Изображения страниц
PDF
EPUB
[graphic][subsumed]

SPIRAL NEBULA M. 101 URSAE MAJORIS, MAR. 10-11, 1910

PHOTOGRAPH BY G. W. RITCHEY

MOUNT WILSON OBSERVATORY

Our Sun will be a tiny brilliant ball, one-hundredth of an inch through, or less. This little Sun and a minute Earth-a mere speck-should be placed just one inch apart.

Following out the same idea, Mercury would be onethird of an inch from the Sun; Venus two-thirds of an inch; and Mars, outside the small Earth, about an inch and a quarter off. Jupiter would be five inches away; Saturn ten inches; Uranus nineteen inches; and Neptune thirty inches off. The whole Solar System could thus be enclosed in a small circle less than two yards across, leaving out only certain comets which would travel farther.

The next question is: What would be the distances of the nearer fixed stars on this scale?

If our Earth is one inch from the Sun, and if Neptune is less than one yard away, then-counting still that each inch means really ninety-three million miles—the star which lies closest of all, Alpha Centauri, must be four miles distant.

And between-nothing! Between that star and the little Solar System, just two yards across-nothing !— at least, nothing in the shape of a star. An occasional tiny comet may lag along in the darkness; and dark bodies, cooled suns, might possibly float here or there. But of bodies radiant with heat and light, not one in all that wide area, four miles in every direction, can be found.

Astronomers sometimes talk of "stars in the vicinity of the Sun." This is what they mean by " vicinity."

Think of the distances implied. First, our whole Solar System, reduced within a circle two yards in

diameter. Then, on every side, and above and below, an encompassing void of four miles, each inch in those miles standing again for ninety-three millions of miles. And then, in one direction, a single star.

66

Only one quite so near. Another in the Sun's vicinity," known as 61 Cygni, would lie seven miles off, and the brilliant Sirius, not so brilliant on this tiny scale, would be farther still. Only about twenty stars are known to be nearer than one million times the distance of our Sun-which here would mean nearer than one million inches, or nearly sixteen miles.

Others would have to be placed at distances of twenty miles, thirty miles, fifty miles, one hundred miles, one or two or more thousand miles. It is not easy to conjecture where one would have to stop.

That the Starry System-our great Universe-has limits somewhere can hardly be doubted. But to define those limits with any kind of precision is not possible. It is believed that some dim stars, barely visible, may lie ten thousand times as far away as our Sun's next neighbour, Alpha Centauri, and this would give a line from the centre of our reduced Universe of thirty-five thousand miles.

Suppose that the limits did lie there. Thirty-five thousand miles, each way outward, would mean a diameter for the whole of seventy thousand miles. Imagine a starry system seventy thousand miles across from side to side, each separate inch in all those tens of thousands of miles representing ninety-three million miles of true distance! And somewhere in the midst our small Solar System, just two yards across, separated

from all other stars in every direction by a wide blank of four miles.

This would be stupendous enough. But we have no reason for thinking that the limits do lie there. The System may extend twice as far, four times as far.

As for the numbers of suns, great and small, which, taken all together, make up this wonderful Universe, who can estimate them? Yet estimates have been made, and one thing is certain-that the grand reality does not fall short of human ideas.

Seen by us, without any help from magnifying glasses, only a few thousands of stars are visible. But with even a small telescope the numbers spring to hundreds of thousands. With more powerful lenses, leap follows leap, from hundreds of thousands to millions, and to tens of millions.

Nor does the widening of our heavenly landscape stop there. When the greatest telescope yet made has done its utmost, we have not reached the limit. Beyond the range of telescopic vision, stars beyond stars still lie in countless hordes, invisible to human eyes, yet within reach of human powers. For then steps in photography; and suns innumerable-suns never yet seen, and perhaps never to be seen from this world by the eyes of men-stamp their feeble image on the photographic plate.

Then higher still the numbers mount, till one hundred millions of stars, two hundred millions of stars, are reckoned to belong to our Universe. And who may say how many more?

« ПредыдущаяПродолжить »