And now I have kept your attention and strained your eyes long enough, and you have objects to study for many a long evening before you will learn to see them plainly. You must not expect to find them every night, for the lightest cloud or the faintest moonlight will hide many of them from view; and, moreover, though you may learn to use the telescope fairly, you will often not know how to get a clear view with it. Still, you may learn a great deal, and before we go in I want to put a thought into your minds which will make astronomy still more interesting. We have seen that the stronger our telescopes the more stars, star-clusters, and nebulæ we see, and we cannot doubt that there are still countless heavenly bodies quite unknown to us. Some years ago Bessel the astronomer found that Sirius, in its real motion through the heavens, moves irregularly, travelling sometimes a little more slowly than at other times, and he suggested that some unseen companion must be pulling at him.
Twenty-eight years later, in 1862, two celebrated opticians, father and son, both named Alvan Clark, were trying a new telescope at Chicago University, when suddenly the son, who was looking at Sirius, exclaimed, "Why, father, the star has a companion!" And so it was. The powerful telescope showed what Bessel had foretold, and proved Sirius to be a "binary" star—that is, as we have seen, a star which has another moving round it.
It has since been proved that this companion is twenty-eight times farther from Sirius than we are from our sun, and moves round him in about forty-nine years. It is seven times as heavy as our sun, and yet gives out so little light that only the keenest telescopes can bring it into view.
Now if such a large body as this can give so very faint a light that we can scarcely see it, though Sirius, which is close to it, shines brightest of any star in the heavens, how many more bodies must there be which we shall never see, even among those which give out light, while how many there are dark like our earth, who can tell?
Now that we know each of the stars to be a brilliant sun, many of them far, far brighter than ours, yet so like in their nature and laws, we can scarcely help speculating whether round these glorious suns, worlds of some kind may not be moving. If so, and there are people in them, what a strange effect those double coloured suns must produce with red daylight one day and blue daylight another!
Surely, as we look up at the myriads of stars bespangling the sky, and remember that our star-sun has seven planets moving round it of which one at least—our own earth—is full of living beings, we must picture these glorious suns as the centres of unseen systems, so that those twinkling specks become as suggestive as the faint lights of a great fleet far out at sea, which tell us of mighty ships, together with frigates and gunboats, full of living beings, though we cannot see them, nor even guess what they may be like. How insignificant we feel when we look upon that starlit sky and remember that the whole of our solar system would be but a tiny speck of light if seen as far off as we see the stars! If our little earth and our short life upon it were all we could boast of we should be mites indeed.
But our very study to-night lifts us above these and reminds us that there is a spirit within us which even now can travel beyond the narrow bounds of our globe, measure the vast distances between us and the stars, gauge their brightness, estimate their weight, and discern their movements. As we gaze into the depths of the starlit sky, and travel onwards and onwards in imagination to those distant stars which photography alone reveals to us, do not our hearts leap at the thought of a day which must surely come when, fettered and bound no longer to earth, this spirit shall wander forth and penetrate some of the mystery of those mighty suns at which we now gaze in silent awe.
[1] Reproduced in the Frontispiece with Mr. Roberts's kind permission. The star-halo at the top of the plate is caused by diffraction of light in the telescope, and comes only from an ordinary star.
[2] The Story of the Heavens.
[3] In Fig. 54 the sickle alone comes within the picture.