AGNES GIBEKNE THIS WONDERFUL UNIVERSE Could the Sun approach to where the Moon is, then at any instant great crimson "flames" of hydrogen gas might leap forth and enwrap our little Earth in their fervid embrace. p. 36 THIS WONDERFUL UNIVERSE A LITTLE BOOK ABOUT SUNS AND WORLDS, MOONS AND METEORS, COMETS AND NEBULAE BY AGNES GIBERNE AUTHOR OF " SUN, MOON AND STARS," ETC. NEW ILLUSTRATED EDITION, COMPLETELY REWRITTEN "It is but the outer hem of God's great mantle our poor stars do gem." RUSKIN. " O then indeed 1 knew how closely knit To stars and flowers we are." ALFRED NOYES. LONDON SOCIETY FOR PROMOTING CHRISTIAN KNOWLEDGE NEW YORK: THE MACMILLAN COMPANY 1920 FOREWORD TO NEW EDITION MANY years ago a small volume under this title was published by the S.P.C.K. When a letter came, asking me to revise it for re-issue in an illustrated form, I speedily found that to " revise " meant to " re- write." And re-written it has been during the past few months, with abundant omissions and still more abundant additions. Except possibly here or there in the first few pages, I doubt if a single sentence has kept its old form unaltered. And though in the main I have roughly followed the outlines of my former plan, it has been largely reconstructed, and very many of the chapters are entirely new. I have to express my grateful thanks to Mr. W. H. Wesley, Assistant Secretary of the Royal Astronomical Society; Mr. E. Walter Maunder, F.R.A.S. ; Professor H. H. Turner, F.R.S., Director of the University Observatory of Oxford ; Professor E. B. Frost, Director of Yerkes Observatory, Wisconsin ; Mr. Harlow Shapley, of Mount Wilson Observatory, California, and others, for most kind help given in the work of re- writing, by their ready response to inquiries on my part about difficult questions and new developments. My thanks also are due to several poets of the present day, whose names will ba found here and there, as well as to their publishers, for leave kindly granted 491581 vi AUTHOR'S FOREWORD for the use of their poems both in this and in a com- panion-volume on the subject of Plant-life, which is to appear a little later. So while the latter will be about flowers on our Earth, this one is about more flaming blossoms in the Garden of the Skies. As wrote Erasmus Wilson, long ago <( Flowers of the sky; ye too to age must yield, Frail as your silken sisters of the field." In both books I have given quotations, not only from modern poets, but from many of bygone genera- tions. It is always interesting to note the manner in which great scientific truths are received by widely- differing minds, gifted with poetic insight. Perhaps not least so with writers of a past age, when that which was known, alike of life on our small world and of conditions in the great Universe, could hardly be compared with what is known to us now. AGNES GIBERNE. CONTENTS PART I OUR OUTLOOK FROM EARTH PA GE I. A RAPID WHIRL ...... 1 II. HEAVENLY BODIES ...... 4 III. THE SHAPE OF OUR EARTH .... 8 PART II STUDYING THE HEAVENS I. GROUPS OF STARS . . . . .15 II. HOW TO KNOW THE STARS .... 20 III. SOME OTHER WORLDS ..... 24 PART III THE SILVER MOON I. OUR PLACID COMPANION ..... 28 II. IN STRONG CONTRAST ..... 33 III. SIZES AND DISTANCES ..... 38 PART IV WHAT THE MOON IS REALLY LIKE I. AIR AND WATER . * . . . .43 II. MOUNTAINS AND CRATERS .... 46 III. DAY AND NIGHT . . .50 vii viii CONTENTS PART V THE FAIR WORLD VENUS PAGE I. COOLING BODIES ...... 55 II. THE PATHWAY OF VENUS .... 58 III. POSSIBLE CLIMATES ..... 61 PART VI A RED PLANET I. WHAT WE SEE OF MARS ..... 65 II. TWO LITTLE MOONS ...... 68 III. CANALS AND MARSHES ..... 74 TV. IS MARS INHABITED? ..... 79 PART VII GIANT WORLDS 1. LITTLE AND GREAT ...... 83 II. STILL RATHER WARM ! . . . . .89 III. IS JUPITER INHABITED ? . . . . .93 IV. A WONDROUS PLANET ..... 97 PART VIII OUR SOLAR SYSTEM I. MUTUAL INFLUENCES . . . . . 1Q4 II. THE POWER OF ATTRACTION .... 107 III. ROUGH ORE OF THE UNIVERSE . . . 114 PART IX DISTANCES AND MEASUREMENTS I. A REDUCED SCALE ..... Ug II. ANGLES AND TRIANGLES ..... 122 III. BUT THE STARS? . 126 CONTENTS ix PART X OUR OWN GREAT SI T \ PACK I. ONE AMONG MANY ...... 131 II. THE SUN'S MAKE . . . 134 in. SPOTS AND "FLAMES" . . . 138 PART XI A BROTHERHOOD OF STARS I. SUNS AND THEIR PLANETS . . 144 II. VARIETIES OF STARS . . . 148 III. SMALL WAVELETS .... .151 IV. THE NATURE OF LIGHT . .153 V. HISTORY IN STARLIGHT ... .160 PART XII "THE HEAVENS ARE TELLING I. A GENERAL WHIRL .... .164 II. STAR-CLUSTERS AND NEBUL/R . .167 in. FAR-REACHING! ... . 172 IV. IMMENSITY AND MAN . 176 INDEX 180 LIST OF ILLUSTRATIONS "If the Sun came as near as the Moon . . . ! " Coloured Frontispiece Pole-Star and Great Bear ..... Comparative sizes of Jupiter and Earth . Phases of the Moon ...... Comparative sizes of Earth and Moon ,, ,, Sun and Earth The Earth and Mars when at their nearest positions Portion of Moon, North Pole to Agrippa Comparative sizes of the Sun as seen from the various Planets Mars Minor Planets between Mars and Jupiter Differing Lengths of Planet- Years, Mercury to Mars ,, ,, ,, ,, Jupiter to Neptune Comparative sizes of Saturn and Earth . Orbit of Comet, which wanders off never to return . Comet, 1908, III Moorhouse ... Comparative sizes of the chief Planets . Total Solar Eclipse, Jan. 22, 1898 . Jan. 1, 1889 .... ,, Aug. 30, 1905 .... Pole- Star, Orion and Sirius ..... Cluster M. 13, Herculis, April 25, 1901 . Great Nebula in Orion, Oct. 19, 1901 Spiral Nebula M. 64 Comae Berenicis, May 5-8, 1910 M. 101 Ursae Majoris, March 10-11, 1910 Facing . . 22 . 26 . 29 . 34 . 35 . . 41 Facing 47 mets . 59 Facing 67 85 . 87 . 88 98 . . 112 Facing 113 . 120 Facing 132 Facing 138 Facing 141 . 146 Facing 167 Facing 168 Facing 171 Facing 172 THIS WONDERFUL UNIVERSE PART I OUR OUTLOOK FROM EARTH I. A RAPID WHIRL . ONCE upon a time a man is reported to have said : " Don't tell me that the world goes round. I know better. 'Cause why? When I get up in the morning I see the very same view all round as when I went to bed." That man, at all events, thought for himself, which is better than not thinking at all, even though his thinking led to a mistaken conclusion. And the reasoning was not out of place. Nay, he had hold of an important truth ; only he used that truth wrongly. He grasped the fact that a man, going from one spot to another, must from time to time have different things about him. If he walks the changes come slowly; if he travels by train they arrive more quickly. In any case he cannot pass onward, hour after hour, moving among objects which do not move, and still see the same houses, the same trees, the same fields, the same hills. As he advances, he leaves the old surroundings behind, and finds himself amid new surroundings. &::; THIS WONDERFUL UNIVERSE The man, of course, knew this. Though not learned in scientific matters, he had his share of common sense. When somebody told him that our solid old world was not, as he supposed, quietly at rest, but was incessantly twirling like a teetotum, he began to use his common sense. He knew that when he went to bed at night he could see certain objects in the country around ; and he knew that when he woke up in the morning he would find those same objects, each in exactly the same position. Then he put two and two together, and decided that the notion of the Earth spinning must be a mistake. " Don't tell me," he said. " I know better ! " And all the time he was himself making a curious mistake. Up to a certain point his reasoning was not incorrect ; but he looked in the wrong direction for the changes of scene which he rightly considered ought to come about. And rather oddly, while taking it for granted that he would move with the moving Earth, he does not seem to have faced the probability that other objects on Earth's surface would do the same. It never occurred to him that not only his own little house and garden, and everything in them, but other houses with all that they contained, and trees and fields, hedges and ponds, hills and valleys one and all must be carried onward just as fast as the surface of the Earth was moving. Otherwise, if everything were left behind by that rushing surface, it would mean a complete and terrific jumble of destruction. Naturally, therefore, the view before his eyes each morning had to be the same as his view of the evening before. OUR OUTLOOK FROM EARTH 3 When a man in a railway carriage is borne along at the rate of fifty miles an hour, all that is inside that carriage travels at the same pace. The cushions, the seats, the people, the luggage, the fly on a window-pane, the air which fills the compartment, are journeying at fifty miles an hour. And when a traveller wishes to find a changing scene, he must not fix his gaze on the floor, or the seats, or on a fellow-traveller. He must look outside at the fields, the trees, the houses, the villages, seen through the windows. This is just what one on Earth must do, if he would discover the movements of our globe from changes in the scenery. He must look right outside, away from Earth altogether ; not at the things on our world, which move with the Earth as he does himself. And that is exactly what the man did not do. He looked only at the things around, all journeying with himself; and he forgot to gaze away outside, away from the hurrying surface of the solid globe on which he stood. " Ah, yes," perhaps you may say. " He ought to have looked right off from everything on the ground. He ought to have watched the clouds. Then he would have understood." No; not even then. That would have meant a second mistake on his part. It is true that he would not, usually, find precisely the same clouds as the evening before; because clouds are perpetually altering their shapes, melting away, re-forming, taking new outlines. But these changes in them would be real. They would not be seeming changes, brought about by his own movements. The clouds would have travelled onward, as he did 4 THIS WONDERFUL UNIVERSE himself, with the Earth's surface. They might be blown hither and thither by currents of air; but as a whole they would have been carried from west to east by the steady whirl of the entire atmosphere, which moves with the surface of the Earth. So if the man wished to get a really outside view, he would have to look beyond the clouds, beyond the great deep ocean of air, which really is a part of our Earth. He would have to lift his gaze into the sky, where float the Moon and Sun, the planets and the stars. Then at last he would find scenery which seems to change, like the objects noticed out of a rushing train, objects which often cannot but seem to move, if this world really does move, because they are not a part of the Earth, as air and clouds, hills and towns, fields and rivers and oceans are. " Now glowed the firmament With living sapphires ; Hesperus, that led The starry host, rode brightest, till the Moon, Rising in clouded majesty, at length Apparent queen unveiled her peerless light, And o'er the dark her silver mantle threw." MILTON : Paradise Lost. II. HEAVENLY BODIES. The first and simplest idea which a child generally has of Earth and sky is of a wide, flat plain, and of a fixed sky above, with clouds and a sun in it by day, and a moon and stars in it by night. Stars always at night, when the sky is clear ; and a sun always by day, unless hidden by clouds; but a moon not always after dark. OUR OUTLOOK FROM EARTH 5 So much as this an intelligent child might be expected to find out for himself, even if not told. And the first men who inhabited this Earth must have seen such things very much as an untaught child now would see them. Probably this was the idea in the mind of the man who could not believe that the Earth revolved. Eut suppose that, instead of making up his mind in such a hurry, he had taken time to watch and to think. Suppose he had glanced away from Earth to the heavens, far beyond cloudland; had looked, not once or twice only, and not carelessly, but day after day with attentive and earnest eyes. Suppose he had kept this up, week after week, month after month, even year after year, trying to find out what changes in that heavenly scenery might mean. He would see what already he knew that the Sun each morning comes up from below the easterly horizon, crosses the sky, higher up or lower down at different seasons, and goes down below the westerly horizon. He would notice that the Moon by night, when visible, does much the same; rising somewhere in the east, crossing part of the sky, and setting somewhere in the west. He would find the stars also to be on the move ; many of them, like the Sun and Moon, rising in an easterly direction, crossing the sky, and setting in a westerly direction, while a certain number towards the north are never seen from our part of the Earth to set, but keep circling round and round a certain point. Then, if left to himself, with no books or teachers, and no help from the thousands of years during which other men before him have watched and waited and 6 THIS WONDERFUL UNIVERSE studied and found explanations, he would doubtless fall into the same mistakes that men of ancient days fell into long ago. He would feel sure that this flat Earth on which he had a footing, which feels so firm and solid, must cer- tainly be at rest. Therefore, he would feel no less sure that the whole sky, with Sun and Moon and hosts of stars, must be whirling round and round our Earth, once in every twenty-four hours. That would indeed be a tremendous feat for the heavens to perform ! Wonderful things are done in the sky; but nothing quite so utterly and hopelessly beyond all human imagination as this ! Only, in far-back days it was not beyond imagination, because men then knew so very little of the real size of our marvellous Universe, or of the enormous numbers of stars contained in it, or of the stupendous distances which divide its stars one from another. To the mind of a man in those times it was much more difficult to imagine that our world could spin day and night like a huge top, than that the entire heavens should perpetually whirl round and round us. Of the two explanations one had to be true; and it was just a question which was the more easy to accept. Men believed that which seemed to them the simpler. Now that we know better what would be meant by such a whirl, we realise how very much more simple and easy is the explanation founded on the idea of our small Earth's daily turning on her own axis. Astronomers gradually discovered that many other OUR OUTLOOK FROM EARTH 7 bodies in the sky the Sun, for instance, and the planets are steadily spinning or revolving, each on its own axis, some more quickly, some more slowly. Ex- amined through a telescope, they are clearly seen to do so. And if other bodies, many of them far larger than this world, are known to behave thus, why not the Earth also ? The idea, far from looking impossible, has become an every-day fact. When once we grant that our world is ever spinning round and round, carrying with her everything on and near her surface, then the daily movements of the Sun, the nightly movements of Moon and stars, are explained. We see them seem to move, merely because we ourselves are moving. We see them seem to come up from the east and go down in the west, because we on Earth are being carried from west to east. It is much the same as when a man, journeying in a train from north to south, sees trees and fields and villages appear to travel from south to north. Not that this particular movement, this daily whirl of our Earth is her only movement ! And not that the Sun and Moon, the planets and stars, have not real movements of their own ! But just now all we have to do with is the fact that the daily and nightly whirl of the skies round us is not real. It is only an appearance, brought about by the ceaseless spin of our small Earth. Other movements may be left alone for a while. " Mysterious Night; when our first parent knew Theo from report Divine, and heard thy name, Did he not tremble for this lovely frame, This glorious canopy of light and dew ? B THIS WONDERFUL UNIVERSE " Yet 'neath a curtain of translucent dew, Bathed in the rays of the great setting flame, Hesperus with the host of heaven came, And lo, Creation widened in man's view. " Who could have thought such darkness lay concealed Within thy beams, O Sun ? or who could find, Whilst fly and leaf and insect stood revealed, That to such countless orbs thou mad'st us blind ? Why do we then shun Death with anxious strife ? If Light can thus deceive, wherefore not Life ? " BLANCO WHITE. III. THE SHAPE OF OUR EARTH. A man standing on the equator is carried, in the course of twenty-four hours, right round under the entire heavens. If he were gazing through all those hours steadily up into the sky he might view the whole land- scape of stars visible from this world but for one hindrance. That hindrance is the radiance of sunlight, which in day-time shuts off the dim nicker of starlight. Could he cover up the sun, and so secure twenty-four hours of darkness, he might survey all at a single stretch. Not that the heavens would journey round him, while he stood on a fixed and motionless world, but that he, on the whirling surface of our revolving globe, would be carried round swiftly under each part of the sky in turn, travelling always from west to east. But a man standing farther north or farther south, and not on the equator, would not gain so full a view. Portions of the heavens would be hidden from him by the intervening solid body of the Earth. There are many stars over the region of the south OUR OUTLOOK FROM EARTH 9 pole, which we in Britain and in other northern parts of Europe and North America can never see. And there are many stars over the region of the north pole, which people in southern Australia and South Africa can never see. It is only from the equator that a man might obtain a complete view. Since the Earth is not, as was once supposed, a flat plain, reaching to endless distances, but a round globe or sphere, its surface curves away from us, wherever we happen to be, till it passes out of sight at the horizon- line. The curve is very gentle; but it is found in all parts of the world alike. A very interesting proof of the round shape of our Earth is given in an eclipse of the Moon. Sometimes in our yearly journeying round the Sun this is another of the Earth's movements we pass exactly between the Sun and the Moon, so that the three bodies are in a direct line. More often it happens that either the Sun or the Moon is just a little higher or a little lower ; and then the three are not in a line. But when it does so come about, the Sun casts a shadow of the Earth upon the Moon. And since the latter shines only by reflected sunlight, she at once becomes dim. And note this ! the shadow thrown by our Earth is a round shadow. As the grey shade creeps slowly over the bright Moon-face, it is always a rounded edge which moves onward. No matter which part of the Earth has its shadow cast, the result is the same. England, India, Australia, America these or other countries may face the Moon; but invariably the 10 THIS WONDERFUL UNIVERSE creeping shadow is round in shape, and the back-edge following is round also. If you hold up an orange between a lighted lamp and the wall rather near the wall, and not too near the lamp you will see that the shadow thrown by it is a round shadow. Turn it about as you will, offer one side after another to the lamp, and still the shadow will be round. Then hold up a flat plate to the lamp; and you will find that the shape of the shadow depends on how you place it. In one position, and one only, it will cast a round shadow. In others the shadow will be more or less oval ; while, if you hold the plate edgeways towards the lamp, the shadow becomes only a straight, broadish line. Do you see how strong a proof is given here as to the shape of the Earth? And it is one that comes again and again, every time we have an eclipse of the Moon. And now about the size of the little world on which we live. If a road could be made straight through its centre, from one side to the other, perhaps on the equator, such a road would be nearly eight thousand miles long. A carriage drawn by quick horses, going at the rate of ten miles an hour, never lessening speed by day or night, might accomplish that distance in thirty-three days, or just over a calendar month. A train, or a motor-car, travelling fifty miles an hour, without a single break, might do the same in less than a week. But with horses and engines, not to speak of pas- sengers, halts are needed. And when we romance OUR OUTLOOK FROM EARTH 11 about going down into the Earth and out on the further side, in any such fashion, we are talking about an unknown region. The outside surface of our globe is more or less familiar; but not the inside. A recent statement gives as the greatest depth of a mine ever yet sunk : " the No. 3 shaft of the Tamarack mine in the county Michigan," which " reached a vertical depth of about 5200 feet;" that is, slightly under one mile. A mere scratching of Earth's crust ! Even if we suggest a larger margin, and say that no mine has reached a depth beyond two miles what are two miles compared with eight thousand ? True, parts of our ocean-bottoms lie six or even seven miles below the ocean-surface; but those depths are far beyond our reach. Imagine what it would mean to delve four thousand miles below the surface of our Earth; four thousand miles away from light and air; nearly four thousand miles beneath our oceans. And to complicate matters, the inside of our world is believed to be intensely heated ; so much so, according to one authority, that about thirty miles down the heat must be great enough to melt all solid rocks. If they are not there in an actually molten state, it is only because the immense pressure tends to keep them solid. Such a road would indeed utterly dwarf the grandest engineering works of man. Though a road of this kind is impossible, and though we cannot hope ever to dig or blast our way downwards until the opposite side is reached, yet the actual size of our Earth has been again and again reckoned. The size of any globe, both through the middle and round 12 THIS WONDERFUL UNIVERSE the outside, may always be found out from careful measurements of parts of its surface. The work of surveyors comes in here; and such measurements have been made times without number, and calculations worked out therefrom. We now know, as a matter of certainty, that the Earth is about eight thousand miles through from pole to pole or from side to side straight through the centre, and about twenty-five thousand miles round at the equator. By the " equator " we mean an imaginary line round the Earth, half-way between the north and south poles. And when we speak of the north pole or the south pole in the heavens, we mean always that point in the sky which lies just over our Earth's north pole or our Earth's south pole. With regard to the shape of our Earth, it is, as already stated, a globe or ball ; more strictly, it is like an orange, since it has slightly flattened poles. In scientific language the Earth is an "oblate spheroid;" and in connection with this term a little scene of past days comes to mind. My father one day was showing cube-shapes to two little girls, aged about nine and seven, explaining their names and uses. In a corner of the room their small sister, only three and a half or possibly as much as four years old, was seated on the floor, playing happily with her toys. Presently, to see how far his explanations had been understood, my father asked a question or two, and among them : " What is the shape of our Earth? " OUR OUTLOOK FROM EARTH 13 Seven-years-old and nine-years-old tried to remem- ber. But the baby in the corner, busied with her dolls, had listened to some purpose, and the pause was broken by a sweet little treble voice piping out " An oblate spheroid, uncle ! " My father's surprise and amusement may well be imagined. And perhaps I cannot do better than mention here how deep is my debt to that dear father for his early lessons in science; lessons which familiarised me as a child with scientific modes of thought and expres- sion; laying a firm foundation, upon which a super- structure of further study could so easily be reared. It was he who first awoke my interest in such subjects ; he who made Astronomy a living force in my imagination. The teaching must have begun very early, for I well remember standing by his side, one wintry day, when I was certainly not more than seven or eight years old, asking why and how it could be that we were nearer to the Sun in winter than in summer, and yet were more cold. A fire was burning, and he sat not far off. I can see now his fine, stately figure, the short-f rocked child standing by his side, and the gesture with which he pointed to a fly on his knee. " See if that fly were one inch nearer to the fire, would it feel any hotter? " No ; it would not. I understood that instantly ; and though the real cause of summer and winter in the slant of Earth's axis did not become evident till long after, I did see then, with daylight clearness, that the difference of three millions of miles, compared with the Sun's whole distance, was no more than that one inch in the fly's 14 THIS WONDERFUL UNIVERSE distance from the fire. There was no need to ask more. " Heaven's ebon vault, Studded with stars unutterably bright, Thro' which the moon's unclouded grandeur rolls, Seems like a canopy which love has spread To curtain her sleeping world." P. B SHELLEY. PART II STUDYING THE HEAVENS I. GROUPS OF STARS LIKE every study, that of Astronomy has to be from small beginnings. To start with a difficult text-book, or with hard calculations, would in most cases have no good result. It is a study which ought to be followed on two lines at the same time. Much can be learnt from books; much also from actual observation of the sky. A beginner may choose the one plan or the other; but the better mode is to use both plans. Without books, a student of the skies stands in much the same position as an ancient astronomer of Chaldean days. He has to find out for himself those things which have taxed the minds of men through centuries. And without some amount of watching of the heavens, the known facts which may be learnt from books can never be quite so real to him, if he does not use his own eyes to verify them, to the small extent which lies in his power. Some teachers of Astronomy prefer to start with the distant stars, and to work their way back to such heavenly bodies as lie nearer to Earth. Others think it wise to tackle first the nearer bodies, and gradually to wander 15 16 THIS WONDERFUL UNIVERSE farther afield. For instance, we may begin with our closest neighbour of all, the Moon ; and with our brother and sister worlds, the planets ; and with the great head and centre of our system, the Sun ; afterwards passing on to the stars. But even from the first we cannot ignore the stars. Night by night, unless hidden by clouds, they shine forth; and from childhood those tiny glimmers are a part of our lives. With them the earliest stage should be just to grow used to their ordinary look, as seen from our Earth ; to learn something of the various groups or " constella- tions ; " to become acquainted with the shapes and names of such constellations, and their places in the heavens ; also to understand a little about their seeming nightly and yearly movements, due to our own daily and yearly revolvings. What they really are, and how far they truly and actually move, must come later. Earth's daily whirl on her own axis has been explained as making all the sky seem to travel round us by day and by night. And her yearly journey round the Sun also causes a slow shifting apparent, not real of the various constellations through summer and winter. Certain constellations, far north, such as the Great Bear and the Little Bear, are always visible to us in Great Britain and in the northern parts of Europe and North America. Certain constellations, such as the Southern Cross, are never visible to us in those regions. But other constellations, not so far north and not so far south, are sometimes to be seen, and sometimes not. Many stars, high up in the southern sky for instance, STUDYING THE HEAVENS 17 those in the constellation of Orion visible to us in winter nights, are hidden in summer nights. We can at any time see only those groups which lie in a direction away from the Sun ; not those which lie on the same side of the heavens with the Sun. Those stars, if seen at all, would have to be seen by daylight ; that is, at the same time as the Sun. And this, under ordinary conditions, is out of the question, because they are veiled from our eyes by the glare of sunlight. So it is not till the Earth, in her twelve-months' voyage, gets round to the other side of the Sun, and sees him against the opposite heavens, that the stars which were hidden months before become visible. While, from the same cause, many stars which have been visible take their turn to disappear. One fact should from the first be absolutely clear. This is thaLJhe stars are jrtways there. They do not come and go. They are always overhead, high in the heavens, round the whole Earth, whether we do or do not see them. I do not mean that the same stars are always over one particular part of the world; but that some stars are there always, which of them depending on which part of the heavens our part of the Earth happens to be under at any particular hour. The whole vast com- pany of stars, each in its own constellation, to which it has belonged through thousands if not millions of years, is always in the skies. If you had a good telescope, with a friend able to use it, you might get a glimpse of certain stars, even in the brightest noonday. 18 THIS WONDERFUL UNIVERSE Picture to yourself a small toy balloon floating in the air of a vast hall, with walls and ceiling and floor, pictures and furniture, surrounding it above and below and on all sides. So our Earth floats in the measureless expanse of space, with countless stars above and below and on all sides. Think of a small spider clinging to that little balloon. He would be able to see only part of the hall, which- ever part towards which his side of the balloon happened to face. If he were looking at the right wall, he could not see the left, because the balloon between would hide it. And just so we on Earth can, at any particular time, see only that part of the heavens towards which our side of this floating globe is turned. Longfellow wrote on the subject " And as the evening twilight fades away, The sky is filled with stars, invisible by day." And Wordsworth " Look for the stars, you'll say that there are none; Look up a second time, and one by one You mark them twinkling out with silvery light. And wonder how they could elude the sight." The above illustration of balloon and hall is, of course, defective, as such illustrations are bound to be. On Earth we know no true " up " or " down," except in the sense of towards and away from our Earth's centre. This is just as true in Australia as in Britain, even though the feet of our fellow-subjects there do point towards the feet of men walking on British soil here. STUDYING THE HEAVENS 19 Picture once again to yourself the small globe floating in the great hall, about half-way between floor and ceil- ing. But now think of it as obeying rule, as floating round and round a centre which is occupied by another and much larger ball. Picture also that a slender needle is thrust through the little balloon's centre, one end coming out at its north pole, the other at its south pole. And as it moves that needle is slanting, not upright, and the slant is always in the same direction. The needle does not wobble about, pointing this way and that way. It points always steadily towards the same wall. So does the axis of our Earth keep always the same slant; and our north pole points always towards one part of the heavens. There lies the celestial north pole, carried straight on from the north pole of our little world. In this slant of our Earth's axis lies the explanation of our seasons. For in one part of our yearly journey round the Sun our north pole points towards the Sun, and our south pole is turned awayjrom him. This jneans the_northern summei_mdJ:tI^^ Six months lateFTt is the south pole which points towards the Sun, and the north pole which is turned away from him. And though, during that northern winter, we are really nearer to the Sun than in our summer, the trifling difference of three million miles is of little account. The main fact is that we have so rmifh ^gg,j>f jfffr" al Hirppj-. sunshine, and that i.t comes to us from a Sun far lower down in the sky. Spring and autumn lie between these two extremes, when the Earth is in a half-way position. 20 THIS WONDERFUL UNIVERSE II. How TO KNOW THE STARS It is a good plan to cultivate the habit of looking from some particular window at certain stated hours after dusk each evening. Much may be learnt thus. The brighter stars should first be picked out and carefully watched. It may be noted how they are placed with respect to neighbour-stars not quite so bright : whether they twinkle or shine steadily ; whether they keep, night after night, at the same distance from those other stars, or whether they slowly alter their positions ; and if they do move, how they move. This is one of the first questions of interest, because thereby one may distinguish between stars and planets. A star twinkles; a planet generally does not. A star keeps always the same position among other stars; a planet wanders about from one place to another among the stars. Many years ago a working-man wrote to my father, begging for help in his efforts to learn about the heavenly bodies. In his letter he made this remark : " If I can once get hold of Venus, I will not let her go." No better plan could be suggested. Try to " get hold " of a planet here, of a star there, and do not let them go, do not lose them, but follow their movements day by day. Bad weather may interrupt and confuse such attempts, and for a while your new friends may slip out of sight, but they can be found again. They never really take their departure; they only change their positions. The stars only change theirs in appearance, though in more ways than one. The planets change theirs, not STUDYING THE HEAVENS 21 only in appearance, but also in reality, yet they always move by rule, and astronomers know at all times where to look for them. Such watching as this means the giving of time and trouble, but it is worth while. Even while we must all depend largely on what others can tell us, since there is an enormous amount which we could never discover for ourselves, yet the little that we can do well repays for the trouble. In a sense stars are more easily " followed " than planets, because through centuries they do not visibly alter their positions, .one with regard to another. The different groups or constellations still look the same to us as they did in the days of the patriarchs. The soft shining of the Pleiades and the armour of Orion we see just as Job saw them. The Great Bear has not appreci- ably altered in shape since the time of Julius Caesar. Even before learning the names of the constellations, you might become familiar with some of their shapes ; and then, with the help of a star-map, you could discover what they are called. Or again, the map may be studied first, and after- ward you can try to find out the constellations and the chief stars belonging to them. Though we speak of star-magnitudes, which means star-sizes, no true star in the sky can show to us any difference of size. The only real difference lies in degrees of brightness. A star of the first magnitude does not mean a star which looks bigger, but only a star which looks brighter. The light of each star comes in a single slender ray of light, and the star itself is to us only a 22 THIS WONDERFUL UNIVERSE point even in the most powerful of telescopes, still only a point ! No telescope yet made has ever been able to show a disc that is, a surface with any breadth of any single star. The planets show discs, or a surface which can be measured, which has breadth but the stars, never ! They are too far distant. THE GREAT BEAR, POINTERS AND POLE-STAR. One of the first to have pointed out to you should be the Pole-star, at the tip of the ^Little Bear's tail. The two pointers of the Great Bear point towards the Pole- star. And in the daily seeming whirl of the heavens that faint Pole-star, lying over our north pole, scarcely stirs, while the constellations near keep circling round and round the Pole-star, as seen by us in the northern hemisphere. Eut this circling is not real. It is due to Earth's own daily spinning on her axis. STUDYING THE HEAVENS 23 So Caesar claimed " But I am constant as the Northern Star, Of whose true -fixed and resting quality There is no fellow in the firmament." * Among those northern circling groups may be found the beautiful star Capella, in the constellation of Auriga, one of the brightest in our sky. Another glorious star, farther off, is Arcturus in Bootes. Others among the brightest are Vega and Aldebaran. But the most radiant in the whole heavens is Sirius ; and this distant sun can only be seen by us in winter months. When once you have found the magnificent constellation of Orion also a winter constellation to us in the north you will find Sirius with ease, because the two feet-stars of Orion point in almost a straight line to that brilliant star, with his gleaming diamond sparkle. On the other side of Sirius may be seen the soft shimmer of the Pleiades, many dim stars which look as if they were close together, and of which not many people, at least in our English climate, can often make out more than six or seven. Not far off is another bright star, Aldebaran. 2 The word " constellation " is from two Latin words which mean " star " and " together," or " connection." So the strict sense seems to be " a group of stars con- nected together." How far such stars really are con- - nected is another question. Sometimes undoubtedly they are, but not always, and not necessarily. 1 Shakespeare, Julius Ccesar. 2 In such studies of the heavens, great help may be obtained from a volume of star-maps, Half-Hours with the Stars, by R. A. Proctor. Their positions at different times and different hours are clearly given, with directions how to use the maps, c 24 THIS WONDERFUL UNIVERSE This grouping of stars into definite constellations, with names, belongs to a very early period in the world's history. " Down steps Orion to the west, High-headed, starry-eyed, Watchful beneath his warrior-crest, His sword upon his side. " Amid the unnumbered stars of night He fills his measured space, And covers under points of light The fashion of his face. " He makes no gesture, gives no sign; Yon form is all we know. So belt and scabbard used to shine Millions of years ago. " Upon his brow endures no frown, No tumult stirs his breast ; In martial stride he still goes down With all his stars at rest. " When Earth was young and Night was old, That harness he put on, And girt for war, with nails of gold, The belted warrior shone." 1 III. SOME OTHER WORLDS The planets which belong to our Solar System that is, to the Family of our Sun are far nearer to us than any of the stars. So much so, that they can easily be seen to move onward in the course of weeks and months. Really to move, I mean ; not merely to seem as if they moved because we ourselves move. They journey round 1 From The Heart of Peace and Other Poems, by Laurence Housman. Pub. : William Heinemann. By permission. STUDYING THE HEAVENS 25 and round the Sun, just as our Earth journeys round and round him. And as they travel, they appear to us to wander in and out, to and fro, among the so-called " fixed stars." Actually, they do nothing of the kind. What hap- pens is that, in their onward movements, we see them against one star-group after another in the sky. It is much the same as if you stood on the beach, watching a small boat some little distance out. You would see it against one far-off ship after another, as it passed along ; and this would not mean that the boat ever went near those ships, but only that you happen to see the two in the same " line of sight," though they might be separated by many miles of water. Again, no stars are truly " fixed," though by reason of their enormous distance they seem to us to be so, keeping their constellation-shapes unchanged through centuries. Most easily found and most easily " kept " of all the planets is Venus, the lovely " Evening Star " of some months in the year, and quite as truly the " Morn- ing Star " of other months. Venus is not a star at all, but a planet or world, much the same in size as this world on which we live. No other planet and no star in all the sky shines with such a lustre as Venus at her best ; not because she is larger or brighter than all other heavenly bodies, but because she is better placed for our powers of sight. Once get this beautiful orb pointed out to you, and you may enjoy her soft resplendence evening after even- ing, or morning after morning, weather permitting. She is never very far away from the Sun, being nearer to 26 THIS WONDERFUL UNIVERSE him than we are ourselves. You will always find her, when she is visible, either in the western sky soon after sunset, or else in the eastern sky a little while before sunrise. Mercury may be seen in the same manner; but as this small world is still closer to the Sun than Venus, he COMPARATIVE SIZES OF JUPITER AND EARTH is much oftener lost in the Sun's radiance. At the best of times he is less easy to find, because he is so small, and also because he rises such a short time before the Sun, and sets such a short time after him. Next to Venus- in brightness, as seen by us, comes Jupiter, often a most beautiful sight. When you notice a particularly bright body, not twinkling like a star, but shining with a strong and steadfast light, in a part STUDYING THE HEAVENS 27 of the sky where Venus cannot be because it is too distant from the rising or setting sun, you may feel pretty sure that you are gazing on Jupiter. The pathway of Jupiter round the sun, unlike that of Venus, is a great deal farther away than our own. You should go to an almanac for news as to his where- abouts in any special month, since he can be seen in many parts of the sky, though, as said above, he may often be recognised simply by his brilliance. And when you have found him, you may follow his movements too by night, for a good while if the weather permits. Mars also may be seen in various parts of the sky ; for the pathway of Mars, like that of Jupiter, lies outside the pathway of Earth. Quite a small world is this interesting little globe, much smaller than Earth, though not so small as Mer- cury. He is one of our nearest celestial friends, while Jupiter decisively the biggest member of the Sun's family lies far away. Saturn, the next in size after Jupiter, a most lovely and marvellous world, is so very distant, and in conse- quence is often so very dim, that he may be less easily found by a beginner. The two outer planets, Uranus and Neptune, can only be seen with the help of a telescope. Of all these brother and sister worlds, none perhaps has awakened keener interest with people generally than Mars. At one time much popular talk went on about the possibilities of intercourse with Martian people supposing that any such people exist. " Flag-wagging " had even been suggested as a mode of interchanging ideas till one authority stated that a flag, to be seen there, would have to be about the size of Ireland ! PART III THE SILVER MOON I. OUR PLACID COMPANION ALL the world knows her, round-faced and calm, serene and distant, yet faithful in comradeship. She never wanders very far away. She never seeks another fellow-traveller. We may count securely upon her, for she is regular in her habits, and is sure to be in those parts of our sky where she is expected by those who understand her ways. If at such times we fail to see her, that is the result of earthly mists which rise between; not her fault. To be sure, she does not shine at one and the same hour upon all parts of this round globe. Manifestly, it would be impossible. When she is on one side of the solid Earth, she cannot be on the other side also. And when she happens to be in the same part of the sky as the Sun, her light is smothered by his greater radi- ance. But still she goes on, travelling around and with her big companion, keeping always over a certain belt of Earth's surface, within a definite distance north or south of the equator. And if she is sometimes large and bright, and some- times only a narrow sickle of light, that, again, is not her 28 THE SILVER MOON 29 fault. She cannot shine except on the side which is turned towards the Sun and reflects his brightness, since she has no light whatever of her own. If that side which faces the Sun is turned partly away from Earth, we see only a portion of it half-Moon, or quarter- Moon, or a mere slender bow, as the case may be. And when it is turned wholly away, as at New Moon, we see nothing of her. These changes are called " phases," and perhaps you C PHASES OF THE MOON know Jean Ingelow's lines, as supposed to be spoken by a child of seven " O Moon, in the night I have seen you sailing And shining, so round and low ; You were bright, ah, bright ; but your light is failing You are nothing now but a bow. " You Moon, have you done something wrong in Heaven, That God has hidden your face ? I hope, if you have, you will soon be forgiven, And shine again in your place." For a little child now, as for a grown man of ancient days with complete ignorance of astronomy, 110 reasons exist, or did exist, why the round Moon should thus alter her shape, week after week, month after month. Have you ever seen a piece of magnesium-wire set alight in a dark room? If so, you may have noticed 30 THIS WONDERFUL UNIVERSE two things first, the dazzling brilliance of the burning wire ; second, the lesser brightness of all around, includ- ing people's faces. That burning wire shone, as the sun shines, by its own radiant light. But the faces and walls and ceiling shone as the moon shines, by a reflection of the light given to them. Half of the Moon shines always in the blaze of sun- light poured upon it ; but not the whole of that half can always be seen by us ; and this, as already said, is why we see often a mere crescent of light ; not because the Moon has a less bright face than usually, but because most of that face is turned away, so that we only catch a glimpse of one edge of its brightness. Still, we must remember that all the while the whole round Moon is there, a solid globe, half-bright, half-dark. A friend l once sent to me a Christmas card, and wrote with it : " Two stars, actually, in the Moon ! Times can't be improving, as we are so fond of imagining ; for Coleridge only spoke of ' one bright star ' within the horned Moon's 'nether tip;' and now, in 1884, some one w r as found capable of putting two stars in the Moon ! " The artist who designed the said card, having sketched a crescent-moon in the sky, proceeded to place a couple of stars inside the crescent. He utterly forgot that the crescent-shape is filled with the solid dark body of the Moon. A star might lie just in that direction, far, far away beyond the Moon, but no one on Earth could see it, because the Moon would lie between. And no star in all the Universe ever comes between the Moon and the Earth. 1 Lady Huggins, wife cf the great spectroscopist. THE SILVER MOON 31 Occasionally we can see for ourselves that the dark body is there. It only happens now and then, but it does happen. The bright Moon-face, lit up by the Sun, is chiefly turned away, so that we have no more than a sickle of light. But the dark Moon-face, which is towards us, catches a gleam from the shin- ing of our Earth. Then we can see faintly the dark body of the Moon inside the bright crescent, and we call it " the Old Moon in the arms of the New." Eut the New Moon and the Old Moon are the same Moon. Perhaps the idea of our Earth shining may be new to you. Yet she does shine. She is just as much a " heavenly body " as the Moon is, and as any planet is. Like them, she shines by borrowed light, reflected from the Sun. If we could see our dull old Earth, as she sometimes may be seen from Venus, for example, we should be; amazed at her radiant beauty. We should not wonder then that the Moon can sometimes borrow some of our' brightness. In her night- journey, as she seems to travel across the sky, she comes between the stars and us, blot- ting out one star after another. At the time of full -moon very few can be visible in her near neigh- bourhood, because of her shining. But when she becomes a mere sickle of light, something else can be observed, which proves the actual presence of the dark body. Watch carefully for a bright star disappearing behind that outer shining Moon-edge. You will not see it when 32 THIS WONDERFUL UNIVERSE quite close to the rounded sickle-edge, but you may notice the Moon's drawing near, till it vanishes. Then you can watch for the reappearance of the same star on the other side the inner side. But you will not see it directly the sickle of light has passed. You will not detect it anywhere within the rim of brightness ; for that rim holds the solid body of the Moon. And the star cannot appear again till the \vhole Moon, both the bright rim and the dark body, has passed by. Then it will once more be visible, not close to the crescent, but beyond the dark Moon-body. Through countless ages the Moon has been our Moon. Not Jupiter's Moon, nor Mars' Moon, nor Saturn's Moon ; but Earth's own particular possession. No world in the whole Solar System, so far as we know, gets any good out of the Moon except this Earth. She is not even the Sun's Moon, in any especial sense, beyond the fact that the Moon, like the Earth, is one of his planets, a very small one. We often speak of Sun and Moon together, because for us the one is king of day, the other is queen of night. The Moon is to us what she can be to no other heavenly body in the Universe. But the Sun is to all his planets, in a greater or less degree, what he is to us. And though we could, so far as light and heat are concerned, manage to exist without the Moon, it is far otherwise with regard to the Sun. Apart from him our world would speedily become one vast tomb of death. Early in the last century a popular song was afloat offering a comparison between the two from an extremely Irish point of view. It began as follows THE SILVER MOON 33 " Och, long life to the Moon for a swate noble cratur, That serves us for lamplight each night in the dark ; While the Sun only shines in the day, which by natur Needs no light at all, as you all may remark. But as for the Moon, sir, I will be bound, sir, 'Twould save the whole nation a great many pound, sir, To subscribe for to light her up all the year round, sir ! " A difficult feat, this last, for even an Irishman to carry through ; while if once that great luminary, the Sun, were blotted out, it would soon be seen how little brightness " day " could boast " by nature." The Sun once gone, all warmth, all life, all growth, would be at an end, and the only light remaining would be that of the dim and twinkling stars. No Moon or planets would then be seen, no bright Venus or Jupiter could gladden our sky; for there would be no Sun to lend them of his brilliance. Even if certain of the planets have some faint power to shine of themselves, it would be too feeble a glimmer to benefit our Earth. II. IN STRONG CONTRAST The Moon is a globe, in shape much like this world, but not nearly so large. A piece of tape, just long enough to be passed straight through the Earth's centre, reaching from one side to the other, would serve to measure the Moon in two ways. One quarter of the tape might be passed in the same manner through the Moon's centre, the two ends just touching her opposite sides ; and the remaining three- quarters could be folded round the Moon's equator, with the two ends meeting. That gives some idea of the comparative sizes of the 34 THIS WONDERFUL UNIVERSE two. You might find a couple of balls, the through- measure of the one just serving for the two measurements of the other. Then you would see this comparison more clearly. If you wanted to make out of several moons, each the size of our Moon, a single globe as large as the Earth, Diameter, 2163 miles. Diameter, 7912 miles. COMPARATIVE SIZES OF EARTH AND MOON you would need for that purpose nearly fifty moons. But if, in the same way, you wished to make a globe as large as the Sun, you would need well over fifty millions of moons. Such a tape, just long enough to be passed through the Moon from side to side, would have to be two thousand miles long. But a tape which could be passed through the Sun, from side to side, would have to be THE SILVER MOON 35 nearly nine hundred thousand miles long ! Rather a difference ! As a mere matter of guess-work, nobody would ever imagine, looking first at the one and then at the other, that the Sun is so huge compared with the Moon. And for ages in the world's history nobody did imagine it. COMPARATIVE SIZES OF SUN AND EARTH So long as the two were supposed to be just about the same distance away, it was impossible that their sizes could be known. Until telescopes were made, and many other astronomical instruments had been invented, until also countless improvements had come about both in telescopes, and in other instruments, the measurement of heavenly bodies was out of the question. 36 THIS WONDERFUL UNIVERSE If the Sun really were, as used to be thought, just as near to us as the Moon, he would be an appalling object. Not alone from his colossal size, but because of the ocean of furious fiery gases which enfold his whole surface, and because of the fierce and whirling storms, the fearful heat, the scorching glare. Could such an event come to pass, as that the Sun should approach to where the Moon now is, then at any instant vast tongues of glowing hydrogen gas great crimson " flames " might leap from the Sun and enwrap our little Earth in their fervid embrace. Such mighty outbursts are no rare matter on the Sun, some- times reaching to a height of more than three hundred thousand miles. And the Moon is only two hundred and forty thousand miles away from us. But that the Earth should remain in her present posi- tion, moving still at her present speed, under such cir- cumstances, would be impossible. So terrific would be the force of the Sun's attraction that, long before he could draw thus near, she would have leapt with light- ning speed to greet him, and would have been lost in that fierce tumultuous sea of fire, as a pebble drops and is lost in the ocean. While therefore we may be thankful for the light and heat bestowed upon us by the Sun without which we could not live we may also be thankful that he is placed at a safe distance. We may congratulate our- selves that it is not the raging and storm-driven Sun, but the cold and quiet Moon which lies only a few thousands of miles away ; even though the poet Tennyson did look upon her as a rather unsympathetic friend, when he wrote THE SILVER MOON 37 " Oh, a cold, cold glance hath the Lady Moon, And a stately step, and slow, As with queenly gaze, so proud and pure, She looketh on all below. " She pauseth not on her onward path, To list to the mourner's sigh ; She pitieth not the throbbing pulse, Nor the dim and sunken eye." Still, if somewhat impassive, she is constant in her attachment. And it is better to depend on her stead- fast shining than to have only the will-o'-the-wisp flash of a shooting-star, or the uncertain visits of a comet. We do at least know when we may expect her ; and she never fails to arrive punctually to the minute. It is fair, however, to add that Shakespeare did not, through the voice of one of his characters, allow her even the virtue of steadfastness " O swear not by the Moon, the unconstant Moon, (That monthly changes in her circled orb) Lest that thy love prove likewise variable." * So though the Sun and Moon fill much the same spade in our sky, this does not mean that they are the same in bulk. Far from it ! The Sun is enormously trje larger of the tw r o, and also he is immensely farther off. To the latter fact is due their seeming likeness in size. The very much greater distance lessens hugely his apparent not his real size. A man who is fifty or a hundred yards away may look to our sight much bigger than a house which is half-a-mile or a mile away, yet that does not make him as large as the house. Our Moon's distance from us is not always exactly 1 Shakespeare : Romeo and Juliet. 38 THIS WONDERFUL UNIVERSE the same. She travels round in a pathway, or orbit, which may be described as slightly oval in shape, and the Earth is not at the precise centre of that oval. In one part of her monthly tour she is more than twenty-six thousand miles nearer to Earth than in another part. The two hundred and forty thousand miles which speaking roughly separate her from Earth, though a good deal when compared with distances on Earth itself, form a very insignificant little gap when compared with the wider heavenly distances which separate star from star. III. SIZES AND DISTANCES Before saying more about the Queen of Night, it may be well to pause, and try to give a general notion of the sizes of a few leading members of our Solar System, and of the distances separating them one from another. A train has been already imagined as going steadily at the rate of fifty miles an hour, never slackening or pausing night or day, travelling direct from one side of our Earth to the other, straight through the centre. Such a train, starting perhaps in the neighbourhood of the British Isles, and coming out in the neighbourhood of Australia, might accomplish its journey in less than a week. The same train, always at the same speed, with no stoppages, may be pictured as making the following journeys Round the whole Earth, on the equator, in nearly three weeks. Through the centre of the Moon, from one side to the other, in about two days. THE SILVER MOON 39 . Round the whole Moon, on the Moon's equator, in about six days. Through the centre of the Sun, from one side to the other, in nearly two years. Round the whole Sun, on the Sun's equator, in some- thing under six years. If you master these simple figures, you will gain a fairly clear idea of the relative sizes of Earth, Moon and Sun. Then about the distances of certain planets from our- selves of Venus, Mars and Jupiter the most easily seen in our sky. With them we will take the nearest positions. Each planet is sometimes on the same side of the Sun as our Earth, and at certain dates each one comes into a direct line with both Earth and Sun. That is the very closest point to which each planet draws. At other times each may be very far away, right off on the other side of the Sun, and then the dividing gap is immensely increased. It may help you to gain an idea of how this comes about if you place on the floor a small ball, then drop round it, lying flat, a small hoop. Round that lay a second and bigger hoop ; round that a third, still larger ; and round that a fourth, much larger still. The ball in the centre is the Sun ; the smallest of the hoops is the pathway of Venus round the Sun ; the next is the path- way of our Earth; then comes the pathway of Mars; and, lastly, you have the pathway of Jupiter. Other planets, nearer or farther than these, we are leaving alone for the present. Suppose that a very tiny ball is journeying round 40 THIS WONDERFUL UNIVERSE and round each hoop, moving at different speeds. Those nearer to the central ball go faster, those farther out go more slowly. So sometimes one on one hoop overtakes another on the next hoop, or lags behind it. Sometimes two are quite near together, and sometimes they are on opposite sides of the little ball which lies between them. That is how the planets travel round the Sun. Only there are many more of them than those three, and the pathways, or orbits, are not round, but slightly oval, and the distances between those various pathways are wide. Each one of these chief planets keeps always to its own orbit. Not one of them ever invades the orbit of another. Venus never gets near to the Earth's orbit from one side, and Mars never approaches it from the other. Now imagine the same train as before, always at the same unchanging speed, making the following trips Straight from the Earth to the Moon in less than seven months. Straight from the Earth to the Sun in about two hundred and ten years. See what a contrast there is between the space which separates the Moon from Earth, and that which separates Earth and Sun. Next come certain planets. Straight from Earth to the planet Venus, when the two are at their very nearest points, in rather less than sixty years. Straight from Earth to the planet Mars, when at their nearest, in somewhere about eighty years. And straight from Earth to the huge planet Jupiter, THE SILVER MOON 41 once more when at their nearest, in about eight hundred and thirty years. THE EARTH AND MARS WHEN AT THEIR NEAREST POSITIONS You see how much nearer we are to the Sun than to outlying members of his family. And Jupiter is the closest of all the four great outer worlds. 42 THIS WONDERFUL UNIVERSE These are the lesser gaps, dividing our Earth from her brother and sister planets. When she is on one side of the Sun, and a planet is on the further side, the gaps widen enormously. The planet-pathways, thus described, and all the other planet-orbits in our Solar System, lie in very much the same plane. That is to say, they are placed in the heavens much as the hoops lie on the floor, tilted, indeed, a little, this way or that way, but keeping in the main nearly to one level, not slanting about in all sorts of directions. PART IV WHAT THE MOON IS REALLY LIKE I. AIR AND WATER THE poet Wordsworth, speaking of the sky, puts one or two questions, in his serious fashion " Is nothing of that radiant pomp so good as we have here ? Or gives a thing but small delight that never can be dear ? The silver Moon, with all her vales and hills of mightiest fame Doth she betray us when they're seen? or are they but a name ? " No, she does not " betray us; " for they really are " hills and vales," or rather, mountains and ravines, of a sort ; but different in kind from those of Earth. And it is not impossible that a great deal of " that radiant pomp " if by the term we may understand the Universe as a whole may be not only as good as, but a great deal better than aught that " we have here." But for the Moon we can have no hesitation in answer- ing with a decisive " No." Fair and bright though she looks, nobody need wish to exchange life on Earth for life on the Moon ; at all events while his spirit inhabits his present body. So long as he must breathe earthly air to live, he could not exist there for ten minutes. Even if, by any mechanical means, that difficulty could at some future 43 44 THIS WONDERFUL UNIVERSE day be overcome, our sister-world would still be a very uncomfortable habitation. Though the distance is a mere nothing compared with other celestial distances, very little could be known of her surface before the invention of telescopes. Just the brightness and the markings the round, com- placent face, or the man w r ith his bundle of sticks and a few guesses whether these might represent lands and seas; and that was nearly all. But telescopes soon made a difference. Not only could grey plains be clearly seen, but lofty mountains also; and great circular mountain ramparts and rings ; and countless volcanic craters, some huge, some small, scattered lavishly about; and curious lighter streaks, amid wide, dusky spaces. As telescopes have been made with greater and greater powers, so our knowledge of the Moon has grown, especially in late years with the added help of photography. The question is sometimes asked how near are we practically brought to the Moon by our largest telescopes ? How much can we really see ? This is not merely a question of the largest telescopes. It is seldom that the highest powers can be used with advantage. If they could, w T e might speak of " bringing the Moon " to a distance of a hundred, or even eighty miles. Actually, it can hardly be said that she can be clearly seen nearer than perhaps a hundred and twenty miles. Even then the distance, though a mere nothing from one point of view, means a good deal with regard to eyesight. If we think of one hundred and twenty miles WHAT THE MOON IS REALLY LIKE 45 side by side with let us say, ten thousand miles the space sinks into a mere speck; yet when we begin to consider how much and how little can be distinguished by the naked eye on Earth, at a distance of a hundred and twenty miles, matters wear another aspect. However, photographs, taken with powerful telescopes and enlarged, do show us " structures " on the Moon not more than two or three miles in diameter. Craters of that size have been detected in numbers ; which is not bad for a world two hundred and forty thousand miles away. During many years it was looked upon as certain that no air existed on the Moon. If any atmosphere in the least like our own were there, the Moon's outline could not be so sharp and clear. It would, and more especially when seen through a telescope, have a softened and blurred look. But this never happens. So, practically, it is correct to say that our com- panion has not an atmosphere, though this does not forbid the possibility of a very, very thin and slight j amount of air, so thin and slight that it would not support any animal -life such as we know on Earth. Once upon a time our sister-globe may have had a more "substantial" atmosphere; but if so it has all but vanished. She is so small in size that her power of attraction has probably been too feeble to hold her atmosphere captive. So gradually all or most of its particles have wandered far away, never to return. Our Earth holds fast her ocean of air simply by the force of her attractive power; and here, seemingly, the Moon has failed, because she is so much smaller and lighter in make. 46 THIS WONDERFUL UNIVERSE When the grey markings on the Moon's face were first examined through telescopes, they were seen to be broad spaces, bordered often by mountain-ranges, and the idea naturally sprang up that they might be oceans, like our earthly oceans. But though they are still called " seas," no one now believes that they are actual oceans. Some astronomers have looked upon them as possible old sea-beds, from which the water has long since disappeared. " Then the Moon in all her pride, Like a spirit glorified, Filled and overflowed the night With revelations of her light." LONGFELLOW. II. MOUNTAINS AND CRATERS With the help of a small telescope, or even of a good binocular or field-glass, it is easy to see mountains and craters at the broken " edge " of brightness of a half- Moon, on a clear night. Some of the tiny tips stand out curiously, quite apart from the main body, because the lower mountain-slopes are in shadow. It is just as, in Switzerland, one may see mountain-summits glowing in sunshine, while the lower parts are deep in shadow. At the same time odd little bright circles may be noted. They are some of the great round mountain- ramparts or crater-like formations which abound there. Though the Moon is so small a globe, she vies with Earth in the height of her ranges. She has her Alps and her Apennines so named by earthly observers. PORTION OF MOON, NORTH POLE TO AGRIPPA PHOTOGRAPH BY G. E. HALE, OCT. 5, IQOQ P- 47 WHAT THE MOON IS REALLY LIKE 47 In those far-off Alps is another Mont Blanc; not so lofty as ours. But the lunar Apennines have no less than three thousand high peaks, all visible from here, and among those peaks are summits from fifteen to eighteen thousand feet high, not only equalling but out-doing our Mont Blanc. Clefts and gorges are seen, and long, narrow channels, sometimes described as grooves or furrows, with high steep sides. And certain of the large craters are sur- rounded with bright streaks, radiating out in a curious star-like pattern. Some astronomers believe these to be cracks in the Moon's crust, many of them hundreds of miles long. It has been suggested that the brightness might be due to deposits of salt perhaps left there by former oceans shining in the sunlight. To an extraordinary degree that bright surface is studded with craters. The larger ones may be as much as a hundred, or even a hundred and fifty miles across ; real circular mountain-ranges, generally enclosing more or less level plains, in the centre of which a solitary mountain sometimes rears its head. From these all varieties of crater-like formations, down to little crater- pits or crater-cones, under three miles in diameter, are lavishly strewn over the face of our satellite ! She is indeed " pock-marked." A well-known crater-like formation is " Copernicus," a circular mountain-wall, fifty-six miles across and rising to thirteen thousand feet in height. It encloses a plain, which is broken by hills, some of which are as much as two thousand feet high ; and many bright rays diverge from it. 48 THIS WONDERFUL UNIVERSE The explanation was long widely held, and is still held in many quarters, that these craters, both large and small, are due mainly to volcanic action in the long past. But if so, the volcanoes now are silent and dead. Another theory of explanation has been lately put forward, to some extent a revival of an old theory, once maintained and then given up. This is that the craters may be due, not to volcanic action, but to the crashing down of huge meteorites on the Moon's surface, in ages when that surface was soft and impressionable, and when enormous multitudes of such meteorites may have circled round the Sun, extending to the Moon's neighbourhood. To some minds the volcanic explanation may seem the easier of belief; at all events as accounting for the larger craters. We can no longer speak w r ith unquestioning confidence of the condition of the Moon as absolutely " dead " changeless lifeless. Observations made during recent years have to a certain extent shaken this belief. Slight alterations of outline have been here or there noticed which, if real, might have been caused by something in the nature of falls of rock or landslides. And these may have been partly due to the tremendous variations of temperature. For during the Moon's long day and long night, changes from blazing heat to unspeakable cold, and from unspeakable cold to blazing heat are said to range between some/owr hundred and fifty degrees ; while we on Earth think much of a range of fifty or sixty degrees of temperature. Another explanation given for these slight changes of outline seen at times is that they may have come about WHAT THE MOON IS REALLY LIKE 49 through the bombardment of the Moon's surface by exceptionally large and heavy meteorites. This too is at least a " may-be," though in the opinion of some eminent Astronomers not very likely. Moreover, through long and careful watching from an observatory in Jamaica, many small and brilliant white spots have been -seen on the summits of mountain- ranges ; and these have been regarded as perhaps snow. The Moon has not ice-caps, like Mars, but such spots suggest the possibility of snow. Certain passing appearances also have been noticed, which the observer translated into probable snow-storms. A difficulty comes in here, however. Both rain and snow with us are the result of the condensation of water- vapour floating in our atmosphere. But the Moon, being so small a globe, has not, it is considered, enough attractive power to hold captive an atmosphere of water-vapour; so it would seem that snow-storms there can hardly come into being. One authority, pointing this out, states that " the white spots would almost certainly slowly melt and evaporate in the sunlight," that, if matters be thus, " it would mean that no gas lighter than carbon dioxide" carbonic acid gas "could be retained by the Moon ; " and that " this leaves open the possibility that the white spots are solid (frozen) carbon dioxide." From that same cause, the small size of the Moon and the consequent very slight pressure of so thin an atmosphere, it is believed that water would boil at the freezing-point ; a curious state of things, with results which it is difficult for us fully to estimate. Again, certain other appearances have been observed 50 THIS WONDERFUL UNIVERSE which are held by some Astronomers to point to the problematic existence of vegetation; a very low order of it at the best ! We are told that this lunar vegetation is not green, but grey or purplish-black; which might suggest something in the nature of fungi. One American Astronomer, 1 while upholding this " vegetation " view, carefully explains that the " form " of any such growth " is of course quite unknown to us, and the phenomena may consist merely in the darkening and fading of its exposed surface. As has been men- tioned in previous articles, we assume the phenomena to be due to vegetation^ because that explanation is plausible, and because none other of any sort has ever been offered for it." But other explanations may yet be forthcoming; and any such " assumed " interpretations should always be held lightly, pending further evidence and more definite proofs. III. DAY AND NIGHT It becomes fairly evident that our nearest neigh- bour in the heavens would hardly do for a summer resort, even if we could manage somehow to cross safely the gulf of more than two hundred thousand airless miles lying between. The Moon's daylight time is always on that part of her surface which faces the Sun; her time of darkness is always on that part which is turned away from the Sun. 1 Prof. W. H. Pickering. WHAT THE MOON IS REALLY LIKE 51 This is with her as with us. But while our day, caused by Earth's whirl on her axis, lasts twenty-four hours including hours both of light and of darkness the Moon's day, caused also by her much slower whirl on her axis, lasts through four of our weeks or twenty- eight of our days. So the length of her " day " taking together as one the hours of light and of darkness is exactly the same as the time that she takes to travel once around our Earth. In consequence of this, she turns always one side to us, and never the opposite side. Whether that side too is studded and pock-marked with countless craters, large and small, we may con- jecture, but we cannot know. Not a single human being in this world has ever gazed on the further side of the Moon. At Full Moon we see the whole of her bright side, as illumined by the Sun, during its day-time. At New Moon that bright side is turned away from us. But what we do see, either at the Full, or before and after the New, is always the same side. Invariably we have the same mountains and plains, taking shape as an old man gathering sticks, or as a comic human face, never changing. Think what the contrast must be, between the fort- night of burning, glaring heat unsoftened by any atmo- sphere worth mentioning, lasting unbroken through two weeks or so of Earth-time and the black darkness, the awful icy chill, of the next two weeks, with no air to capture and keep any of the Sun's warmth. The cold then must be simply appalling. And even in the long day of blazing heat, though in 52 THIS WONDERFUL UNIVERSE direct sunshine the thermometer might rise to any extent, yet the climate must be similar to that of our loftiest mountain-tops, where hard freezing goes on side by side with considerable heat. Far more so, indeed, on the Moon, where practically no air exists. The slightest shade, cutting off direct heat, would mean at once overwhelming cold. One beautiful sight may be seen from the Moon if any beings were there to enjoy it ! and that is the Earth in the Moon's sky, a splendid globe, more than a dozen times as large as the Moon in our sky, and gloriously bright. Eut only on part of the Moon can this wonderful vision appear that side which in- variably faces us, and from which Earth is visible as a fixed globe, steadily turning round and round, but always at a single spot in the heavens. The other unfortunate side of our satellite has no such help in its long winter nights. Stars and planets alone can be seen from there. r i Though the Moon may possibly have come into being later than the Earth, she is really the older of the two. Age is not a question of years alone. Even with human , KJ beings we sometimes see a man of sixty-five who is . younger than another of fifty-five, and it is the same with heavenly bodies. Earth still enjoys a hale and vigorous middle a