CHAPTER XXIX.

A WHIRLING UNIVERSE.

No rest, no quiet, no repose, in that great universe, which to our dim eyesight looks so fixed and still, but one perpetual rush of moving suns and worlds. For every star has its own particular motion, every sun is pressing forward in its own appointed path. And among the myriads of stars--bright, blazing furnaces of white or golden, red, blue, or green flame--sweeping with steady rush through space, our sun also hastens onwards.

The rate of his speed is not very certain, but it is generally believed to be about one hundred and fifty million miles each year. Possibly he moves in reality much faster.

When I speak of the sun’s movement, it must of course be understood that the earth and planets all travel with him, much as a great steamer on the sea might drag in his wake a number of little boats. From one of the little boats you could judge of the steamer’s motion quite as well as if you were on the steamer itself. Astronomers can only judge of the sun’s motion by watching the seeming backward drift of stars to the right and left of him; and the watching can be as well accomplished from earth as from the sun himself.

After all, this mode of judging is, and must be, very uncertain. Among the millions of stars visible, we only know the real distances of about twenty-five; and every star has its own real motion, which has to be separated from the apparent change of position caused by the sun’s advance.

It seems now pretty clear that the sun’s course is directed towards a certain point in the constellation Hercules. If the sun’s path were straight, he might be expected by and by, after long ages, to enter that constellation. But if orbits of suns, like orbits of planets, are ellipses, he will curve away sideways long before he reaches Hercules.

[Illustration: HERCULES]

One German astronomer thought he had found the center of the sun’s orbit. He believed the sun and the stars of the Milky Way to be traveling round the chief star in the Pleiades, Alcyone. This is not impossible; but it is now felt that much stronger proof will be required before the idea can be accepted.

In the last chapter mention was made of star-streams as a late discovery. Though a discovery still in its infancy, it is one of no small importance. Briefly stated, the old theory as to the plan of the Milky Way was as follows: Our sun was a single star among millions of stars forming the galaxy, some comparatively near, some lying at distances past human powers of calculation, and all formed upon much the same model as to size and brightness. Where the band of milky light showed, stars were believed to extend in countless thousands to measureless distances. Where dark spaces showed, it was believed that we looked beyond the limits of our universe into black space. Stars scattered in other parts of the sky were supposed generally to be outlying members of the same great Milky Way. Many of the nebulæ and star-clusters were believed to be vast and distant gatherings of stars, like the Milky Way itself, but separated by unutterably wide reaches of space. Some of these views may yet be found to contain truth, though at the present moment a different theory is afloat.

It is still thought probable that our sun is one among many millions of suns, forming a vast system or collection of stars, called by some a universe. It is also thought possible that other such mighty collections of stars may exist outside and separate from our own at immense distances. It is thought not impossible or improbable that some among the nebulæ may be such far-off galaxies of stars; though, on the other hand, it is felt that every star-cluster and nebula within reach of man’s sight may form a part of our own “universe.”

According to this view of the question, the Milky Way, instead of being an enormous universe of countless suns reaching to incalculable distances, may rather be a vast and mighty star-stream, consisting of hundreds of brilliant leading suns, intermixed with thousands or even millions of lesser shining orbs. If this be the true view, the lesser suns would often be nearer than the greater suns, although more dim; and the Milky Way would not be itself a universe, though a very wonderful and beautiful portion of our universe.

Which of these two different theories or opinions contains the most truth remains to be found out. But respecting the arrangement of stars into streams, interesting facts have lately been discovered. We certainly see in the Solar System a tendency of heavenly bodies to travel in the same lines and in companies. Not to speak of Jupiter and his moons, or Saturn and his moons, we see it more remarkably in the hundreds of asteroids pursuing one path, the millions of meteorites whirling in herds. Would there be anything startling in the same tendency appearing on a mightier scale? Should we be greatly astonished to find streams of stars, as well as streams of planets?

For such, indeed, appears to be the case. Separated by abysses of space, brother suns are plainly to be seen journeying side by side through the heavens, towards the same goal.

The question of star-drift is too complex and difficult to be gone into closely in a book of this kind. One example, however, may be given. Almost everybody knows by sight the constellation of the Great Bear--the seven principal stars of which are called also Charles’s Wain, a corruption of the old Gothic _Karl Wagen_, the churl’s or peasant’s wagon. It is also called the Great Dipper. Four bright stars form a rough sort of oblong, and from one of the corners three more bright stars stretch away in a curve, representing the Bear’s tail. Many smaller stars are intermixed.

[Illustration: THE GREAT BEAR.]

These seven bright stars have always been bound together in men’s minds, as if they belonged to one another. But who, through the centuries past, since aught was known of the real distances of the stars from ourselves and from one another, ever supposed that any among the seven were _really_ connected together?

One of these seven stars, the middle one in the tail, has a tiny companion-star, close to it, visible to the naked eye. For a good while it was uncertain whether the two were a “real double,” or only a seeming double. In time it became clear that the two did actually belong to one another.

Mizar is the name of the chief star, and Alcor of the companion. Alcor is believed to be about three thousand times as far away from Mizar, as our earth from the sun. Now, if this be the width of space between those two bright points, lying seemingly so close together as almost to look to the naked eye like one, what must be the distance between the seven leading stars of the Great Bear, separated by broad sky-spaces? Who could imagine that one of these suns had aught to do with the rest?

Yet among other amazing discoveries of late years it has been found by means of the new instrument, the spectroscope, that _five_ out of these seven suns are traveling the same journey, with the same speed. Two of the seven appear to be moving in another direction, but three of the body-stars and two of the tail-stars are hastening in the direction away from us, all in the same line of march, all rushing through space at the rate of twenty miles each second. Some smaller stars close to them are also moving in the same path. Is not this wonderful? We see here a vast system of suns, all moving towards one goal, and each probably bearing with him his own family of worlds.

Many such streams have been noticed, and many more will doubtless be found. For aught we know, our own sun may be one among such a company of brother-suns, traveling in company.

It is difficult to give any clear idea of the immensity of the universe--even of that portion of the universe which lies within reach of our most powerful telescopes. How far beyond such limits it may reach, we lose ourselves in imagining.

Earlier in the book we have supposed possible models of the Solar System, bringing down the sun and worlds to a small size, yet keeping due proportions. What if we were to attempt to make a reduced model of the universe; that is of just so much of it as comes within our ken?

Suppose a man were to set himself to form such a model, including every star which has ever been seen. Let him have one tiny ball for the sun, and another tiny ball for Alpha Centauri; and let him, as a beginning, set the two _one yard apart_. That single yard represents ninety-three millions of miles, two hundred and seventy-five thousand times repeated. Then let him arrange countless multitudes of other tiny balls, at due distances--some five times, ten times, twenty times, fifty times, as far away from the sun as Alpha Centauri.

It is said that the known universe, made upon a model of these proportions, would be many miles in length and breadth. But the model would appear fixed as marble. The sizes and distances of the stars being so enormously reduced, their rates of motion would be lessened in proportion. Long intervals of time would need to pass before the faintest motion in one of the millions of tiny balls could become visible to a human eye.