Now the brightness of a star depends not only on the size of the star but also on its light and its distance from the earth. It may be said that the brightest stars are generally the nearest, though several of the most brilliant stars are exceptions, and that those whose pale glimmer is scarcely caught by our telescopes are enormously distant from us.
We know now that the sky is not a concave sphere in which, as some of the ancients believed, bright nails are fastened-the nail-heads being the stars-and that there is no vault, but only infinite space around the earth in every direction. We know also that the stars are suns and are scattered various distances apart in the vastness of space.
When, therefore, we notice two or more stars close together, their apparent1 nearness does not in any way prove that they are really not far apart. They may be very distant from one another-at greater distance indeed than we are from the nearest of them.
Looking at a group of several stars, like the Pleiades, we1 Apparent: seeming.
might suppose that all the stars in it are on the same plane and equally distant from the earth. By no means. Dispersed in all directions in space, the arrangement which they display to our eyes is only an appearance caused by the position of the earth with regard to them. This is purely a matter of perspective. We see them from the earth, and this view-point is at a vast distance from even the nearest fixed star.
When we find ourselves at night in the midst of a large square in which numerous electric lights are placed, it is difficult to distinguish the most remote lights from those which are somewhat nearer. Moreover, the arrangement of the lights depends entirely on our point of view, and varies according as we ourselves retreat or advance, stand on a side of the square, or survey the lights from a point midway between the sides.
This simple comparison may help us to understand why the stars, which are lights in dark space, do not reveal the distances which really separate them, and why their arrangement on the apparent vault of the sky depends only on the spot where we place ourselves to see them.
If we could transport ourselves to Neptune, the outermost planet of the solar1 system, we should not perceive a different arrangement of the celestial bodies, for Neptune is not far enough away; it is less than three billion miles from our planet. To see the outlines of the constellations changed, it would be necessary to station ourselves on the nearest star, and that is so distant that even the rays of light from it require three1 Solar: of or pertaining to the sun.
years and a half to reach our globe, although light moves at the inconceivably swift rate of one hundred and eighty-six thousand miles a second.
The other near stars succeed each other at greater distances. All the stars, each as vast as our sun, separated from one another by such prodigious distances, succeeding each other in an endless manner in the immensity of space, are in motion in the heavens. Nothing is stationary in the universe; there is not a single atom of matter in absolute repose. The great forces with which matter is animated, regulate its action. The movements of the suns in space are imperceptible1 to our eyes because they are performed at too great a distance; but they are in more rapid motion than is our own globe. There are some stars which are whirling through space with a velocity of fifty miles a second. To the eye which could master time as well as space, the sky would be a moving swarm of stars-a spectacle splendid and awe-inspiring.
1 Imperceptible: not to be seen; invisible.