CONCLUSION.
And now, my young friends, I am drawing near the close of that course of lectures which has occupied us, I hope you will think not unprofitably, for a portion of our Christmas holidays. We have spoken of the sun and of the moon, of comets and of stars, and I have frequently had occasion to allude to the relative position of our earth in the universe. No doubt it is a noble globe which we inhabit, but I have failed in my purpose if I have not shown you how insignificant is this earth when compared with the vast extent of some of the other bodies that abound in space. We have, however, been endowed with a feeling of curiosity which makes us long to know of things beyond the confines of our own earth. Astronomers can tell us a little, but too often only a little. They will say—That is a star, and That is a planet, and That is so big, and That so far; such is the meagre style of information with which we often have to be content. The astronomers who live on other worlds, if their faculties be in any degree comparable with ours, must be similarly ignorant with regard to this earth. Inhabitants of our fellow-planets can know hardly anything more than that the earth on which we dwell is a globe 8000 miles across, with many clouds around us. Some of the planets would not even pay us the compliment of recognizing our existence; while from the other systems—the countless other systems—of space we are absolutely imperceptible and unknown.
Out of all the millions of bodies which we can see, you could very nearly count on your fingers those from which our earth would be visible. This reflection is calculated to show us how vast must be the real extent of that universe around us. Here is our globe, with its inhabitants, with its great continents, with its oceans, with its empires, its kingdoms, with its arts, its commerce, its literature, its sciences, and yet it would seem that all these things are absolutely unknown to any inhabitants that may exist elsewhere. I do not think that any reasonable person will doubt that there must be inhabitants elsewhere. There are millions of globes, many of them more splendid than ours. Surely it would be presumptuous to say that this is the only one of all the bodies in the universe on the surface of which life, with all that life involves, is manifested. You will rather think that our globe is but one in the mighty fabric, and that other globes may teem with interest just as ours does. We can, of course, make no conjecture as to what the nature of the life may be elsewhere. Could a traveller visit some other globes and bring back specimens of the natural objects that he found there, no collections that the world has ever seen could rival them in interest. When I go into the British Natural History Museum and look around that marvellous collection, it awakens in me a feeling of solemnity. I see there the remains of mighty extinct animals which once roamed over this earth; also objects which have been dredged from the bottom of the sea at a depth of some miles; there I can examine crystals which have required incalculable ages for their formation; and there I look at meteorites which have travelled from the heavens above down on to the earth beneath. Such sights, and the reflections they awaken, bring before us in an imposing manner the phenomena of our earth, and the extent and interest of its past history. Oliver Wendell Holmes said that the only way to see the British Museum was to take lodgings close by when you were a boy, and to stay in the Museum from nine to five every day until you were an old man; then you would begin to have some notion of what this Institution contains. Think what millions of British Museums would be required were the universe to be adequately illustrated: one museum for the earth, another for Mars, another for Venus—but it would be useless attempting to enumerate them!
Most of us must be content with acquiring the merest shred of information with regard even to our own earth. Perhaps a schoolboy will think it fortunate that we are so ignorant with respect to the celestial bodies. What an awful vista of lessons to be learned would open before his view, if only we had a competent knowledge of the other globes which surround us in space! I should like to illustrate the extent of the universe by following this reflection a little further. I shall just ask you to join with me in making a little calculation as to the extent of the lessons you would have to learn if astronomers should succeed in discovering some of the things they want to know.
Of course, all of us learn geography and history. We must know the geography of the leading countries of the globe, and we must have some knowledge of their inhabitants and of their government, their resources and their civilization. It would seem shockingly ignorant not to know something about China, or not to have some ideas on the subject of India or Egypt. The discovery of the New World also involves matters on which every boy and girl has to be instructed. Supposing we were so far acquainted with the other globes scattered through space that we were able to gain some adequate knowledge of their geography and natural history, of the creatures that inhabit them, of their different products and climates, then everybody would be anxious to learn those particulars; and even when the novelty had worn off, it would still be right for us to know something about countries perhaps more populous than China, about nations more opulent than our own, about battles mightier than Waterloo, about animals and plants far stranger than any we have ever dreamt of. An outline of all such matters should, of course, be learned, and as the amount of information would be rather extensive, we will try to condense it as much as possible.
To aid us in realizing the full magnificence of that scheme in the heavens of which we form a part, I shall venture to give an illustration. Let us attempt to form some slight conception of the number and of the bulk of the books which would be necessary for conveying an adequate description of that marvellous universe of stars which surround us. These stars being suns, and many of them being brighter and larger than our own sun, it is but reasonable to presume that they may be attended by planetary systems. I do not say that we have any right to infer that such systems are like ours. It is not improbable that many of the suns around us have a much poorer retinue than that which dignifies our sun. On the other hand, it is just as likely that many of these other suns may be the centres of systems far more brilliant and interesting, with far greater diversity of structure, with far more intensity and variety of life and intelligence than are found in the system of which we form a part. It is only reasonable for us to suppose that, as our earth is an average planet, so our sun is an average star both in size and in the importance of its attendants. We may take the number of stars in the sky at about one hundred millions; and thus we see that the books which are to contain a description of the entire universe—or rather, I should say, of the entire universe that we see—must describe 100,000,000 times as much as is contained in our single system. Of course, we know next to nothing of what the books should contain; but we can form some conjecture of the number of those books, and this is the notion to which I now ask your attention.
So vast is the field of knowledge that has to be traversed, that we should be obliged to compress our descriptions into the narrowest compass. We begin with a description of our earth, for nearly all the books in the libraries that exist at this moment are devoted to subjects connected with this earth. They include various branches of history, innumerable languages and literatures and religions, everything relating to life on this globe, to its history in past geological times, to its geography, to its politics, to every variety of manufacture and agriculture, and all the innumerable matters which concern our earth’s inhabitants, past and present. But this tremendous body of knowledge must be much condensed before it would be small enough to retire to its just position in the great celestial library. I can only allow to the earth one volume of about 500 pages. Everything that has to be said about our earth must be packed within this compass. All terrestrial languages, histories, and sciences that cannot be included between its covers can find no other place on our shelves. I cannot spare any more room. Our celestial library will be big enough, as you shall presently see. I am claiming a good deal for our earth when I regard it as one of the most important bodies in the solar system. Of course it is not the biggest—very far from it; but it seems as if the big planets and the sun were not likely to be inhabited, so that if we allow one other volume to the rest of the solar system, it will perhaps be sufficient, though it must be admitted that Venus, of which we know next to nothing, except that it is as large as the earth, may also be quite as full of life and interest. Mars and Mercury are also among the planets with possible inhabitants. We are, therefore, restricting the importance of the solar system as much as possible, perhaps even too much, by allowing it two. Within those two volumes every conceivable thing about the entire solar system—sun, planets (great and small), moons, comets, and meteors—must be included, or else it would not be represented at all in the great celestial library.
We shall deal on similar principles with the other systems through space. Each of the 100,000,000 stars will have two volumes allotted to it. Within the two volumes devoted to each star we must compress our description of the body itself and of the system which surrounds it; the planets, their inhabitants, histories, arts, sciences, and all other information. I am not, remember, discussing the contents, but only the number of books we should have to read ere we could obtain even the merest outline of the true magnificence of the heavens. Let us try to form some estimate as to the kind of library that would be required to accommodate 200,000,000 volumes. I suppose a long straight hall, so lofty that there could be fifty shelves of books on each side. As you enter you look on the right hand and on the left, and you see it packed from floor to ceiling with volumes. We have arranged them according to the constellations. All the shelves in one part contain the volumes relating to the worlds in the Great Bear, while upon the other side may repose ranks upon ranks of volumes relating to the constellation of Orion.
I shall suppose that the volumes are each about an inch and a half thick, and as there are fifty shelves on each side, you will easily see that for each foot of its length the hall will accommodate 800 books. We can make a little calculation as to the length of this library, which, as we walk down through it, stretches out before us in a majestic corridor, with books, books everywhere. Let us continue our stroll, and as we pass by we find the shelves on both sides packed with their thousands of volumes; and we walk on and on, and still see no end to the vista that ever opens before us. In fact, no building that was ever yet constructed would hold this stupendous library. Let the hall begin on the furthest outskirts of the west of London, carry it through the heart of the city, and away to the utmost limits of the east—not a half of the entire books could be accommodated. The mighty corridor would have to be fifty miles long, and to be packed from floor to ceiling with fifty shelves of books on each side, if it is to contain even this very inadequate description of the contents of the visible universe. Imagine the solemn feelings with which we should enter such a library, could it be created by some miracle! As we took down one of the volumes, with what mysterious awe should we open it, and read therein of some vast world which eye had never seen! There we might learn strange problems in philosophy, astonishing developments in natural history; with what breathless interest we should read of inhabitants of an organization utterly unknown to our merely terrestrial experience! Notwithstanding the vast size of the library, the description of each globe would have to be very scanty. Thus, for instance, in the single book which referred to the earth I suppose a little chapter might be spared to an island called England, and possibly a page or so to its capital, London. Similarly meagre would have to be the accounts of the other bodies in the universe; and yet, for this most inadequate of abstracts, a library fifty miles long, and lined closely with fifty shelves of books on each side, would be required!
Methuselah lived, we are told, nine hundred and sixty-nine years; but even if he had attained his thousandth birthday he would have had to read about 300 of these books through every day of his life before he accomplished the task of learning even the merest outline about the contents of space.
If, indeed, we were to have a competent knowledge of all these other globes, of all their countries, their geographies, their nations, their climates, their plants, their animals, their sciences, languages, arts and literatures, it is not a volume, or a score of volumes, that would be required, but thousands of books would have to be devoted to the description of each world alone, just as thousands of volumes have been devoted to the affairs of this earth without exhausting the subjects of interest it presents. Hundreds of thousands of libraries, each as large as the British Museum, would not contain all that should be written, were we to have anything like a detailed description of the universe which we see. I specially emphasize the words just written, and I do so because the grandest thought of all, and that thought with which I conclude, brings before us the overwhelming extent of the unseen universe. Our telescopes can, no doubt, carry our vision to an immeasurable distance into the depths of space. But there are, doubtless, stars beyond the reach of our mightiest telescopes. There are stars so remote that they cannot record themselves on the most sensitive of photographic plates.
On the blackboard I draw a little circle with a piece of chalk. I think of our earth as the centre, and this circle will mark for us the limit to which our greatest telescopes can sound. Every star which we see, or which the photographic plate sees, lies within this circle; but, are there no stars outside? It is true that we can never see them, but it is impossible to believe that space is utterly void and empty where it lies beyond the view of our telescopes. Are we to say that inside this circle stars, worlds, nebulæ, and clusters are crowded, and that outside there is nothing? Everything teaches us that this is not so. We occasionally gain accession to our power by adding perhaps an inch to the diameter of our object-glass, or by erecting a telescope in an improved situation on a lofty mountain peak, or by procuring a photographic plate of increased sensibility. It thus happens that we are enabled to extend our vision a little further and to make this circle a little larger, and thus to add a little more to the known inside which has been won from the unknown outside. Whenever this is done we invariably find that the new region thus conquered is also densely filled with stars, with clusters, and with nebulæ; it is thus unreasonable to doubt that the rest of space also contains untold myriads of objects, even though they may never, by any conceivable improvement in our instruments, be brought within the range of our observation. Reflect that this circle is comparatively small with respect to the space outside. It occupied but a small spot on this blackboard, the blackboard itself occupies only a small part of the end of the theatre, while the end of the theatre is an area very small compared with that of London, of England, of the world, of the solar system, of the actual distance of the stars. In a similar way the region of space which is open to our inspection is an inconceivably small portion of the entire extent of space. The unknown outside is so much larger than the known inside, it is impossible to express the proportion. I write down unity in this corner and a cipher after it to make ten, and six ciphers again to make ten millions, and again, six ciphers more to make ten billions; but I might write six more, ay, I might cover the whole of this blackboard with ciphers, and even then I should not have got a number big enough to express how greatly the extent of the space we cannot see exceeds that of the space we see. If, therefore, we admit the fact, which no reasonable person can doubt, that this outside, this unknown, this unreachable and, to us, invisible space does really contain worlds and systems as does this small portion of space in which we happen to be placed—then, indeed, we shall begin truly to comprehend the majesty of the universe. What figures are to express the myriads of stars that should form a suitable population for a space inconceivably greater than that which contains 100,000,000 stars? But our imagination will extend still further. It brings before us these myriads of unseen stars with their associated worlds, it leads us to think that these worlds may be full to the brim with interests as great as those which exist on our world. When we remember that, for an adequate description of the worlds which we can see, one hundred thousand libraries, each greater than any library on earth, would be utterly insufficient, what conception are we to form when we now learn that even this would only amount to a description of an inconceivably small fragment of the entire universe?
Let us conceive that omniscience granted to us an adequate revelation of the ample glories of the heavens, both in that universe which we do see and in that infinitely greater universe which we do not see. Let a full inventory be made of all those innumerable worlds, with descriptions of their features and accounts of their inhabitants and their civilizations, their geology and their natural history, and all the boundless points of interest of every kind which a world in the sense in which we understand it does most naturally possess. Let those things be written every one, then may we say that were this whole earth of ours covered with vast buildings, lined from floor to ceiling with book-shelves—were every one of these shelves stored full with volumes, yet, even then this library would be inadequate to receive the books that would be necessary to contain a description of the glories of the sidereal heavens.
CONCLUDING CHAPTER.
HOW TO NAME THE STARS.
Every one who wishes to learn something about astronomy should make a determined effort to become acquainted with the principal constellations, and to find out the names of the brighter and more interesting stars. I have therefore added to Star-land this little chapter, in which I have tried to make the study of the stars so simple that, by taking advantage of a few clear nights, there ought to be no difficulty in obtaining a knowledge of a few constellations.
The first step is to become familiar with the Great Bear, or Ursa Major, as astronomers more generally call the group. We begin with this, because after it has been once recognized, then you will find it quite easy to make out the other constellations and stars. It may save you some trouble if you can get some one to point out to you the Great Bear; but even without such aid, I think you will be able to make out the seven bright stars which form this remarkable group, from the figure here given ([Fig. 92]). Of course, the position of this constellation, as of every other in the heavens, changes with the hour of the night, and changes with the seasons of the year. About April the constellation at 11 o’clock at night is high over your head. In September at the same hour, the Great Bear is low down in the north. It is to be seen in the west in July, and at Christmas it lies in the east at convenient hours in the evening for observation. One of the advantages of using the Great Bear as the foundation of our study of the stars arises from the fact that to an observer in the British Islands or in similar latitudes this group never sets. Whenever the sky is clear after nightfall, the Great Bear is to be seen somewhere, while the brightness of its component stars makes it a conspicuous object. Indeed, there is only one constellation in the sky, namely, that of Orion, which is a more brilliant group than the Great Bear. We shall tell you about Orion presently, but it does not suit to begin with, because it can only be seen in winter, and is then placed very low down in the heavens.
Fig. 92.—The Great Bear and the Pole Star.
Your next lesson will be to utilize the Great Bear for the purpose of pointing out the Pole Star. Look at the two stars marked α and β. They are called the “Pointers,” because if you follow the direction they indicate along the dotted line in the figure, they will conduct your glance to the Pole. This is the most important star in the heavens to astronomers, because it happens to mark very nearly the position of the Pole on the sky. You will easily note the peculiarity of the Pole Star if you will look at it two or three times in the course of the night. It will appear to remain in the same place in the sky, while the other stars change their places from hour to hour. It is very fortunate that we have a star like this in the northern heavens; the astronomers in Australia or New Zealand can see no bright star lying near the Southern Pole which will answer the purposes that the Pole Star does so conveniently for us in the north.
The Pole Star belongs to a constellation which we call the Little Bear; two other conspicuous members of this group are the two “Guards”; you will see how they are situated from [Fig. 82], [p. 322]. They lie nearly midway between the Pole Star and the last of the three stars which form the Great Bear’s Tail. The same figure will also introduce us to another beautiful constellation, namely, Cassiopeia. You will never find any difficulty in identifying the figure that marks this group if you will notice that the Pole lies midway between it and the Great Bear.
Fig. 93.—The Great Square of Pegasus.
Cassiopeia is also one of the constellations that never set to British observers; but now we have to speak of groups which do set, and which, therefore, can only be observed when the proper season comes round. The first of these is “the Great Square of Pegasus”; you cannot see this group conveniently in the spring or summer, but during the autumn and winter it is well placed after nightfall. There are four conspicuous stars forming the corners of the square, and then three others marked α, γ, and β ([Fig. 93]), which form a sort of handle to the square. In fact, if you once recognize this group, you will perhaps see in it a resemblance to a great saucepan with a somewhat bent handle, and then you will be acquainted with a large tract of Star-land near the Square of Pegasus. From the figure you will see that a line imagined to be drawn from the Pole Star over the end of Cassiopeia, and then produced as far again, will just lead to the Great Square. I have also marked on this figure two objects that are of great telescopic interest; one of them is the Nebula in Andromeda, of which we had an account in the last lecture. You see it lies halfway between the corner α of the square and the group of Cassiopeia. Another interesting object is the star marked γ Andromedæ. The telescope shows it to consist of a pair of stars, the colors of which are beautifully contrasted.
At the end of this handle to the Great Square of Pegasus is the star α, in the constellation of Perseus. It lies between two other stars γ and δ. We refer to [Fig. 84], in which these stars are shown. We there employed the figure to indicate the position of Algol, the remarkable variable star. Your map will also point out some other important stellar features. If we curve round the three marked γ, α, and δ of Perseus, the eye is conducted to Capella, a gem of the first magnitude in the constellation of Auriga. Close to Capella is a long triangle, the corners of which are the “Hœdi,” the three kids—which Capella is supposed to nurture.
If we carry a curve through γ, α, δ, of Perseus, and now bend it in the opposite way, the eye is led through ε and ζ in the same constellation, and then on to the Pleiades, of which we have already spoken.
Fig. 94.—Orion and Sirius.
Perseus lies in one of the richest parts of the heavens. The Milky Way stretches across the group, and the sky is strewn with stars beyond number. Even an opera-glass directed to this teeming constellation cannot fail to afford the observer a delightful glimpse of celestial scenery.
We may, however, specially remind the beginner that the objects on this map are not always to be seen, and as an illustration of the way in which the situation and the visibility of the constellations are affected by the time of year, I shall take the case of the Pleiades and follow them through a season. Let us suppose that we make a search for this group at 11 P.M. every night. On the 1st of January, the Pleiades will be found high up in the sky in the southwest. On the 1st of March, they will be setting in the west at the same hour. On the 1st of May, the Pleiades are not visible, neither are they on the 1st of July. On the 1st of September, they will be seen low down in the east. On the 1st of November, they will be high in the heavens in the southeast. On the ensuing 1st of January, the Pleiades will be found back in the same place which they occupied on the same date in the preceding year, and so on throughout the cycle. Of course, you will not suppose that their changes are due to actual motions in the group of stars themselves. They are merely apparent, and are to be explained by the motion of the earth round its axis, and the revolution around the sun.
Next we are to become acquainted with the glory of our winter skies, the constellation of Orion, [Fig. 94]. I dare say many of my readers are already familiar with the well-known twin stars which form the belt of Orion, but if not, they will be able to recognize it by the help of the groups already learned. Imagine a line drawn from the Pole Star through Capella, and then produced as much further again, and we shall be conducted into the precincts of Orion. This group lies on the equator, and, consequently, it is equally familiar to southern astronomers and to those of the north. It can be best seen by those who observe it from or near the equator.
The brightest star in Orion is known either as α Orionis or as Betelgeuze, by which name it is represented in the figure. This star is of the first magnitude, and so is Rigel on the opposite side of the belt. The three stars of the belt and the two others, γ and κ, at which they point above and below, are of second magnitude.
The owner of a telescope finds especial attractions in this constellation. Notably among the subjects which will interest him is the Great Nebula, the position of which is indicated in our figure. Under the middle of the belt are a few stars, around which is a hazy light that is perceptible with the smallest telescopic aid. Viewed by instruments of adequate proportions, these have developed into a marvellous nebula of glowing gas, attaining to dimensions so vast that no one has yet ever attempted to estimate them.
The vicinity of Orion is also enriched with some of the most interesting stellar objects. Follow the line of the belt upwards to the right, and your eye is conducted to a ruddy first magnitude star named Aldebaran, in the constellation of the Bull. This is a pleasing object, which the beginner will sometimes be apt to confuse with the planet Mars, to which, under certain circumstances, it certainly bears a resemblance. Another very pleasing little group, known as the Hyades, will be found near Aldebaran. If the line of the belt of Orion be carried down to the left, it will be found to point to Sirius, or the Dog Star.
You will find it an interesting occupation to make for yourself maps of small parts of the heavens. First copy out the chief stars in their proper places from the star atlas, and then fill in the smaller stars with your own observations. Try first on some limited region of the heavens; take the figure of Cassiopeia, for instance, or the Square of Pegasus, and see if you can produce a fair representation of those groups by marking in the stars that your instrument will show you; or take the Pleiades and make a tracing of the principal stars of the group from the sketch that we have given ([Fig. 89]), then take an opera-glass and fill in as carefully as you can all that it will show. I can assure you that you will find a little definite work of this kind full of interest and instruction.
But I hope you will desire to advance further in the study of the heavens. It is to be remembered that with even the most moderate instruments there is much to be done. Many comets have been detected, and many planets have been discovered, by the use of telescopes so small that they could be easily carried out from the house for the evening’s work and brought back again after the observations were over.
It remains for me to add a few words which will help you in finding the planets. It is, of course, impossible to represent such objects as Jupiter, Saturn, Venus, Mars, and Mercury on maps of the heavens, because these bodies are constantly moving about, and if their places were right to-day they would be wrong to-morrow. The almanac will be necessary for you here. You must find out by its help what planets are visible and in what part of the sky they are placed. Then you will have to compare your maps with the heavens, and when you find a bright star-like body that is not shown on your maps you may conclude at once that it is the planet. Although these objects are so star-like to the unaided eye, yet the resemblance is at once dispelled when we use a telescope. The star is only a bright point of light and white, the planet shows a visible shape. This is, at least, the case with the five planets I have named; for there are others, such as Uranus and Neptune, which are too far to be much more than star-like points in ordinary telescopes. The minor planets would not interest you.
I hope that the reading of Star-land will, at all events, induce you to make a beginning of the study of the heavens, if you have not already done so. If you have the advantage of a telescope, so much the better; but, if this is impossible, make the best use of your own eyes. Do not put it off or wait till you get some one to teach you. If it be clear this very night, go out and find the Great Bear and the Pole Star, and as many of the other constellations as you can, and at once commence your career as an astronomer.