
 43 
 
 1917 
 
 44 
 
 46 
 
 47 
 
 48 
 
 49 
 
 39 
 
 40 
 
 41 
 
 42 
 
 44 
 
 45 
 
 45 
 
 1918 
 
 45 
 
 45 
 
 46 
 
 47 
 
 48 
 
 49 
 
 50 
 
 39 
 
 40 
 
 42 
 
 43 
 
 44 
 
 1919 
 
 46 
 
 47 
 
 48 
 
 49 
 
 50 
 
 40 
 
 41 
 
 41 
 
 41 
 
 41 
 
 41 
 
 42 
 
 1920 
 
 44 
 
 45 
 
 46 
 
 47 
 
 49 
 
 50 
 
 39 
 
 40 
 
 42 
 
 43 
 
 44 
 
 45 
 
 1921 
 
 47 
 
 48 
 
 48 
 
 49 
 
 48 
 
 49 
 
 49 
 
 39 
 
 40 
 
 41 
 
 42 
 
 43 
 
 1922 
 
 45 
 
 46 
 
 47 
 
 49 
 
 50 
 
 39 
 
 40 
 
 42 
 
 43 
 
 43 
 
 43 
 
 43 
 
 1923 
 
 44 
 
 45 
 
 46 
 
 47 
 
 48 
 
 49 
 
 50 
 
 40 
 
 41 
 
 42 
 
 44 
 
 45 
 
 1924 
 
 46 
 
 47 
 
 49 
 
 50 
 
 50 
 
 50 
 
 50 
 
 39 
 
 40 
 
 41 
 
 42 
 
 43 
 
 1925 
 
 44 
 
 46 
 
 47 
 
 48 
 
 49 
 
 39 
 
 40 
 
 41 
 
 42 
 
 44 
 
 45 
 
 45 
 
 1926 
 
 45 
 
 45 
 
 46 
 
 47 
 
 48 
 
 49 
 
 50 
 
 39 
 
 40 
 
 42 
 
 43 
 
 44 
 
 1927 
 
 46 
 
 47 
 
 48 
 
 49 
 
 50 
 
 40 
 
 41 
 
 41 
 
 41 
 
 41 
 
 41 
 
 42 
 
 19'28 
 
 44 
 
 45 
 
 46 
 
 47 
 
 49 
 
 50 
 
 39 
 
 40 
 
 42 
 
 43 
 
 44 
 
 45 
 
 1929 
 
 47 
 
 48 
 
 48 
 
 49 
 
 48 
 
 49 
 
 49 
 
 39 
 
 40 
 
 41 
 
 42 
 
 43 
 
 1930 
 
 45 
 
 46 
 
 47 
 
 49 
 
 50 
 
 39 
 
 40 
 
 42 
 
 43 
 
 43 
 
 43 
 
 43 
 
 1931 
 
 44 
 
 45 
 
 46 
 
 47 
 
 48 
 
 49 
 
 50 
 
 40 
 
 41 
 
 42 
 
 44 
 
 45 
 
 1932 
 
 46 
 
 47 
 
 49 
 
 50 
 
 50 
 
 50 
 
 50 
 
 39 
 
 40 
 
 41 
 
 42 
 
 43 
 
 1933 
 
 44 
 
 46 
 
 47 
 
 48 
 
 49 
 
 39 
 
 40 
 
 41 
 
 42 
 
 44 
 
 45 
 
 45 
 
 1934 
 
 45 
 
 45 
 
 46 
 
 47 
 
 48 
 
 49 
 
 50 
 
 39 
 
 40 
 
 42 
 
 43 
 
 44 
 
 1935 
 
 46 
 
 47 
 
 48 
 
 49 
 
 50 
 
 40 
 
 41 
 
 41 
 
 41 
 
 41 
 
 41 
 
 42 
 
 1936 
 
 44 
 
 45 
 
 46 
 
 47 
 
 49 
 
 50 
 
 39 
 
 40 
 
 42 
 
 43 
 
 44 
 
 45 
 
 1937 
 
 47 
 
 48 
 
 48 
 
 49 
 
 48 
 
 49 
 
 49 
 
 39 
 
 40 
 
 41 
 
 42 
 
 43 
 
 1938 
 
 45 
 
 46 
 
 47 
 
 49 
 
 50 
 
 39 
 
 40 
 
 42 
 
 43 
 
 43 
 
 43 
 
 43 
 
 1939 
 
 44 j 45 
 
 46 
 
 47 
 
 48 
 
 49 
 
 50 
 
 40 
 
 41 
 
 42 
 
 44 
 
 45 
 
 1910 
 
 46 
 
 47 
 
 49 
 
 50 
 
 50 
 
 50 
 
 50 
 
 39 
 
 40 
 
 41 
 
 42 
 
 43 
 
 1941 
 
 44 
 
 46 
 
 47 
 
 48 
 
 49 
 
 39 
 
 40 
 
 41 
 
 42 
 
 44 
 
 45 
 
 45 
 
 1942 
 
 45 
 
 45 
 
 46 
 
 47 
 
 48 
 
 49 
 
 50 
 
 39 
 
 40 
 
 42 
 
 43 
 
 44 
 
 1943 
 
 46 
 
 47 
 
 48 
 
 49 
 
 39 
 
 40 
 
 40 
 
 40 
 
 40 
 
 40 
 
 41 
 
 43 
 
 1944 
 
 44 
 
 45 
 
 46 
 
 48 
 
 49 
 
 50 
 
 39 
 
 41 
 
 42 
 
 43 
 
 44 
 
 45 
 
 1945 
 
 47 
 
 48 
 
 48 
 
 49 
 
 48 
 
 49 
 
 49 
 
 39 
 
 40 
 
 41 
 
 42 
 
 43 
 
 1946 
 
 45 
 
 46 
 
 47 
 
 49 
 
 50 
 
 39 
 
 40 
 
 42 
 
 43 
 
 43 
 
 43 
 
 43 
 
 1947 
 
 44 
 
 45 
 
 46 
 
 47 
 
 48 
 
 49 
 
 50 
 
 40 
 
 41 
 
 42 
 
 44 
 
 45 
 
 1948 
 
 46 
 
 47 
 
 49 
 
 50 
 
 50 
 
 50 
 
 50 
 
 39 
 
 40 
 
 41 
 
 42 
 
 43 
 
 1949 
 
 44 
 
 46 
 
 47 
 
 48 
 
 49 
 
 39 
 
 40 
 
 41 
 
 42 
 
 44 
 
 45 45 
 
 1950 
 
 45 
 
 45 
 
 46 
 
 47 
 
 48 
 
 49 
 
 50 
 
 39 
 
 40 
 
 42 
 
 43 
 
 44 
 
42 POPULAR GUIDE TO THE HEAVENS. 
 
 MARS. 
 
 We have already explained, in connection with Plate 6, the phases of Mars and the 
 effect of the eccentricity of his orbit, whereby the distance of the planet, and its consequent 
 apparent diameter, is dependent upon the time of year at which opposition occurs the most 
 favourable date being the end of August, and the least favourable the end of February. It 
 should not be forgotten, however, that in countries as far north as England, Mars at an 
 August opposition is very low down in the south, and unfavourably placed for telescopic 
 scrutiny. It may well happen that at an opposition occuring later in the year, say in October, 
 the planetary detail is better seen, because of the greater elevation at which the planet crosses 
 the meridian, although the planet is farther away and apparently smaller. 
 
 The conditions for a favourable view of Mars and other exterior planets are much simpler 
 than those for Venus and Mercury. The planet is best seen when it is in opposition to the 
 Sun ; it is then on the meridian at midnight, and is up for practically the whole of the night. 
 
 The table of planetary phenomena gives the dates of the opposition of Mars, and we can 
 judge from them at once how favourable the opposition will be. The Index to Mars enables 
 us to find in what region of the sky the planet will be at any time. 
 
 EXAMPLES TO ILLUSTRATE THE USE OF THE INDEX TO MARS. 
 
 Example 1. Find the place of Mars in August, 1907. 
 
 Solution. The Index gives the reference 45, and the corresponding chart shows 
 that the planet lies between Capricornus and Sagittarius. It is on the 
 meridian about 10 p.m., but is considerably south. A reference to the Table of 
 Planetary Phenomena shows that Opposition occurred in June, which is not a 
 very favourable case, and, since the planet is also far south, it will not be very 
 favourably placed for observation in England in 1907, August. 
 
 Example 2. When is Mars on the meridian in April, 1938 ? 
 
 Solution. The index gives 48, and the corresponding map shows that Mars is in 
 Aries. Reference to the table in the top corner shows that Aries is on the 
 meridian at noon in April, during daylight ; the planet will, therefore, not be 
 visible. 
 
(43) 
 INDEX TO MARS. 
 
 A.D. 
 
 Jan. 
 
 Feb. 
 
 March 
 
 April 
 
 May 
 
 June 
 
 July 
 
 August 
 
 Sept. 
 
 Oct. 
 
 Nov. 
 
 Dec. 
 
 1901 
 
 41 
 
 40 
 
 40 
 
 40 
 
 40 
 
 41 
 
 41 
 
 42 
 
 43 
 
 43 
 
 44 
 
 45 
 
 1902 
 
 40 
 
 46 
 
 47 
 
 48 
 
 49 
 
 49 
 
 50 
 
 39 
 
 40 
 
 40 
 
 41 
 
 41 
 
 1903 
 
 42 
 
 42 
 
 41 
 
 41 
 
 41 
 
 41 
 
 42 
 
 4-2 
 
 43 
 
 44 
 
 44 
 
 45 
 
 1904 
 
 46 
 
 47 
 
 47 
 
 48 
 
 49 
 
 50 
 
 50 
 
 39 
 
 40 
 
 40 
 
 41 
 
 42 
 
 1905 
 
 42 
 
 42 
 
 43 
 
 43 
 
 43 
 
 43 
 
 43 
 
 43 
 
 44 
 
 44 
 
 45 
 
 46 
 
 1906 
 
 47 
 
 47 
 
 48 
 
 49 
 
 50 
 
 50 
 
 39 
 
 40 
 
 40 
 
 41 
 
 42 
 
 42 
 
 1907 
 
 43 
 
 44 
 
 44 
 
 45 
 
 45 
 
 44 
 
 45 
 
 45 
 
 45 
 
 46 
 
 46 
 
 47 
 
 1908 
 
 48 
 
 48 
 
 49 
 
 50 
 
 50 
 
 39 
 
 40 
 
 40 
 
 41 
 
 42 
 
 42 
 
 43 
 
 1909 
 
 44 
 
 45 
 
 45 
 
 46 
 
 47 
 
 47 
 
 47 
 
 47 
 
 47 
 
 47 
 
 47 
 
 47 
 
 1910 
 
 48 
 
 48 
 
 49 
 
 50 
 
 50 
 
 39 
 
 40 
 
 40 
 
 41 
 
 42 
 
 43 
 
 43 
 
 1911 
 
 44 
 
 44 
 
 45 
 
 46 
 
 47 
 
 47 
 
 48 
 
 49 
 
 49 
 
 49 
 
 49 
 
 49 
 
 1912 
 
 49 
 
 49 
 
 50 
 
 50 
 
 39 
 
 40 
 
 40 
 
 41 
 
 41 
 
 42 
 
 43 
 
 43 
 
 1913 
 
 44 
 
 45 
 
 46 
 
 47 
 
 47 
 
 48 
 
 49 
 
 49 
 
 50 
 
 39 
 
 39 
 
 39 
 
 1914 
 
 39 
 
 39 
 
 39 
 
 39 
 
 40 
 
 40 
 
 41 
 
 42 
 
 42 
 
 43 
 
 44 
 
 44 
 
 1915 
 
 45 
 
 46 
 
 47 
 
 48 
 
 48 
 
 49 
 
 50 
 
 39 
 
 39 
 
 40 
 
 40 
 
 41 
 
 1916 
 
 41 
 
 40 
 
 40 
 
 40 
 
 40 
 
 41 
 
 41 
 
 42 
 
 43 
 
 43 
 
 44 
 
 45 
 
 1917 
 
 46 
 
 46 
 
 47 
 
 48 
 
 49 
 
 49 
 
 50 
 
 39 
 
 40 
 
 40 
 
 41 
 
 41 
 
 1918 
 
 42 
 
 42 
 
 41 
 
 41 
 
 41 
 
 41 
 
 42 
 
 42 
 
 43 
 
 44 
 
 44 
 
 45 
 
 1919 
 
 46 
 
 47 
 
 47 
 
 48 
 
 49 
 
 50 
 
 50 
 
 39 
 
 40 
 
 40 
 
 41 
 
 42 
 
 1920 
 
 42 
 
 42 
 
 43 
 
 42 
 
 42 
 
 42 
 
 42 
 
 43 
 
 43 
 
 44 
 
 45 
 
 46 
 
 1921 
 
 47 
 
 47 
 
 48 
 
 49 
 
 49 
 
 50 
 
 39 
 
 40 
 
 40 
 
 41 
 
 41 
 
 42 
 
 1922 
 
 43 
 
 43 
 
 44 
 
 44 
 
 44 
 
 44 
 
 44 
 
 44 
 
 44 
 
 45 
 
 46 
 
 46 
 
 1923 
 
 47 
 
 48 
 
 48 
 
 49 
 
 50 
 
 39 
 
 39 
 
 40 
 
 41 
 
 41 
 
 42 
 
 42 
 
 1924 
 
 43 
 
 44 
 
 45 
 
 45 
 
 46 
 
 46 
 
 46 
 
 46 
 
 46 
 
 46 
 
 46 
 
 47 
 
 1925 
 
 47 
 
 48 
 
 49 
 
 49 
 
 50 
 
 39 
 
 39 
 
 40 
 
 41 
 
 41 
 
 42 
 
 43 
 
 1926 
 
 43 
 
 44 
 
 45 
 
 46 
 
 46 
 
 47 
 
 48 
 
 48 
 
 48 
 
 48 
 
 48 
 
 48 
 
 1927 
 
 48 
 
 49 
 
 49 
 
 50 
 
 39 
 
 39 
 
 40 
 
 41 
 
 .41 
 
 42 
 
 43 
 
 43 
 
 1928 
 
 44 
 
 45 
 
 45 
 
 46 
 
 47 
 
 48 
 
 48 
 
 49 
 
 50 
 
 50 
 
 50 
 
 50 
 
 1929 
 
 50 
 
 50 
 
 50 
 
 39 
 
 39 
 
 40 
 
 41 
 
 41 
 
 42 
 
 42 
 
 43 
 
 44 
 
 1930 
 
 45 
 
 46 
 
 46 
 
 47 
 
 48 
 
 49 
 
 49 
 
 50 
 
 39 
 
 39 
 
 40- 
 
 40 
 
 1931 
 
 39 
 
 39 
 
 39 
 
 39 
 
 40 
 
 40 
 
 41 
 
 42 
 
 42 
 
 43 
 
 44 
 
 44 
 
 1932 
 
 45 
 
 46 
 
 47 
 
 48 
 
 48 
 
 49 
 
 50 
 
 39 
 
 39 
 
 40 
 
 40 
 
 41 
 
 1933 
 
 41 
 
 41 
 
 41 
 
 41 
 
 41 
 
 41 
 
 42 
 
 42 
 
 43 
 
 44 
 
 44 
 
 45 
 
 1934 
 
 46 
 
 47 
 
 47 
 
 48 
 
 49 
 
 50 
 
 50 
 
 39 
 
 40 
 
 40 
 
 41 
 
 42 
 
 1935 
 
 42 
 
 42 
 
 43 
 
 42 
 
 42 
 
 42 
 
 42 
 
 43 
 
 43 
 
 44 
 
 45 
 
 46 
 
 1936 
 
 47 
 
 47 
 
 48 
 
 49 
 
 49 
 
 50 
 
 39 
 
 40 
 
 40 
 
 41 
 
 41 
 
 42 
 
 1937 
 
 43 
 
 43 
 
 44 
 
 44 
 
 43 
 
 43 
 
 43 
 
 43 
 
 44 
 
 44 
 
 45 
 
 46 
 
 193S 
 
 47 
 
 47 
 
 48 
 
 49 
 
 50 
 
 50 
 
 39 
 
 40 
 
 40 
 
 41 
 
 42 
 
 42 
 
 1939 
 
 43 
 
 44 
 
 44 
 
 45 
 
 45 
 
 45 
 
 45 
 
 45 
 
 45 
 
 45 
 
 46 
 
 46 
 
 1940 
 
 47 
 
 48 
 
 48 
 
 49 
 
 50 
 
 50 
 
 39 
 
 40 
 
 40 
 
 41 
 
 42 
 
 42 
 
 1941 
 
 43 
 
 44 
 
 45 
 
 45 
 
 46 
 
 47 
 
 47 
 
 47 
 
 47 
 
 47 
 
 47 
 
 47 
 
 1942 
 
 48 
 
 48 
 
 49 
 
 50 
 
 50 
 
 39 
 
 40 
 
 40 
 
 41 
 
 42 
 
 42 
 
 43 
 
 1943 
 
 44 
 
 44 
 
 45 
 
 46 
 
 47 
 
 47 
 
 48 
 
 49 
 
 49 
 
 50 
 
 50 
 
 50 
 
 1944 
 
 50 
 
 50 
 
 50 
 
 39 
 
 39 
 
 40 
 
 41 
 
 41 
 
 42 
 
 42 
 
 43 
 
 44 
 
 1945 
 
 45 
 
 46 
 
 46 
 
 47 
 
 48 
 
 49 
 
 49 
 
 50 
 
 39 
 
 39 
 
 40 
 
 40 
 
 1946 
 
 39 
 
 39 
 
 39 
 
 39 
 
 40 
 
 40 
 
 41 
 
 42 
 
 42 
 
 43 
 
 44 
 
 44 
 
 1947 
 
 45 
 
 46 
 
 47 
 
 48 
 
 48 
 
 49 
 
 50 
 
 39 
 
 39 
 
 40 
 
 40 
 
 41 
 
 194S 
 
 41 
 
 40 
 
 40 
 
 40 
 
 40 
 
 41 
 
 41 
 
 42 
 
 43 
 
 43 
 
 44 
 
 45 
 
 1949 
 
 46 
 
 46 
 
 47 
 
 48 
 
 49 
 
 49 
 
 50 
 
 39 
 
 40 
 
 40 
 
 41 
 
 41 
 
 1950 
 
 42 
 
 42 
 
 41 
 
 41 
 
 41 
 
 41 
 
 42 
 
 42 
 
 43 
 
 44 
 
 44 
 
 45 
 
44 POPULAR GUIDE TO THE HEAVENS. 
 
 JUPITER. 
 
 Since the eccentricity of Jupiter's orbit is not large, and it lies far outside the orbit of 
 the Earth, successive oppositions of the planet, every thirteen months, would be almost 
 equally favourable, were it not for the fact that at a summer opposition the planet is always 
 low in England, whereas at a winter opposition it is high. The dates of opposition from 
 1901 1950 are found in the Table of Planetary Phenomena. The position of the planet in 
 the sky at any time can be found as usual from the following index. 
 
 EXAMPLES TO ILLUSTRATE THE USE OF THE INDEX TO JUPITER. 
 Example I. In what part of the heavens will Jupiter be in January, 1910 1 
 
 Solution. The index to Jupiter gives for this month the number 41, and the 
 
 corresponding Plate shows that the planet is between Leo and Virgo, and 
 
 consequently close to the equator. The Table at the top shows that this 
 
 region is on the meridian about 4 a.m. in January. The planet will therefore 
 
 . rise about 10 p.m., and will be well visible after midnight. 
 
 Example 2. In July, 1919, a bright planet is seen in the west at sunset. Is it 
 Jupiter ? 
 
 Solution. The index to Jupiter gives for July, 1919, the reference to chart 40, 
 which shows that Jupiter is a little to the west of the Sickle in Leo. Turning on 
 to Plates 43 and 44, we see that the Sickle is low down at 8 p.m., and is on the 
 horizon at 10 p.m. Jupiter will therefore be scarcely visible at Sunset, and the 
 planet in question is probably not Jupiter. Reference to the Index to Venus 
 shows that the planet higher up in the west at that time is Venus. 
 
(45) 
 INDEX TO JUPITER. 
 
 A.D. 
 
 Jan. 
 
 Feb. 
 
 March 
 
 April 
 
 May 
 
 June 
 
 July 
 
 August 
 
 Sept. 
 
 Oct. 
 
 Nov. 
 
 Dec. 
 
 1901 
 
 44 
 
 44 
 
 44 
 
 44 
 
 44 
 
 44 
 
 44 
 
 44 
 
 44 
 
 44 
 
 44 
 
 45 
 
 1902 
 
 45 
 
 45 
 
 45 
 
 45 
 
 45 
 
 45 
 
 45 
 
 46 
 
 46 
 
 46 
 
 46 
 
 46 
 
 1903 
 
 40 
 
 47 
 
 47 
 
 47 
 
 47 
 
 47 
 
 47 
 
 47 
 
 47 
 
 47 
 
 47 
 
 47 
 
 1904 
 
 47 
 
 47 
 
 48 
 
 48 
 
 48 
 
 48 
 
 48 
 
 48 
 
 48 
 
 48 
 
 48 
 
 48 
 
 1905 
 
 48 
 
 48 
 
 48 
 
 49 
 
 49 
 
 49 
 
 49 
 
 49 
 
 49 
 
 49 
 
 49 
 
 49 
 
 1906 
 
 49 
 
 49 
 
 49 
 
 49 
 
 50 
 
 50 
 
 50 
 
 50 
 
 50 
 
 50 
 
 50 
 
 50 
 
 1907 
 
 50 
 
 50 
 
 50 
 
 50 
 
 50 
 
 39 
 
 39 
 
 39 
 
 39 
 
 39 
 
 39 
 
 39 
 
 1908 
 
 39 
 
 39 
 
 89 
 
 39 
 
 39 
 
 39 
 
 40 
 
 40 
 
 40 
 
 40 
 
 40 
 
 40 
 
 190!) 
 
 40 
 
 40 
 
 40 
 
 40 
 
 40 
 
 40 
 
 40 
 
 41 
 
 41 
 
 41 
 
 41 
 
 41 
 
 1910 
 
 41 
 
 41 
 
 41 
 
 41 
 
 41 
 
 41 
 
 41 
 
 41 
 
 42 
 
 42 
 
 42 
 
 42 
 
 1911 
 
 42 
 
 42 
 
 42 
 
 42 
 
 43 
 
 43 
 
 43 
 
 43 
 
 43 
 
 43 
 
 44 
 
 44 
 
 1912 
 
 44 
 
 44 
 
 44 
 
 44 
 
 44 
 
 44 
 
 44 
 
 44 
 
 44 
 
 44 
 
 44 
 
 45 
 
 1913 
 
 45 
 
 45 
 
 45 
 
 45 
 
 45 
 
 45 
 
 45 
 
 45 
 
 45 
 
 45 
 
 45 
 
 45 
 
 ' 1914 
 
 46 
 
 46 
 
 46 
 
 46 
 
 46 
 
 46 
 
 46 
 
 46 
 
 46 
 
 46 
 
 46 
 
 46 
 
 1915 
 
 46 
 
 47 
 
 47 
 
 47 
 
 47 
 
 47 
 
 47 
 
 47 
 
 47 
 
 47 
 
 47 
 
 47 
 
 1916 
 
 47 
 
 47 
 
 48 
 
 48 
 
 48 
 
 48 
 
 48 
 
 48 
 
 48 
 
 48 
 
 48 
 
 48 
 
 1917 
 
 48 
 
 48 
 
 48 
 
 49 
 
 49 
 
 49 
 
 49 
 
 49 
 
 49 
 
 49 
 
 49 
 
 49 
 
 1918 
 
 49 
 
 49 
 
 49 
 
 49 
 
 50 
 
 50 
 
 50 
 
 50 
 
 50 
 
 50 
 
 50 
 
 50 
 
 1919 
 
 39 
 
 39 
 
 39 
 
 39 
 
 39 
 
 39 
 
 40 
 
 40 
 
 40 
 
 40 
 
 40 
 
 40 
 
 1920 
 
 40 
 
 40 
 
 40 
 
 40 
 
 40 
 
 40 
 
 40 
 
 41 
 
 41 
 
 41 
 
 41 
 
 41 
 
 1921 
 
 41 
 
 41 
 
 41 
 
 41 
 
 41 
 
 41 
 
 41 
 
 41 
 
 42 
 
 42 
 
 42 
 
 42 
 
 1922 
 
 42 
 
 42 
 
 42 
 
 42 
 
 42 
 
 42 
 
 42 
 
 42 
 
 42 
 
 43 
 
 43 
 
 43 
 
 1923 
 
 43 
 
 43 
 
 43 
 
 43 
 
 43 
 
 43 
 
 43 
 
 43 
 
 43 
 
 43 
 
 44 
 
 44 
 
 1924 
 
 44 
 
 44 
 
 44 
 
 44 
 
 44 
 
 44 
 
 44 
 
 44 
 
 44 
 
 44 
 
 44 
 
 45 
 
 1925 
 
 45 
 
 45 
 
 45 
 
 45 
 
 45 
 
 45 
 
 45 
 
 45 
 
 45 
 
 45 
 
 45 
 
 45 
 
 1926 
 
 46 
 
 46 
 
 46 
 
 46 
 
 46 
 
 46 
 
 46 
 
 46 
 
 46 
 
 46 
 
 46 
 
 46 
 
 1927 
 
 46 
 
 47 
 
 47 
 
 47 
 
 47 
 
 47 
 
 47 
 
 47 
 
 47 
 
 47 
 
 47 
 
 47 
 
 1928 
 
 47 
 
 47 
 
 48 
 
 48 
 
 48 
 
 48 
 
 48 
 
 48 
 
 48 
 
 48 
 
 48 
 
 48 
 
 1929 
 
 48 
 
 48 
 
 48 
 
 49 
 
 49 
 
 49 
 
 49 
 
 49 
 
 49 
 
 49 
 
 49 
 
 50 
 
 1930 
 
 50 
 
 50 
 
 50 
 
 50 
 
 50 
 
 39 
 
 39 
 
 39 
 
 39 
 
 39 
 
 39 
 
 39 
 
 1931 
 
 39 
 
 39 
 
 39 
 
 39 
 
 39 
 
 39 
 
 40 
 
 40 
 
 40 
 
 40 
 
 40 
 
 40 
 
 1932 
 
 40 
 
 40 
 
 40 
 
 40 
 
 40 
 
 40 
 
 40 
 
 41 
 
 41 
 
 41 
 
 41 
 
 41 
 
 1933 
 
 41 
 
 41 
 
 41 
 
 41 
 
 41 
 
 41 
 
 41 
 
 41 
 
 42 
 
 42 
 
 42 
 
 42 
 
 1934 
 
 42 
 
 42 
 
 42 
 
 42 
 
 42 
 
 42 
 
 42 
 
 42 
 
 42 
 
 43 
 
 43 
 
 43 
 
 1935 
 
 43 
 
 43 
 
 43 
 
 43 
 
 43 
 
 43 
 
 43 
 
 43 
 
 43 
 
 43 
 
 44 
 
 44 
 
 1936 
 
 44 
 
 44 
 
 44 
 
 44 
 
 44 
 
 44 
 
 44 
 
 44 
 
 44 
 
 44 
 
 44 
 
 45 
 
 1937 
 
 45 
 
 45 
 
 45 
 
 45 
 
 45 
 
 45 
 
 45 
 
 45 
 
 45 
 
 45 
 
 45 
 
 46 
 
 1938 
 
 46 
 
 46 
 
 46 
 
 46 
 
 46 
 
 46 
 
 46 
 
 46 
 
 46 
 
 46 
 
 46 
 
 46 
 
 1939 
 
 46 
 
 47 
 
 47 
 
 47 
 
 47 
 
 47 
 
 47 
 
 47 
 
 47 
 
 47 
 
 47 
 
 47 
 
 1940 
 
 47 
 
 47 
 
 48 
 
 48 
 
 48 
 
 48 
 
 48 
 
 48 
 
 48 
 
 48 
 
 49 
 
 49 
 
 1941 
 
 49 
 
 49 
 
 49 
 
 49 
 
 50 
 
 50 
 
 50 
 
 50 
 
 50 
 
 50 
 
 50 
 
 50 
 
 1942 
 
 50 
 
 50 
 
 50 
 
 50 
 
 50 
 
 39 
 
 39 
 
 39 
 
 39 
 
 39 
 
 39 
 
 39 
 
 1943 
 
 39 
 
 39 
 
 39 
 
 39 
 
 39 
 
 39 
 
 40 
 
 40 
 
 40 
 
 40 
 
 40 
 
 40 
 
 1944 
 
 40 
 
 40 
 
 40 
 
 40 
 
 40 
 
 40 
 
 40 
 
 41 
 
 41 
 
 41 
 
 41 
 
 41 
 
 1945 
 
 41 
 
 41 
 
 41 
 
 41 
 
 41 
 
 41 
 
 41 
 
 41 
 
 42 
 
 42 
 
 42 
 
 42 
 
 1946 
 
 42 
 
 42 
 
 42 
 
 42 
 
 42 
 
 42 
 
 42 
 
 42 
 
 42 
 
 43 
 
 43 
 
 43 
 
 1947 
 
 43 
 
 43 
 
 43 
 
 43 
 
 43 
 
 43 
 
 43 
 
 43 
 
 43 
 
 43 
 
 44 
 
 44 
 
 1948 
 
 44 
 
 44 
 
 44 
 
 44 
 
 44 
 
 44 
 
 44 
 
 44 
 
 44 
 
 44 
 
 44 
 
 45 
 
 1949 
 
 45 
 
 45 
 
 45 
 
 45 
 
 45 
 
 45 
 
 45 
 
 45 
 
 45 
 
 45 
 
 45 
 
 45 
 
 1950 
 
 46 
 
 46 
 
 46 
 
 46 
 
 46 
 
 46 
 
 46 
 
 46 
 
 46 
 
 46 
 
 46 
 
 46 
 
46 POPULAR GUIDE TO THE HEAVENS. 
 
 SATURN. 
 
 What we have said of Jupiter applies equally well to Saturn. An opposition is 
 favourable or unfavourable according as the planet is in the northern or southern part of the 
 ecliptic. But there is the further consideration, that in the telescope a great deal, and to 
 the naked eye something, depends upon whether the rings are seen well open or closed up. 
 When the rings are fully open the planet is nearly a magnitude brighter than when they are 
 edgewise. For the appearance of the rings at any time reference may be made from the last 
 column of the Table of Planetary Phenomena to Plate 6. 
 
 EXAMPLES TO ILLUSTRATE THE USE OF THE INDEX TO SATURN. 
 Example 1. When will Saturn be found near the Pleiades ? 
 
 Solution. The Pleiades are close to the central meridian of Chart 49. The index 
 gives the reference number, 49, for Saturn from May, 1911 to May, 1913. 
 During these two years the planet will pass from west to east across the section 
 of the "track of the planets" central on Chart 49, and will be close to the Pleiades 
 in the summer of 1912. The last column of the Table of Planetary Phenomena 
 gives the number 11, and reference to Plate 6 shows that the rings are nearly at 
 their widest open. A repetition of the circumstance occurs in 1941 and 1942. 
 
 Example 2. When will Saturn be found near the meridian at 10 p.m. in February ? 
 
 Solution. Eefereuce to the monthly maps shows that the region of the sky which 
 comes to the meridian at 10 p.m. in February is on the meridian at midnight in 
 January, and the Index number is 39. We therefore look for this number in 
 the Index to Saturn in the column for February, and find the years 1917, 1918, 
 1946, 1947. On these years the planet will be on the meridian about 10 p.m. 
 in February. 
 
(47) 
 INDEX TO SATURN. 
 
 A.D. 
 
 Jan. 
 
 Feb. 
 
 March 
 
 April 
 
 May 
 
 June 
 
 July 
 
 August 
 
 Sept. 
 
 Oct. 
 
 Nov. 
 
 Dec. 
 
 1901 
 
 4o 
 
 45 
 
 45 
 
 45 
 
 45 
 
 45 
 
 45 
 
 45 
 
 45 
 
 45 
 
 45 
 
 45 
 
 1902 
 
 45 
 
 45 
 
 45 
 
 45 
 
 45 
 
 45 
 
 45 
 
 45 
 
 45 
 
 45 
 
 45 
 
 45 
 
 1903 
 
 45 
 
 45 
 
 45 
 
 45 
 
 45 
 
 45 
 
 45 
 
 45 
 
 45 
 
 45 
 
 45 
 
 45 
 
 mot 
 
 45 
 
 46 
 
 46 
 
 46 
 
 46 
 
 46 
 
 46 
 
 46 
 
 46 
 
 46 
 
 46 
 
 46 
 
 1905 
 
 46 
 
 46 
 
 46 
 
 46 
 
 46 
 
 46 
 
 46 
 
 46 
 
 46 
 
 46 
 
 46 
 
 46 
 
 1906 
 
 46 
 
 46 
 
 47 
 
 47 
 
 47 
 
 47 
 
 47 
 
 47 
 
 47 
 
 47 
 
 47 
 
 47 
 
 1907 
 
 47 
 
 47 
 
 47 
 
 47 
 
 47 
 
 47 
 
 47 
 
 47 
 
 47 
 
 47 
 
 47 
 
 47 
 
 1908 
 
 47 
 
 47 
 
 47 
 
 47 
 
 47 
 
 47 
 
 47 
 
 47 
 
 47 
 
 47 
 
 47 
 
 47 
 
 1909 
 
 47 
 
 47 
 
 47 
 
 48 
 
 48 
 
 48 
 
 48 
 
 48 
 
 48 
 
 48 
 
 48 
 
 48 
 
 1910 
 
 48 
 
 48 
 
 48 
 
 48 
 
 48 
 
 48 
 
 48 
 
 48 
 
 48 
 
 48 
 
 48 
 
 48 
 
 1911 
 
 48 
 
 48 
 
 48 
 
 48 
 
 49 
 
 49 
 
 49 
 
 49 
 
 49 
 
 49 
 
 49 
 
 49 
 
 1912 
 
 49 
 
 49 
 
 49 
 
 49 
 
 49 
 
 49 
 
 49 
 
 49 
 
 49 
 
 49 
 
 49 
 
 49 
 
 1913 
 
 49 
 
 49 
 
 49 
 
 49 
 
 49 
 
 50 
 
 50 
 
 50 
 
 50 
 
 50 
 
 50 
 
 50 
 
 1914 
 
 50 
 
 50 
 
 50 
 
 50 
 
 50 
 
 50 
 
 50 
 
 50 
 
 50 
 
 50 
 
 50 
 
 50 
 
 1915 
 
 50 
 
 50 
 
 50 
 
 50 
 
 50 
 
 50 
 
 50 
 
 50 
 
 50 
 
 50 
 
 50 
 
 50 
 
 1916 
 
 50 
 
 50 
 
 50 
 
 50 
 
 50 
 
 50 
 
 39 
 
 39 
 
 39 
 
 39 
 
 39 
 
 39 
 
 1917 
 
 39 
 
 39 
 
 39 
 
 39 
 
 39 
 
 39 
 
 39 
 
 39 
 
 39 
 
 39 
 
 39 
 
 39 
 
 1918 
 
 39 
 
 39 
 
 39 
 
 39 
 
 39 
 
 39 
 
 39 
 
 40 
 
 40 
 
 40 
 
 40 
 
 40 
 
 1919 
 
 40 
 
 40 
 
 40 
 
 40 
 
 40 
 
 40 
 
 40 
 
 40 
 
 40 
 
 40 
 
 40 
 
 40 
 
 1920 
 
 40 
 
 40 
 
 40 
 
 40 
 
 40 
 
 40 
 
 40 
 
 40 
 
 41 
 
 41 
 
 41 
 
 41 
 
 1921 
 
 41 
 
 41 
 
 41 
 
 41 
 
 41 
 
 41 
 
 41 
 
 41 
 
 41 
 
 41 
 
 41 
 
 41 
 
 1922 
 
 41 
 
 41 
 
 41 
 
 41 
 
 41 
 
 41 
 
 41 
 
 41 
 
 41 
 
 42 
 
 42 
 
 42 
 
 1923 
 
 42 
 
 42 
 
 42 
 
 42 
 
 42 
 
 42 
 
 42 
 
 42 
 
 42 
 
 42 
 
 42 
 
 42 
 
 1924 
 
 42 
 
 42 
 
 42 
 
 42 
 
 42 
 
 42 
 
 42 
 
 42 
 
 42 
 
 42 
 
 42 
 
 42 
 
 1925 
 
 42 
 
 42 
 
 42 
 
 42 
 
 42 
 
 42 
 
 42 
 
 42 
 
 42 
 
 42 
 
 43 
 
 43 
 
 1926 
 
 43 
 
 43 
 
 43 
 
 43 
 
 43 
 
 43 
 
 43 
 
 43 
 
 43 
 
 43 
 
 43 
 
 43 
 
 1927 
 
 43 
 
 43 
 
 43 
 
 43 
 
 43 
 
 43 
 
 43 
 
 43 
 
 43 
 
 43 
 
 43 
 
 44 
 
 1928 
 
 44 
 
 44 
 
 44 
 
 44 
 
 44 
 
 44 
 
 44 
 
 44 
 
 44 
 
 44 
 
 44 
 
 44 
 
 1929 
 
 44 
 
 44 
 
 44 
 
 44 
 
 44 
 
 44 
 
 44 
 
 44 
 
 44 
 
 44 
 
 44 
 
 44 
 
 1930 
 
 44 
 
 44 
 
 44 
 
 44 
 
 44 
 
 44 
 
 44 
 
 44 
 
 44 
 
 44 
 
 44 
 
 44 
 
 1931 
 
 45 
 
 45 
 
 45 
 
 45 
 
 45 
 
 45 
 
 45 
 
 45 
 
 45 
 
 45 
 
 45 
 
 45 
 
 1932 
 
 45 
 
 45 
 
 45 
 
 45 
 
 45 
 
 45 
 
 45 
 
 45 
 
 45 
 
 45 
 
 45 
 
 45 
 
 1933 
 
 45 
 
 46 
 
 46 
 
 46 
 
 46 
 
 46 
 
 46 
 
 46 
 
 46 
 
 46 
 
 46 
 
 46 
 
 1934 
 
 46 
 
 46 
 
 46 
 
 46 
 
 46 
 
 46 
 
 46 
 
 46 
 
 46 
 
 46 
 
 46 
 
 46 
 
 1935 
 
 46 
 
 46 
 
 46 
 
 46 
 
 46 
 
 46 
 
 46 
 
 46 
 
 46 
 
 46 
 
 46 
 
 46 
 
 1936 
 
 46 
 
 46 
 
 47 
 
 47 
 
 47 
 
 47 
 
 47 
 
 47 
 
 47 
 
 47 
 
 47 
 
 47 
 
 1937 
 
 47 
 
 47 
 
 47 
 
 47 
 
 47 
 
 47 
 
 47 
 
 47 
 
 47 
 
 47 
 
 47 
 
 47 
 
 1938 
 
 47 
 
 47 
 
 47 
 
 48 
 
 48 
 
 48 
 
 48 
 
 48 
 
 48 
 
 48 
 
 48 
 
 48 
 
 1939 
 
 48 
 
 48 
 
 48 
 
 48 
 
 48 
 
 48 
 
 48 
 
 48 
 
 48 
 
 48 
 
 48 
 
 48 
 
 1940 
 
 48 
 
 48 
 
 48 
 
 48 
 
 49 
 
 49 
 
 49 
 
 49 
 
 49 
 
 49 
 
 49 
 
 49 
 
 1941 
 
 49 
 
 49 
 
 49 
 
 49 
 
 49 
 
 49 
 
 49 
 
 49 
 
 49 
 
 49 
 
 49 
 
 49 
 
 1942 
 
 49 
 
 49 
 
 49 
 
 49 
 
 49 
 
 49 
 
 49 
 
 49 
 
 49 
 
 49 
 
 49 
 
 49 
 
 1943 
 
 49 
 
 49 
 
 49 
 
 49 
 
 49 
 
 50 
 
 50 
 
 50 
 
 50 
 
 50 
 
 50 
 
 50 
 
 1944 
 
 50 
 
 50 
 
 50 
 
 50 
 
 50 
 
 50 
 
 50 
 
 50 
 
 50 
 
 50 
 
 50 
 
 50 
 
 1945 
 
 50 
 
 50 
 
 50 
 
 50 
 
 50 
 
 50 
 
 39 
 
 39 
 
 39 
 
 39 
 
 39 
 
 39 
 
 1946 
 
 39 
 
 39 
 
 39 
 
 39 
 
 39 
 
 39 
 
 39 
 
 39 
 
 39 
 
 39 
 
 39 
 
 39 
 
 1947 
 
 39 
 
 39 
 
 39 
 
 39 
 
 39 
 
 39 
 
 39 
 
 40 
 
 40 
 
 40 
 
 40 
 
 40 
 
 1948 
 
 40 
 
 40 
 
 40 
 
 40 
 
 40 
 
 40 
 
 40 
 
 40 
 
 40 
 
 40 
 
 40 
 
 40 
 
 1949 
 
 40 
 
 40 
 
 40 
 
 40 
 
 40 
 
 40 
 
 40 
 
 40 
 
 41 
 
 41 
 
 41 
 
 41 
 
 1950 
 
 41 
 
 41 
 
 41 
 
 41 
 
 41 
 
 41 
 
 41 
 
 41 
 
 41 
 
 41 
 
 41 
 
 41 
 
48 POPULAR GUIDE TO THE HEAVENS. 
 
 THE NAMING OF AN UNKOWN PLANET. 
 
 The beginner will sometimes notice a bright star-like object which he knows is not a 
 Star, for it is not represented on the maps. He infers that it must be a planet, and he desires 
 to find its name. 
 
 It may be assumed that the object must be one of the four bodies Venus, Mars, Jupiter, 
 or Saturn. With the aid of the Planetary Index it is a simple matter to determine which of 
 the four the unknown object must be. 
 
 We will illustrate the process by two examples : 
 
 Example 1. In May, 1905, a planet is seen in the south at midnight. It is 
 certainly, therefore, not Venus. Plate 43 shows that it is in Scorpio, and its 
 index number is 43. The index numbers in May, 1905, for Mars, Jupiter, and 
 Saturn are respectively, 43, 49, 46. The planet is therefore Mars. This might 
 also be inferred from the Table of Planetory Phenomena. Since the planet is 
 near the meridian at midnight it is close to opposition ; and in 1905 the table 
 shows that Jupiter is in opposition in November, Saturn in August, and Mars 
 in May. 
 
 Example 2. In April, 1916, two planets will be seen at 8 p.m., not far from one 
 another, fairly well up in the west, and a third is in the south. Name the 
 planets. Chart 40 gives the aspect of the sky at 8 p.m. in April, and the 
 planets in the west will be in Taurus or Gemini ; that in the south will be in 
 Leo, and its index number will be 40, the number of the chart. To find the 
 index numbers of the others we must turn to the chart which shows the region 
 between Taurus and Gemini on the central meridian, that is, to Chart 50. The 
 index numbers of the two planets in the west will probably both be 50, but may 
 possibly be 49 or 39. The indexes for April, 1916, give for Venus 50, for Mars 
 40, for Jupiter 48, and for Saturn 50. The planet in the south is therefore 
 Mars. In the west are Saturn and Venus ; the latter will be the brighter of 
 the two. 
 
BALL'S POPULAR GUIDE TO THE HEAVENS 
 
 Plate 3 9 
 
 January Midnight 
 
 itiul also as 
 
 Jan.? Midnight 
 
 Fel? JO. P.M. 
 
 Mc^k S. P.M. 
 
 April 6. P MfDti^iflfo) 
 
 May 4. P. M " 
 
 June 2. P M. 
 
 Sou ill 
 or at Sidei'ealTime 7^ 57 
 

 
 OF 
 
 ORNl 
 
BALL'SPOPUUARGUIDE TO THE HEAVENS 
 
 Plate 40 
 
 February Midnight 
 f o 
 
 ajid also as follows 
 
 Jan? 2. A.M. 
 Feb? Midnight 
 March lO.p'.M. 
 April 8. P. M. 
 May 6. P. 
 Jwie 4. PN. 
 
 July 2, P2(Da0itf*t 
 Auyt Noon 
 Sept r 10. A.M. " 
 Oet r 8. A.M. " 
 
 M. 
 
 M. 
 
 6. A. 
 
 l.A. 
 
 South 
 or at Sidereal Time 9 h 37 m 
 
 Z 3 4 
 
 
 
 ffeorye Pruti* A S,j 
 
BALL'S POPULAR GUIDE TO THEHEAVENS 
 
 Plate 41 
 
 Marr.li Midnight 
 
 curd also as follows 
 
 Jan.y 4. AM. 
 feb? 2. A.M.. 
 March Mi,liii,ilil 
 April 10. P M 
 May S.P K 
 June 6. 
 
 July 4. P.M. (Davliriht) 
 2. P.M. ' 
 
 South 
 or at Sidereal Time II 11 37 m 
 
 George FhjUp & Son 
 
BALL'S POPULAR GUIDE TO THE HEAVENS 
 
 Plate 42 
 
 April Midnight 
 
 and also as folio n-s 
 
 Jan? 6. A.M. 
 Fcb? 4. A.M. 
 
 Xai-ch 2. A.M. 
 
 July 0. P. MjDajhght, 
 Aug* 4.PM. 
 
 Sept? 2. P. M 
 
 South 
 or at Sidereal Time B 1 . 1 3? m 
 
 George. Philip <fe Son 
 
'VERS 
 
BALL'S POPULAR GUIDE TO THE HEAVENS 
 
 Plate 43 
 
 J, i.n-7 a, A.M. 
 
 Pel? 6. A.M. 
 
 M,n;-h 4. A.M. 
 
 April 2. A.M. 
 
 Ma-y Midnight 
 
 June. 10. P. K. 
 
 May Midnight 
 
 <m<l (i I so us follow* 
 
 . Inly 8 
 dug! 6. P. 11 
 SepT 4.PM 
 2 PM. 
 
 >n, 
 
 South 
 or at Sidereal Time 
 
 234 
 
 The Lond^JT'i. Geapraphi&il Irisa 
 
OF THE 
 
 "NIVERSITY 
 
BALL'S POPULAR GUIDE TO THEHEAVENS 
 
 Plate 44 
 
 Jan?' 10. A. M (Daylight] 
 
 F&b? a A.M. 
 
 M.u-clv 6. A.M. 
 
 April 4-, A.M. 
 May 2, A.M. 
 
 Jwr^e. 
 
 June Midnight 
 and also as follows 
 
 July 10. P.M. 
 
 Aiy! 8 . P. M. 
 Sf.ptT 6. P 
 
 oar 4. P. M. 
 
 2. P. M 
 
 South 
 or at Sidereal Time 17> 37 m 
 
" 
 
BALL'S POPULAR GUIDE TO THE HEAVENS 
 
 Plate 45 
 
 Jan r v Noon (tttLylight) 
 />/,:' 10. A.M. 
 M,i,:-h 8. A.M. 
 A/>ril 6 AM 
 
 M, 
 
 Jl 
 
 July Midnight 
 and a,2.s0 /.< fttunf 
 
 4. A.M. 
 
 2. 
 
 July MuJniijht 
 Septr 8. P. M. 
 
 Oct." 6. P.M. 
 
 JVov!' 4 P. M fDayliffht, 
 
 Dec.! 2PM. 
 
 South 
 or at Siclei-ealTime 19 h 37 m 
 
 2 3 4 
 
UN' 
 
BALL'S POPULAR GUIDE TO THE HEAVENS 
 
 Plate 4 6 
 
 Jan? 2. P.M.fDaylif/lit; 
 
 Fehr N&Ofl* 
 
 March. 10, AM. " 
 April 
 
 May 
 
 August Midnight 
 
 and, also us follows 
 
 July 2. A.M. 
 ? Midniaht 
 
 ^ 
 
 South 
 or at Sidevejaiime 2 
 
 
' ' **" ' - *r t> ^ 
 
 f . or - 
 
 (UNIVERSITY 
 
 \ OF 
 
BALL'S POPULAR GUIDE TO THE HEAVENS 
 
 PI ate 47 
 
 September Midnight 
 
 also a.s follows 
 
 J:tn .-' 4. P M/ 
 
 FeV 2. P. M. 
 
 Murch Nofin 
 
 April 10.A..M 
 
 Xnv 8. A M. 
 
 Jun<- H. A. If 
 
 Sozith 
 or at SidercalTime 
 
 orge Philip 
 
BALL'S POPULAR GUIDE TO THE HEAVENS 
 
 Plate 48 
 
 Jan? 6, P. M 
 
 Fcl? 4. P M.(DayKyhbl 
 
 Xarah -?, P M. 
 
 April \',>,m 
 Xa.ij W. A.M. 
 Ju.ne 8. A . M. 
 
 October Mi 
 
 o 
 
 an J. also fis fodowy 
 
 July 6, A 
 
 Aug? 4, A. ,!/ . 
 Sept r 2. A.M. 
 OctT Midrdaht 
 
 Nm. r LO.P.'M. 
 
 M . 
 
 South 
 or at SiderealTime'l 11 37 1 ! 1 
 
 The- IioruiaTi, GeoffrapJiLcaL 
 
OP THE 
 
 UNIVERSITY 
 
 OF 
 
BALL'S POPULAR GUIDE TO THE HEAVENS 
 
 Plate 49 
 
 Jan? 8. P.M. 
 Frb? 6. P.M. 
 Ma.r-.-Ji 4. P 
 April Z.P M. 
 Ma.\ Niton 
 June 10. A.M. 
 
 November Midniplit 
 
 o 
 
 O7i.cZ also CLS folltrws 
 
 JWy 8, A M. (Daylight I 
 Autjt 6, A.M. 
 Sep'tr 4. A.M. 
 2, A.M. 
 yht 
 
 South 
 or at Sidereal Time 
 
 LoncUm, GeoffraphLcal In,sta#u 
 
BALL'S POPULAR GUIDE TOTHEHEAVENS 
 
 Plate 50 
 
 December Midnight 
 
 mul ditto us Follows 
 
 
 South 
 
 or at SiderealTime 5 1 . 1 37 m 
 
 2 a <; 
 
 Geerge Philip & 
 
 rhe- London. GeagraphLcaL 
 
(49) 
 
 CHAPTER VII. TEE STAR MAPS. 
 
 PLATES 51 TO 70. 
 
 The student who has made himself familiar with the appearance and movements of the 
 Constellations, and has acquired a facility in identifying the brighter Stars, will soon feel the 
 need of something further. More especially will this be the case if he has the use of a 
 telescope of even moderate dimensions ; and it is to meet these requirements that the Star 
 Maps on Plates 51 to 70 have been prepared 
 
 The first step in drawing a map is to decide on the nature of the projection to be 
 employed. It must be understood that no flat maps can give a perfectly faithful representation 
 of a curved surface, and whatever method of projection is resorted to, the result must represent 
 the surface in a more or less distorted form. The Stars appear to be situated on the surface 
 of a sphere, and however we may attempt to depict them, we cannot include any large portion 
 of the sphere exactly as it appears to the eye. The form of projection which I have used 
 in these maps is that known as the conical projection, and in adopting it I follow Argelande; 
 who employed this method in his great Durchmusterung Atlas, which represents more th;m 
 300,000 Stars in the Northern Hemisphere alone. 
 
 Imagine two cones touching the sphere around the 
 circle of 45 declination, north and south. These are 
 intersected by tangent planes at the Poles, and by a 
 cylinder touching the sphere around the Equator; see ad- 
 joining figure. Each star on the sphere is joined to the 
 centre, and the joining line when produced necessarily 
 cuts some one of the enveloping surfaces in a point which 
 is the projection of the star. The equatorial girdle and 
 the two cones are each divided into six equal parts, 
 which admit of being laid out flat ; and the eighteen 
 parts thus obtained, together with the two polar planes, 
 make up the twenty maps which represent the entire 
 sphere. 
 
 The top and bottom margins of each of these maps, 
 with the exception of the first and last, are divided so 
 as to read Right Ascensions. 
 
 Only the hour lines have been drawn on the maps, 
 so as to avoid overcrowding, and for the same reason 
 only the circles corresponding to every tenth degree in 
 
 Declination have been given. But by the aid of the divisions around the margin, it is easy to 
 read the position of a star, or to enter any desired object with all requisite accuracy. For this 
 purpose it will be found convenient to copy the scale in Declination, which is given on the 
 margin of each map, on the edge of a sheet of paper. If, then, it is desired to enter on the map 
 the position of any object (say a comet) whose R. A. and Declination are known, it is only neces- 
 sary to set this sheet of paper so that the graduated edge cuts the top and bottom circles at 
 
50 POPULAR GUIDE TO THE HEAVENS. 
 
 the R.A. of the object, and to put a dot on the map at the point of the scale corresponding to 
 its Decimation. In the same way the position of any object entered on the map may be read 
 off. In the case of maps 51 and 70, the method of reading off positions is somewhat different 
 In these the declination scale will be found on the radius corresponding to O h -, 6 h -, 12 h - or 24h. 
 This scale should be rotated around the centre until it passes through the star whose position 
 is required. The R.A. will then be found at the point of the circumference where the scale 
 cuts it, and the Declination will be read from the scale itself. The epoch for which the places 
 are given is 1880. 
 
 It has been arranged that each zone of maps overlaps those north and south of it for a 
 distance of five degrees in Declination, and each map of a zone overlaps those preceding and 
 following it for a space of 40 mins. in R.A. 
 
 In order to avoid breaking up conspicuous star groups, I have made the zero, from which 
 the hour circles are measured, pass through the centre of the first map (No. 52) of the inter- 
 mediate zones, while the same circle divides the first and last maps of the equatorial zone- 
 By this mode of dividing the heavens it has been found possible to comprise each of the 
 more striking configurations of stars within a single map. The only exception is the great 
 square of Pegasus, which will be found on Plates 52, 58, and 63. For convenience in passing 
 from one map to another, the numbers of the plates which represent adjacent portions of the 
 sky have been printed just inside the margin. 
 
 In the construction of these maps I have followed, to a great extent, the Uranometrie 
 Generate of Houzeau. It contains all the stars visible to the naked eye under the most favour- 
 able circumstances, and the number amounts to nearly 6,000. 
 
 In the nomenclature of the stars, however, I have departed considerably from Houzeau, 
 doing away in general with letters (other than those of the Greek alphabet), and substituting, 
 wherever possible, Flamsteed's numbers. 
 
 I have followed Houzeau throughout in the estimation of star magnitudes, as by so doing 
 I obtained a uniform system over the whole sky, both in the Northern and Southern Hemi- 
 spheres, determined by a single observer in the same climate and within a short time. His 
 work, besides, is more recent than that of Argelander, Heis, or Behrmann. I have further, for 
 simplicity, limited the number of magnitudes given by Houzeau to six, namely, 1, 2, 3, 4, 5, 
 and 6, which will be found sufficient for all ordinary purposes. These I have indicated on the 
 maps themselves, as shown by the scale at the foot of each map, where, in addition to the size 
 of the dot representing the star, its magnitude is denoted by the number of rays diverging from 
 it. Thus all stars of the first magnitude possess 6 rays, those of the second magnitude 5 rays, 
 and so on. The magnitude of a star may be found by subtracting the number of the rays 
 from seven, except for the sixth magnitude, in which case the single ray has been omitted, stars 
 of this class being represented by a simple dot. 
 
 Throughout the maps a large number of the stars will be found accompanied by the 
 letter D. This signifies that the star, though appearing as a single body to the naked eye, 
 is in reality double. This does not however denote necessarily any physical connection 
 between the two stars, but merely that the point of light thus characterized will be 
 found to break up into two with the aid of a small telescope. In many cases there is 
 a real connection ; the two stars form a binary pair, and revolve round their common 
 centre of gravity under the action of their mutual gravitation ; a number of the most 
 interesting cases will be found in the list of select telescopic objects. In other cases, 
 the connection is merely apparent ; the stars happen to be nearly in the same direction as 
 seen from the solar system ; but they are probably at very different distances from us. 
 
THE STAR MAPS. 
 
 51 
 
 VARIABLE STARS. 
 
 A number of stars will be found in the maps marked (Var.), which indicates that 
 their light is not constant, but is subject to fluctuations, in some cases perfectly regular, 
 so that their times of greatest brightness can be predicted to the minute ; in other cases, 
 more or less regular, so that their maxima can be predicted to within a week or a month ; 
 in yet other cases, so irregular that no law has yet been found for their variation. In 
 the following tables I have given those variable stars which are plainly visible to the 
 naked eye at least at their maximum brightness. They may be easily identified from 
 the star maps. There are many hundreds of variable stars which never rise to naked 
 eye brilliancy, but for their identification means more elaborate than those of the present 
 work are required. Without detailed charts of the fainter stars it is very hard to find 
 them. For information regarding them the student is referred to the lists published in 
 the Companion to the Observatory; for their identification one needs the star maps of 
 Argelander's Durchmusterung, and of the Cordoba Durchmusterung, or, better still, the 
 Atlas of Variable Stars, published by Father Hagen, of Georgetown, D.C. 
 
 "ALGOL" VARIABLES. 
 
 There is a small class of stars whose type of variation is characteristic, and of which 
 the explanation is certain. The stars are partially eclipsed by a dark companion revolving 
 round them. Algol is the typical star, which has given its name to the group. 
 
 The type of variation of a variable star is best shown by the light curve. The light 
 curve of an invariable star is a horizontal straight line. A decrease of magnitude is shown 
 by the line dipping down, and if the curve is carefully drawn, so that equal distances 
 horizontally denote equal intervals of time, while equal intervals vertically denote equal 
 changes of magnitude, the curve is a complete representation of the light variability. 
 
 Thus, for Algol, the light curve is drawn thus : 
 
 Mag. 
 
 ao- 
 
 30 
 
 I9O3 
 Dec IO II 12 13 14 IS 16 17 18 
 
52 
 
 POPULAR GUIDE TO THE HEAVEXS. 
 
 and the interpretation is as follows. Daring the greater part of the time the light of 
 Algol is uniformly of magnitude, 2'3 ; but every 2 d. 20 h. 49 m. the star drops down 
 to magnitude 3'6, and without pausing regains its original light, the whole change occupying 
 9h. 20m. The figure further shows minima are predicted for 1903 (December 12th, at 
 about 9 o'clock in the evening, and for December 15th, at 6 o'clock). 
 The three Algol variables which are visible to the naked eye are : 
 
 Name. R.A. Decl. *W%. Period. 
 
 j8 Persei (Algol) 3 h - 0- +40 29' 2'3 to 3'6 2 d - 20 h - 49 m 
 
 X Tauri 3 54 + 12 9 3'4 to 4'2 3 22 52 
 
 ^Librae 14 55 82 5'0 to 6.2 2 7 51 
 
 These may be readily found from the star maps ; and the times when they undergo 
 eclipse may be found in the Companion to the Observatory. 
 
 SHORT PERIOD VARIABLES. 
 
 Our second class comprises stars which are regularly variable in periods of not many 
 days, but whose variation is not due to eclipse by a dark companion. In many cases 
 the spectroscope has shown that these stars are binary, and it is probably so in all ; 
 but the way in which the duplicity of the star explains its variation is quite uncertain. 
 The light variation is continuous, and by the shape of the light curves, these short 
 period variables are divided into two classes. In the first, the rise to maximum is steep 
 and the fall to minimum gentle ; in the second the curve is symmetrical. The two 
 types may be represented thus : 
 
THE STAR MAPS. 
 
 53 
 
 The following is a list of short period variables which rise above naked eye brightness. 
 They may be found upon the maps whose numbers are given in the last column. 
 
 R.A. Decl. 
 
 h. m. 
 
 Geminorum 6 57 4- 20 45' 
 
 V Puppis 7 55 - 48 5 
 
 N Velorum 9 28 - 56 30 
 
 I Carinse 9 42 - 61 57 
 
 X 3 Sagittarii 17 40 - 27 47 
 
 W 7l Sagittarii 17 57 - 29 35 
 
 YSagittarii 18 14 - 18 55 
 
 K Pavonis 18 45 - 67 23 
 
 /SLyrse 18 46 + 33 13 
 
 RLyme 18 52 + 43 48 
 
 T> Aquihe 19 46 +0 42 
 
 S Sagittse 19 51 +16 19 
 
 TVulpecula? 20 46 +27 48 
 
 o Cephei 22 55 + 57 48 
 
 In case the limits of variation are not well determined, the magnitudes are given 
 in round numbers. 
 
 Range. 
 
 Period in Days. 
 
 Map. 
 
 m. m. 
 
 
 
 3'7 to 4'5 
 
 10'15 
 
 59 
 
 4-4 to 5'2 
 
 2-25 
 
 66 
 
 3'4 to 4'4 
 
 Not well known 
 
 66 
 
 37 to 5'2 
 
 35'05 
 
 66 
 
 4 to 6 
 
 7-01 
 
 68 
 
 4'8 to 5'8 
 
 7'59 
 
 68 
 
 5'8 to 6'6 
 
 577 
 
 62 
 
 4'0 to 5'5 
 
 9'10 
 
 69 
 
 3'4 to 4'5 
 
 12-91 
 
 57 
 
 4'0 to 47 
 
 46'4 
 
 57 
 
 3'5 to 47 
 
 7-18 
 
 62 
 
 5 '6 to 6'4 
 
 8-38 
 
 62 
 
 5'5 to 6'5 
 
 4-44 
 
 57 
 
 37 to 4'9 
 
 5.37 
 
 52 
 
 LONG PERIOD VARIABLES. 
 
 These stars have periods which average between 300 and 400 days, and only one regular 
 variable is known to have a period greater than 600 days. Almost all these stars show at 
 maximum bright lines of hydrogen in their spectra ; they are mostly capricious in their 
 behaviour, rising higher at some maxima than at others, and sinking lower at some minima. 
 Nothing is certainly known as to the cause of their variability, but there is no reason to 
 suppose that it is due in any way to a companion. 
 
 The more conspicuous of the long period variables are as follows : 
 
 R.A. 
 h. m. 
 2 13 
 
 6 8 
 
 7 10 
 
 Decl. 
 
 Ceti (Mira) 2 13 3 32' 
 
 ? Geminorum 6 8 + 22 32 
 
 Lo Puppis 7 10 - 44 27 
 
 R Carhue 9 29 - 62 15 
 
 R Hydra) 13 23 - 22 40 
 
 X Cygni 19 46 + 32 37 
 
 R Cassiopeise 23 52 + 50 43 
 
 Where the magnitude given is followed by a colon ( : ) it is subject to irregularity. 
 
 Range. 
 
 Period in 
 
 Map. 
 
 
 Days. 
 
 
 3 : to 9 : 
 
 331 
 
 58 
 
 3'2 to 4 : 
 
 231 
 
 59 
 
 3'5 to 6'3 
 
 140 
 
 66 
 
 5 : to 10 : 
 
 309 
 
 66 
 
 4: to 97 
 
 425 
 
 61 
 
 5 : to 13-5 
 
 406 
 
 57 
 
 5 : to 12 
 
 429 
 
 52 
 
 IRREGULARLY VARIABLE STARS. 
 
 The stars in the first three classes vary in periods which are, on the whole, the less 
 regularly followed the longer the period. We now come to a class of stars which fluctuate 
 so irregularly that no law of variation has yet been discovered. In such cases the magnitudes 
 given are generally the highest and lowest which have been observed, and there is every 
 probability that the range may be exceeded at some time or another. 
 
54 
 
 POPULAR GUIDE TO THE HEAVENS. 
 
 T Ceti 
 
 a Cassiopeia? 
 
 P Persei 
 
 t Aiiri "roe 
 
 a Orionis 
 
 U Hydra 
 
 11 Carinee (/ Argus) 
 
 W Bootis 
 
 R Corona; 
 
 g Herculis 
 
 a Herculis 
 
 u Herculis 
 
 R Scuti .. 
 
 B.A. 
 
 h. in. 
 
 16 
 34 
 2 57 
 
 4 53 
 
 5 49 
 10 32 
 10 40 
 
 14 38 
 
 15 44 
 
 16 25 
 
 17 9 
 
 17 13 
 
 18 41 
 
 Decl. 
 
 -20 44' 
 
 + 55 53 
 
 + 38 22 
 
 + 43 38 
 
 + 7 23 
 
 - 12 46 
 
 -59 3 
 
 + 27 2 
 
 + 28 32 
 
 + 42 8 
 
 + 14 32 
 
 + 33 14 
 
 - 5 50 
 
 Range. 
 
 5 to 7 
 
 2'2 to 2'8 
 
 3'4 to 4'2 
 
 3'0 to 4'5 
 
 0-5 to 1-4 
 
 4'5 to 6 
 
 >1 to 7'4 
 
 5'2 to 6.1 
 
 5'8 to 13'0 
 
 5 to 6 
 
 3'1 to 3'9 
 
 4'6 to 5'4 
 
 5 to 9 
 
 Map. 
 
 58 
 52 
 53 
 53 
 59 
 60 
 67 
 56 
 56 
 56 
 62 
 56 
 62 
 
 TEMPORARY OR "NEW" STARS. 
 
 So called " new " stars are stars that have suddenly appeared once, and then faded away 
 They all seem to follow essentially the same course. They blaze up very suddenly, gradually 
 fade away, often with fluctuations, then appear to turn into small gaseous nebulae, and 
 finally, as has recently been shown, become merely very faint stars, very probably their 
 original condition. There is no theory that satisfactorily accounts for more than a part of 
 the facts known about them. 
 
 The following is a list of temporary stars which have been observed, arranged in order of 
 discovery. 
 
 Greatest br. R.A. 
 
 h. in. 1880. 
 
 1572 Tycho's Nova in Cassiopeia >1 018 
 
 1604 Nova in Serpentarius, discovered by Fabricius ... >1 17 23 
 
 1670 Nova in Vulpecula, discovered by Anthelm 3'0 1943 
 
 1848 Nova Ophiuchi, discovered by Hind 5'5 1653 
 
 1860 Nova Scorpii, discovered by Auwers in the 
 
 cluster Messier 80 7'0 1610 
 
 1866 Nova Coronse, discovered by Birmingham 2'0 1555 
 
 1876 Nova Cygni, discovered by Schmidt 3'2 21 37 
 
 1885 Nova Andromedae, discovered by Hartwig in 
 
 the Andromeda Nebula 7'0 037 
 
 1887 Nova Persei, No. 1., discovered on Harvard 
 
 photographs by Mrs. Fleming, 1895 9'0 1 54 
 
 1891 Nova Aurigae, discovered by Anderson, January, 
 1892, and afterwards found on a photograph 
 
 taken at Harvard, December 10th, 1891... 4 '5 5 24 
 
 1893 Nova Normae, discovered by Mrs. Fleming on 
 
 Harvard photographs 7 1520 
 
 1895 Nova Carinae, discovered by Mrs. Fleming on 
 
 Harvard photographs 11 3 
 
 1895 Nova Centauri, discovered by Mrs. Fleming on 
 
 Harvard photographs 7'2 13 33 
 
 1898 Nova Sagittarii, discovered by Mrs. Fleming, 1899 47 18 55 
 
 1899 Nova Aquilse, discovered by Mrs. Fleming on 
 
 Harvard photographs, 1900 7 
 
 1901 Nova Persei, discovered by Anderson O'O 323 
 
 1903 Nova Geminorum, discovered by Turner; on 
 
 Oxford Astrographic Chart plates 7 636 
 
 Decl. 
 
 + 63 29' 
 -21 22 
 + 27 1 
 -12 43 
 
 -22 41 
 + 26 15 
 + 42 18 
 
 + 40 37 
 + 56 9 
 
 + 30 21 
 
 -50 9 
 -61 18 
 
 -31 2 
 -13 19 
 
 + 43 30 
 
 + 30 4 
 
 Map. 
 
 52 
 62 
 57 
 
 62 
 
 62 
 56 
 57 
 
 52 
 53 
 
 53 
 
 68 
 67 
 
 67 
 62 
 
 53 
 
 54 
 
THE STAK MAPS. 55 
 
 METEOR SHOWERS. 
 
 In some of the maps will be found an asterisk, closely accompanied by a date. This 
 marks a region from which meteors may be expected about the date in question in the lan- 
 guage of the meteor observer, it is the radiant point of a meteor shower. It may be well, 
 however, to caution the beginner against expecting too much of a display from such a shower. 
 For most othe points a dozen meteors in the night rank as a rich display, and in many years 
 the radiants are almost completely quiescent. Many of the radiants seem to be persistent, 
 furnishing occasional meteors throughout the year : a fact for which no easy explanation is 
 forthcoming ; for if the meteors of one radiant really belonged to one system, one would 
 oxpect that radiant to shift during the year, as the radiant of the Perseids is supposed to do. 
 For information as to the smaller and sparser showers reference may be made to the memoir 
 by Mr. Denning (Memoirs, Royal Astron. Soc., Vol. LIIL). A list of radiant points is given 
 in the Companion to the Observatory. We may limit ourselves here to four principal 
 showers. 
 
 The LYRIDS. April 19-22. R.A. 18h. 8m., Declination + 34* 
 
 In some years this radiant gives a number of meteors ; in others they are almost entirely 
 absent. 
 
 The PERSEIDS. August 9-11. R.A. 3h. Om., Declination + 57 
 
 These are the well-known August meteors, which are, on the whole, the most reliable 
 shower of the year. They leave long, yellow streaks. For a month before the date of 
 maximum, similar meteors appear from radiants lying to the west of the above place, and it is 
 believed that they are a real case of a moving radiant. 
 
 The LEONIDS. November 12-14. R.A. lOh. Om., Declination + 23 
 This shower is visible more or less every November, giving swift meteors with greenish 
 streaks. For a number of centuries they had given brilliant displays every 33 years, but in 
 1899 and 1900 the expected display completely failed. It is fairly certain that the swarm had 
 been perturbed by the planet Jupiter. There is reason to believe that the swarm was 
 captured and introduced into the solar system by the planet Uranus in the year 126 A.D. 
 
 The ANDROMEDIDS. November. R.A. Ih. 40m., Declination + 43. 
 This is the shower associated with the lost Biela's Comet. Rich displays may be 
 expected with some certainty every thirteen years. Of late years the perturbations of the 
 planet upon the swarm have had the effect of throwing back the date of maximum and 
 number of days, and it is impossible at present to give exact dates for the future. 
 
 PLATES 71 AND 72. 
 
 As I have already pointed out, the region of the sky which corresponds to any one of 
 the general series of maps, is indicated by the dotted lines in the series of monthly maps 
 (Plates" 39 to 50). This, however, is chiefly useful at localities about the latitude of the 
 British Islands. For the convenience of those living in other latitudes, to whom it is hoped 
 this Atlas will recommend itself, as well as to enable the student at home to choose the 
 maps suitable for his purpose with greater rapidity, I have added the Northern and Southern 
 Index Maps (Plates 71 and 72). In these the principal constellations are marked, and the 
 outlines of each map of the general series, with the numbers of the corresponding plates in 
 bold figures. Each Index Map includes from the Pole to 25 beyond the Equator, so that 
 both contain the series of Equatorial maps. Around the circumferences is marked each hour 
 of R.A. The Declination is not indicated, but it can be ascertained with sufficient accuracy 
 for the purpose of finding the required map by remembering that the Equatorial zone extends 
 to 25 Declination, and the intermediate zones to 70 Declination, while each zone overlaps 
 that above and below it by 5. 
 
56 POPULAR GUIDE TO THE HEAVENS. 
 
 PRECESSION. 
 
 The Precession of the Equinoxes, or the slow motion of the Earth's axis, in Consequence 
 of which the intersection of the Equator with the Ecliptic travels along the latter, brings 
 about a constant change in the R. A. and Declination of the Stars from year to year. It is thus 
 clear that the values of these quantities as read from the maps will only be strictly accurate 
 at the epoch for which the maps are drawn. In order to find the R.A. and Declination for any 
 other date, it is necessary to apply a correction for this precessional effect, and if it is desired 
 to mark upon the maps the position of any star or other object whose co-ordinates are given 
 for a date different from that of the Atlas, a similar correction must be applied. 
 
 It must, however, be borne in mind that no change takes place from this cause in the 
 relative position of the stars, the effect being merely to give the whole system of Right 
 Ascension and Declination circles a shift, and thus to alter the positions of all the stars with 
 regard to them. 
 
 For accurate astronomical work, the correction for precession must in general be computed 
 to a small fraction of a second, and elaborate tables have been prepared to facilitate this 
 operation ; but for all purposes coming within the scope of the present work, the following 
 tables will be found amply sufficient. 
 
 That given on the next page contains the correction to the R.A. for 10 years' precession. 
 The quantity found in the table is to be added, with the sign there indicated to the R.A. at 
 any time, in order to obtain the K.A. for an epoch 10 years later, or it is to be subtracted to 
 find the R.A. at an epoch 10 years earlier. For intervals other than 10 years a proportional 
 allowance must be made. The top and bottom lines contain the Declination, and the first 
 and last columns the R.A. 
 
 For most purposes it will be sufficient in finding the precession to take the R.A. to the 
 nearest whole hour, and the Declination to the nearest multiple of 10 degrees. If the star is 
 situated in the Northern Hemisphere, we find its Declination in the first or last line, and run 
 the eye down the corresponding column till we reach the line which contains the star's R.A. in 
 the first column ; the corresponding figure in the table is the precession in R.A. for 10 years. 
 If the star is in the Southern Hemisphere, we look for its Declination as before, but we find its 
 R.A. in the last column. 
 
 The second table, containing the correction to the Declination for 10 years, is still more 
 simple. We have merely to enter it with the nearest hour of R.A. in the extreme columns, 
 and we find in the central column the corresponding correction to the Declination. For all 
 R.A.'s found on the left side the correction is positive, and negative for all those on the right 
 side. 
 
 The signs of the precessions given in both tables show the correction necessary to bring 
 the star's place up to a subsequent date ; to bring it back to an earlier date the signs must 
 be altered. The table of precession in R.A. extends to 70 north and south of the Equator, 
 so that it is applicable to all the stars except those around the North and South Poles, 
 contained in Plates 51 and 70. 
 
THE STAR MAPS. 
 
 TABLE FOR PRECESSION IN R.A. 
 
 57 
 
 R.A.forN.Decl. 
 
 
 
 10" 
 
 20 
 
 30 
 
 40 
 
 50 
 
 60 
 
 70 
 
 R.A.forS.Decl. 
 
 h. h. 
 
 m. 
 
 m. 
 
 m. 
 
 m. 
 
 m. 
 
 m. 
 
 m. 
 
 m. 
 
 h. h. 
 
 18 or 18 
 
 + 0-51 
 
 + 0-47 
 
 + 0-43 
 
 + 0-38 
 
 + 0-33 
 
 + 0-25 
 
 + 013 
 
 -O'lO 
 
 6 or 6 
 
 19 17 
 
 51 
 
 47 
 
 43 
 
 39 
 
 33 
 
 26 
 
 14 
 
 08 
 
 5 , 7 
 
 20 16 
 
 51 
 
 48 
 
 44 
 
 40 
 
 35 
 
 28 
 
 18 
 
 -0-02 
 
 4 , 8 
 
 21 15 
 
 51 
 
 48 
 
 45 
 
 42 
 
 38 
 
 32 
 
 24 
 
 + 0-08 
 
 3 , 9 
 
 22 14 
 
 51 
 
 49 
 
 47 
 
 45 
 
 42 
 
 38 
 
 32 
 
 -21 
 
 2 , 10 
 
 23 13 
 
 51 
 
 50 
 
 49 
 
 48 
 
 46 
 
 44 
 
 41 
 
 35 
 
 1 , 11 
 
 12 
 
 51 
 
 51 
 
 51 
 
 51 
 
 51 
 
 51 
 
 51 
 
 51 
 
 , 12 
 
 1 11 
 
 51 
 
 52 
 
 53 
 
 54 
 
 56 
 
 58 
 
 61 
 
 67 
 
 23 , 13 
 
 2 ., 10 
 
 51 
 
 53 
 
 55 
 
 58 
 
 61 
 
 64 
 
 70 
 
 82 
 
 22 , 14 
 
 3 9 
 
 51 
 
 54 
 
 57 
 
 60 
 
 64 
 
 70 
 
 78 
 
 0-94 
 
 21 , 15 
 
 4 8 
 
 51 
 
 55 
 
 58 
 
 62 
 
 67 
 
 74 
 
 85 
 
 1-04 
 
 20 , 16 
 
 5 7 
 
 51 
 
 55 
 
 59 
 
 64 
 
 69 
 
 77 
 
 88 
 
 1-10 
 
 19 , 17 
 
 6 6 
 
 + 0-51 
 
 + 0-55 
 
 + 0-59 
 
 + 0-64 
 
 + 070 
 
 + 078 
 
 + 0'90 
 
 + 1-12 
 
 18 , 18 
 
 E.A. forN.Decl. 
 
 
 
 10 
 
 20 
 
 30 
 
 40 l> 
 
 50 
 
 60 
 
 70 
 
 R.A.forS. Decl. 
 
 TABLE FOR PRECESSION IN DECLINATION. 
 
 R.A. 
 
 Precession. 
 
 R.A. 
 
 h. h. 
 
 
 h. h. 
 
 or 24 
 
 + 0'06 - 
 
 12 or 12 
 
 1 23 
 
 05 
 
 13 11 
 
 2 22 
 
 05 
 
 14 10 
 
 3 21 
 
 04 
 
 15 9 
 
 4 20 
 
 03 
 
 16 8 
 
 5 19 
 
 01 
 
 17 7 
 
 6 18 
 
 00 
 
 18 6 
 
 Example The star Capella is situated in 1880 in R.A. 5 h. 8 m., Declination + 45'9 : 
 find what its R.A. and Declination will be in 1905. 
 
 Entering the first Table with R.A. 5 h., and Declination 50, we find 10 years' precession 
 in R.A. is + 077 m. Hence the corresponding correction for 25 years will be to the nearest 
 whole minute + 2 m. 
 
 Entering the second Table with R.A. 5 h., we find 10 years' precession in Declination 
 is + 0- 01, hence to the tenth of a degree the correction for 25 years is negligible, so that 
 we find in 1905 R.A. = 5 h. 8 m. + 2 m. = 5 h. 10 m., and Decimation = + 45 '9. 
 
 If it were required to find the place of the star at the beginning of the century (i.e., 80 
 years previously), we have to multiply + 0'77 m. and + 0'01 by - 8, and we find the cor- 
 rections 6m. and 0'l, so that the place of this star in 1800 is R.A. 5 h. 2 m., Declina- 
 tion + 45'8. 
 
 As another example, let us find the R.A. and Declination of <" Draconis in 1940. Its 
 place in 1880 is 17 h. 38 m. ; + 68'8. We find from the Tables O'lO m. as correction for 10 
 years' precession, and 0'00 as the correction in Declination ; we thus obtain for 1940 R.A. = 
 17 h. 38 m. 0'6 m. = 17 h. 37 m. to the nearest minute, and Declination + 68'8. 
 
53 
 
 POPULAR GUIDE TO THE HEAVENS. 
 
 Once more, suppose that in 1950 it is announced that a comet has been seen in R.A. 3 h. 
 42'9 m., and Declination + 23'96. We find the precession in R.A. and Declination from the 
 tables to be, for 10 years, + 0'58 m. and + 0'03. Hence, to bring the place back to 1880, 
 we have the correction 4'1 m. and 0'21. We thus have 
 
 Comet's R.A. 
 h. m. 
 1950 3 42-9 
 
 Correction for Precession... 4*1 
 
 Comet's Declination. 
 
 + 23-96 
 0-21 
 
 18SO. 
 
 3 33-8 
 
 + 23-75 
 
 That is to say, the place occupied by the comet is indicated on these maps by the figures just 
 found for 1880, so that it would be found at the time of the announcement in the centre of 
 the group of the Pleiades. 
 
 The star maps of this work were drawn for the Epoch 1880, and as has been already 
 explained, they no longer give the R.A. and Declination of the stars as they are measured 
 to-day. It will be convenient if we add a table showing how much the system of circles 
 should be shifted on each map relatively to the stars, to make them approximately right for 
 the Epoch 1900, to which for a number of years the places of the stars will generally be 
 referred. 
 
 The following table gives the number of the map, and the amount the system of circles 
 must be shifted in millimetres. 
 
 52. 0'4 right. 0.2 down. 
 
 58. 0'4 right. 0.2 down. 
 
 64. 0'4 right. 0.2 down. 
 
 53. 0'6 
 
 , 0.1 
 
 59. 0'4 
 
 , 0.0 
 
 65. 0'3 
 
 0.1 
 
 54. 0'6 
 
 , 0.1 up 
 
 60. 0'4 
 
 , 0.2 up 
 
 66. 0'3 
 
 0.1 up 
 
 55. 0'4 
 
 , 0.2 
 
 61. 0'4 
 
 , 0.2 
 
 67. 0-4 
 
 0.2 
 
 56. 0'3 
 
 0.1 
 
 62. 0'4 
 
 , 0.0 
 
 68. 0'6 
 
 0.1 
 
 57. 0'3 
 
 , 0.1 down. 
 
 63. 0'4 
 
 , 0.2 down. 
 
 69. 0-6 
 
 0.1 
 
 It will be seen that for the purposes of these maps the change is almost insensible. 
 
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BALLS POPULAR GUIDE TO THE HEAVENS NORTHERN INDEX MAP 
 
 Plata 71 
 
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ULLS POPULAR GU.DE TO TKE HEAVENS SOUTHERN INDEX MAP 
 
 Plate 72 
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(59) 
 
 CHAPTER VIII. 
 
 PLATE 73. 
 THE GREAT NEBULA IN ORION. 
 
 The Great Nebula which lies around the central star in the Sword of Orion is dimly visible 
 to the naked eye as a blurring of the star disc. In the telescope it is a splendid object, full of 
 intricate detail. But to bring out its full beauty we must, as always with the nebula?, 
 photograph it. It is shown then as an object of extraordinary complexity, but without any 
 obvious plan. Enclosed in it are .many stars which certainly belong to it, and are not merely 
 seen by chance in the same direction ; for they share a typical spectrum whose characteristic 
 is lines of helium which are strong also in the nebula itself. 
 
 The nebula shown in the plate is only the brighter and central portion of a much larger 
 structure whose existence has recently been made clear, an immense spiral winding about the 
 whole constellation of Orion. In a sense, then, the more familiar nebula is to be ranked with 
 the spiral nebulae, yet it is clearly distinguished from them by its spectrum, which shows that 
 the light of the nebula comes from luminous gas, hydrogen, and helium, and the gas hitherto 
 undetected upon Earth which has been called nebulum. 
 
 Of the real size and distance of the nebula practically nothing is known, beyond the fact 
 that it is certainly immensely distant and large. And in this, as in many nebulas, we find 
 black holes with edges surprisingly sharp which are very hard to explain, except upon the 
 highly speculative assumption that they represent dark material structures of some kind 
 interposed between us and the shining nebula. 
 
 In this, as in all pictures taken with reflecting telescopes, the discs of the brighter stars 
 are disfigured by rays which are of purely instrumental origin. 
 
 This plate, and the one that follows, were taken at the Yerkes' Observatory, Chicago, 
 by Mr. Ritchey, with a reflecting telescope of two feet aperture made in the workshops of the 
 Observatory. They owe a part of their beauty to the fact that the negatives have been 
 reduced in the bright central portions which are inevitably over-exposed during the long time that 
 is required to photograph the faint outlying portions of the nebula. Only by such a process 
 is it possible to show on one plate the details both of the central and the remote parts of the 
 nebula. 
 
 PLATE 74. 
 THE GREAT NEBULA IN ANDROMEDA. 
 
 In a telescope of moderate power this Great Nebula appears almost structureless, a soft 
 elliptical mass of light steadily brightening towards the centre. In a large telescope, under 
 
60 POPULAR GUIDE TO THE HEAVENS. 
 
 exceptionally fine conditions, its outlying portions are seen to be furrowed with dark passages. 
 But no eye has ever seen directly a hundredth part of the structure that is revealed by photo- 
 graphy. Surrounding the central nucleus, which remains structureless, are a number of fainter 
 rings, or perhaps more probably the convolutions of a spiral it is almost impossible to say 
 which and the whole is mottled with brighter patches and perforated with dark holes of 
 remarkable sharpness. The light of the nebula is such as would be given by vast numbers 
 of stars crowded together that is to say, the spectrum is continuous, the light is white. But 
 in the present state of knowledge it is altogether premature to argue from that, that the 
 nebula is really an enormous system of stars very far away. The most we can say is that its 
 composition is certainly very different from that of the gaseous nebulae. 
 
 PLATE 75. 
 
 THE GREAT STAR-CLUSTER IN HERCULES 
 AND A NEBULA IN CYGNUS. 
 
 The photographs reproduced in this plate were taken by Mr. W. E. Wilson, at his 
 observatory at Daramona, Westmeath, with a two-foot reflector. 
 
 Star-clusters may be roughly divided into two classes : loose and condensed. Of the 
 former, the Pleiades cluster is the most conspicuous example. (See Plates 79 and 80.) The 
 stars in it do not crowd towards the centre ; on the contrary, the density of stars in the 
 centre of that cluster is less than the density in the surrounding sky ; but the individual 
 stars are brighter. In a globular cluster, on the other hand such as the Hercules cluster 
 small stars are so crowded towards the centre that, in all but the largest instruments, they 
 become indistinguishable from one another. 
 
 PLATE 76. 
 THE SPIRAL NEBULA IN CANES VENATICI. 
 
 This, the most famous of the Spiral Nebula, had its true character first recognised by Lord 
 Rosse with his great reflector at Parsonstown in Ireland. We are so happily situated with 
 respect to it that we get a fair side view of it, and can trace in considerable detail how its 
 branches are interlaced and studded with condensations which look as if they are on the way 
 to become stars. Recent photographic work has shown that a large proportion of the nebulae, 
 both known and hitherto unknown, are spirals, and this form must now be considered almost 
 the rule instead of the exception. 
 
 This photograph, and the two following, were taken at the Lick Observatory by the late 
 Professor Keeler, with the three foot Orossley Reflector, which was mounted at Baling by the late 
 Dr. Common, sold to Mr. Crossley, of Halifax, and afterwards presented by him to the Lick 
 Observatory, in order that it might be worked under skies more favourable than those of 
 England. 
 
NEBULA. 61 
 
 PLATE 77. 
 THE DUMB-BELL NEBULA. 
 
 It is a striking illustration of the power of photography in depicting nebulae, that it has 
 brought out a distinct resemblance between the Dumb-bell in Vulpecula and the Ring in 
 Lyra, which could hardly have been suspected from the visual appearance of those objects- 
 If we imagine the nebulosity, which exists inside the Ring, to shine a little more brightly, so 
 that it fills up the Ring, and at the same time imagine the tendency towards thinning out at 
 the ends of the longest diameter to be a little more pronounced, we shall see how easily the 
 Ring might be transformed into the Dumb-bell. Both are gaseous, and both have a central 
 star. It is difficult to resist the conclusion that the two nebuloe are closely related in kind. 
 
 PLATE 78. 
 THE RING NEBULA IN LYRA. 
 
 The Ring Nebula in Lyra can be easily found. It lies in the line from /3 to 7 Lyrse, 
 about one third of the distance from /3 to 7. It may be seen with a telescope of a few inches 
 aperture, but it is doubtful if any telescope in the world, excepting perhaps Lord Rosse's 
 reflector when in its finest condition, has ever shown to the eye so much as is presented in 
 the photograph here reproduced, which was taken by Prof. Keeler at the Lick Observatory, 
 with the Crossley Reflector. 
 
 The central star, which is so conspicuous on the photograph, is barely visible in the 
 largest telescopes. It is much brighter photographically than visually, probably because its 
 light is composed chiefly of those rays of short wave length to which the plate is sensitive 
 but the eye nearly insensitive. 
 
 The photograph shows quite plainly that the ring is not uniformly bright ; there are 
 even some indications that it is composed of several interlacing or over-lapping rings, and it is 
 remarkable how the ring thins out at the ends of its longest diameter. With longer 
 exposures the centre of the ring fills up, and the nebula becomes a disk. It follows that the 
 ring-like appearance is in a sense deceptive ; that the real shape of the nebula is something 
 like a hollow shell of gas, of which the borders look brighter, perhaps, because one is then 
 looking through a greater depth of the shining matter : but this is at best a conjecture. 
 What is certainly known is that the matter which shines is of the nature of self-luminous gas, 
 giving a bright line spectrum. About the distance and the real size of the object very little 
 is known, but it is practically certain that were our solar system placed in the centre of it, it 
 would all lie within the space covered by the photographic image of the central star. 
 
 A fine example of a nebula with no central condensation is that in Oygnus. (No. 6992 in 
 Dreyer's New General Catalogue.) Irregular and far-stretching nebulae such as this are not 
 uncommon in the Milky Way. They are probably all gaseous, and seem to belong to a class 
 altogether different from the spiral nebulae. 
 
62 POPULAR GUIDE TO THE HEAVENS. 
 
 PLATES 79 & 80. 
 THE PLEIADES. 
 
 Plates 79 and 80 are representations of the Pleiades made with telescope? of different 
 types. Plate 79 is from a photograph obtained by Dr. Isaac Eoberts with his reflecting 
 telescope of 20 inches aperture and 98 inches focal length a ratio of aperture to focal length 
 of about 1 : 5. Such an instrument is the most efficient kind of telescope for photographing 
 faint nebulosity, and with similar instruments at different observatories the photographs of 
 plates 73 to 78 have also been obtained. Plate 80 is engraved from a photograph made at 
 the Paris Observatory by the Brothers Henry with the .refracting telescope of 13 inches 
 aperture and 135 inches focal length, which is the standard pattern in use at eighteen obser- 
 vatories cooperating in making the photographic chart and catalogue of the heavens. Such 
 an instrument is not so suitable for photographing faint nebulae ; but it makes better photo- 
 graphs for measurement. And in presenting a series of the best pictures of some of the 
 most beautiful objects in the sky, one must not fail to call attention to the other branch of 
 astronomical photography, the making of plates which are not so pictorially effective, but 
 which are more suitable for accurate measurement. Year by year the measurement of 
 photographs replaces the older method of measurement at the telescope, and at the present 
 time (1903) several observatories have nearly finished their share of the great International 
 Photographic Catalogue of Stars mentioned above, which will include the places of about 
 2,000,000 stars. 
 
 The Pleiades cluster is the finest example of a loose cluster of bright stars intermixed 
 with nebulosity. And in this cluster the nebulosity is of a very remarkable character. It 
 takes the form in many places of long straight wisps connecting directly the brighter stars. 
 In examining Plate 79 care must be taken not to confuse these' with the eight symmetrical 
 rays proceeding from each of the brighter stars, which are caused by an instrumental defect 
 unavoidable in reflecting telescopes. Taking the key map to Plate 80 as a guide we may 
 trace on Plate 79 the straight extension of nebula from Electra towards Alcyone, the ray 
 proceeding from below Electra straight through the stars numbered 1 and 7, and the 
 remarkable ray which runs from star No. 10 in a straight line through several stars above 
 Alcyone and close below 24. Of a somewhat different character, yet still with a marked 
 tendency to arrangement in straight lines, is the nebula which involves Maia and Merope. 
 
 Even apart from the evidence of the connecting nebula, there is little doubt that the 
 Pleiades is a real cluster of bright stars, and not a chance gathering of stars seen nearly in the 
 same direction but at very different distances from us. Of relative motion among the stars of 
 the group there is little or none ; but the whole group is drifting together at the rate of 
 about 9" of arc per century past the other stars in the neighbourhood. 
 
 PLATE 81. 
 
 THE MILKY WAY, AROUND THE STAR-CLUSTER 
 
 MESSIER n. 
 
 This is a reproduction of one of the celebrated photographs of the " star clouds " of the 
 Milky Way, taken by Professor Barnard at the Lick Observatory in 1889. His description 
 
NEBULA. 63 
 
 of it is as follows : "The small cluster, Messier 11, lies on the upper or north edge of the 
 neck of the large cloud, and looks like a nucleus. The western side of the great cloud has 
 several rather sharply-marked indentations and several detached masses of stars. The star 
 j3 Aquilae, on the upper north edge of the great head, has two curious sprays of stars 
 extending from it, giving the appearance of a ram's horns. The great star-cloud seems to be 
 made up of very small stars, apparently very uniform in size. Near the lower right-hand 
 
 corner of the plate is shown a beautiful bright nebulous star The nebulosity about 
 
 this star is somewhat elliptical. It was discovered on the plates of 1899, and is quite 
 noticeable visually. The bright star near the N.E. edge of the plate is X Aquilae. The 
 great star-cloud seems to stretch out to and surround this star." 
 
 No less striking than the brilliant clouds of stars are the dark holes and lanes which 
 pierce them. These sharply-defined vacuities are characteristic features of the star-clouds, 
 and they give some cause for suspicion that there may exist in space regions of light-stopping 
 material which cut out the light of the stars beyond. It is difficult otherwise to account for 
 the existence of so many well-defined empty spaces in a field of stars otherwise so rich. 
 
 PLATE 82. 
 NOVA PERSEI AND THE NEBULA IN MOTION. 
 
 The appearance of a new star in Perseus was first observed by Dr. Anderson at 
 Edinburgh, on 1901, Feb. 21, at G-.M.T. 14h. 40m. The star was then of magnitude 27. 
 On the previous night a photograph had been taken by Mr. Stanley Williams at Brighton 
 which showed stars down to the 12th magnitude, but no trace of the Nova. It is, therefore, 
 certain that in little more than 24 hours the star must have increased in brightness more 
 than ten thousand times. On Plate 82 we have the photograph above mentioned ; and, for 
 comparison with it, a second photograph taken after the appearance of the star. So promptly 
 was the discovery made and the news circulated that on the evening of February 22nd the 
 star was under observation all over . the northern hemisphere, and it was found that the 
 brightness was still increasing. But in a few days it began to fail rapidly though with 
 very strongly-marked fluctuations until by midsummer it was invisible to the naked eye 
 while its spectrum, as is usual in such cases, had become that of a gaseous nebula. 
 
 In spite of the enormous amount of information which was given by this outburst 
 unsurpassed since the days of Tycho Brahe it does not seem that we are much nearer an 
 understanding of its cause. But one thing seems to be clear ^-the outburst of a new star is 
 not due to the collision of two dark bodies which are thereby raised to a transcendant heat. 
 
 Almost more remarkable than the star itself was the nebula which was discovered 
 around it in the autumn of 1901. The first satisfactory photograph of it was obtained at the 
 Yerkes Observatory on September 20th. On November 7th and 8th a photograph obtained 
 at the Lick Observatory showed that parts of the nebula were in rapid motion ; and the 
 same thing was found independently at the Yerkes Observatory on the 9th and 13th. In 
 the lower portion of our plate diagrams drawn to scale from the original negatives show 
 these changes unmistakeably. If the pointed structures, lettered a and e, are compared on 
 the two diagrams, and reference made to the surrounding stars and the scale at the side, it 
 
64 POPULAR GUIDE TO THE HEAVENS. 
 
 will be seen at once that these points have moved about a minute of arc in six weeks. Such 
 a rate of motion is unprecedented, and many theories have been advanced to account for it. 
 The most generally accepted theory is that there was around the star a complicated nebula 
 too faint to be photographed until it was lit up by the burst of light which proceeded from 
 the star ; and, that the motion which was observed was not a real motion of the nebula 
 itself, but the effect of successive lighting-up of different parts of the nebula as the light 
 passed outwards over it. It is scarcely possible otherwise to acconnt for a motion which 
 must have been at least very nearly equal to the velocity of light itself. 
 
BALL'S POPULAR GUIDE TO THE HEAVENS. 
 
 Scale : Minutes of Arc. 
 I 
 
 Plate 73. 
 
 fO 
 
 20 
 
 THE GREAT NEBULA IN ORION. 
 
 G. W. RITCHEY. 2-ft. Reflector, YERKES OBSERVATORY. 
 
BALL'S POPULAR GUIDE TO THE HEAV 
 
 Scale : Minute: of Arc. 
 
 _1 L_ 
 
 Plate 74. 
 
 10 
 
 20 
 
 SO 
 
 60 
 
 THE GREAT NEBULA IN ANDROMEDA. (M. 31 ) G. W. RITCHEY. 2-ft. Reflector, YERKES OBSERVATORY 
 
- L o 
 
 U D 
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 uJ O 
 
 OS "" 
 
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 dl 
 
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BALL'S POPULAR GUIDE TO THE HEAVENS. Scale : Minutes of Ar 
 
 Plate 76. 
 
 SPIRAL NEBULA IN CANES VENATICI. (M. 51) J. E. KEELER. Crossley Reflector, LICK OBSERVATORY. 
 
BALL'S POPULAR GUIDE TO THE HFAVCNS 
 
 Plate 77. 
 
 Scale : Minutes of Arc. 
 J | I 
 
 THE RING NEBULA IN LYRA. (M. 57.) 
 
 J. E. KEELER. Crossley Reflector. LICK OBSERVATORY. 
 
BALL'S POPULAR GUIDE TO THE HEAVENS. Scale : Minutes of Arc. 
 
 Plate 78. 
 
 IO 
 
 THE DUMB-BELL NEBULA IN VULPECULA J. E. KEELER. Crossley Reflector. LICK OBSERVATORY 
 
BALL'S POPULAR GUIDE TO THE HEAVENS. 
 
 10 20 
 
 Scale : Minutes of Arc. 
 
 30 40 
 
 Plate 79. 
 
 JO 6O 
 
 THE NEBUL/E IN THE PLEIADES. 
 
 ISAAC ROBERTS, 20-in. Reflector.Crowborough.Sussex. 
 
V 
 
- 
 
 '^. 
 
 
 
 ^^ 
 
V o' 
 
 
BALL'S POPULAR GUIDE TO THE HEAVFNS 
 
 Plate 81. 
 
 a 
 
 _L 
 
 9 
 
 _L 
 
 THE MILKY WAY AROUND THE STAR CLUSTER MESSIER II E. E. BARNARD, 6-in. Portrait Lens. LICK OBSERVATORY 
 
Plate 82 
 
 Scale : Degrees. 
 
 1901, February 20th. 
 Before appearance of Nova. 
 
 1901, February 28th. 
 The Nova. 
 
 NOVA PERSEI. Photographs by A. STANLEY WILLIAMS, Hove, Sussex. 
 
 Scale : Squares are Two Minutes of Arc. 
 
 N N 
 
 THE MOVING NEBULA SURROUNDING NOVA PERSEI. 
 1901, September 20th. 1901, November 13th. 
 
 Drawn by G. W. RITCHEY. from Photographs taken with the 24-in. Reflector, YERKES OBSERVATORY. 
 
A SELECT LIST 
 
 OF 
 
 STARS, STAR CLUSTERS, AND 
 NEBULA. 
 
(67) 
 
 CHAPTER IX. 
 
 A SELECT LIST OF STARS, STAR CLUSTERS, 
 AND NEBULAE. 
 
 In preparing a list of objects which are suitable for observation with small instruments 
 the author naturally turns in the first place to Admiral Smyth's "Celestial Cycle" for 
 suggestions ; and for the results of the most modern work upon those objects to Miss 
 Clerke's " Problems in Astrophysics," Dr. See's " Evolution of the Stellar Systems," and Prof. 
 Simon Newcomb's " The Stars : A Study of the Universe " ; to the " Companion to the 
 Observatory," the publications of the Royal Astronomical Society, and the scientific journals. 
 The student will find more extensive lists of interesting objects in Mr. Gore's " The Stellar 
 Heavens." 
 
 An attempt has been made in these notes to give some of the most recent results for the 
 distance, mass, &c. of the star systems. A very brief summary of the principles from which 
 these results have been deduced is here given : 
 
 Distance of the Stars. 
 
 Astronomers find it convenient to express the distance of a star from the solar system by 
 a quantity which is the apparent angular radius of the Earth's orbit as seen from the star ; 
 this quantity is called the annual parallax of the star. For example, the annual parallax 
 of a Centauri, our nearest stellar neighbour, is 0"'75 ; that is to say, the radius of the Earth's 
 orbit, as viewed from the star, would subtend an angle of three-quarters of a second of arc. 
 Since a unit of length viewed at a distance of 200,000 units makes an angle of a second of 
 arc very nearly, we have the following convenient rule : 
 
 To find how many million times farther away than the Sun any given star is : 
 
 Take the number expressing its annual parallax in seconds of arc ; multiply it by five ; 
 and find the reciprocal of the product. This is the number of millions required. 
 
 For example : The parallax of Capella is 0"'09. The reciprocal of 5 times 0'09 is about 2j. 
 Hence Capella is about 2j million times as far away as the Sun. 
 
 Distance of Star in Light -Years. 
 
 We have seen that astronomers generally express the distance of a star in terms of its 
 annual parallax, always a very small angle, which decreases as the distance of the star 
 increases. It is inconvenient to try to express the distances in the ordinary astronomical 
 unit of length, the distance of the Earth from the Sun ; the numbers are too large. But the 
 distance which light travels in one year makes a unit of convenient size. Thus, since 
 according to the best determination, the time taken by light to travel the distance R from 
 
QQ POPULAR GUIDE TO THE HEAVENS. 
 
 the Earth to the Sun is 498'46 sees., in one year (365d. 5h. 48m. 46s.) light travels about 
 3,300 R. 
 
 This is called a light-year. 
 
 And a star which has a parallax of 1" is distant 206,265 R. 
 
 Hence light would take 3'26 years to come from that star to the Earth. 
 
 And for any other star whose parallax expressed in seconds of arc is given, the time 
 
 3'26 
 taken by light to come from it to our system is allax 
 
 3'26 
 Example : The parallax of Capella is 0"'09. Hence light takes -^ ^ = about 36 years 
 
 on its journey. 
 
 Velocity of Star at Right Angles to the Line of Sight. 
 
 This can be found when the star's parallax and proper motion are known. If the star 
 has a parallax of 1" and a proper motion of l'', it moves during the year a distance at right 
 angles to the line of sight equal to the radius of the Earth's orbit,' that is, about 92,900,000 
 miles. This corresponds to a speed of 2'94 miles per second. If for any star we multiply 
 this number by the annual proper motion, and divide by the parallax, we get the velocity of 
 the star at right angles to the line of sight. 
 
 Example : a Lyrte. Proper motion 0"'36 ; parallax O'"08. Velocity at right angles to 
 
 line of sight = x 2 '94 = about 13 miles per second. 
 
 0'08 
 
 Brightness of Stars Compared with the Sun. 
 
 To give an account of the methods of comparing the relative brightness of the Sun and 
 stars would be beyond the limits of the present work. But the formula which represents 
 the relation is comparatively simple. If *r is the parallax of the star, m its magnitude, 
 -and r the ratio of its light to the light of the Sun removed to the distance of the star 
 
 4 1 
 
 logr = JQ (5 log-- m.). 
 
 Example : For Procyon we have mag. 0'47, parallax 0"'33 ; whence log. r = 0'77, r = 5'9 
 It should be noticed that estimates of this kind are very much affected by small 
 
 changes in the adopted value of the parallax of the star, and are therefore necessarily 
 
 rather uncertain. 
 
 Masses of the Stars Compared with the Sun. 
 
 Can bs found only for binary stars. 
 
 When a binary star has completed enough of a revolution to make it possible to compute 
 all the circumstances of its apparent orbit, it is possible to compute the shape and position of 
 the real orbit, which will differ from the apparent orbit, unless it happens to lie square to the 
 line of sight ; we also know its size in seconds of arc. If, in addition, we know the parallax, 
 i.e., the distance of the star, we know the length of the major axis of the real orbit in terms 
 of the distance of the Earth from the Sun. 
 
 For example : The major axis of the real orbit of the companion of Sirius about that star 
 subtends to us an angle 8"'03 ; the major axis of the Earth's orbit round the Sun subtends at 
 
A SELECT LIST OF STARS, STAR CLUSTERS; AND NEBULA. 69 
 
 the distance of Sirius the angle 0"'37 (the annual parallax). Hence the distance of its 
 
 8 '03 
 companion from Sirius is --r- times, = 217 times the distance of Earth from Sun. The 
 
 (j'o I 
 
 companion of Sirius revolves in 52'2 years. It follows from an extension of Kepler's 3rd law, 
 
 (21'7Y ! 
 that mass of Sirius + companion = ; 2 - mass of Sun + Earth. The mass of the Earth is 
 
 \&2t A)" 
 
 negligible compared with that of the Sun, and we have, therefore, on reducing the fraction, 
 Mass of Sirius + companion = 37 times mass of Sun. 
 
 Spectroscopy. 
 
 Without entering into the complicated theory and methods of spectrum analysis, it is 
 possible to indicate broadly the facts upon which spectroscopic determinations of various 
 kinds are based. 
 
 When the source of light is transparent glowing gas, the spectrum consists of a number 
 of isolated bright lines. 
 
 When the source of light is a glowing solid body, the spectrum consists of a continuous 
 rainbow band of colour, with no details at all. It is visible from the red to the violet ; below 
 the red it can be detected by its heating effects ; beyond the visible violet it continues for 
 some distance to affect the photographic plate. 
 
 If the hot solid body is overlaid by cooler layers of gas, dark absorption lines appear in 
 the continuous spectrum, in the exact places where bright lines would be seen were that gas 
 shining alone. 
 
 Upon this fact rests the possibility of determining what substances are present in the 
 vapours surrounding the Sun and stars, and in the nebulae. If iron, for example, is vapourised 
 in the electric arc its spectrum consists of bright lines. 
 
 In the spectrum of the Sun are found dark lines corresponding exactly in position with 
 each one of these bright lines. The conclusion is that iron exists in a state of vapour above 
 the Sun, relatively cooler than the glowing solid particles in the photosphere below. In a 
 similar way the presence of a great number of other elements is detected in the Sun 
 and stars. 
 
 Again, if hydrogen is made to glow electrically in a vacuum tube its spectrum consists of 
 certain bright lines. In the spectrum of a gaseous nebula bright lines are found in the same 
 positions. It follows that hydrogen is shining in the nebula. 
 
 But the comparative positions of these lines remain fixed only so long as the sources of 
 light are at rest with respect to one another. If a star is in motion with respect to the Earth 
 all the lines of its spectrum are slightly shifted towards the violet if the star is approaching, 
 towards the red if it is receding. By measuring the amount of this shift it is possible to 
 decide what is the velocity of approach or recession of the star. 
 
 Spectroscopic Binaries. 
 
 The velocities of a great number of stars relative to the solar system have been 
 measured by this method. In a great many cases the velocity has been found to vary 
 regularly in a definite period. The conclusion is that the star is in orbital motion round the 
 centre of gravity of itself and a companion. 
 
 In the majority of cases the companion does not give enough light to affect very much 
 
70 POPULAR GUIDE TO THE HEAVENS. 
 
 the spectrum of the principal star. In some cases, however, the two stars are nearly of the 
 same brightness. Then one star will necessarily be approaching while the other is receding, 
 and vice versd ; and the spectrum will be doubled, each star will show its own set of dark 
 lines, which will alternately close up on and open out from each other, and in such cases the 
 duplicity of the star is obvious, without need of reference to the positions of comparison lines 
 obtained terrestrially. 
 
 If the velocities in their orbits of the components of a binary are known, and the period 
 of revolution, it is possible to calculate the real size of the orbits, and thence the masses as 
 above. In the case of spectroscopic binaries one cannot usually solve the problem completely, 
 but can determine that the mass of the pair must be at least as much as a certain quantity. 
 
 35 Piscium. Oh. 10m. + 8 13'. 
 
 A fine, double star, 6th magnitude white, and 8th magnitude purplish. The components 
 appear to be relatively fixed, in position angle 150, and distance 12". 
 
 Globular Cluster 47 Toucani. Oh. 20m. - 72 39'. 
 
 A magnificent cluster containing about 1,500 stars within a radius of about 3'. Visible 
 to the naked eye as a hazy star, of light equivalent to 4 magnitude. The cluster contains 
 six variable stars. 
 
 Nebula M. 31 Andromedae. Oh. 37m. + 40 43'. 
 
 One of the most splendid nebulae in the sky, but not very interesting as a telescopic 
 object. The best way to see nebulae in the telescope is to set the instrument just ahead of 
 the nebula and allow it to drift into the field. If close attention is paid it is possible to see 
 in the Andromeda nebula certain dark and apparently straight lanes ; otherwise the nebula 
 appears almost structureless, fading away gradually from the bright centre. Its real 
 complicated structure can only be seen well in the photographs (see Plate 74), where it 
 appears as a fine spiral seen obliquely with a great deal of curious detail. Its spectrum is 
 continuous, and dark lines are suspected in it j it is not, therefore, it would seem, one of the 
 transparent gaseous nebulae. 
 
 i] Cassiopeia. Oh. 43m. + 57 17'. 
 
 A binary star of rapid motion, and large parallax. Magnitude 3 and 7$ ; distance 5'"68 ; 
 position-angle 226'4 (Maw, 1903'2). Its period is 196 years, and its parallax is 0"20. 
 From these data it may be concluded that the mass of this pair of suns is 1'8 times the mass 
 of our Sun, that their luminosity is together about equal to that of the Sun, and that their 
 mean distance apart is 41 times the distance of the Earth from the Sun. But the caution 
 should be given that all such deductions may be considerably modified by a small change 
 in the value of the parallax adopted ; and the numbers must be taken as examples of the 
 kind of information that these researches will give us, rather than as absolutely determined 
 quantities. 
 
 a Ursse Minoris (Polaris). lh. 23m. + 88 46'. 
 
 The Pole Star is the best known and most practically important star in the sky. On 
 account of its proximity to the North Pole of the sky it appears to the eye to be almost 
 
A SELECT LIST OF STARS, STAR CLUSTERS, AND NEBULAE. 71 
 
 devoid of the ordinary daily movement of the stars about the Pole. The -actual diameter of 
 the small'circle which it describes daily is 2 25' (1903), about five times the apparent 
 diameter of the Moon. The Pole Star can easily be found by the aid of the "pointers," 
 a and /3 Urste Majoris. It is a standard 2nd magnitude star, with a small 9th magnitude 
 companion distant 19" in position-angle 212. 
 
 It has been shown quite recently by Campbell that the Pole Star is a spectroscopic 
 binary, with a period of very nearly four days, and a slow orbital motion of four miles per 
 second. But irregularities have been found in this motion, and it seems probable that 
 Polaris has two dark companions. 
 
 y Arietis. lh. 48m. + 18 49'. 
 
 This star is interesting as having been discovered as a double star by Hooke, as early as 
 1664, when he was observing the Comet of that year "a like instance to which I have not 
 else met with in all the heavens." Magnitude 4*2, 4'4 ; distance 8"'3 ; position-angle 358. 
 Easily visible with a small telescope. 
 
 a Piscium. lh. 57m. + 2 17'. 
 
 A fine double star ; components about 3 and 4 magnitude ; distance 3|" ; position-angle 
 359. 
 
 7 Andromedae. lh. 58m. + 41 51'. 
 
 One of the finest double stars in the sky. Magnitude 2|, yellow, and 5^, blue green. 
 Distance 10"'2 ; position-angle 62. The blue star is itself a binary, distance 0"'45 (1903), a 
 difficult object at present in any telescope less than 12-in. aperture. The period of this small 
 binary is 55 years, and the eccentricity of its orbit is very great. In 1890 the stars were only 
 two or three-hundredths of a second apart, and no telescope could separate them. 
 
 i Trianguli. 2h. 7m. + 29 50'. 
 
 An exquisite double star, of which the primary is yellow, 5th magnitude, and the 
 companion blue, 7th magnitude. Distance about 3"'5, and position-angle 75. During the 
 80 years in which the star has been under observation there has been a slight diminution in 
 position-angle and increase in distance, so the star is probably a very slow binary. 
 
 The Star Clusters in Perseus. 2h. 12m. + 56 41'. 
 
 A splendid pair of clusters of bright stars, visible to the naked eye as a bright patch in 
 the Milky way, on the line joining a Persei with S Cas-iopei;)e, at about three-fifths of the 
 distance from the former. The preceding cluster contains two bright stars of the 7th 
 magnitude and a beautiful "horse-shoe" of 9th and 10th magnitude stars. The cluster 
 which follows about 3m. on the same parallel is not so fine, but contains two conspicuous 
 triangles of stars. 
 
 o (Mira) Ceti. 2h. 14m. - 3 26'. 
 
 A very remarkable variable star discovered three hundred years ago by the German 
 astronomer Fabricius, who was the first observer of sun spots with the telescope. It varies 
 
72 POPULAR GUIDE TO THE HEAVENS. 
 
 in a period of 330 days, more or less, from about the 3rd magnitude (on the average) down to 
 9 ; it is impossible to define its behaviour accurately since no two successive cycles are 
 similar. The student will readily find its place with reference to other stars from the charts, 
 and will find great interest in observing its variations. 
 
 Persei. 2h. 37m. + 48 49'. 
 
 An interesting triple star A of the 4th, B and C of the 10th magnitudes. A and B are 
 affected with the same proper motion, amounting to nearly 1" annually, and probably form a 
 binary system. Distance 17"'4, position-angle 299 (1900). C is at distance 80", and position- 
 angle 225 (1900), and does not share the proper motion of the other two, so that they are 
 rapidly separating from it. 
 
 7 Ceti. 2h. 38m. + 2 49'. 
 
 A beautiful double star, A3'0m. yellow, and B 6 '8m. b'ue, with common proper 
 motion. Probably a slow binary. Distance 3'"5 ; position angle 292. (1899). 
 
 9 Eridani. 2h. 55m. - 40 41'. 
 
 A fine double star for southern observers, magnitudes 3'5 and 5'5 ; distance 8"'2 ; position 
 angle 85. It is practically certain that this pair, now a star of the 3rd magnitude to the 
 naked eye, is identical with Ptolemy's " Last of the river " and with the Achernar of Al-Sufi, 
 who describes it as of the first magnitude. This is one of the clearest cases of a star having 
 lost a large percentage of its light within historical times. 
 
 ]3 Persei (Algol). 3h. 2m. + 40 34'. 
 
 The most famous variable star in the sky. Every 2d. 21h. its light suddenly begins to 
 diminish from magnitude 2'4, until in a little over 4 hours it has sunk to 3'6 ; without any 
 appreciable pause it then rises again in nearly the same time to its normal brightness. The 
 conjecture that this is due to an eclipse by a dull companion has been confirmed by the 
 spectroscope. Algol is thus a spectroscopic binary whose plane passes nearly through the 
 solar system. This being determined we have the following data : Velocity of Algol in 
 orbit 26 miles per second ; radius of orbit 1,000,000 miles. Diameter of bright star about 
 1 ,000,000 miles ; of dull companion about 800,000. In default of a knowledge of the mass 
 of the companion we cannot determine the separation in miles of the two stars, but they 
 must be relatively very cl%e together, only a few million miles apart. If we assume 
 that the two stars have the same density, their masses are nearly in the ratio of 2 : 1, and 
 their distance apart about 3j million miles. They, like all eclipsing variables, seem to be a 
 great deal less dense than the Sua 
 
 The Pleiades. Central Star, Alcyone. 3h. 41m. + 23 48'. 
 
 The well known naked eye cluster of bright stars, seen to greatest advantage in a 
 telescope of low magnifying power. Most of the brighter stars have a common proper 
 motion, and form, without doubt, a real group. Although the cluster is so rich in bright stars 
 it contains actually fewer fainter stars than equal areas of the surrounding sky. The cluster 
 is full of nebulosity which has an apparent connection with the stars. (See Plate 79). 
 
A SELECT LIST OF STARS, STAR CLUSTERS, AND NEBUL.E. 73 
 
 a Tauri (Aldebaran). 4h. 30m. + 16 18'. 
 
 This star, Mag. 1'2, conspicuous for its ruddy colour, is the principal object in the group 
 of the Hyades. (Map 59). Its proper motion is 0"'19 and parallax 0"'12, whence its light 
 is about 23 times that of the Sun, and its motion across the line of sight about 4 miles per 
 second. An occupation of Aldebaran by the Moon, which not infrequently occurs, 
 is a striking phenomenon. 
 
 a Aurigae (Capella). 5h. 9m. + 45 54'. 
 
 One of the brightest stars in the sky. Newall and Campbell found independently that 
 it is a spectroscopic binary, components unequally bright, but nearly equal in mass, moving 
 in orbits of radius about 50,000,000 miles in a period of 104 days ; joint mass about seventeen 
 times Sun. The parallax of the stars has been carefully determined as 0"'08 ; and this implies 
 that the stars give together about 130 times as much light as the sun ; they must there- 
 fore be much brighter mass for mass. From the data just given it is easy to see that they 
 might be seen telescopically as a double star with distance 0"'l, and the Greenwich observers 
 believe that they have seen the star elongated though not clearly divided. 
 
 Proper motion 0"'43 ; annual parallax 0"'08, whence its velocity at right angles to the 
 line of sight is about 16 miles per second. 
 
 Nebula M. i Tauri. oh. 29m. + 21 57'. 
 
 The " Crab " nebula, so called by Lord Rosse because of the claw-like protuberances 
 which he observed. In a small telescope it is not very interesting ; but it is famous as the 
 object which induced Messier to draw up his celebrated catalogue of nebulae, by the numbers 
 of which the brighter nebulae are known to this day. The Crab Nebula is No. 1. 
 
 Orionis. 5h. 29m. - 5 28'. 
 
 A splendid multiple star involved in the brightest part of the great nebula in Orion. 
 Four bright stars, of magnitude 6, 7, 7i, and 8, are the well-known " trapezium." There are 
 a number of fainter stars included in the group. 
 
 (T Orionis. 5h. 34m. - 2 39'. 
 
 A very fine multiple star. In small telescopes it presents the appearance described by 
 Sir William Herschel of " a double-treble star, or two sets of treble stars almost similarly 
 situated." Larger instruments show a number of other stars, and Burnham has found that 
 the brightest star is itself double, and a rapid binary. 
 
 Orionis. 5h. 36m. - 2 0'. 
 
 This, the following of the three stars in Orion's belt, is a fine double, with a distant 
 faint companion. The components of the double are of magnitude 2 and 6 ; distance 2"'4 ; 
 position-angle 156, slowly increasing. The faint companion, magnitude 10, is in position- 
 angle 9, at distance 57". 
 
74 POPULAR GUIDE TO THE HEAVENS. 
 
 Cluster M. 37 Aurigae. 5h. 46m. + 32' 31'. 
 
 A magnificent cluster of small stars, loose and little condensed. It does not appear that 
 there is any nebulosity in this cluster, though in small instruments the crowd of small stars 
 presents the appearance of it, " Even in smaller instruments extremely beautiful, one of the 
 finest of its class. Gaze at it well and long." Webb. 
 
 a Orionis (Betelgueuse). 5h. 50m. 4 7 23'. 
 
 A bright yellowish-red star, whose light is somewhat variable, about 0'9 usually. Like 
 nearly all stars in the constellation of Orion it has a small proper motion, 0"'027 per 
 annum, and a small parallax, 0" - 024. It follows that this star gives several hundred times 
 the light of the Sun, but its motion across the line of sight is slow, about 3 miles per second. 
 
 |3 Aurigae. oh. 52m. + 44 56'. 
 
 Telescopically a single star. But the lines in its spectrum appear alternately double 
 and single every 48 hours, and the displacement indicates a relative velocity of 150 miles a 
 second. It follows that the star is double, with components nearly equally bright, revolving 
 in a period of just less than 4 days. The orbit is somewhat eccentric ; the stars are at least 
 7,500,000 miles apart, and their combined mass 4| times that of the Sun. 
 
 Star Cluster M.35 Geminorum. 6h. 3m. + 24 21. '. 
 
 A fine and bright, but loose cluster of stars, without much trace of the condensation 
 towards the centre which characterizes a globular cluster. 
 
 II Monocerotis, 6h. 24m. - 6 57'. 
 
 A very striking triple star, A of the 5th magnitude, B and C of the 6th. B is in position 
 angle 131 and distance 7" ; C in 120, distance 9|". There is no evidence of relative motion 
 in this system. 
 
 a Canis Majoris (Sirius). 6h. 41m. - 16 34'. 
 
 The brightest star in the sky, Mag. - T6, of large proper motion, and large parallax. 
 Irregularities in its proper motion suggested that the star must have a companion, which was 
 discovered in 1862. Its magnitude is about 9, but it is visible only in the largest telescopes 
 being very hard to see on account of its nearness to the brilliant primary. In 1903'! its 
 distance was 6"'3, in position angle 128. The parallax of Sirius as determined by Gill and 
 Elkin is 0"'37. The period of the companion is 52 years, and mean distance from Sirius 8" '03- 
 From these data we may conclude that the total mass of the pair is 3'7 times that of the Sun, 
 but their combined light is 32 times ; that their distance apart is 22 times that of the Earth 
 from the Sun. From the irregularity in the proper motion of Sirius it may further be, 
 shown that Sirius is only about twice as massive as its companion, though it is 10,000 
 times as bright. The great intensity of the light of Sirius, 30 times that of the Sun, with only 
 2| times its mass, and the dimness of the companion are very remarkable. 
 
 a Geminorum (Castor). 7h. 28m. -f 32 6'. 
 
 A very fine double star, one of the best objects for small telescopes. Magnitude 2'0 and 
 2'8 ; distance (1902) 5"7 ; position angle 223. Period of revolution about 1,000 years. The 
 
A SELECT LIST OF STARS, STAR CLUSTERS, AND NEBULA. 75 
 
 interest of this system has been greatly increased by the discovery that the fainter component 
 is a spectroscopic binary with a heavy dark companion. Period 2 95 days ; velocity of bright 
 star in orbit 22 miles per second ; radius of orbit at least 1,800,000 miles. 
 
 a Canis Minoris (Procyon). 7h. 34m. + 5 29'. 
 
 One of our nearer neighbours among the stars. Annual parallax 0'"33 ; proper motion 
 1"'25 ; Mag. 0'47, whence its light is about six times that of the Sun, and its velocity at right 
 angles to the line of sight about 1 1 miles a second. 
 
 A binary star with a faint but relatively very massive companion, whose presence first 
 became known by the large irregularities which its attraction produces in the motion of the 
 principal star. The disturbing companion was at last discovered with the great Lick 
 telescope in 1895. Its mass is about equal to that of the Sun, but the light that it gives 
 is very much less, perhaps about one-thousandth. 
 
 4 Cancri. Sh. 6m. + 17 59'. 
 
 One of the most remarkable multiple stars in the heavens. It is composed in the first 
 place of two stars, A and B, of the 5 and 57 magnitude respectively, whose orbit has been 
 well determined. These two revolve around each other, in a period of 60 years, at a distance 
 of less than 1", and are accompanied by a third star, C, of 5 '5 magnitude, which revolves 
 around the centre of gravity of all in an opposite direction. From irregularities in the 
 motion of C, which take place in a period of 17| years, it i-i concluded that it is but a satellite 
 of an invisible body around which it revolves in that time, describing an ellipse with a radius 
 of about one-fifth of a second, and that the two together circle around A and B in 600 or 
 700 years. 
 
 Cluster M.44 Cancri. Sh. 34m. + 20 21'. 
 
 A large and loose cluster of stars known as Prsesepe, or the Bee-hive. To the naked eye 
 it appears as a nebulous patch of light a little south preceding 7 Cancri. A fine object in 
 small telescopes. 
 
 Hydrae. 8h. 42m. + 6 50'. 
 
 A beautiful triple star. A and B are respectively of the 4th and 6th magnitude, and are 
 so close that only the most powerful telescopes can separate them. Position-angle 23", 
 distance 0"'13 (1902), yellow. The companion C is 7th magnitude, blue, in position-angle 
 234, distance 3"'47 (1902). 
 
 a Leonis (Regulus). lOh. 3m. + 12 27'. 
 
 This bright star (magnitude 1'23) has quite a large proper motion, 0"'27 per annum, but 
 a small parallax, 0"02, whence it follows that its light must be equal to that of 1,000 of 
 our Suns. 
 
 7 Leonis. lOh. 14m. + 20 22'. 
 
 A very fine double star, orange yellow. Magnitude 2 and 4 ; distance 3" '81 ; position 
 angle 1157 (1903.8, Lewis). Binary with a period of about 400 years. 
 
76 POPULAR GUIDE TO THE HEAVENS. 
 
 Planetary Nebula H. IV. 27 Hydrae. lOh. 20m. - 18 8'. 
 
 A typical planetary nebula, whose light is equal to that of an 8th magnitude star. 
 Admiral Smyth describes it as "resembling Jupiter in size, equable light, and colour," 
 though of course it is not nearly so bright. Its spectrum consists of bright lines, and it is 
 therefore gaseous. 
 
 i] Argus. 10h. 41m. - 59* 10'. 
 
 This, one of the most remarkable stars in the sky, set in the middle of one of the most 
 remarkable nebulae, is unfortunately too far south to be visible in European latitudes. 
 During the 18th and early part of the 19th centuries it was a naked-eye star between the 
 2nd and 4th magnitude. In 1837 it rose quickly in brightness to first magnitude, faded a 
 little, and in 1843 rose very nearly to the brightness of Sirius. In the following 30 years it 
 sank steadily to magnitude 7, where it remains. Its spectrum is of the peculiar type 
 associated with the temporary stars, and it seems to differ from them principally in being 
 semi-permanent. 
 
 Planetary Nebula M. 97 Ursae Majoris. lib. 9m. + 55 34'. 
 
 In small telescopes a faintly luminous disc about the size of Jupiter. In very large 
 telescopes it appears to have a very complicated structure. The Earl of Rosse found two 
 condensations surrounded by spirals in opposite directions, from which it obtained the name 
 of the " Owl Nebula." This, like nearly all planetary nebulae, gives a spectrum of bright 
 lines, and is therefore gaseous. 
 
 I Ursae Majoris. lib. 13m. + 32 6'. 
 
 A beautiful double star, rather close for small telescopes. Magnitude 4 and 5 ; distance 
 2"'3; position-angle 144 (1902). Period about 60 years. The brighter component has been 
 shown to have a variable velocity in the line of sight, which shows that there is a third star 
 in the system, but the data are not yet complete. 
 
 This star was one of the first stars recognized as binary, having components which move 
 about their common centre of gravity in accordance with the law of universal gravitation, 
 and it was actually the first whose orbit was computed on gravitational principles. 
 
 i Leonis. lib. 19m. + 11 5'. 
 
 A rather close double star. A, 4th magnitude, pale yellow, and B, 7i magnitude, blue. 
 Position-angle 53 ; distance 2"'17 (1900). There is considerable relative motion, and it is 
 almost certainly a binary. 
 
 24 Comae. 12h. 30m. + 18 56', 
 
 A fine, but wide, double star. A, 5^ magnitude, orange, and B, 7 magnitude, blue. 
 Position-angle 271 ; distance 20". The colours form " a striking and beautiful contrast." 
 
 a Crucis- 12h. 21m. - 62 33'. 
 
 This, the brightest star in the Southern Cross, is a very fine triple star. Magnitudes 1'5, 
 1'8, and 6 ; the bright stars a fairly close pair, distance 5"'0, position-angle 118; and the 
 fainter, distant 90" in position-angle 202. The parallax of the bright stars is 0"'05. 
 
A SELECT LIST OP STARS, STAR CLUSTERS, AND NEBULA. 77 
 
 y Virginia. 12h. 37m. - 54'. 
 
 A most interesting binary system, consisting of two stars of the 3rd magnitude ; distance 
 5"'74 ; position-angle 328'l (1902). Period about 194 years. Its orbit is very eccentric. 
 In 1831 the distance was 1"'5, and in 1832 Sir John Herschel predicted that within the next 
 year or two it would close up to such an extent that " none but the very finest telescopes 
 will have any chance of showing this magnificent phenomenon." This prediction was verified 
 in 1836, when the Dorpat refractor alone was able to elongate the star. 
 
 a Canum Venaticorum. 12h. 51m. + 38 52'. 
 
 A very easy and interesting double, showing no signs at present of a binary character. 
 Magnitude 3 and 6 ; distance 19" '8 ; position-angle 227. This star was named Cor Caroli 
 by Halley, at the suggestion of the court physician, who believed that it appeared more 
 brilliant than usual on the evening before the return of King Charles II. to London. 
 
 Ursae Majoris. 13h. 20m. + 55 27'. 
 
 Probably the best known double star in the sky, and certainly one of the easiest to find 
 and most effective to look at in a small telescope. It is the middle star of the Bear's Tail. 
 Magnitude 2'1 and 4'2 ; position-angle 147'4 ; distance 14"'4 ; revolution very slow. The 
 larger star of this pair is itself double, though telescopically single. It was the first 
 discovered spectroscopic binary. Both components are bright, and of nearly equal magnitude. 
 They revolve in 20 clays 14 hours, in an eccentric orbit ; their combined mass is at least four 
 times that of the Sun, and they are many times more luminous. 
 
 About 11' away is the 5th magnitude star, Alcor, forming, with Ursse, the best-known 
 example of a naked-eye pair. 
 
 a Virginia. 13h. 20m. - 10 38'. 
 
 A first magnitude star whose spectrum is shifted backwards and forwards every four 
 days by an amount denoting a revolution at the rate of 57 miles a second round the common 
 centre of gravity of itself and a companion whose spectrum is just perceptible. Combined 
 mass at least 2j times Sun. 
 
 Globular Cluster Centauri. 13h. 21m. - 46 57'. 
 
 The finest cluster of its kind in the sky, containing about 6,000 stars in a space of about 
 20' diameter. Visible to the naked eye as a hazy comet-like object, giving as much light as 
 a 4th magnitude star. The cluster contains 125 variable stars, of which 98 have periods less 
 than 24 hours. 
 
 Cluster M. 3 Canum Venaticorum 13h. 38m. + 28 53'. 
 
 A very fine cluster of stars of the llth magnitude and fainter, not very easily resolvable 
 with small telescopes. This cluster is extraordinarily rich in variable stars ; no less than 132 
 out of 900 stars examined are regularly variable, many of them in very short periods. 
 
 a Bootis (Arcturus). Hh. llm. + 19 42'. 
 
 The brightest star of the northern sky, with the very large proper motion of 2"'27 per 
 year, which in the course of 1,600 years carries it across a space in the sky equal the apparent 
 
78 POPULAR GUIDE TO THE HEAVENS. 
 
 diameter of the Sun or Moon. Yet its parallax with respect to the fainter surrounding stars 
 is small only 0" 026 (Chase), whence it follows that its velocity at right angles to the line of 
 light is about 200 miles a second, and its light is many hundred times that of the Sun. 
 
 a Centauri. 14h. 33m. - 60 25'. 
 
 A splendid binary star. Components of the first magnitude ; distance 2l'"6 ; position- 
 angle 211 (1902). Period 81 years. This is the nearest star to the Solar System, with a 
 parallax 0"75. The masses of the stars are very nearly equal, and one of them is in spectrum 
 and in mass an almost precise counterpart of our Sun. The semi-major axis of the orbit 
 is 23'6 times the length of the distance from Earth to Sun, or about a mean between the 
 distances of Uranus and Neptune. 
 
 Bobtis. Hh. 41m. + 27 30'. 
 
 A most beautiful binary star. Magnitude 3, yellow, and 6|, blue ; distance 2'"65 ; 
 position-angle 328'4 (1900.5). 
 
 Bootis. 14h. 47m. + 19 31'. 
 
 A very interesting binary star of great eccentricity of orbit. A, magnitude 45, yellow ; 
 B, magnitude 6'5, purple. According to See's orbit, published in 1896, the period is 128 
 years ; but inasmuch as the place predicted from his orbit for 1903.5 was 154'7, 1"'25, 
 whereas at that time it was measured as 186'9, 2" "36, it is evident that this orbit requires 
 modification. 
 
 Cluster M. 5 Librae. 15h. 14m. + 2 27'. 
 
 A globular cluster of faint stars remarkable for the number which are variable, about 
 one in eleven, in periods mostly about 12 hours. 
 
 a Coronas. 16h. llm. + 34 7'. 
 
 An interesting binary star, with a period probably about 400 years. A, 6th magnitude, 
 yellow ; B, 7th magnitude, bluish. Position-angle 210 ; distance 4"'38 (1900). The stars 
 were at their closest about 1830, when their distance was only a little more than 1" ; since 
 that time they have been gradually opening out, and will continue to do so yet for about 
 100 years. 
 
 a Scorpii. 16h. 23ra. - 26 13'. 
 
 This fine reddish first magnitude star, the heart of the Scorpion, has a green 7th 
 magnitude companion at a distance of 3", in position-angle 270 ; but it is not easy to 
 see on account of the glare of the bright star. 
 
 Herculis. 16h. 38m, + 31- 47'. 
 
 A rapid binary star, which has performed more than three complete revolutions since it 
 was discovered by Sir William Herschel on July 18th, 1782. A is 3rd magnitude, yellow ; 
 and B is 6th magnitude, bluish. Its period is about 35 years, and the greatest separation of 
 
A SELECT LIST OP STARS, STAR CLUSTERS, AND NEBULAE. 79 
 
 the components l". The companion passed periastron last in 1899 at a distance of 0"'5 ; 
 since then it has opened out considerably, and a recent observation gives position-angle 
 205'6, distance 1"'04 (1902'5). There is considerable evidence that the companion varies in 
 colour from red to blue. 
 
 Globular Cluster M. 13 Herculis. 16h. 38m. + 36 37'. 
 
 The finest globular cluster in the northern sky, and effective even in a small telescope, 
 thoiigh the richest parts of the cluster can scarcely be resolved in the largest instruments. 
 The whole contains at least 5,000 stars, of which only two of a thousand examined proved to 
 be variable. 
 
 /ii Scorpii. 16h. 45m. - 37 53'. 
 
 Shown by the spectroscope to be a binary star with the short period of 34 hours 
 42 minutes. The two components have at maximum a relative velocity of nearly 300 miles 
 a second ; this gives their separation as at least 6,000,000 miles ; and this their combined mass 
 as at least 15 times that of the Sun. 
 
 a Herculis. 17h. 10m. + 14 30'. 
 
 One of the finest coloured double stars. Magnitudes 2|, orange, and 6, blue ; distance 
 4"'88 ; position-angle 112'l (1901*5). The position-angle is very slowly diminishing. 
 
 Nebula M. 17 Sagittarii. 18h. 15m. - 16 15'. 
 
 The Omega or Horse-shoe Nebula. This is one of the nebulae that can be seen with 
 comparatively small optical power. It is gaseous. 
 
 Nebula and Cluster M. 8 Sagittarii. 17h. 58m. - 24 22'. 
 
 A magnificent irregular nebula in a very rich field of stars, too far south to be well seen 
 in the latitude of England, where it rises only from 10 to 15 above the southern horizon. 
 In a fine climate it is easily visible to the naked eye, and Gore speaks of it as " a glorious 
 object with a 3-in. refractor in the Punjaub." 
 
 Planetary Nebula H. IV. 37 Draconis. 17h. 59m. + 66 38'. 
 
 One of the most conspicuous planetary nebulse in the sky, of a decided pale blue colour, 
 looking, as do all such objects, very much like a star out of focus. Gaseous. 
 
 This object lies close to the north pole of the ecliptic. 
 
 a Lyrae (Vega). 18h. 34m. + 38 41'. 
 
 The second brightest star of the northern sky. A very white star, in whose atmosphere 
 hydrogen is conspicuously absorbent. Proper motion 0"'36 ; annual parallax 0"'08 ; whence 
 its light is about 100 times that of the Sun, and its velocity at right angles to the line of 
 sight about 13 miles per second. 
 
 Lyrae. 18h. 41m. + 39 30', 
 
 A double star with components about 3' apart, separated to a good eye on clear moonless 
 nights, and beautifully seen in an opera glass. A 3-in. telescope will show that each of the 
 
80 POPULAR GUIDE TO THE HEAVENS 
 
 stars is itself a double, distance 2|" and 3". Between the two pairs are three smaller stars 
 visible in a 4-in. telescope. 
 
 Nebula M, 57 Lyrse. 18h. 50m. + 32 54'. 
 
 The famous Ring Nebula, very easy to find on the line between /3 and y Lyrae. In a 
 small telescope it appears as a faint ring, " a nebula with a hole in it " ; in large instruments 
 it is seen that the central opening is not entirely clear of nebulosity. Exactly in the centre 
 is a star which is very faint in the largest instruments, but which photographs comparatively 
 easily. For the picture of it made with a very powerful photographic telescope see 
 Plate 77. 
 
 ft Cygni. 19h. 27m. + 27 45'. 
 
 The finest coloured double star in the sky for small telescopes. Magnitudes 3, yellow, 
 and 5, blue. Distance 34"'2 ; position-angle 55'2. 
 
 a Aquilse (Altair). 19h. 46m. + 8 36'. 
 
 Magnitude 0'95 ; parallax 0'"23 ; whence the light is about eight times that of the Sun. 
 
 a Capricorn*. 20h. 13m. - 12 51'. 
 
 A fine pair of stars of the 3rd and 4th magnitude, about 6' apart, and easily separable to 
 the naked eye. The preceding star has a 9th magnitude companion, distant about 45" in 
 position-angle 221 ; and the following a 9th magnitude companion, distant 154" in position- 
 angle 156. There are also several faint closer companions to these stars, and the whole form 
 a very fine group. 
 
 y Delphini. 20h. 42m. + 15 46'. 
 
 An easy double star. Magnitudes 4, yellowish, and 5, bluish ; distance 11" '2 ; position- 
 angle 270 '6 ; relative motion, if any, very slow. 
 
 6l Cygni. 21h. 2m. + 38 13'. 
 
 A double star. Magnitudes 5*3 and 5'9 ; distance 22" ; position-angle 125 (1900). 
 Famous as the first star whose distance was determined. The pair has a very large common 
 proper motion of over 5" per year, which pointed it out as probably near to the Solar System. 
 The mean of the best determinations of its parallax is 0"'39 ; it is therefore, with one rather 
 doubtful exception, the nearest star in the northern sky. Its light takes nearly 8 years to 
 reach us, and the two stars together give only about one-tenth the light of the Sun. 
 
 // Cygni. 21h. 40m. + 28 18'. 
 
 A fine double star, probably a binary, a good test for a small telescope. Magnitudes 4 and 
 5 ; distance 2"'60 ; position-angle 122'l (Lewis, 1901 '9). There is a companion, magnitude 7 ; 
 distant 209", in position-angle 57, which does not form part of the system. Since they were 
 observed by Sir William Herschel in 1779, the pair has closed up from a separation of 7" to 
 its present distance. 
 
A SELECT LIST OF STARS, STAR CLUSTERS, AND NEBULA. 81 
 
 Aquarii. 22h. 24m. - 32'. 
 
 A well-known and striking double star, easy to find in the centre of a triangle of naked- 
 eye stars ; probably binary of long period. Magnitudes 4 and 4 ; distance 3" g l ; position- 
 angle 321 (1899'9, Maw). 
 
 3 Cephei. 22h. 25m. + 57 54'. 
 
 A remarkable double star, of which the brighter component is variable from 37m. to 
 4'9m. in a period of 5d. 8h. 48m., and is a spectroscopic binary of the same period. But the 
 variation of light is not due to an eclipse, since at the time of minimum the motion in the line 
 of sight is at a maximum. The variation is nevertheless undoubtedly due to the influence of 
 the dark companion, possibly something of the nature of a tidal disturbance. This star is 
 typical of quite a numerous class of variable stars of short period, which are probably all 
 spectroscopic binaries of the same type. All have the characteristic that the rise in light is 
 much quicker than the decline. 
 
 (T Cassiopeise 23h. 54m. + 55 12'. 
 
 A fine double star. A, magnitude 5, white, and B, magnitude 7i, blue. Position-angle 
 324 ; distance 3"'0. 
 
82 POPULAR (5UIDE TO THE HEAVENS. 
 
 PLATE 83. 
 STANDARD TIME. 
 
 As soon as communication by railway and telegraph is established in a country, it is 
 convenient to adopt throughout the country a uniform system of time. Very usually the 
 time adopted has been at first the mean time of the capital. But as communication between 
 different countries increases, great inconvenience arises when allowance has to be made for a 
 difference of adopted time involving an odd number of minutes and seconds. A large number 
 of countries and states have therefore adopted a standard system of time based upon that of 
 Greenwich, and differing from it by an exact number of hours, with occasionally an odd half 
 hour. 
 
 Plate 83 shows the system of standard time adopted throughout the world, so far as it 
 depends upon Greenwich. In Europe the time is generally that of Greenwich or one hour 
 fast of it. Quite recently France has prepared to adopt Greeewich Time, and the only 
 countries not included in the system are Portugal, Russia, Turkey, and Greece. The time 
 one hour fast on Greenwich is known as Mid. Europe Time ; that two hours fast as Eastern 
 Europe Time. 
 
 In the United States and Canada there are five divisions. Inter-Colonial or Atlantic 
 Time is four hours slow, Eastern or New York is five hours, Central six hours, Mountain 
 seven hours, and Pacific Time eight hours slow on Greenwich. 
 
 On the 180th meridian the time is 12 hours different from Greenwich, and provision has 
 to be made for the change of date. Since it would be very inconvenient to use a different 
 date in different islands of the same group, the " date line" does not follow exactly the 180th 
 meridian, but is drawn in a zig-zag course to avoid land. The greatest departure from the 
 meridian is in the North Pacific Ocean, where the line takes a wide sweep west to give the 
 Aleutian Islands the American date and then turns sharply eastward of the 180th meridian 
 to avoid the extreme eastern portion of Siberia. To the east of the line the date prevails 
 which has come round via America ; to the west the date that has come by the Old World. 
 Thus in the extreme east of Siberia the date is more than a day ahead of that in the 
 Aleutian Islands. 
 
(83) 
 
 INDEX. 
 
 PAGE. 
 
 ABENEZRA, Lunar Object No. 88, PI. 26 30 
 
 ABERRATION. An apparent displacement of a 
 
 star, arising from the progressive movement 
 
 of light combined with the orbital movement 
 
 of the Earth. 
 ABNEY, Sir W., Photograph of Solar Corona, 
 
 PL 16 19 
 
 ABULPEDA, Lunar Object No. 85, PL 26, 31 30 
 
 ACHROMATIC. Applied to a combination of 
 
 lenses which conduct rays of diiferent 
 
 colours to the same focus. 
 
 ADAMS, Lunar Object No. 17, PI. 26 30 
 
 ^ESTUUM SINDS, in Moon, N, PL 24, 32, 33 33 
 
 AGATHARCHIDES, Lunar Object No. 346, PL 25, 
 
 35 32 
 
 AGRIPPA, Lunar Object No. 244, PL 23, 31 31 
 
 AIRY, Lunar Object No. 106, PL 26, 31 30 
 
 ALBATEGNIUS, Lunar Object No. 109, PL 26, 31 30 
 
 ALCYONE, in Pleiades, PL 80 62, 72 
 
 ALDEBAEAN or a TAURI, PL 59 73 
 
 ALEXANDER, Lunar Object No. 209, PL 23, 27, 31 31 
 
 ALFRAGANDS, Lunar Object No. 77, PL 26 25, 30 
 
 ALGOL, or /3 PERSEI, remarkable Variable Star, 
 
 PL 53 51,72 
 
 ALGOL VARIABLES .51, 52 
 
 ALHAZEN, Lunar Object No. 151. PL 23, 27 31 
 
 ALIACENSIS, Lunar Object No. 97, PL 26, 31 ... 30 
 
 ALMANON, Lunar Object No. 86, PL 26, 31 30 
 
 ALPETRAGIUS. Lunar Object No. 267, PL 25, 32, 
 
 33 31 
 
 ALPHONSDS, Lunar Object No. 265, PL 25, 32, 33 31 
 ALPINE VALLEY, GREAT, Lunar Object No. 211, 
 
 PL 23, 32 31 
 
 ALPS, Lunar Mountains, a, PL 23, 24, 32, 33, 
 
 34, 35 33 
 
 ALTAI, Lunar Mountains, A, PL 30 33 
 
 ALTITUDE. The elevation of a body above the 
 
 horizon, expressed in angular measure. 
 ANAXAGORAS, Lunar Object No. 418, PL 24, 33 32 
 ANAXIMANDER, Lunar Object No. 431, PL 24, 36 32 
 ANAXIMENES, Lunar Object No. 421, PL 24, 
 
 35, 36 . 32 
 
 ANDERSON, T. D., Discovery of Nova Persei 63 
 
 ANDROMEDA, PL 52, 71. 
 
 ANDROMEDA, Great Nebula in, M. 31, PL 18, 
 
 52, 74 21,59,70 
 
 ANDROMEDA, R, regularly Variable Star, PL 52 41 
 
 ANDROMEDA, Nova 1885, PL 52 54 
 
 ANDROMEDA, 7, a Double Star, PL 52, 53 ... 71 
 
 ANDRDMEDIDS, Meteor Shower 5, 55 
 
 ANNUAL PARALLAX, PL 1 3 
 
 ANNULAR ECLIPSE OF SUN, PL 14 17 
 
 ANNULAR NEBULA, M. 57, in Lyra, PL 57, 78 61 
 ANOMALY. The angle subtended at the Sun by 
 
 a Planet, and the point of its orbit nearest 
 
 the Sun, called the perihelion. 
 
 ANSGARIUS, Lunar Object No. 6, PL 26 30 
 
 ANTARES or a SCORPII, PL 68 78 
 
 ANTLIA, PL 66, 67. 
 
 APENNINES, Lunar Mountains, c, PL 20, 24, 32, 
 
 33, 34, 35 25,33 
 
 APERTURE. When applied to a telescope, means 
 
 the diameter of the object glass. 
 APHELION. The point of a Planet's orbit which 
 
 is furthest from the Sun 5 
 
 APIANUS, Lunar Object No. 99, PL 26, 31 30 
 
 APOGEE. The point of the Moon's orbit which is 
 
 most distant from the Earth. 
 
 APOLLONIUS, Lunar Object No. 136, PL 23, 27, 28 30 
 APSE. In a planetary orbit the apses are the 
 
 points otherwise known as perihelion and 
 
 aphelion 4 
 
 APUS, PL 68, 70. 
 
 AQUARII, , a Double Star, PL 63 81 
 
 AQUARIUS, PL 63, 64, 69, 71, 72 3 
 
 AQUILA, PL 62, 63, 71, 72. 
 
 , a, (Altair) 80 
 
 , j, regularly Variable Star, PL 62 53 
 
 , Nova 1899 54 
 
 ARA, PL 68, 72. 
 
 ARAGO, Lunar Object No. 250, PI: 23, 30 .31 
 
 ARATUS, Lunar Object No. 238, PI . 23 31 
 
 ARCHIMEDES, Lunar Object No. 399. PL 24, 32, 
 
 33,34,35 25,32 
 
84 
 
 INDEX. 
 
 ARCH YTAS, Lunar Object No. 206, PI. 23 31 
 
 ARCTURUS or a BOOTIS, PI. 55, 56, 61 77 
 
 ARG.EUS, Lunar Mountain, s, PL 30 33 
 
 ARGELANDER, Durphmusterung Atlas 51 
 
 ARGELANDSR, Lunar Object No. 107, PI. 26 30 
 
 ARGUS, T) Variable Star 54,76 
 
 ARIADJEUS, Lunar Object No. 251, PI. 23 31 
 
 ARIEL, Satellite of Uranus, PI. 7 11 
 
 ABIES.IP1. 52, 53, 58, 71, 72. 
 
 ARIBTIS, y, a Double Star, PI. 58 71 
 
 ARISTARCHUS, Lunar Object No. 447, PL 24 36, 
 
 37,38 33 
 
 AlUSTlLLUS, Lunar Object No. 259, PL 23, 32, 
 
 33 25, 31 
 
 ARISTOTELES, Lunar Object No. 207, PL 23, 30, 
 
 31 '. 31 
 
 ARNOLD, Lunar Object No. 194, PL 23 .' 31 
 
 ARZACHEL, Lunar Object No. 266, PL 25, 32, 33 31 
 
 ASCENDING NODE of Planetary Orbit, PI. 3,4... 5 
 
 ASTEROIDS, PL 4 6 
 
 ASTRONOMICAL SYMBOLS 4 
 
 ATLAS, Lunar Object No. 186, PL 23, 28, 29, 30 31 
 AURIGA, PI. 53, 54, 71. 
 
 AURIGA, Cluster in, M. 37. PL 53 74 
 
 AURIGA, a, Capella, Binary Star 73 
 
 AURIGA, /3, Spectroscopic Binary 74 
 
 AURIGJE, Nova 1891, PL 53 54 
 
 AURIGA, e, irregularly Variable Star 54 
 
 AURORA SINUS, on Mars, PL 8 12 
 
 AUSONIA, on Mars, PL 8 12 
 
 AUSTRALE, MARE, in Moon, C, PL 26, 27, 28 33 
 AUTOLYCUS, Lunar Object No. 260, PL 23, 32, 
 
 33 31 
 
 Axis MAJOR OF ELLIPTIC ORBIT 4 
 
 Axis MINOR OF ELLIPTIC ORBIT 4 
 
 Axis, POLAR, PI. 1 1 
 
 AZIMUTH. The angle between a point on the 
 
 horizon and the north or south. 
 
 AZOPHI, Lunar Object No. 89, PL 26 30 
 
 AZOUT, Lunar Object, No. 138, PL 23 .. ,. 30 
 
 BABBAGE, Lunar Object No. 434, PI. 24 32 
 
 BACON, Lunar Object No. 126, PL 26, 30 30 
 
 BAILLY, Lunar Object No. 316, PL 25, 38 32 
 
 BAILY, Lunar Object No. 216, PL 23 31 
 
 BALL, Lunar Object No. 285, PL 25, 32 31 
 
 BERNARD. E. E . Drawing of Jupiter's Satellite 
 
 I., PI. 9 13 
 
 BARNARD, E E., Drawing of Saturn, PL 10 . . 13 
 
 BARNARD, E. E., Photograph of prominences, 
 
 PL 12 15 
 
 BARNARD, E. E., Photograph of Solar Corona 
 
 PL 16 .' 19 
 
 BARNARD E. E., Photograph of Holmes' Comet, 
 
 PL 18 ' 21 
 
 BARNARD, E. E., Photograph of Milky Way 
 
 PI- 81 \ 62 
 
 BAROCIUS, Lunar Object No. 122, PL 26 30 
 
 BARROW, Lunar Object No. 203, PL 23 31 
 
 BAYER, Lunar Object No. 318, PL 25, 35, 36 ... 32 
 
 BEAUMONT, Lunar Object No. 83, PL 26 30 
 
 BBER, Lunar Object No. 400, PL 24 32 
 
 BEHAIM, Lunar Object No. 141 31 
 
 BELL, Mr. J. HIND. See Preface. 
 
 BELLOT, Lunar Object No. 39, PL 26 30 
 
 BBRNOUILLI, Lunar Object No. 174, PL 23 .. . 31 
 
 BEROSUS, Lunar Object No. 171, PL 23 31 
 
 BERZELIUS, Lunar Object No. 176, PL 23, 28 ... 31 
 
 BESSARION, Lunar Object No. 388, PL 24 32 
 
 BESSEL, Lunar Object No. 236, PL 23, 30 31 
 
 BETTINUS, Lunar Object No. 309, PL 25, 35 32 
 
 BIANCHINJ, Lunar Object No. 425, PL 24, 35, 36 32 
 
 BIELA, Lunar Object No. 23, PL 26 30 
 
 BIELA'S COMET, Orbit of, and of Meteors of 
 
 November 27th, PL 3, 4 5 
 
 BILLY, Lunar Object No. 356, PL 25, 36 32 
 
 BINARY STAR. A Double Star whereof the two 
 components are found to be revolving 
 around each other. 
 
 BIRMINGHAM, Lunar Object No. 415, PL 24 32 
 
 BIRT, Lunar Object No. 276, PL 25 31 
 
 BLANCANUS, Lunar Object No. 312, PL 25, 34... 32 
 BLANCHINUS, Lunar Object No. 101, PL 26, 31 30 
 
 BODB, Lunar Object No. 376, PL 24 32 
 
 BODE'S Law of Planetary Distances 6 
 
 BOGUSLAWSKY, Lunar Object No. 26, PL 26, 28 30 
 BOHNENBERGER, Lunar Object No. 60, PL 26 ... 30 
 BOND, G. P., Drawing of Comet of Donati, PL 17 21 
 
 BOND, G. P., Lunar Object No. 222, PL 23 31 
 
 BOND, W. C., Lunar Object No. 204, PL 23 31 
 
 BONPLAND, Lunar Object No. 272, PL 25, 33 ... 31 
 BOOTES, PL 55, 56, 61, 71. 
 
 BOOTIS, a, or ARCTUHUS, PL 55, 56, 61 -77 
 
 BOOTIS, e, a Double Star, PL 56 78 
 
 BOOTIS, 5, a Double Star, PL 61 78 
 
 BOOTIS, W. .Variable Star, PL 56 54 
 
 BORDA, Lunar Object No. 40, PL 26 30 
 
 BOSCOVICH, Lunar Object No. 232, PL 23, 31 25, 31 
 
INDEX. 
 
 85 
 
 BOUSSINGAULT, Lunar Object No. 25. PI. 26, 27, 
 
 28 .' 30 
 
 BRADLEY, Lunar Mountain, 10, PL 23 33 
 
 BKAYLEY, Lunar Object No. 452, PI. 24 33 
 
 BRIGGS, Lunar Object No. 445, PI. 24, 37, 38 ... 33 
 
 BRIGHTNESS of Stars compared with Sun 68 
 
 BROOKS' COMET, 1893, IV.. PI. 18 22 
 
 BUCK, Lunar Object No. 71, PI. 26, 30 30 
 
 BULIJALDUS, Lunar Object No. 342, PI. 25, 34 32 
 
 BURCKHARDT, Lunar Object No. 169, PI. 23, 27 31 
 
 BURG, Lunar Object No. 215, PI. 23 31 
 
 BUSCHING, Lunar Object No. 70, PL 26, 30 30 
 
 BYRGIUS, Lunar Object No. 352, PL 25 32 
 
 CABEUS, Lunar Object No. 304, PL 25 32 
 
 CALIPFUS, Lunar Object No. 256, PL 23, 31, 32 31 
 
 CALLISTO, Satellite of Jupiter, PL 7 10 
 
 CAMELOPARDALUS, PL 51, 53, 54. 
 
 CAMPANUS, Lunar Object No. 340, PL 25, 34 ... 32 
 
 CANCER, PL 54, 59, 60. 
 
 CANCER, Cluster M44, PL 60 75 
 
 CANCRI, , Multiple Star 75 
 
 CANES VENATICI, PL 55, 56. 
 
 CANES VENATICI, Spiral Nebula in, PL 55, 76... 60 
 
 CANIS MAJOR, PL 59, 66, 71, 72. 
 
 CANIS MAJORIS a, or SIRIUS, PL 59 74 
 
 CANIS MINOR, PL 59, 72. 
 
 CANIS MINORIS, a. (Procyon) Binary Star 75 
 
 CANUM VENATICORUM, M. 3, Cluster 77 
 
 CAN DM VENATICORUM, , (Cor Caroli), Double 
 
 Star 77 
 
 CAPE OF GOOD HOPE, R. Observatory, Photo- 
 graph of Comet, 1901, I., PI. 19 22 
 
 CAPELLA, or a AURIGA, PL 53 '73 
 
 CAPELLA, Lunar Object No. 57, PL 26, 29 30 
 
 CAPRICORNDS, PL 63, 69, 71, 72. 
 
 CAPRICORNI, a, Pair of Stars 80 
 
 CAPUANUS, Lunar Object No. 337, PL 25, 34, 35 32 
 
 CARDANUS, Lunar Object No, 394, PL 24, 38 32 
 CARINA, PL 66, 67, 70. 
 
 CARINJE, ;, Variable Star, PL 67 54 
 
 CARING, I, regularly Variable Star 53 
 
 CARING, R, regularly Variable Star 53 
 
 CARING, Nova 1895, PL 67 54, 76 
 
 CARLINI, Lunar Object No. 408, PL 24, 34 32 
 
 CARPATHIANS, Lunar Mountains, d, PL 24, 34, 35 33 
 
 CASATUS, Lunar Object No. 305, PL 25, 35 32 
 
 CASSINI, Lunar Object, No. 258, PI. 23, 32 31 
 
 CASSINI, J. J., Lunar Object No. 422, PL 24, 32 32 
 
 CASSIOPEIA, PL 51, 52, 53, 71. 
 
 CASSIOPEIA:, o, Variable Star, PL 52 54 
 
 CASSIOPE^;, R, regularly Variable Star, PL 52 53 
 
 CASSIOPEIA, rj, Double Star, PL 52 70 
 
 CASSIOPEIA, ff, a Double Star 81 
 
 CASSIOPEIA, Nova 1572, PL 52 54 
 
 CATHARINA, Lunar Object No. 81, PL 26, 30 ... 30 
 CAUCASUS, Lunar Mountains, b, PL 23, 31, 32, 
 
 33, 34, 35 25, 33 
 
 CAUCHY, Lunar Object No. 161, PL 23 31 
 
 CAVALERIUS, Lunar Object No. 392, PL 24, 37, 38 32 
 CAVENDISH, Lunar Object No. 351, PL 25, 36, 37 32 
 
 CAYLBY, Lunar Object No. 254, PL 23 31 
 
 CENSORINUS, Lunar Object No. 55, PL 26 30 
 
 CENTADRUS, PL 67, 68, 72. 
 
 CENTAURI, u>, Globular Cluster 77 
 
 CENTAURI, a, Binary Star 78 
 
 CENTAURI, Nova 1895, PL 67 54 
 
 CENTRAL MERIDIAN. The line joining the north 
 point to the south point on one of the 
 Monthly Maps in this Atlas. 
 
 CEPHEI, S, regularly Variable Star, PL 52 53, 81 
 
 CEPHEUS, Lunar Object No. 182, PL 23 31 
 
 CEPHEUS, PL 51, 52, 57, 71. 
 
 CERBERUS (Canal), on Mars, PL 8 12 
 
 CERES, diameter of 8 
 
 CETI, T, Variable Star, PL 63, 64 54 
 
 CETI, 7, a Double Star, PL 58 72 
 
 CETI, v, a Double Star, PL 58 48 
 
 CETI, o, (Mira), Variable Star, PL 58 53, 71 
 
 CETUS, PL 58, 63, 64, 71, 72. 
 
 CHAMELEON, PL 70. 
 
 CHACORNAC, Lunar Object No. 219, PL 23, 29, 30 31 
 
 CHALLIS, Lunar Object No. 199, PL 23 31 
 
 CHARONTIS LACUS, on Mars, PL 8 12 
 
 CHARTS FOR SUN SPOT OBSERVATIONS, PL 13 ... 16 
 
 CHART OF MARS, PL 8 11 
 
 CHEVALLIER, Lunar Object No. 185, PL 23, 24, 
 
 28 31 
 
 CHRISTIAN MAYER, Lunar Object No. 205, PI 23 31 
 
 CICHUS, Lunar Object No. 338, PL 25, 34 32 
 
 CIRCINUS, PL 68. 
 
 CIRCLE (Great). A circle which divides the 
 sphere into two equal portions. 
 
 CIRCLES OF THE SPHERE 
 
 CIRCUMPOLAR STARS 3 
 
 CLAIRAUT, Lunar Object No. 123, PL 26, 31 ... ( 
 
 CLAUSIUS, Lunar Object No. 336, PI. 25 32 
 
 CLAVIUS, Lunar Object No. 298, PL 21, 25, 26, 
 33,34 35 32 
 
86 
 
 INDEX. 
 
 PAGE. 
 
 CLEOMEDES, Lunar Object No. 167, PI. 23, 27, 28 31 
 
 CLEOSTRATUS, Lunar Object No. 437, PI. 24, 38 32 
 CCELUM, PI. 65. 
 
 COLOMBO, Lunar Object No. 34, PI. 26, 28 30 
 
 COLUMBA, PI. 65, 66, 72. 
 COMA BERENICIS, PI. 55, 61. 
 
 COM^B BERENICIS, 24, a Double Star, PI. 61 76 
 
 COMET OF BIELA, PI. 3 5 
 
 COMET OF BROOKS, 1893, PI. 18 22 
 
 COMET OF DONATI, Oct. 5, 1858, PI. 17 21 
 
 COMET OF PERRINE, 1902, III., PI. 19 23 
 
 COMET OF HOLMES, 1892, PI. 18 21 
 
 COMET OF 1882, PI. 4 _ 6 
 
 COMET I., 1866, Orbit of, PI. 3 5 
 
 COMET III., 1862, Orbit of, PI. 3 5 
 
 COMET I., 1901, PL 19 22 
 
 COMPANION TO THE OBSERVATORY 51 
 
 COMPARATIVE SIZES OF THE PLANETS, PI. 5 7 
 
 CONDAMINE, Lunar Object No. 423, PI. 24, 34, 
 
 35,36 32 
 
 CONDORCET, Lunar Object No. 140, PI. 23, 27 31 
 
 CONICAL PROJECTION FOR STAR MAPS 49 
 
 CONJUNCTION. Used of two planets when they 
 
 have the same longitude, viewed from the 
 
 Sun. 
 
 CONON, Lunar Object No. 239, PI. 23 31 
 
 COOK, Lunar Object No. 35, PI. 26 30 
 
 COPERNICUS, Lunar Object No. 380, PI. 22, 24, 
 
 33, 34, 35 24, 32 
 
 COR CAHOLI, a Double Star 77 
 
 CORDILLERAS, Lunar Mountains 33 
 
 CORDOBA, Durchmusterung Atlas 51 
 
 COROLLA, PI. 69. 
 
 CORONA BOREAHS, PI. 56, 71. 
 
 CORONA OF SUN, PI. 16 18 
 
 CORONA a, a Double Star, PI. 56 78 
 
 CORONA II. , irregularly Variable Star, PI. 56 54 
 
 CORONET., Nova, 1866, PI. 56 54 
 
 COHONIUM, Unknown Gas in Sun 19 
 
 CORVUS, PI. 60, 61, 71, 72. 
 CRATER, PI. 60, 67, 71, 72. 
 CRISIUM MARE, Lunar Sea, A, PL 23, 27, 28, 
 
 29,30,31 33 
 
 CROZIEB, Lunar Object No. 38, PI. 26 30 
 
 CRUGER, Lunar Object No. 361, PI. 25, 37 32 
 
 CRUX, PI. 67, 72. 
 
 CRUCIS, a, Brightest of Southern Cross 76 
 
 CULMINATION, The passage of a heavenly body 
 
 across the meridian. 
 
 CURTIUS, Lunar Object No. 132, PI. 26, 31 30 
 
 PAGE. 
 
 CUVIER, Lunar Object No. 125, PI. 26 ............ 30 
 
 CYGNI, /3, a Double Star, PL 57 ..................... 80 
 
 CYGNI, p, a Double Star, PL 57 ..................... 80 
 
 CYGNI, x. regularly Variable Star, PL 57 ......... 53 
 
 CYGNI, 61, a Double Star, PL 57 ..................... 80 
 
 CYGNI, Nova 1876, PL 57 .............................. 54 
 
 CYGNUS, PL 52, 57, 71. 
 
 CYGNUS, Nebula in, PL 7o ........................... 60 
 
 CYRILLUS, Lunar Object No. 80, PL 26, 30 ...... 30 
 
 CYSATUS, Lunar Object No. 299, PL 25, 33 ...... 32 
 
 D'ALEMBERT MTS., Lunar Object .................. 
 
 DANIELL, Lunar Object No. 217, PL 23 ............ 
 
 DAMOISEAU, Lunar Object No. 364, PL 25 ...... 
 
 DATE, Change of, PL 83 ................................. 
 
 DAVIS, H., Photograph of Solar Corona, PL 16 
 DAVY, Lunar Object No. 269, PL 25 ............... 
 
 DAWES, Lunar Object No. 226, PL 23, 30 ......... 
 
 DECLINATION. The angular distance of a celes- 
 
 tial body from the Equator ..................... 
 
 DEIMOS, one of the Satellites of Mars, PL 7 ...... 
 
 DELAMBRE, Lunar Object No. 73, PL 26 ......... 
 
 DE LA RUE, Lunar Object No. 189, PL 23, 28, 29 
 DELAUNAY, Lunar Object No. 103, PL 26 ......... 
 
 DELISLE, Lunar Object No. 406, PL 24, 35 ...... 
 
 DELPHIN, PL 63, 71, 72. 
 
 DELPHINI, 7, a Double Star, PL 63 ............... 
 
 DELUC, Lunar Object No. 297, PL 25, 32 ......... 
 
 DEMOCRITUS, Lunar Object No. 193, PI. 23 ...... 
 
 DE MORGAN, Lunar Object No. 253, PL 23 ...... 
 
 DESCARTES, Lunar Object No. 84, PL 26 ......... 
 
 DESCENDING NODE OF ORBIT OF PLANET, PL 3, 4 
 DE Vico, Lunar Object No. 354, PI. 25 ............ 
 
 DIONE, Satellite of Saturn, PI. 7 ..................... 
 
 DftNYSius, Lunar Object No. 248, PL 23 ...... 25 
 
 DIOPHANTUS, Lunar Object No. 405, PL 24, 35 
 
 DIP of the horizon 
 
 DISTANCE OF THE STARS .............................. 
 
 DIURNAL PARALLAX ...................... . ............. 
 
 DOERFEL MOUNTAINS, Lunar Object ............... 
 
 DONATI, Lunar Object, No. 105, PL 26, 31 ...... 
 
 DONATI'S COMET, Oct. 5th, 1858, PL 17 ......... 
 
 DOPPELMAYER, Lunar Object No. 333, PL 25, 35 
 
 DORADO, PI. 65, 70, 72. 
 
 DOUGLASS, Mr. A. E., Map of Mars, PL 8 ...... 
 
 DRACO, PI. 51, 55, 56, 57, 71. 
 
 DRACO, Planetary Nebula in, H IV. 37, PL 51, 
 
 56,57 ................................................... 
 
 DREBBEL, Lunar Object No. 324, PI. 25 ............ 
 
 DUMB-BELL NEBULA, in Vulpecula, PL 77 ...... 
 
 10 
 30 
 31 
 30 
 32 
 
 80 
 32 
 31 
 31 
 30 
 
 5 
 
 32 
 
 H 
 
 , 31 
 
 32 
 
 2 
 67 
 
 2 
 
 33 
 30 
 
 79 
 32 
 
 61 
 
INDEX. 
 
 87 
 
 EARTH, Dimensions of and position oi Axis, PI. 5 7 
 
 EARTH-LIGHT on Moon 17 
 
 EARTH, Periodic Time of, PI, 3. 
 
 ECCENTRICITY OF A PLANETARY ORBIT, PI. 3 ... 5 
 
 ECLIPSES, PL 14 17 
 
 ECLIPTIC. The apparent path of the Sun among 
 
 the Stars, PI. 1 1 
 
 EDOM PROMONTORIUM, on Mars, PL 8 12 
 
 EGEDB, Lunar Object No. 210, PI. 23 31 
 
 EICHSTADT, Lunar Object No. 353, PI. 25, 38 ... 32 
 
 EINMART, Lunar Object No. 162, PL 23 31 
 
 ELECTHA, in Pleiades, PI. 80 62 
 
 ELEMENTS, -Used of a Planet's Orbit 4 
 
 ELGER, MR. T. GWYN. See Preface. 
 
 ELLIPSE. The form of a Planetary Orbit 4 
 
 ELONGATION. The apparent angular distance 
 
 of a body from its centre of motion. 
 
 ENCELADUS, Satellite of Saturn, PL 7 11 
 
 ENCKE, Lunar Object No. 386, PI. 24, 35, 36 ... 32 
 
 ENCKE'S COMET, PL 4 6 
 
 ENDYMION, Lunar Object No. 188, PL 23, 27, 
 
 28, 29 31 
 
 EPIGENES, Lunar Object No. 416, PL 24, 32 32 
 
 EQUATOR (Celestial). The great Circle midway 
 
 between the Poles, PL 1 1 
 
 EQUATORIAL. A Telescope mounted so as to 
 
 follow a Star in its apparent daily motion. 
 EQUINOX. Either of the points on the Equator 
 
 at which the Sun crosses in its annual course 
 
 among the Stars 1 
 
 EQUULEDS, PI. 63 
 
 ERATOSTHENES, Lunar Object No. 382, PL 24, 33, 
 
 34 32 
 
 ERIDANUS, PL 58, 59, 64, 65, 71, 72. 
 
 ERIDANI, 9, Double Star 72 
 
 EROS, small Planet, PL 3 5 
 
 EUCLIDES, Lunar Object No. 370, PL 25, 34, 35 32 
 
 EUCTEMON, Lunar Object No. 198, PL 23, 29 ... 31 
 
 EUDOXUS, Lunar Object No. 208, PL 23, 30, 31 31 
 
 EULER, Lunar Object No. 404, PL 21, 34, 35, 36 32 
 
 EUMENIDES (Canal), on Mars, PL 8 12 
 
 EUROPA, Satellite of Jupiter, PI. 7 10 
 
 FABRICIUS, Lunar Object No. 45, PI. 26, 28, 29 30 
 FACUL^E. Patches on the Sun which are brighter 
 than other parts of the photosphere. 
 
 F^CUNDIT ATIS MARE, in Moon , B, PL 27-31 33 
 
 FARADAY, Lunar Object No. 120, PL 26 30 
 
 FASTIGIUM ARYN, on Mars, PL 8 12 
 
 FAYE, Lunar Object No. 104, PL 26 30 
 
 FENYI, Drawings of prominences, PL 12 15 
 
 FERMAT, Lunar Object No. 91, PI. 26,30 30 
 
 FERNELIUS, Lunar Object No. 118, PL 26,31 ... 30 
 
 FERMICUS, LunarObject No. 137, PL 23, 27 30 
 
 FIRST point of Aries 1 
 
 FLAMSTEED, Lunar Object No. 368, PL 25, 35, 36 32 
 
 Foci of an elliptic orbit 4 
 
 Focus. A point where converging rays meet. 
 FOMALHAUT (a Piscis Australis), PL 64, 72 
 
 FOOTANA, Lunar Object No. 359, PL 25, 36, 37 32 
 FONTENELLE, Lunar Object No 419, PL 24, 33, 
 
 34, 36 32 
 
 FORNAX, PL 65. 
 
 FOUCAULT, Lunar Object No. 428, P1.24 ...' 32 
 
 FOURIER, Lunar Object No. 331, PL 25 32 
 
 FRACASTORIUS, Lunar Object No. 62, PL 26, 29, 
 
 30 30 
 
 FBA MAURO, Lunar Object No. 273, PI. 25, 33 31 
 
 FRIGORIS, MARE, in Moon, PL 23, 31-36, 38 33 
 
 FRANKLIN, Lunar Object No. 181, PL 23, 28...... 31 
 
 FRAUNHOFER, Lunar Object No. 19, PL 26, 27 30 
 FURNERIUS, Lunar Object No. 14, PL 26, 27, 28 
 
 29 . .30 
 
 GALILEO, Lunar Object No. 453, PL 24 33 
 
 GAMBART, Lunar Object No. 372, PI 24, 33 32 
 
 GANGES (Canal), on Mars, PL 8 12 
 
 GANYMEDE, Satellite ol Jupiter, PL 7 .... 10 
 
 GASSENDI, Lunar Object No. 347, PL 25, 35, 36 32 
 
 GARTNER, LunarObject No. 192, PL 23 31 
 
 GAURICUS, Lunar Object No. 282, PL 25, 33 31 
 
 GAUSS, Lunar Object No. 172, PL 23, 27, 28 31 
 
 GAY LUSSAC, Lunar Object No. 383, PL 24, 33, 
 
 34,35 32 
 
 GEBER, Lunar Object No. 87, PL 26 30 
 
 GEMINI, PL 54, 59, 71, 72. 
 
 GEMINORUM, a (Castor), a Double Star, PL 54 74 
 
 GEMINORUM, r], Variable Star, PL 54, 59 53 
 
 GEMINORUM, , regularly Variable Star, PL 54, 
 
 59 53 
 
 GEMINORUM, M. 35, Star Cluster 74 
 
 GEMINORUM, Nova 1903, PL 54 54 
 
 GEMINUS, Lunar Object No. 173, PL 23, 27 31 
 
 GEMMA FRISIUS, Lunar Object No. 95, PL 26 ... 30 
 
 GERARD, Lunar Object No. 441, PL 24 33 
 
 GIBBOUS, Planet when so called, PL 6 8 
 
 GIOJA, Lunar Object No. 201, PL 23 31 
 
 GODENIUS, Lunar Object No. 31, PL 26, 28, 29 30 
 
 GODIN, Lunar Object No. 245, PL 23, 31 31 
 
INDEX. 
 
 GOLDSCHMIDT, Lunar Object No. 417, PI. 24, 32 
 
 33 32 
 
 GREAT ALPINE VALLEY, Lunar Object No. 211, 
 
 PI. 23, 32 31 
 
 GREENWICH, Royal Observatory, Photograph of 
 
 Sun, PI. 11 15 
 
 GREENWICH, Royal Observatory, Photograph of 
 
 Perrine's Comet, 1902, PL 19 23 
 
 GHIMALDI, Lunar Object No. 363, PL 25, 37, 38 32 
 
 GROVE, Lunar Object No. 212, PL 23 31 
 
 GRUEMBERGEU, Lunar Object No. 303, PL 25 ... 32 
 GRUITHUISEN, Lunar Object No. 451. PL 24, 35 33 
 GRUS, PL 64, 69, 72. 
 GUERIKE, Lunar Object No. 270, PL 25, 33...... 31 
 
 GUTTEMBERG, Lunar Object No. 32, PL 26, 28, 
 
 29 .. . 30 
 
 HADLEY, Lunar Mountain, t 33 
 
 H^MUS, Lunar Mountain,/, PL 23, 31, 32 33 
 
 HAGECIUS, Lunar Object No. 24, PL 26 30 
 
 HAGEN'S Atlas of Variable Stars 51 
 
 HAHN, Lunar Object No. 170, PL 23 31 
 
 HAINZEL, Lunar Object No. 326, PL 25, 34, 35 32 
 
 HALLEY, Lunar Object No. Ill, PL 26, 31 30 
 
 HALLEY'S COMET, PL 4 6 
 
 HANNO, Lunar Object No. 143, PL 26 31 
 
 HANSEN, Lunar Object No. 150, PL 23 31 
 
 HANSTEEN, Lunar Object No. 357, PL 25, 36 ... 32 
 
 HARBINGER MOUNTAINS, in Moon, o, PL 24 33 
 
 HARDING, Lunar Object No. 440, PI. 24 33 
 
 HARKNESS, W., Photograph of Solar Corona, 
 
 PI. 16 19 
 
 HARPALUS, Lunar Object No. 429, PI. 24, 35 ... 32 
 
 HASE, Lunar Object No. 10, PI. 26 30 
 
 HAUSEN, Lunar Object No. 320, PL 25 32 
 
 HEAVENS, Sphere of the 1 
 
 HECATJEUS, Lunar Object No. 5, PL 26, 27 30 
 
 HEINSIDS, Lunar Object No. 292, PL 25, 33, 34 32 
 
 HELICON, Lunar Object No. 410, PL 24. 34 32 
 
 HELL, Lunar Object No. 279, PL 25 SI 
 
 HELLAS, on Mars, PL 8 12 
 
 HENRY, Photographs of Pleiades, PL 80 62 
 
 HERCULES, PL 56, 57, 62, 71. 
 
 HERCULES, Globular Cluster in, M. 13, PL 75, 76 79 
 
 HERCULES, Lunar Object No. 187, PL 23, 29 ... 31 
 
 HERCULIS, a, irregularly Variable Star, PL 62... 62 
 
 HERCULIS, o, a Double Star, PL 62 79 
 
 HERCULIS, g, Variable Star, PL 56 54 
 
 HBRCULIS. u, Variable Star, PI. 56 54 
 
 HKRCULIS, , a Double Star, PL 56 .. .78 
 
 HERCYNIAN MOUNTAINS, in Moon, p, PL 24 ... 33 
 
 HERIGONIUS, Lunar Object No. 348, PL 25, 35 32 
 
 HERMANN, Lunar Object No. 367, PL 25 32 
 
 HERODOTUS, Lunar Object No. 448, PL 24, 36, 
 
 37,38 33 
 
 HERSCHEL, J. F. W., Lunar Object No. 430, PL 
 
 24, 35 32 
 
 HERSCHEL, Lunar Object No. 263, PL 25, 32 ... 31 
 HERSCHEL, CAROLINE, Lunar Object No. 407, 
 
 PI. 24, 34 32 
 
 HESIODUS, Lunar Object No. 281, PL 25, 33 ... 31 
 
 HEVEL, Lunar Object No. 391, PL 24, 37, 38 ... 32 
 
 HILDA. One of the Minor Planets, PI. 4 6 
 
 HIND, Lunar Object No. 112, Pi. 26, 31 30 
 
 HIPPALUS, Lunar Object No. 345, Pl/25, 34, 35 32 
 HIPPARCHUS, Lunar Object No. 110, PL 26, 31, 
 
 32 30 
 
 HOLMES' COMET, PL 18 21 
 
 HOMMEL, Lunar Object No. 51, PL 26 30 
 
 HOOKE, Lunar Object No. 177, PL 23 31 
 
 HORIZON, PL 1 2 
 
 HOROLOGIUM, PL 65. 
 
 HORREBOW, Lunar Object No. 454, PI. 24 33 
 
 HORROCKS, Lunar Object No. 113, PL 26., 31, 32 30 
 
 HORTENSIUS, Lunar Object No. 378, PI. 24, 35 32 
 HOUR ANGLE. The angle between the meridian 
 
 and a great circle from the pole to a celes- 
 tial body. 
 
 HOUZEAU, Star Places given by 50 
 
 HUGGINS, Lunar Object No. 146, PL 23 31 
 
 HUMBOLDT MOUNTAINS, Lunar Object 33 
 
 HUMBOLDTIANUM MARE, in Moon, PL 23, 27, 28, 
 
 29, 30 33 
 
 HUMBOLDT, W., Lunar Object No. 12, PL 26, 27 30 
 
 HUMORUM MARE, in Moon, T, PL 25,35,36,37,38 33 
 
 HUYGENS, Lunar Mountains, v, PL 23 33 
 
 HYADES, a group in Taurus, PL 71, 72. 
 
 HYDRA, PL 59, 60, 61, 66, 67, 68, 71, 72. 
 
 HYDRA, Planetary Nebula in, H IV. 27, PL 60 76 
 
 HYDROS R., regularly Variable Star, PL 61 53 
 
 HYDR* U., Variable Star, PL 60 54 
 
 HYDRA; e, a Double Star, PL 60 75 
 
 HYDRUS, PL 64, 65, 70, 72. 
 
 HYGINUS, Lunar Object No. 243, PL 23 31 
 
 HYPATIA, Lunar Object No. 72, PL 26, 30 30 
 
 HYPERION, Satellite of Saturn, PL 7 11 
 
 IAPETUS, Satellite of Saturn, PL 7 11 
 
 IMBRIUM MARE, in Moon, L, PL 24, 32-38 33 
 
 INDEX TO THE PLANETS ... . 37 
 
INDEX. 
 
 89 
 
 INDUS, PI. 64, 69, 70, 72. 
 
 INFERIOR CONJUNCTION 9 
 
 INGHIRAMI, Lunar Object No. 325, PL 25, 37, 38 32 
 
 lo, Satellite of Jupiter, PL 7 ' 10 
 
 IRIDUM SINUS, in Moon, R, PL 24, 34, 35, 37, 38 33 
 
 IRREGULARLY VARIABLE STARS 53 
 
 ISIDORUS, Lunar Object No. 58, PL 26, 29 ... . 30 
 
 JACOBI, Lunar Object No. 127, PL 26 30 
 
 JANSEN, Lunar Object No. 158, PL 23, 28 31 
 
 JANSSEN, Lunar Object No. 46, PL 26, 28, 29... 30 
 JULIUS C.ESAR, Lunar Object No. 231, PL 23, 
 
 31 25, 31 
 
 JUNO, diameter of 8 
 
 JUPITER, Dimensions of, PL 5 7 
 
 JUPITER, Drawings of, PL 9 12 
 
 JUPITER, First Satellite, Drawings of, PL 9 ... 13 
 
 JUPITER, Howtofind 44 
 
 JUPITER, Index to 44, 45 
 
 JUPITER IN OPPOSITION 38 
 
 JUPITER, Orbit of, PI, 4 6 
 
 JUPITER, Rotation Period of 7 
 
 JUPITER, Satellites of, PI. 7 ... ...10, 11 
 
 KANT, Lunar Object No. 78, PL 26 30 
 
 KASTNER, Lunar Object No. 2, PL 26, 27 30 
 
 KEARNEY, J., Photograph of Solar Corona, PL 16 19 
 KEELER, J. E. , Photograph of Spiral Nebula in 
 
 Canes Venatici, PL 76 .f. 60 
 
 KEELER, J. E., Photograph of the Dumb-bell 
 
 Nebula, PL 77 61 
 
 KEELER, J. E., Photograph of Ring Nebula in 
 
 Lyra, PL 78 61 
 
 KEPLER, Lunar Object No. 387, PL 24, 35. 36... 32 
 
 KIES, Lunar Object No. 341, PL 25, 34 32 
 
 KINAU, Lunar Object No. 130, PL 26 30 
 
 KIRCH, Lunar Object No. 411, PL 24 32 
 
 KIRCHER, Lunar Object No. 308, PL 25 32 
 
 KLAPROTH, Lunar Object No. 306, PL 25, 35 ... 32 
 
 KRAFKT, Lunar Object No. 395, PL 24, 38 32 
 
 KUNOWSKY, Lunar Object No. 385, PL 24, 35... 32 
 
 LACAILLE, Lunar Object No. 102, PL 26 30 
 
 LACERTA, PL 52. 
 
 LACROIX, Lunar Object No. 328, PL 25 32 
 
 LACUS MORTIS, in Moon, PL 23, 29, 30, 31 33 
 
 LACUS SOMNIORUM, in Moon, PI. 23, 29, 30, 31 33 
 
 LAGUANGE, Lunar Object No. 330, PL 25, 37, 38 32 
 
 LA HIRE, j, Lunar Mountain 33 
 
 LALANDE, Lunar Object No. 262, PL 25, 33 31 
 
 LAMBERT, Lunar Object No. 402, PL 24, 33, 34 
 
 35 32 
 
 LANDSBERG, Lunar Object No. 371, PL 24, 25, 
 
 34, 35 32 
 
 LANGRENUS, Lunar Object No. 1, PI. 26, 27, 28, 
 
 29 30 
 
 LA PEYROUSE, Lunar Object No. 142 31 
 
 LAPLACE PROMONTORY, in Moon, u, PL 24, 34, 
 
 35,36,37 '. 33 
 
 LASSELL, Lunar Object No. 268, PL 25 31 
 
 LATITUDE. The angular distance of a heavenly 
 
 body from the Ecliptic. 
 
 LAVOISIER, Lunar Object No. 442, PL 24 33 
 
 LEE, Lunar Object No. 334, PL 25, 35 32 
 
 LEGENDRE, Lunar Object No. 11, PL 26, 27 30 
 
 LE GENTIL, Lunar Object No. 144, PL 25 31 
 
 LEHMANN, Lunar Object No. 327, PL 25, 36 ... 32 
 
 LEIBNITZ MOUNTAINS, Lunar Object 33 
 
 LE MONNIER, Lunar Object No. 220, PL 23, 29, 
 
 30,35 31 
 
 LEO, PL 54, 55, 60, 71, 72. 
 LEO MINOR, PL 54, 55. 
 
 LEONIDS, Meteor Shower, PI. 4 5, 55 
 
 LEONIS, a, (Regulus) 75 
 
 LEONIS, y, a Double Star, PL 54, 60 75 
 
 LEONIS, i, a Double Star, PL 60 76 
 
 LEPUS, PL 59. 65, 71, 72. 
 
 LETRONNE, Lunar Object No. 349, PL 25, 35, 36 32 
 
 LEVERRIER, Lunar Object No. 409, PL 24, 34... 32 
 
 LEXELL, Lunar Object No. 286, PI. 25 31 
 
 LIBRA, PL 61, 62, 68, 71,72. 
 
 LIBRA, Cluster M. 5 78 
 
 LIBRAE, S, Algol Variable, PL 61 52 
 
 LIBRATION The swinging of the Moon by which 
 
 we can sometimes see a margin beyond the 
 
 half which is commonly directed towards 
 
 us. 
 
 LICETUS, Lunar Object No. 124, PL 26, 31 30 
 
 LICHTENBERO, Lunar Object No. 444, PL 24 ... 33 
 
 LIGHT YEARS 67 
 
 LILIUS, Lunar Object No. 128, PL 26, 31 30 
 
 LINDENAU, Lunar Object No. 68. 'PL 26 30 
 
 LINNE, Lunar Object No. 237, PL 20, 23, 25, 31 31 
 
 LITTROW, Lunar Object No. 224, PL 23 31 
 
 LOHRMANN, Lunar Object No. 366, PL 25, 37, 38 32 
 
 LOHSE, Dr. 0. , on Jupiter. See Preface. 
 
 LONG PERIOD VARIABLES ... 53 
 
90 
 
 INDEX. 
 
 LONGITUDE. If a great circle perpendicular to 
 the Ecliptic be drawn through any celestial 
 body, its longitude is the angle from the 
 vernal equinox measured towards the east 
 to the foot of the perpendicular. 
 LONGITUDE OF PERIHELION, PI. 3. 
 LONGOMONTANUS, Lunar Object No. 294, PI. 25, 
 
 33,34 / 32 
 
 LOWELL OBSERVATORY, Map of Mars, PI. 8 12 
 
 LUBBOCK, Lunar Object No. 30, PI. 26, 28 30 
 
 LUBINIEZKY, Lunar Object No. 343, PL 25, 34... 32 
 
 LUNA; LACUS, on Mars, PL 8 12 
 
 LUNAR OBJECTS 28 
 
 LUNATION. The period from one new Moon to 
 
 to the next. 29'5305879 days. 
 LUPUS, PL 68, 72. 
 LYNX, PI. 54. 
 LYRA, PI. 57, 71. 
 
 LYRA, Annular Nebula, PL 57, 78 61, 80 
 
 LYRA; a, or VEGA, PL 57 79 
 
 LYRA; t , a Double-double Star, PI . 57 79 
 
 LYR.S; j3, regularly Variable Star, PI. 57 53 
 
 LYRA;, R., Variable Star, PL 57 53 
 
 LYRID METEOR SHOWER ., 55 
 
 MACLAUIUN, Lunar Object No. 4, PI. 26 30 
 
 MACLEAR, Lunar Object No. 229, PI. 23, 30 31 
 
 MACROBIUS, Lunar Object No. 166, PI. 23, 28 ... 31 
 
 MADLER, Lunar Object No. 59, PL 26, 30 30 
 
 MAGELHAENS, Lunar Object No. 33, PL 26 30 
 
 MAGINUS, Lunar Object No. 296, PL 25, 32, 33 32 
 
 MAI A, in Pleiades, PL 80 62 
 
 MAIN, Lunar Object No. 200, PL 23 31 
 
 MAIRAN, Lunar Object No. 427, PL 24, 35, 36... 32 
 
 MALUS, PI. 60, 66. 
 
 MANILIUS, Lunar Object No. 240, PL 23, 31 ... 31 
 
 MANNERS, Lunar Object No. 249, PL 23 31 
 
 MANZINUS, Lunar Object No. 54, PL 26, 29 30 
 
 MARALDI, Lunar Object No. 160, PL 23, 29 ... 31 
 
 MARCO POLO, Lunar Object No. 398, PL 24 ... 32 
 
 MARE AUSTRALE, C, in Moon, PL 26, 27, 28 ... 33 
 
 MARE CHRONIUM, on Mars, PL 8 12 
 
 MARE CIMMERIUM, on Mars, PL 8 12 
 
 MARE CRISIUM, A, in Moon, PL 23, 27, 28, 29, 
 
 30,31 '. 33 
 
 MARE ERYTHRA;UM, on Mars, PL 8 12 
 
 MARE FA:CUNDITATIS, in Moon, B, PL 26, 
 
 27-31 33 
 
 MARE FRIGORIS, K, in Moon, PI. 23, 31, 36, 38... 33 
 
 MARE HUMBOLDTIANUM, in Moon, D, PL 23, 27, 
 
 28,29,30 33 
 
 MARE HUMORUM, in Moon, T, PL 25, 35, 36, 37 
 
 38 \ 33 
 
 MARE TCARIUM, on Mars, PL 8 12 
 
 MARK IMBRIUM, in Moon, L, PL 24, 32-38 33 
 
 MARE NECTARIS, in Moon, F., PL 26, 29. 30, 31 33 
 MARE NUBIUM, in Moon, Q, PI. 25, 33, 34, 35, 
 
 36, 37 ' 33 
 
 MARE SERENITATIS, in Moon, J, PL 20, 23, 30, 
 
 31,32 25 33 
 
 .MARE SIRENUM, on Mars, PL 8 12 
 
 MARE SMYTHII, in Moon, Y, PL 23, 27 33 
 
 MARE TRANQUILLITATIS, in Moon, E, PL 23, 29, 
 
 30,31 33 
 
 MARE TYRRHENIUM, on Mars, PL 8 12 
 
 MARE VAPORUM, in Moon, M, PL 23, 31 33 
 
 MARGAHITIFER SINUS, on Mars, PL 8 12 
 
 MARINUS, Lunar Object No. 18, PI. 26 30 
 
 MARIUS, Lunar Object No. 390, PI. 24, 36 32 
 
 MARS, Chart of, PL 8 11 
 
 MARS, Dimensions, &c., PL 5 7 
 
 MARS, How to find 42 
 
 MARS, Index to 42, 43 
 
 MARS IN OPPOSITION 38 
 
 MARS, Orbit of, PI. 3, 4 5 
 
 MARS, Periodic time of, PL 2; 
 
 MARS, Phases of, PL 6 8 
 
 MARS, SATELLITES of, PL 7 10 
 
 MASKELYNE, Lunar Object No. 157, PL 23 31 
 
 MASON, Lunar Object No. 213, PL 23 31 
 
 MASSES of Stars compared with Sun 68 
 
 MAUPERTUIS, Lunar Object No. 424, PL 24 32 
 
 MAUROLYCUS, Lunar Object No. 121, PL 26, 30, 
 
 31 30 
 
 MAURY, Lunar Object No. 223, PL 23 31 
 
 McCLURE, Lunar Object No. 37, PL 26 30 
 
 MEAN DISTANCE OF A PLANET 5 
 
 MEDII SINUS, in Moon, P, PL 24. 32, 33, 34 33 
 
 MEDUSA, PI 4 6 
 
 MENELAUS, Lunar Object No. 234, PL 23, 31 ... 31 
 MENSA, PL 70. 
 
 MERCATOR, Lunar Object No. 339, PL 25, 34 32 
 
 MERCURIUS, Lunar Object No. 180, PL 23, 27, 28 31 
 
 MERCURY, Dimensions of, PL 5 7 
 
 MERCURY, Orbit of, PL 3 ... 5 
 
 MERCURY, Periodic time of, PL 2. 
 
 MERCURY, when to be seen, 38, 39 
 
 MERIDIAN. At any place the Celestial Meridian 
 
 is the great circle through the Poles and the 
 
 Zenith. 
 
INDEX. 
 
 91 
 
 MERIDIAN (CENTRAL). Means in this Atlas the 
 line joining the Nortli point to the South 
 point on the monthly maps. 
 
 MEROPE, in Pleiades, Ph80 62 
 
 MERSENIUS, Lunar Object No. 350, PI. 25, 36, 37 32 
 MESSALA, Lunar Object No. 175, PI. 23, 27, 28 31 
 MESSIER, Lunar Object No. 29, PI. 26, 28, 29 ... 30 
 
 METIUS, Lunar Object No. 44, PI. 26, 28, 29 30 
 
 METON, Lunar Object No. 197, PI. 23, 30 31 
 
 MICROMETER An instrument for the measure- 
 ment of small quantities. 
 MiCRoscoi'iUM, PI: 69. 
 
 MILICHIUS, Lunar Object No. 379, PI. 24, 35 32 
 
 MILLER, Lunar Object No. 134, PI. 26 30 
 
 MILKY WAY, Photograph around Cluster M. 11, 
 
 PI. 81 62 
 
 MIMAS, Satellite of Saturn, PI. 7 11 
 
 MOIGNO, Lunar Object No. 195, PI. 23 31 
 
 MONOCEROS, PI. 59,60: 
 
 MONOCEROTIS, 11, a Triple Star, PI. 59 74 
 
 MONTHLY MAPS OF STARS, PI. 39-50 35 
 
 MOON, Elger's drawings of, PI. 23-38. 
 MOON, Key Map of Objects, PI. 27-38. 
 
 MOON, List of Lunar Objects 30-33 
 
 MOON, List of Mountain Ran jes 33 
 
 MOON, List of Seas in 33 
 
 MOON, Mountains near limb of 33 
 
 MOON, Orbit of, PL 7 10 
 
 MOON, Photographs of, PI. 20, 21, 22 25 
 
 MOON, Plates of, at different Phases, PI. 27-38. 
 MOON, Sectional Charts of, PI. 23-26. 
 
 MOON, Table for finding Place with Age 27 
 
 MOON'S PHASES AND ECLIPSES, PI. 14 17 
 
 MORETUS, Lunar Object No. 300, PI. 25, 32, 33... 32 
 
 MORTIS LACUS, in Moon, PI. 23, 23, 30, 33 33 
 
 MOSTIXG, Lunar Object No. 261, PI. 25, 32, 33 ... 31 
 
 MUSCA, PI. 67, 70. 
 
 MUTUS, Lunar Object No. 53, PI. 26, 29 30 
 
 NADIR. The point of the celestial sphere be- 
 neath out feet to which a plummet points. 
 
 NASIREDDIN, Lunar ObjectNo.287, PI. 25 31 
 
 NEANDER, Lunar Object No. 43, PI, 26, 28 30 
 
 NEAP TIDE, Cause of, PI. 2 3 
 
 NEARCHUS, Lunar Object No. 50, PI. 26 30 
 
 NEBDLARUM PALUS, in Moon, X, PI. 23, 31, 32 33 
 
 NECTARIS MARE, in Moon, F, PI. 26, 29, 30, 31 33 
 
 NEPER, Lunar Object No. 139, PI. 23, 27 31 
 
 NEPTUNE, Dimensions of, PI. 5 7 
 
 NEPTUNE, Orbit of, PI. 4 6 
 
 NEPTUNE, Satellite of, PI. 7 11 
 
 NEWCOMB, Lunar Object No. 225, PI. 23 31 
 
 NEWTON, Lunar Object No. 302, PI. 25, 34 32 
 
 NEW MOON, Plate 7. 
 
 NEW STARS 54 
 
 NICOLAI, Lunar Object No. 69, PI. 26 30 
 
 NICOLLET, Lunar Object No. 344, PI. 25, 33 ... 32 
 NODE. A point in which an Orbit intersects 
 the plane to which it is referred. 
 
 NONIUS, Lunar Object No. 117, PI. 26 30 
 
 NORMA, PI. 68. 
 
 NORM*;, Nova 1893, PI. 68 54 
 
 NUBIUM MARE, in Moon, Q, PI. 25, 33, 34, 35, 
 
 36, 37 33 
 
 NUTATION. A small oscillation in the direction 
 of the Earth's axis, due to the fact that the 
 forces producing precession do not act uni- 
 formly. 
 
 OBERON, Satellite of Uranus, PL 7 11 
 
 OBLATE. Applied to a globular body flattened 
 
 at the poles, like the Earth. 
 OBLIQUITY OF THE ECLIPTIC. The inclination of 
 
 the Ecliptic to the Equator. 
 
 OBSERVATORY, Companion to the (quoted) 67 
 
 OCCULTATION. Applied to the passage of the 
 
 Moon over a star, or of Jupiter over one of 
 
 his satellites. 
 OCEANUS PROCELLARUM, in Moon, S, PI. 24, 35, 
 
 36,37,38 33 
 
 OCTANS, PI. 70. 
 
 (ENOPIDES, Lunar Object No, 435, PI. 24 32 
 
 OERSTED, Lunar Object No. 183, PI. 23 31 
 
 OKEN, Lunar Object No 20. PI. 26 30 
 
 OLBERS, Lunar Object No. 393, PL 24, 38 32 
 
 OPHIUCHI, Nova 1848, PI. 62 , 54 
 
 OPHIUCHUS, PI. 62, 68, 71, 72. 
 
 OPPOLZER, Work on Eclipses 18 
 
 OPPOSITION a Planet is in opposition to the 
 
 Sun when its longitude differs from that of 
 
 the Sun by 180. Symbol lor opposition... 5 
 ORBIT. The track pursued by a planet round 
 
 the Sun, or by a Satellite round its primary 
 
 planet. 
 
 ORCUS (Canal), on Mars, PI. 8 12 
 
 ORIANI, Lunar Object No 163, PL 23 31 
 
 ORION, PI. 59, 71, 72. 
 
 ORION, Great Nebula in, PI. 73 59 
 
 ORIONIS, a, or BETELGEUX, PI. 59, Variable... 54, 74 
 ORIONIS, 8, Multiple Star 73 
 
92 
 
 INDEX. 
 
 ORIONIS, Z, Triple Star, PI. 59 73 
 
 ORIONIS, ff, MultipleStar 73 
 
 ORONTIUS, Lunar Object No. 288, PI. 25 31 
 
 PALITZSCH, Lunar Object No. 9, PL 26 30 
 
 PALLAS, Lunar Object No. 375, PL 24, 32 32 
 
 PALLAS, minor Planet , diameter of 8 
 
 PALUS NEBULARUM, in Moon, X, PL 23, 31, 32 33 
 
 PALUS PUTREDINIS, in Moon, Z, PL 23, 32 33 
 
 PALUS SOMNII, in Moon, V, PL 23, 28, 29 33 
 
 PARALLAX. The difference in direction between 
 the positions of a heavenly body as seen 
 
 from two different points, PI. 1 2 
 
 PARALLELS. Circles parallel to the Equator, 
 having one of the Poles as centre. 
 
 PARROT, Lunar Object No. 108, PL 26 30 
 
 PARRY, Lunar Object No. 271, PL 25, 33 31 
 
 PATHS OF SPOTS ACROSS THE SUN'S Disc, PL 13 16 
 
 PAVO, PL 68, 69, 70, 72. 
 
 PAVONIS, K, regularly Variable Star, PI. 69, 70 53 
 
 PEGASUS, PL 52, 57, 58, 63, 71, 72. 
 
 PEIRCE, Lunar Object No. 153, PL 23, 27, 28, 29 31 
 
 PENTLAND, Lunar Object No. 131, PL 26 30 
 
 PERCY, MTS., in Moon, n, PL 25 33 
 
 PERIHELION OF A PLANETARY ORBIT 5 
 
 PERIODIC TIME IN A PLANETARY ORBIT 2 
 
 PERRINE'S COMET, 1902, III., PL 19 23 
 
 PERSEI, /3, or ALGOL, regularly Variable Star, 
 
 PL 53 51, 72 
 
 PERSEI, 0, a Triple Star, PL 53 72 
 
 PERSEI, p, Variable Star, PL 53 54 
 
 PERSEI, Nova 1887, PL 53 54 
 
 PERSEI, Nova 1901, PL 53 54 
 
 PERSEI, Nova 1901, Photographs of Star and 
 
 surrounding Nebula, PL 82 63 
 
 PF,RSEIDS, Orbit of, PL 3 5 
 
 PERSEIDS, Meteor Shower 3,55 
 
 PERSEUS, PL 52, 53, 71. 
 
 PERSEUS, Great Clusters in, PL 52, 53 71 
 
 PERTURBATION. A disturbance in the orbit of a 
 heavenly body caused by some other attrac- 
 tion besides that which chiefly controls the 
 motion. 
 
 PETAVIUS, Lunar Object No. 7, PL 26, 27, 28, 29 30 
 
 PETERS, Lunar Object No. 196, PL 23 31 
 
 PHASES OF THE MOON, PL 14 17 
 
 PHASES OF THE PLANETS, PL 6 8 
 
 PHILLIPS, Lunar Object No. 13, PI. 26 30 
 
 PHILOLAUS, Lunar Object No. 420, PL 24, 34, 
 
 35, 36 '....' 32 
 
 PHOBOS, Satellite of Mars, PL 7 10 
 
 PHOCYLIDES, Lunar Object No. 321, PL 25, 36, 
 
 37, 38 32 
 
 PHOEBE, Satellite of Saturn n 
 
 PHCENIX, PL 64, 65, 72. 
 
 PIAZZI, Lunar Object No. 329, PI. 25, 37, 38 ... 32 
 
 PICARD, Lunar Object No. 152, PL 23, 27, 28, 29 31 
 
 PICCOLOMINI, Lunar Object No. 63, PL 26, 29, 30 30 
 PICKERING, W. H., Photograph of Solar Corona, 
 
 PI 16 19 
 
 Pico, Lunar Mountain, q, PL 24, 33, 34. 35 33 
 
 PICTET, Lunar Object No. 289, PL 25 32 
 
 PICTOR, PL 65, 66. 
 
 PINGRE, Lunar Object No. 319, PL 25 32 
 
 PISCES, PL 52, 58, 63, 71, 72 3 
 
 PISCIS AUSTRALIS, PL 64, 69, 72. 
 
 PISCIUM, 35, Double Star, PL 58, 63 70 
 
 PISCIUM, a, Double Star, PI. 58 71 
 
 PITATUS, Lunar Object No. 280, PL 25, 33 31 
 
 PITISCUS, Lunar Object No. 52, PL 26, 29 30 
 
 PITON, Lunar Mountains, r, PL 24, 34, 35 33 
 
 PLANA, Lunar Object No. 214, PL 23, 29 31 
 
 PLANET, Naming an unknown 48 
 
 PLANETS, Inner, PL 3 4 
 
 PLANETS, Comparative Sizes of, PL 5 7 
 
 PLANET, Mean Distance of a 5 
 
 PLANETARY PHENOMENA 38 
 
 PLANETS, Symbols for the 5 
 
 PLATO, Lunar Object No. 413, PL 24, 32, 33, 
 
 34, 35 29, 32 
 
 PLAYFAIR, Lunar Object No. 100, PL 26, 31 ... 30 
 PLEIADES, Photographs of Stars and Nebulae, 
 
 PL 79-80 62 
 
 PLEIADES, PL 53, 58, 71, 72, 79, 80 72 
 
 PLINIUS, Lunar Object No. 227, PL 23, 30, 31... 31 
 
 PLUTARCH, Lunar Object No. 164, PL 23 31 
 
 POISSON, Lunar Object No. 96, PL 26 30 
 
 POLAR Axis, PL 1 1 
 
 POLE STAR, as a Double Star, PL 51 ....*. 70 
 
 POLYBIUS, Lunar Object No. 92, PL 26 30 
 
 PONS, Lunar Object No. 93, PL 26, 30 30 
 
 PONTANUS, Lunar Object No. 94, PL 26 30 
 
 PONTECOULANT, Lunar Object No. 22, PL 26, 27, 
 
 28 30 
 
 POSIDONIUS, Lunar Object No. 218, PL 23, 29, 
 
 30 31 
 
 POSITION ANGLE OF THE SUN'S A xis 16 
 
 PR^SEPE CANCRI a Cluster, PL 54, 60 75 
 
INDEX. 
 
 93 
 
 PKKCESSION IN DECLINATION, Table of 57 
 
 PRECESSION in R. A., Table of 57 
 
 PRECESSION OF THE EQUINOXES. An alteration 
 in the position of the Equinoxes, due to a 
 continuous revolution of the pole of the 
 Equator round the pole of the Ecliptic, in 
 
 about '26,000 years 56 
 
 PRIME VERTICAL, PI. 1. 
 
 PROCELLARUM OCEANUS, in Moon, S, PI. 24, 35, 
 
 36,37,38 33 
 
 PROCLUS, Lunar Object No. 156, PI. 23, 28, 29 31 
 
 PROMINENCES on the Sun, PI. 12 15 
 
 PROMONTORY, LAPLACE, in Moon, u, PL 24, 34, 
 
 35, 36, 37 33 
 
 PTOLEM,>:US, Lunar Object No. 264, PL 25, 32, 33 31 
 PUPPIS, PI. 59, 60, 66. 
 
 PUPPIS L 2? regularly Variable Star, PL 66 53 
 
 PUPPIS V, Variable Star, PL 66 53 
 
 PURBACH, Lunar Object No. 277, PI. 25, 32 31 
 
 PUTREDINIS PALUS, Z, in Moon, PL 23, 32 33 
 
 PYRENEES, in Moon, g. PL 26, 28, 29, 30 33 
 
 PYHIPHLEGETHON, on Mars. PL 8 12 
 
 PYTHAGORAS, Lunar Object No. 432, PL 24, 37, 
 
 38 32 
 
 PYTHEAS, Lunar Object No. 403, PL 24, 33, 34 32 
 
 QUADRATURE. The position of a heavenly body 
 
 when 90 from the Sun.... 5 
 
 RABBI LKVI, Lunar Object No. 66, PL 26, 30... 30 
 RADIANT POINT. The point on the heavens from 
 
 which the Shooting Stars, in a shower of 
 
 such bodies, appear to diverge. 
 RAMBAUT, Dr. Arthur A. See Preface. 
 RAMSDEN, Lunar Object No. 355, PL 25, 34, 35 32 
 
 REAUMUR, Lunar Object No. 115, PL 26 30 
 
 RED SPOT ODJUPITER, PI. 9 12 
 
 REFRACTION. The bending of a ray of light on 
 
 passing from one medium into another 2 
 
 REFRACTIONS, Table of 2 
 
 REGIOMONTANUS, Lunar Object No. 278, PL 25, 
 
 32 - 31 
 
 REGULARLY VARIABLE STARS 51 
 
 REICHENBACH, Lunar Object No. 41, PL 26, 28 30 
 
 REINER, Lunar Object No. 389, PL 24, 38 32 
 
 REINHOLD, Lunar Object No. 377, PL 24, 33, 34, 
 
 35 32 
 
 REPSOLD, Lunar Object No. 439, PL 24, 38 33 
 
 RETICULUM, PL 65, 70. 
 
 PAGK. 
 
 RETROGRADE applied to the motion of a planet 
 or satellite when it is in the direction oppo- 
 site to the general direction of motion. 
 
 RH.KTICUS, Lunar Object No. 114, PL 26, 31 ... 30 
 
 RHEA, Satellite of Saturn, PI. 7 '.. 11 
 
 RHEITA, Lunar Object No. 42, PI. 26 30 
 
 RICCIOLI, Lunar Object No. 365, PL 25, 38 32 
 
 RICCIUS, Lunar Object No. 65, PL 26, 30 30 
 
 RIGHT ASCENSION 1 
 
 RIPH/EAN MOUNTAINS, in Moon, i, PL 25, 35 ... 33 
 RITCHEY, G. W., Photograph of prominences, 
 
 PL 12 15 
 
 RITCHEY, G. W., Photographs of the Moon, 
 
 PI. 20, 21, 22 25 
 
 RITCHEY, G. W., Photograph of Orion Nebula, 
 
 PL 73 59 
 
 RITCHEY, G. W., Photograph of Andromeda 
 
 Nebula, PL 74 '59 
 
 RITCHEY, G. W., Nova Persei Nebula,, PL 82 ... 68 
 
 RITTER, Lunar Object No. 246, PL 23, 30 31 
 
 ROBERTS, Isaac, Photograph of Nebulae in 
 
 Pleiades, PL 79 62 
 
 ROBINSON, Lunar Object No. 436. PL 24 32 
 
 ROCCA, Lunar Object No. 362, PL 25, 37, 38 ... 32 
 
 ROMER, Lunar Object No. 221, PL 23 31 
 
 ROOK MOUNTAINS, Lunar Object 33 
 
 RORIS SINUS, in Moon, W, PL 24, 37, 38 33 
 
 ROSENBERGER, Lunar Object No. 49, PL 26, 28, 
 
 29 30 
 
 Ross, Lunar Object No. 228, PL 23, 30 31 
 
 ROSSE, Lunar Object No. 61, PL 26 30 
 
 ROST, Lunar Object No. 3150P1. 25, 34, 35 32 
 
 SABINE, Lunar Object No. 247, PL 23, 30 31 
 
 SACROBOSCO, Lunar Object No. 90, PL 26, 30 ... 30 
 SAGITTA, PL 62, 63. 
 
 SAGITTJE, S, Variable Star, PL 6^2 53 
 
 SAGITTARII, X 3, regularly variable Star, PL 68 53 
 SAGITTARII, Wyi regularly Variable Star, PL 
 
 68,69 53 
 
 SAGITTARII, Nova 1898, PL 62 54 
 
 SAGITTARII, Y, Variable Star PL 62 53 
 
 SAGITTARIUS, PL 62, 68, 69, 72- 9 
 
 SAGITTARIUS, Nebula M. 17 in, PL 62 79 
 
 SAGITTARIUS, Cluster M. 8 in, PL 62, 69 79 
 
 SANTBECH, Lunar Object No. 36, PL 26, 28, 29 30 
 
 SAROS, The Eclipse Cycle 18 
 
 SASSERIDES, Lunar Object No. 284, PL 25, 33... 31 
 
 SATELLITES, Systems of, PL 7 ,.. 10 
 
 SATURN, Description of Orbit of, PL 4 g 
 
94 
 
 INDEX. 
 
 SATURN, Description of, PI. 10 13 
 
 SATURN, Dimensions of Rings, PI. 5 7 
 
 SATURN, Drawing of, PI. 10 13 
 
 SATURN IN OPPOSITION, to 1950 38 
 
 SATURN, Index to 46, 47 
 
 SATURN, Orbit of, PI. 4. 
 
 SATURN, Phases of Rings, PI. 6 9, 38 
 
 SATURN, Satellites of, PI. 7 11 
 
 SAUSSURE, Lunar Object No. 290, PI. 25, 32, 33 25, 32 
 SCHEINER, Lunar Object No. 313, PI. 25, 34, 35 32 
 SCHIAPARELLI, Lunar Object No. 450, PI. 24 ... 33 
 SCHICKARD, Lunar Object No. 323, PI. 25, 36, 
 
 37,38 32 
 
 SCHILLER, Lunar Object No. 317, PI. 25, 35, 36 32 
 SCHOMBERGER, Lunar Object No. 27, PI. 26, 29 30 
 SCHROTER, Lunar Object No. 374. PI. 24, 32 ... 32 
 
 SCHUBERT, Lunar Object No. 135, PI. 23 30 
 
 SCHUMACHER, Lunar Object No. 178, PL 23 31 
 
 SCHUSTER, A., Photograph of Solar Corona, 
 
 PI. 16 19 
 
 SCHWABE, Lunar Object No. 149, PI. 23 31 
 
 SCORESBY, Lunar Object No. 202, PI. 23, 30 31 
 
 SCORPII, T.Nova (1860), PL 61, 62.68 54 
 
 SCORPII, a, or ANTARES, PI. 68 78 
 
 SCORPII, IJL, Spectroscopic Binary ^.. 79 
 
 SCORPIO, PI. 61, 62, 68, 72. 
 SCULPTOR, PL 58, 64. 
 
 SCUTI, R., Variable Star, PL 62 54 
 
 SEASONS, Cause of, PL 2 1 
 
 SECCHI, Lunar Object No. 155, PL 23, 28 31 
 
 SEGNER, Lunar Object No. 311, PL 25, 35 32 
 
 SELEUCUS, Lunar Object No. 397, PL 24, 37, 38 32 
 
 SENECA, Lunar Object No. 165, PL 23 31 
 
 SERENITATIS MARE,- in Moon, J, PI. 23, 30, 31, 
 
 32 33 
 
 SERPENS, PL 56, 61, 62, 71, 72. 
 
 SERPENTARII, Nova 1604, PI. 62 54 
 
 SEXTANS, PL 60. * 
 
 SHARP, Lunar Object No. 426, PL 24, 35, 36 32 
 
 SHORT, Lunar Object No. 301, PL 25 32 
 
 SHORT PERIOD VARIABLES 52 53 
 
 SHUCKBURGH, Lunar Object No. 184, PI. 23 . . 31 
 SIDEREAL DAY 35 
 
 SILBERSCHLAG, Lunar Object No. 252, PL 23 31 
 
 SIMPELIUS, Lunar Object No. 133, PI. 26 30 
 
 SINUS ^ESTUUM, in Moon, N, PL 24, 32, 33, 34... 33 
 
 SINUS IRIDUM, in Moon, R, PI. 24, 34, 35, 37, 38 33 
 SINUS IRIDUM HIGHLANDS, in Moon, e, PL 24, 35, 
 
 36 - 37 ' ' 33 
 
 SINUS MEDII, in Moon, P, PL 24, 32, 33 33 
 
 Six us RORIS, in Moon, W, PL 24, 37, 33 . 33 
 
 SIRENIUS LACUS, on Mars, PI. 8 ... 12 
 
 SIRIUS, Binary Star ................. 7-4 
 
 SIUSALIS, Lunar Object No. 358, PL 25 .32 
 
 SMYTH, PIAZZI. Lunar Object No. 412, PI. 24 ' 32 
 
 SMYTHII MARE, in Moon, Y, PL 23. 27*.. 33 
 
 SMYTH'S CELESTIAL CYCLE ......... ... ' QJ 
 
 SNELLIUS, Lunar Object No. 16, PI. 26, 28 ' 30 
 
 SOLAR CORONA, Description of, PI. 16.... jg 
 
 SOLAR PHENOMENA, Corona and Prominences 
 
 ; . .......................................... 15,18 
 
 SOLIS LACUS, on Mars, PL 8 ......... 12 
 
 SOLSTICES. The points of the Ecliptic attained 
 by the Sun at Midsummer and Midwinter, 
 
 PL 1 
 
 1 
 
 SOMMERING, Lunar Object No. 373, Pi. 24, 32 32 
 
 SOMNH PALUS, in Moon, V, PI. 23, 28 ... 33 
 
 SOMNIORUM LACUS, in Moon, G, PL 23.. 29, 30, 31 33 
 
 SOSIGENES, Lunar Object No. 230, PL 23 25 
 
 SOUTH, Lunar Object No. 433, PI. 24.... ' 32 
 
 SPECTROSCOPY gg 
 
 SPECTROSCOPIC BINARIES gg 
 
 SPHERE, Circles of the, PL 1. 
 
 SPHERE OF THE HEAVENS j 
 
 SPRING TIDE, PL 2 3 
 
 STADIUS, Lunar Object No. 381, PI. 24, 33 32 
 STAR MAPS, PL 51-72. 
 
 STAR MAPS, Description of 49-58 
 
 STAR MAPS, correction Jor Precession 58 
 
 STARS, Variable, Lists of ....51-54 
 
 STEINHEIL, Lunar Object No. 47, PL 26 30 
 
 STEVINUS, Lunar Object No. 15, PL 26, 28 . 30 
 
 STIBORIUS, Lunar Object No. 64, PL 26, 29, 30... 30 
 
 STOFLER, Lunar Object No. 119, PL 26, 31 30 
 
 STRABO, Lunar Object No. 190, PL 23 31 
 
 STRAIGHT RANGE, Lunar Mountains, m, PL 24 33 
 STRAIGHT WALL, Lunar Object No. 275. PL 25, 
 
 33 31 
 
 STREET, Lunar Object No. 295, PL 25 32 
 
 STRUVE, Lunar*0bject No. 179 *.. . 31 
 
 STRUVE, Otto, Lunar Object No. 446, PL 24, 38 33 
 SULPICIUS GALLUS, Lunar Object No. 235, PL 23, 
 
 31 31 
 
 SUMMER SOLSTICE, PL 2 i 
 
 SUN, Corona of, PL 16 y .'.... 18 
 
 SUN, Eclipse of, PL 14 .'. 17 
 
 SUN, Node of Solar Equator, PL 3. 
 
 SUN, Paths of Spots across face, PL 13 16 
 
 SUN, Paths of Total Eclipses, PI. 15 18 
 
 SUN, Photograph of Sun Spot, PL 11 15 
 
 SUN, Prominences surrounding, PL 12 . ,15 
 
INDEX. 
 
 95 
 
 SUN SPOT, Photograph of, PI. 11 15 
 
 SYKTIS MINOR, on Mars, PI. 8 12 
 
 SVRTIS MAJOR, on Mars, PI. 8 12 
 
 TACITUS, Lunar Object No. 82, PI. 26, 30 30 
 
 TANNERUS, Lunar Object No. 145, PI. 26 31 
 
 TAQUET, Lunar Object No. 233, PI. 23, 31 31 
 
 TARUNTIUS, Lunar Object No. 154, PI. 23, 28, 
 
 29 31 
 
 TAURI, a, or ALDEBARAN, PI. 59 73 
 
 TAURI, X, Algol Variable, PI. 58, 59 52 
 
 TAURUS, Lunar;Moimtains, k, PL 29, 30, 31 ... 33 
 TAURUS. PI. 53, 58, 59, 71, 72. 
 
 TAURUS, Nebula, M. 1 in, PI. 53, 59 73 
 
 TAYLOR, Lunar Object No. 76, PI. 26 30 
 
 TELESCOPIUM, PL 68, 69. 
 
 TEMPORARY STABS 54 
 
 TENERIFFE RANGE, Lunar Mountains, I, PI. 24 33 
 
 TERMINATOR OF MOON 28 
 
 TETHYS, Satellite of Saturn, PI. 7 11 
 
 THALES, Lunar Object No. 191, PI. 23 31 
 
 THE^ETETUS, Lunar Object No. 257, 23, 31, 32... 31 
 
 THEBIT, Lunar Object No. 274, PI. 25, 32, 33... 31 
 
 THEON, JUN., Lunar Object No. 75, PI. 26 30 
 
 THEON, SEN., Lunar Object No. 74, PL 26 30 
 
 THEOPHILUS, Lunar Object No. 79, PL 26, 30... 30 
 
 TIDES, PL 2 3 
 
 Tisucus, Lunar Object No. 414, PL 24, 32 32 
 
 TIM*:, Standard, PL 83 82 
 
 TIMOCHARIS, Lunar Object No. 401, PL 24, 33 
 
 34, 35 32 
 
 TIMOLEON, Lunar Object No. 147, PL 23 31 
 
 TITAN, Satellite of Saturn, PL 7 11 
 
 TITANIA, Satellite of Uranus, PI. 7 11 
 
 TOBIAS MAYER, Lunar Object No. 384, PL 24, 
 
 34, 35 32 
 
 TORRICELLI, Lunar Object No. 56, PL 26 30 
 
 TOTAL ECLIPSE OF SUN, PL 16 18 
 
 TOUCANA, PL 70. 
 
 TOUCANI, 47, Globular Cluster 70 
 
 TRALLES, Lunar Object No. 168, PL 23, 28 31 
 
 TRANQUILLITATIS MARE, in Moon.E, PL 23,29, 
 
 30, 31 33 
 
 'TRANSIT. The passage of a celestial body across 
 
 a fixed line, of a planet across the Sun, or 
 
 of one of his satellites across Jupiter. 
 TRIANGULA, PL 52, 53, 71. 
 
 TRIANGULI i, a Double Star, Pi. 52, 53 71 
 
 TPIANGULUM, PL 68, 70, 72. 
 
 TRIESNECKER, Lunar Object No. 242 PI 23 31 
 
 '** 31 
 
 TRIVIUM CHARONTIS. on Mars, PI. 8 ... ]2 
 
 TURNER, H. H. , Discoverer of Nova Geminorum 54 
 TYCHO, Lunar Object No. 291, PI. 21, 25, 33, 
 
 34 25.32 
 
 UKERT, Lunar Object No. 241, PI. 23 31 
 
 ULUGH BEIGH, Lunar Object No. 433, PL 24 ... 33 
 
 UMBRIEL, Satellite of Uranus, PI. 7 n 
 
 URANOMETRIE GENERALE of HOUZEAU f>0 
 
 URS.E MAJORIS, , a Double Star, PI. 55 76 
 
 URS.E MAJORIS, , a Double Star, PL 55 77 
 
 URSA MAJOR, PL 51, 54, 55, 56, 71. 
 
 URSA MAJOR, Planetary Nebula, M. 97, PL 55 76 
 
 URSA MINOR, PL 51, 56, 71. 
 
 URS.E MINORIS, a, as a Double Star, PL 51 70 
 
 URANUS, Dimensions of, PL 5 7 
 
 URANUS, Orbit of, PI. 4 6 
 
 URANUS, Satellites of, PL 7 11 
 
 VAPORUM MARE, in Moon, M, PI. 23, 31 ......... 33 
 
 VARIABLE STARS ....................................... 51-55 
 
 VASCO DE GAMA, Lunar Object No. 396, PL 24 
 VEGA, Lunar Object No. 21, PL 26 ............... 
 
 VEGA, or a LYR.W, PL 57 .............................. 
 
 32 
 30 
 
 79 
 63 
 
 VELOCITY of Star at right angles to line of Sight 
 
 VELA, PL 66, 67. 
 
 VELORUM N., Variable Star, PL 66 ............... 53 
 
 VENDELINUS, Lunar Object No. 3, PL 26, 27, 
 
 28, 29 ................................................... 30 
 
 VENUS, as an Evening Star ........................... 38 
 
 VENUS, as a Morning Star ........................... 38 
 
 VENUS, Dimensions of, and position of Axis, 
 
 PL 5 ... .............................................. 7 
 
 VENUS, how to find .................................... 40 
 
 VENUS, Index to ....................................... 39-41 
 
 VENUS, Orbit of, PL 3. 
 
 VENUS, Periodic Time of, PL 3. 
 
 VENUS, Phases of, PL 6 ................................. 8, 9 
 
 VERTICAL, PRIME, PL 1. 
 
 VESTA, diameter of ....................................... 8 
 
 VIETA, > unar Object No. 332, PL 25, 36, 37 ... 32 
 
 VIRGINIS, a, (Spica), Spectro.scopic Binary ...... 77 
 
 VIRGINIS7, a Double fctar. PL 61 .................. 77 
 
 VIRGO, PL 60, 61,71, 72 .............................. 3 
 
 VITELLO, Lunar Object No. 335, PL 25, 35 ...... 32 
 
 VITRUVIUS, Lunar Object No. 159, PI. 23, 29 31 
 
 VLACQ, Lunar Object No. 48, PI. 26, 29 ...... 30 
 
96 
 
 INDEX. 
 
 TAKE. 
 
 VOLANS, PI. 66, 70. 
 VULPECDLA, PI. 57, 62, 6:j. 
 
 VCLPECUL.S;, Nova, 1670, PI. 57 54 
 
 VULPECULA, Dumb-bell Nebula in, PI. 57,62, 
 
 77 61 
 
 "VULPECUUE T., regularly Variable Star, PI. 57 53 
 
 WALTER, Lunar Object No. 116, PL 26, 32 30 
 
 WAKGENTIN, Lunar Object No. 322, PI. 25,37,38 32 
 
 WEBB, Lunar Object No. 28, PI. 26 30 
 
 WEIGEL, Lunar Object No. 314, PI. 25 32 
 
 WEKNER, Lunar Object No. 98, PI. 26, 31, 32 30 
 
 WHEWELL, Lunar Object No. 255, PI. 23 ol 
 
 WICHMANN, Lunar Object No. 369, PI. 25, 35 32 
 
 WILHELM I., Lunar Object No. 293, PI. 25, 33, 34 32 
 WILHELM HUMBOLDT, Lunar Object No. 12, 
 
 PI. 26,27 30 
 
 WILLIAMS, A. STANLEY, Photographs of Nova 
 
 Persei, PI. 82 63 
 
 WILSON, W. E., Photographs of Cluster in 
 
 Hercules and Nebula in Cygnu?, PI. 75 ... 60 
 
 WILSON, Lunar Object No. 307, PL 25, 35 32' 
 
 WOLLASTON, Lunar Object No. 449, PL 24, 36... 33- 
 
 WROTTESLEY, Lunar Object No. 8, PL 26 30 
 
 WUR/ELBAUER, Lunar Object No. 283, PL 25, 33 31 
 
 XENOPHANES, Lunar Object No. 438, PL 24, 38 32' 
 
 ZACH, Lunar Object No. 129, PL 26. 31, 32 30- 
 
 ZAGUT, Lunar Object No. 67, PL 26, 30 30' 
 
 ZENITH. The point of the celestial sphere 
 directly overhead to which a plumb line 
 points. 
 
 ZENO, Lunar Object No. 148, PI, 23 31 
 
 ZODIAC. A belt on the heavens within which 
 the larger planets chiefly remain. It is 
 practically what is marked on the Monthly 
 Maps as the "Track of the Planets." 
 
 ZODIAC, Signs of the 4 
 
 ZUCHIUS, Lunar Object No. 310, PL 25 32 
 
 ZUPUS, Lunar Object No. 360, PI. 25 32. 
 
,, n 
 
 u 
 
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 6 
 
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 13Apr52Ll! 
 
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