3R YOUNG FOL ELM ASTRONOMY FOR YOUNG FOLKS NORTHERN PORTION OF THE MOON AT LAST QUARTER Taken with loo-inch Hooker Telescope of the Mt. Wilson Observatory (See Chapter XXI) ASTRONOMY for YOUNG FOLKS BY ISABEL MARTIN LEWIS, A. M. (Connected with the Nautical Almanac Office of the U. S. Naval Observatory) NEW YORK DUFFIELD AND COMPANY 1922 Copyright, 1921, by THE CENTURY COMPANY Copyright, 1922, by DUFFIELD AND COMPANY Printed in U. S. A. CONTENTS CHAPTER PAGE Preface ...... , . . xiii I. The Constellations ...... 3 II. January . .... . . . . . 15 III. February . . ... . . . . 21 IV. March . . . . . . . . . . 28 V. April . ... v .-""^ ' * * 35 VI. May . . . . f . . . . . 41 VII. June ;/. . ...... . . 49 VIII. July . ; . . . . . . .-..-. 56 IX. August , . . . . . . , . 64 X. September . -, ... . . . . 71 XL October . . . . , . . . . 78 XII. November . , .... . . . 84 XIII. December . . 90 XIV. Stars of the Southern Hemisphere . . 96 XV. The Milky Way or Galaxy . . . .107 XVI. The Surface of the Sun . . . . .113 XVII. The Solar System ... .' . .119 XVIII. The Origin of the Earth . . . , . 127 XIX. Jupiter and His Nine Moons . . .139 XX. The Rings and Moons of Saturn . . 148 XXI. Is the Moon a Dead World 156 XXII. Comets . . . . . . . V . 165 XXIII. Meteorites ........ 173 V 493929 vi CONTENTS CHAPTER PAGE XXIV. The Earth As a Magnet 183 XXV. Some Effects of the Earth's Atmosphere Upon Sunlight . 193 XXVI. Keeping Track of the Moon .... 207 XXVII. The Motions of the Heavenly Bodies . 216 XXVIII. The Evolution of the Stars From Red Giants to Red Dwarfs 225 XXIX. Double and Multiple Stars .... 230 XXX. Astronomical Distances 241 XXXI. Some Astronomical Facts Worth Remem- bering 250 ILLUSTRATIONS PAGE Northern Portion of the Moon at Last Quarter Frontispiece The Great Hercules Cluster A Universe of Suns ....... . facing page 56 A Dark Nebula: The Dark Bay or Dark Horse Nebula in Orion facing page 110 A. Venus. B. Mars. C. Jupiter. D. Saturn facing page 122 Spiral Nebula in Canes Venatici . . facing page 216 Spiral Nebula in Andromeda Viewed Edgewise facing page 222 Vll LIST OF TABLES PAGE I. The Principal Elements of the Solar System 261 II. The Satellites of the Solar System ... 262 III. The Twenty Brightest Stars in the Heavens . 263 IV. A List of the Principal Constellations . . 264-265 V. Pronunciations and Meanings of Names of Stars and Constellations . 266-267 IX PREFACE ASTRONOMY, it has been said, is the oldest and the noblest of the sciences. Yet it is one of the few sci- ences for which most present-day educators seem to find little, if any, room in their curriculum of study for the young, in spite of its high cultural value. It is, we are told, too abstruse a subject for the youthful student. This is doubtless true of theoretical or mathe- matical astronomy and the practical astronomy of the navigator, surveyor and engineer, but it is not true of general, descriptive astronomy. There are many dif- ferent aspects of this many-sided science, and some of the simplest and grandest truths of astronomy can be igrasped by the intelligent child of twelve or fourteen years of age. Merely as a branch of nature study the child should have some knowledge of the sun, moon, stars and planets, their motions and their physical features, for they are as truly a part of nature as are the birds, trees and flowers, and the man, woman or child who goes forth beneath the star-lit heavens at night abso- lutely blind to the wonders and beauties of the uni- verse of which he is a part, loses as much as the one who walks through field or forest with no thought of the beauties of nature that surround him. The astronomer is the pioneer and explorer of to- xii PREFACE day in realms unknown just as the pioneers and ex- plorers of several centuries ago were to some extent astronomers as they sailed unknown seas and traversed unexplored regions. As the years pass by the astron- omer extends more and more his explorations of the universe and brings back among the fruits of dis- covery measures of giant suns and estimates of the form and extent of the universe, views of whirling, seething nebulae, mysterious dark clouds drifting through space, tremendous solar upheavals or glimpses of strangely marked surfaces of nearby planets. In the following pages the author has endeavored to tell in words not beyond the comprehension of the average fourteen-year-old child something of the nature of the heavenly bodies. In Part I an effort is made to make the child familiar with the stars by indicating when and where they can be found in the early evening hours. In addition to identifying the principal constellations and their brightest stars by means of diagrams an attempt has been made to acquaint the child with the most inter- esting recent discoveries that have been made concerning the principal stars or objects in each group as well as with some of the stones and legends that have been as- sociated with these groups of stars for centuries, and that have been handed down in the folk-lore of all nations. Chapters 2-13, inclusive, appeared originally with diagrams similar to those shown here, under the depart- ment of Nature and Science for Young Folk in St. Nicholas from May, 1921, to April, 1922, inclusive. The Introductory Chapter and Chapters 14 and 15, PREFACE xiii on the Milky Way and Stars of the Southern Hemi- sphere, respectively, are published here for the first time, as is also the chapter in Part II on the Evolution of the Stars from Red Giants to Red Dwarfs, which gives the order of the evolution of the stars as now accepted as a result of the brilliant astronomical researches of Dr. Henry Norris Russell of the United States and Prof. A. S. Eddington, of England. The remaining chapters in Part II have been chosen from a series of articles that have appeared in Science and Invention, formerly The Electrical Experimenter, in the past four years, and have been considerably revised and in some parts rewritten to adapt them to the understanding of more youthful readers. These chapters deal with a variety of astronomical subjects of gen- eral popular interest and an effort has been made to select subjects that would cover as wide an astronomical field as possible in a limited space. The author's aim has not been to write a text-book of astronomy or to treat in detail of any one aspect of this extensive science, but simply to give the average child some general knowledge of the nature of the heav- enly bodies, both those that form a part of our own solar system and those that lie in the depths of space beyond. It has been necessary to write very briefly, and we feel inadequately, of many topics of special interest such as the sun and moon. Books have been written on these two subjects alone as well as upon such sub- jects as Mars, eclipses, comets, meteors, etc., but the XIV PREFACE object has been to acquaint the child with the out- standing features of a variety of celestial objects rather than to treat of a few in detail. If the writer succeeds in arousing the child's inter- est in the stars so that he may look forth with intelli- gence at the heavens and greet the stars as friends and at the same time grasps some of the simplest and most fundamental of astronomical truths such as the dis- tinction between stars and planets, the motions of the heavenly bodies and their relative distances from us and the place of our own planet- world in the universe, this book will have served its purpose. ASTRONOMY FOR YOUNG FOLKS "The heavens declare the glory of God, and the firmament showeth His handiwork." Psalm XIX. Astronomy for Young Folks THE CONSTELLATIONS "Canst thou bind the sweet influences of the Pleiades Or loose the bands of Orion ? thou bring forth lazzaroth in Is season Or canst thou guide Arcturus with his sons?" BOOK OF JOB. WHO would not like to know the stars and constella- tions by their names and in their seasons as we know the birds and the trees and the flowers, to recognize at their return, year by year, Sirius and Spica, Arcturus and Antares, Vega and Altair, to know when Ursa Major swings high overhead and Orion sinks to rest be- neath the western horizon, when Leo comes into view in the east or the Northern Crown lies overhead? Often we deprive ourselves of the pleasure of making friends with the stars and sfiut our eyes to the glories of the heavens above because we do not realize how simple a matter it is to become acquainted with the various groups of stars as they cross our meridian, one by one, day after day and month after month in 3 , ;< t . ! ASTRONOMY FOR YOUNG FOLKS the same orderly sequence. When the robin returns once more to nest in the same orchard in the spring time, Leo and Virgo may be seen rising above the eastern horizon in the early evening hours. When the first snow flies in the late fall and the birds have all gone southward the belt of Orion appears in the east and Cygnus dips low in the west. When we once come to know brilliant blue-white Vega, ruddy Arc- turus, golden Capella and sparkling Sirius we watch for them to return each in its proper season and greet them as old friends. In the following pages we give for each month the constellations or star-groups that are nearest to our meridian, that is, that lie either due north or due south or exactly overhead in the early part of the month and the early part of the evening. We do not need to start our study of the constella- tions in January. We may start at any month in the year and we will find the constellations given for that month on or near the meridian at the time indicated. In using the charts or diagrams of the constellations, we should hold them in an inverted position with the top of the page toward the north or else remember that the left-hand side of the page is toward the east and the right-hand side of the page toward the west, which is the opposite of the arrangement for charts and maps of the earth's surface. We should also bear in mind that the constellations are all continually shifting westward for the stars and the moon and the planets as well as the sun rise THE CONSTELLATIONS 5 daily in the east and set in the west. This is due to the fact that the earth is turning in the opposite direction on its axis, that is from west to east. In twenty-four hours the earth turns completely around with respect to the heavens or through an angle of 360, so in one hour it turns through an angle of 360 -f- 24 or 15. As a result the stars appear to shift westward 15 every hour. This is a distance about equal in length to the handle of the Big Dipper, which I am sure we all know, even if we do not know another constellation in the heavens. If, then, we look at the heavens at a later hour than that for which the constellations are given we will find them farther westward and if our time of observation is earlier in the evening than the hour mentioned we will find them farther eastward. In the course of a year the earth makes one trip around the sun and faces in turn all parts of the heavens. That is, it turns through an angle of 360 with respect to the heavens in a year or through an angle of 360 -f- 12 or 30 in one month. So as a result of our revolution around the sun, which is also in a west to east direction, we see that all the constella- tions are gradually shifting westward at the rate of 30 a month. It is for this reason that we see different constellations in different months, and it is because of the turning of the earth on its axis that we see different constellations at different hours of the night If we should sit up from sunset to sunrise and watch the stars rise in the east, pass the meridian and set 6 ASTRONOMY FOR YOUNG FOLKS in the west as the sun does by day we should see in turn the same constellations that are to pass across the heavens in the next six months. This is because in twelve hours' time we are carried through the same angle with respect to the heavens by the earth's rota- tion on its axis that we are in the next six months by the motion of the earth around the sun. Let us suppose then that the time we choose for our observation of the heavens is the last of the month while our charts are given for the first of the month. We must look then farther westward for our con- stellations just as we must look farther westward if we chose a later hour in the evening for our observa- tions. Let us suppose that we choose for our time of observation half-past eight in the early part of December. On or close to the meridian we will find the constellations outlined in the charts for Decem- ber. To the east of the meridian we will find the constellations that are given for January and Feb- ruary, and to the west of the meridian the constella- tions that are given for November and October. So if we are particularly ambitious or wish to be- come acquainted with the constellations more rapidly we may study at the same time the constellations for the preceding months now west of the meridian and the constellations for the following months now east of the meridian as well as the constellations for the month which will be due north or south or directly overhead as the case may be. If we were able to see the stars by day as well as THE CONSTELLATIONS 7 by night we would observe that as the days go by the sun is apparently moving continuously eastward among certain constellations. This is a result of the earth's actual motion around the sun in the same direction. The apparent path of the sun among the stars is called the ecliptic and the belt of the heavens eight degrees wide on either side of the ecliptic is called the zodiac. The constellations that lie within this belt of the zodiac are called zodiacal constellations. The zodiac was divided by the astronomer Hipparchus, who lived 161-126 B.C., into twelve signs 30 wide, and the signs were named for the constellations lying at that time within each ( of these divisions. These zodiacal constellations are Aries, Taurus, Gemini, Can- cer, Leo, Virgo, Libra, Scorpio, Sagittarius, Capri- cornus, Aquarius and Pisces. With the exception of Libra, the Scales, all of these constellations are named for people or animals and the word zodiac is derived from the Greek word meaning 'W animals." Each month the sun moves eastward 30 through one of these zodiacal constellations. In the days of Hip- parchus the sun was in Aries at the beginning of spring, at the point where the ecliptic crosses the celes- tial equator which lies directly above the earth's equator. This point where the ecliptic crosses the equator was then known as the First Point in Aries. The autumnal equinox was 180 distant in Aquarius and the two points were called the equinoxes because when the sun is at either equinox the day and night are equal in 8 ASTRONOMY FOR YOUNG FOLKS length all over the world. Now for certain reasons which we will not explain here the equinoctial points are not fixed in position but shift gradually westward at the rate of 1 in 70 years. It is as if the equinoxes were advancing each year to meet the sun on its return and their westward motion is therefore called "The Precession of the Equinoxes." Since the days of Hipparchus this motion has amounted to about 30 so that the constellations no longer occupy the signs of the zodiac that bear their names. The sun is now in Pisces instead of Aries at the beginning of spring and in Virgo instead of Aquarius at the beginning of fall. Not only the sun but the moon and planets as well move through the zodiacal constellations. In fact a limit for the zodiac of 8 on either side of the ecliptic was chosen because it marks the extent of the excursions of the moon and planets from the ecliptic. Neither moon nor planets will be found at a greater distance than 8 on either side of the ecliptic. For convenience in determining the positions of the heavenly bodies the astronomer assumes that they lie upon the surface of a celestial sphere that has its center at the center of the earth. The north pole of the celestial sphere lies directly above the north pole of the earth and the south pole of the celestial sphere directly above the south pole THE CONSTELLATIONS 9 of the earth. The celestial equator is the great circle of the celestial sphere that lies midway between its north and south poles and directly above the earth's equator. The ecliptic is also a great circle of the celestial sphere and cuts the celestial equator at an angle of 23^ in the two points 180 apart known as the equinoctial points, of which we have already spoken. The zodiacal constellations lie nearly overhead within the tropics and can be seen to advantage all over the world except in polar regions. For every position of the earth's surface except at the equator we have also our circumpolar constellations which are the ones that never pass below the horizon for the place of observation. In 40 N. Latitude the Big Dipper is a circumpolar constellation for it is above the horizon at all hours of the day and night and all times of the year. If our latitude is 40 N., all stars within 40 of the north pole of the heavens are. circumpolar and never set, while stars within 40 of the south pole of the heavens never rise. All other stars rise and set daily. If we were at the north pole all stars within 90 of the north pole of the heavens would be circumpolar and would describe daily circuits of the pole parallel to the horizon remaining always above it. If we were at the equator all stars within zero degrees of either pole would be circumpolar, that is no 10 ASTRONOMY FOR YOUNG FOLKS stars would be circumpolar, all stars rising and setting daily. As a general rule, then, we may say that stars within an angular distance of the nearest pole of the heavens equal to the latitude never set and stars within an equal distance of the opposite pole never rise while all stars outside of these limits rise and set daily. The beginner who attempts to make the acquain- tance of the principal stars and constellations occasion- ally may find a bright star in a constellation that is not noted in the diagrams. In this case he has prob- ably happened upon one of the bright planets. It is not possible to include the planets in our dia- grams for the reason that they are not fixed in position but apparently wander among the stars. The name planet is, in fact, derived from a Greek word meaning "wanderer." The stars shine by their own light but the planets shine only by reflected light from the sun. Of the seven planets, in the solar system additional to our own planet earth, there are two, Uranus and Neptune that we need not consider for Neptune is not visible without the aid of a telescope and Uranus is fainter than any of the stars included in our diagrams. Mercury will never appear except in the morning or evening twilight, when none but the very brightest stars are visible, since it never departs far from the sun. It will only be seen under certain favorable con- ditions, and usually it will escape our notice altogether THE CONSTELLATIONS 11 unless we know exactly where to look for it although there are but two or three stars in the heavens that surpass it in brightness. Venus, we will probably never mistake for any star in the heavens for it far surpasses all stars in bright- ness. It will always be seen in the west after sunset or in the east before sunrise and it is never seen more than three hours before or after the sun. This leaves us but three planets, Jupiter, Saturn and Mars that we may mistake for bright stars. There is little chance that Jupiter will be thus mistaken for it also is far brighter than all of the stars except Sirius which differs greatly from Jupiter in color. Sirius is a brilliant white and Jupiter is a golden yellow. The planets do not twinkle as the stars do and this is particularly true of Jupiter which is remarkable for the quiet steadiness of its yellow light. This alone would serve to identify it. Saturn is probably mistaken for a star oftener than any of the other planets. It moves so slowly among the stars that we would have to watch it for a number of successive evenings before we could discover that it is moving with respect to the stars. Saturn is yel- lowish in color and we can probably best distinguish it by the steadiness of its light. If we find in one of the zodiacal groups of stars for the planets appear among no other constellations a bright yellowish star where no bright star is indicated on the diagram we may be 12 ASTRONOMY FOR YOUNG FOLKS reasonably certain that we have found the planet Saturn. Mars is the only planet that is reddish in color. Once in fifteen or seventeen years, when it is particularly near to the earth, it surpasses even Jupiter in brightness, but ordinarily it appears no more brilliant than one of the brighter stars. There are only two stars with which we are likely to confuse Mars, Aidebaran and Antares which are very similar to it in color, and, at times, in brightness. Moreover, both of these stars are zodiacal stars and Mars frequently passes through the constellations to which they belong. There should be no trouble about identifying Aldebaran and Antares, however, from their distinctive positions in the dia- grams so that any other reddish star appearing in any of the zodiacal groups we may feel certain is the planet Mars. In the following diagrams of the constellations the brightest and most conspicuous stars, called first-mag- nitude stars, are represented by white stars. These are the stars we should all be able to recognize and call by name and in every instance the name of a first-mag- nitude star is given on the diagram. All other stars are represented by circles, and the size of the circle is an indication of the brightness of the star. Stars visible without the aid of a telescope are referred to usually as "naked-eye stars." They are classed as first, second, third, four, fifth or sixth magnitude stars, according to their relative brightness. THE CONSTELLATIONS 13 A star of the first magnitude is about two and one-half times brighter than a star of the second magnitude, which in turn is two and one-half times brighter than a star of the third magnitude and so on. A first- magnitude star is, then, one hundred times brighter than a sixth magnitude star which is the faintest star that can be seen without the aid of the telescope. This ratio between successive magnitudes continues among the telescopic stars. A star of the sixth magnitude is one hundred times brighter than a star of the eleventh magnitude which in turn is one hundred times brighter than a star of the sixteenth magnitude. The faintest stars that can be seen visually in the greatest telescopes are of the seventeenth or eighteenth magnitude, though stars two or three magnitudes fainter can be photographed. The faintest stars shown in the diagrams are fifth- magnitude stars and stars of this magnitude as well as stars of the fourth magnitude are only given when needed to fill out the distinctive outlines of the con- stellations which have been formed by connecting the principal stars in each group by dotted lines. All stars of first, second and third magnitude are given in the diagrams without exceptions as such stars are visible to everyone on clear nights. The constellations given in the following pages in- clude practically all of the constellations that can be seen in 40 N. Latitude. A diagram is given for each constellation. 14 ASTRONOMY FOR YOUNG FOLKS In this latitude it is impossible to see the constella- tions of the southern hemisphere that lie within 40 of the south pole of the heavens. A brief chapter with diagram treats of these constellations that are invisible in mid-latitudes of the northern hemisphere. II JANUARY ONE of the most easily recognized constellations in the heavens is Taurus, The Bull, a zodiacal group which lies just south of the zenith in our latitudes in the early evening hours about the first of January. Taurus is distinguished by the V-shaped group of The Hyades, which contains the bright, red, first-mag- nitude star Aldebaran, representing the fiery eye of the bull. It also contains the famous cluster of faint stars known as The Pleiades, lying a short distance northwest of The Hyades. No group of stars is more universally known than The Pleiades. All tribes and nations of the world, from the remotest days of recorded history up to the present time, have sung the praises of The Pleiades. They were "The Many Little Ones" of the Babylonians, "The Seven Sisters" of the Greeks, "The Seven Broth- ers" of the American Indians, "The Hen and Chick- ens" of many nations of Europe, "The Little Eyes" of the South Sea Islanders. They were honored in the re- ligious ceremonies of the Aztecs, and the savage tribes of Australia danced in their honor. Many early tribes of men began their year with November, the Pleiad 15 16 ASTRONOMY FOR YOUNG FOLKS month; and on November 17th, when The Pleiades crossed the meridian at midnight, it was said that no petition was ever presented in vain to the kings of ancient Persia. JANUARY TAURUS Poets of all ages have felt the charm of The Pleiades. Tennyson gives the following beautiful description of The Pleiades in Locksley Hall: "Many a night I saw the Pleiades, rising through the mellow shade, Glitter like a swarm of fireflies tangled in a silver braid/' JANUARY 17 A well-known astronomer, not so many years ago, also felt the mysterious charm of The Pleiades and seriously expressed the belief that Alcyone, the bright- est star of The Pleiades, was a central sun about which all other suns were moving. But we know that there is no foundation whatever for such a belief. A fairly good eye, when the night is clear and dark, will make out six stars in this group arranged in the form of a small dipper. A seventh star lies close to the star at the end of the handle and is more difficult to find. It is called Pleione, and is referred to in many legends as the lost Pleiad. Persons gifted with exceptionally fine eyesight have made out as many as eleven stars in the group; and with the aid of an or- dinary opera-glass, anyone can see fully one hundred stars in this cluster. Astronomers have found that The Pleiades cluster contains at least two hundred and fifty stars, all drifting slowly in the same general direction through space, and that the entire group is enveloped in a fiery, nebulous mist which is most dense around the brightest stars. It is not known whether the stars are being formed from the nebula or whether the nebula is being puffed off from the stars. The brightest star, Alcyone, is at least two hundred times more brilliant than our own sun, and all of the brighter stars in the group surpass the sun many times in brightness. It is believed that this cluster is so large that light takes many years to cross from one end of it to the other, and that it is so far from the earth that its light takes 18 ASTRONOMY FOR YOUNG FOLKS over three centuries to reach us, traveling at the rate of 186,000 miles a second. The Hyades is a group of stars scarcely less famous than The Pleiades, and the stars in the group also form a moving cluster of enormous extent at a distance of 140 light-years from the earth. Among the ancients, The Hyades were called the rain- stars, and the word Hyades is supposed to come from the Greek word for rain. Among the many superstitions of the past was the belief that the rising or setting of a group of s.tars with the sun had some special influence over human affairs. Since The Hyades set just after the sun in the showery springtime and just before sun- rise in the stormy days of late fall, they were always associated with rain. In Tennyson's Ulysses we read: "Through ' scudding drifts the rainy Hyades Vex'd the dim sea." Trie Hyades outline the forehead of Taurus, while two bright stars some distance to the northeast of the V form the tips of the horns. Only the head and fore- quarters of the bull are shown in the star-atlases that give the mythological groups, for, according to one legend, he is swimming through the sea and the rest of his body is submerged. According to another legend, Taurus is charging down upon Orion, The Warrior, represented by the magnificent constellation just to the southeast of Taurus, of which we shall have more to say next month. Aldebaran is the Arabic word for "The Hindmost," JANUARY 19 and the star is so called because it follows The Pleiades across the sky. It is one of the most beautiful of all the many brilliant stars visible at this time and we might profit by following the advice of Mrs. Sigourney in The Stars: "Go forth at night And talk with Aldebaran, where he flames In the cold forehead of the wintry sky." Next to Aldebaran in the V is the interesting double star Theta, which we can see as two distinct stars without a telescope. Directly south of Taurus is Eridanus, sometimes called Fluvius Eridanus, or The River Eridanus. Start- ing a little to the southeast of Taurus, close to the brilliant blue-white star Rigel in Orion, it runs to the westward for a considerable distance in a long curving line of rather faint stars, bends sharply southward for a short distance, then curves backward toward the east once more, and, after running for some distance, makes another sharp curve to the southwest and disappears below the southern horizon. Its course is continued far into the southern hemisphere. Its brightest star, Achernar, is a star of the first magnitude, but it lies below the horizon in our latitudes. Eridanus contains no star of particular interest to us. Most of the numerous stars that mark its course are of the fourth and fifth magnitude. It contains but two stars of the third magnitude, one at the beginning of its course and one close to the southwestern horizon. 20 ASTRONOMY FOR YOUNG FOLKS The beautiful constellation of Perseus lies just to the north of Taurus and should rightfully be considered among the constellations lying nearest to the meridian in January, but we give this constellation among the star JANUARY ERIDANUS groups for December because of its close association with the nearby constellations Andromeda and Pegasus in legend and story. m FEBRUARY ACROSS the meridian, due south, between eight and nine o'clock in the evening in the early part of Feb- ruary, lies Orion, The Warrior, generally considered to be the finest constellation in the heavens. Orion is directly overhead at the equator, and so is seen to advantage from all parts of the world except the extreme northern and southern polar regions. A group of three faint stars outlines the head of Orion. His right shoulder is marked by the deep-red, first-magnitude star Betelgeuze (meaning armpit), and his left shoulder by the bright white star Bellatrix, The Amazon. Orion stands facing Taurus, The Bull, and brandishes in his right hand a club, outlined by a number of faint stars extending from Betelgeuze toward the northeast. The top of the club lies near the tips of the horns of Taurus. In his left hands he holds up a lion's skin, which we can trace in another curving line of faint stars to the west and northwest of Bella- trix. The brilliant, blue-white, first-magnitude star Rigel lies in the left foot, and the second-magnitude star Saiph, a little to the east of Rigel, is in the right knee. Three evenly spaced stars lying in a straight line that is exactly three degrees in length form the 21 22 ASTRONOMY FOR YOUNG FOLKS Belt of Orion, and from the Belt hangs the Sword of Orion, outlined by three faint stars. The central star in the Sword appears somewhat blurred and is the multiple star Theta, in the midst of the great Orion nebula, the finest object of its kind in the heavens. Entangled in the meshes of this glowing nebula are a number of brilliant suns, appearing to us as faint stars because of their great distance. The star Theta, in the heart of the nebula, is seen with a powerful telescope to consist of six stars; that is, it is a sextuple star. Even with a small telescope, four of these stars can readily be seen, arranged in the form of a small tra- pezium. The lowest star in the Sword is a triple star, and the entire constellation abounds in double, triple, and multiple stars. From the central portion of the nebula extend many branches and streamers of nebulous light, and it is known that the entire constellation of Orion is en- wrapped in the folds of this nebulosity, which forms a glowing, whirling mass of fiery gases in rapid rota- tion. This constellation is remarkable for the fact that all of its brighter stars, with the exception of the deep- red Betelgeuze, form one enormous, connected group of stars. They are all more or less associated with the great nebula and its branches, and are all extremely hot, white or bluish-white stars, known as helium stars, because the gas helium is so conspicuous in their atmospheres. The Orion stars are the hottest and brightest of all the stars. Blazing Rigel, Bellatrix, and Saiph, marking three FEBRUARY 23 corners of the great quadrilateral, of which Betelgeuze marks the fourth corner, are all brilliant helium stars. So are the three stars in the Belt -and the fainter stars in the Sword and the great nebula. FEBRUARY ORION It has been estimated that the great Orion group of stars is over six hundred light-years from the earth, or about forty million times more distant than the sun. For more than six centuries the rays of light that now enter our eyes from these stars have been traveling through space with the speed of lightning. So we see Orion not as it exists today, but as it was 24 ASTRONOMY FOR YOUNG FOLKS six centuries ago. The extent of the Orion group of stars is also inconceivably great. Even the central part of the great nebula, which appears to our unaided eyes only as a somewhat fuzzy star, would extend from here to the nearest star and beyond, while our entire solar system would be the merest speck in its midst. Betelgeuze, the red star that marks the right shoulder of Orion, is, as we have said, not a member of the Orion group. It has been estimated that it is about two hundred light-years from the earth, or only about one-third as far away as the other stars of the constellation. Betelgeuze very recently has attracted universal at- tention, and will probably be considered an object of historic interest in the future, because it is the first star to have its diameter measured with the new Michelson interferometer, which is now being used so successfully to measure the diameters of the largest stars. The truly sensational discovery has been made that Betelgeuze is a supergiant of the universe, with a diameter of about 275,000,000 miles. Our own sun, which is known as a "dwarf" star, has a diameter of 864,000 miles. That is, Betelgeuze would make about thirty million suns the size of our own. If placed at the center of the solar system, it would fill all of the space within the orbit of Mars; and the planets Mercury, Venus, and the Earth would lie far beneath its surface. Measurements of the diameters of other giant stars which are now being made with the in- FEBRUARY 25 terferometer give results quite as startling as have been obtained in the case of Betelgeuze; and it has been found that several of these stars may even exceed Betel- geuze in size. Such a star is Antares, the fiery-red star in the heart of Scorpio, which is such a conspicu- ous object in the summer evening skies. All these huge stars are deep red in color, and some of them vary irregularly in brightness. Betelgeuze is one of the stars that changes in brightness in a peculiar manner from time to time. When shining with its greatest brilliancy it is a brighter object than the nearby Aldebaran, in Taurus ; but a few months or a year later it may lose so much of its light as to be decidedly inferior to Aldebaran. We may note for ourselves this remarkable change in the brightness of Betelgeuze by comparing the two stars from time to time. Directly south of Orion lies the small constellation of Lepus, The Hare, which is made up of third- magnitude and fourth-magnitude stars. The four brighter stars -are arranged in the form of a small, but distinct, quadrilateral, or four-sided figure, which may be easily seen in our latitudes. The small constellation of Columba, The Dove, which lies just south of Lepus, is so close to the horizon that it can not be seen to advantage in the mid-latitudes of the northern hemi- sphere. Neither Lepus nor Columba contain any object of unusual interest. Due north of Orion, and lying in the zenith at this time, is Auriga, The Charioteer, represented, strange to say, with Capella, a goat, in his arms. The beautiful 26 ASTRONOMY FOR YOUNG FOLKS first-magnitude star Capella, golden-yellow in color, serves us in identifying the constellation. Close at hand are The Kids, represented by a group of three faint stars. Capella is one of the most brilliant stars of the FEBRUARY AURIGA northern hemisphere. It is almost exactly equal in brightness to Arcturus and Vega, stars conspicuous in the summer months, and it is a shade brighter than magnificent blue-white Rigel in Orion. Capella is about fifty light-years distant from the earth and is fully two hundred times more brilliant than our own sun. At the distance of Capella, the sun would appear FEBRUARY 27 to be considerably fainter than any one of the three stars in the nearby group of The Kids. Capella is attended by a companion star so close to its brilliant ruler that it can not be seen as a separate star save with the aid of the most powerful telescopes. Its distance from Capella has been very accurately mea- sured, however, by means of the interferometer, which is giving us the measurements of the diameters of the giant stars. It is known that this companion sun is closer to Capella than our planet earth is to the sun. At no time of the year shall we find near the meridian so many brilliant and beautiful stars as appear in the month of February at this time in the evening. In addition to Capella, which is one of the three most brilliant stars in the northern hemisphere of the heavens, we have, in Orion alone, two stars of the first magnitude, Betelgeuze and Rigel, and five stars of the second magnitude, Bellatrix and Saiph and the three stars in the Belt. In addition, we have not far distant in the western sky, fiery Aldebaran in Taurus, and close on the heel of Orion in the east, Sirius, the brightest star in the heavens, in the constellation of Canis Major, The Greater Dog, as well as the first- magnitude star Procyon in Canis Minor, The Lesser Dog. Of these two groups we shall have more to say under the constellations for March. IV MARCH To the southeast of Orion and almost due south at eight o'clock in the evening on the first of March lies the constellation of Canis Major, The Greater Dog, containing Sirius, the Dog-star, which far surpasses all other stars in the heavens in brilliancy. Sirius lies almost in line with the three stars that form the Belt of Orion. We shall not have the slightest difficulty in recognizing it, owing to its surpassing brilliancy as well as to the fact that it follows so closely upon the heels of Orion. Sirius is the Greek for "scorching" or "sparkling," and the ancients attributed the scorching heat of summer to the fact that Sirius then rose with the sun. The torrid days of midsummer they called the "dog-days" for this reason, and we have retained the expression to the present time. Since Sirius was always associated with the discomforts of the torrid season, it did not have an enviable reputation among the Greeks. We find in Pope's translation of the Iliad this reference to Sirius : 'Terrific glory! for his burning breath Taints the red air with fever, plagues, and death." 28 MARCH 29 In Egypt, however, many temples were dedicated to the worship of Sirius, for the reason that some five thousand years ago it rose with the sun at the time of the summer solstice, which marks the beginning of summer, and heralded the approaching inundation of the Nile, which was an occasion for great rejoicing among the Egyptians. It was, therefore, called the Nile Star and regarded by them with the greatest reverence. Sirius is an intensely white hydrogen star; but owing to its great brilliancy and to the fact that it does not attain a great height above the horizon in our lati- M ARCH CAN is MAJOR 30 ASTRONOMY FOR YOUNG FOLKS tudes, its rays are greatly refracted or broken up by the atmosphere, which is most dense near the horizon, and as a result, it twinkles or scintillates more noticeably than other stars and flashes the spectrum colors chiefly red and green like a true "diamond in the sky" a magnificent object in the telescope. Sirius is one of our nearest neighbors among the stars. Only two stars are known to be nearer to the solar system. Yet its light takes about eight and a half years to flash with lightning speed across the great intervening chasm. It is attended also by a very faint star that is so lost in the rays of its brilliant companion that it can only be found with the aid of a powerful telescope. The two stars are separated by a distance of 1,800,000,000 miles; that is they are about as far apart as Neptune and the sun. They swing slowly and majestically about a common center, called their center of gravity, in a period of about forty -nine years. So faint is the companion of Sirius that it is estimated that twenty thousand such stars would be needed to give forth as much light as Sirius. The two stars together, Sirius and its companion, give forth twenty- six times as much light as our own sun. They weigh only about three times as much, however. The com- panion of Sirius, in spite of its extreme faintness, weighs fully half as much as the brilliant star. There are a number of bright stars in the constella- tion of Canis Major. A fairly bright star a little to the west of Sirius marks the uplifted paw of the dog, MARCH 31 and to the southeast, in the tail