In the case of the stars this plan was found useless. So closely has the sky been mapped out, and so exactly is the place of each star known, that the tiniest change would have been at once noticed. Not a star showed the smallest movement. The eight thousand miles of the earth’s diameter was a mere point with regard to them. A bright idea came up. Here was our earth traveling round the sun, in an orbit so wide that in the middle of summer she is over one hundred and eighty millions of miles away from where she is in the middle of winter. Would not that make a magnificent base-line? Why not observe a star in summer and observe the same star again in winter, and then calculate its distance. This, too, was done. For a long while in vain! The stars showed no signs of change, beyond those due to causes already known. Astronomers persevered, however, and with close and earnest care and improved instruments, success at last rewarded their efforts. A few--only a few, but still a few--of those distant suns have submitted to the little measuring-line of earth, and their distance has been roughly calculated. Now, what is their distance? Alpha Centauri, the second star which was attempted with success, is the nearest of all whose distance we know. You have heard how far the sun is from the earth. The distance of Alpha Centauri is _two hundred and seventy-five thousand times as much_. Can you picture to yourself that vast reach of space--a line ninety-three millions of miles long, repeated over and over again two hundred and seventy-five thousand times? But Alpha Centauri is one of the very nearest. The brilliant Sirius is at least twice as far away. Others utterly refuse to show the smallest change of position. It is with them, as had been said, much the same as if a man were to look at a church-steeple, twenty miles distant, out of one pane in a window, and then were to look at it out of the next pane. With the utmost attention he would find no change of position in the steeple. And like the base-line of two glass panes to that steeple, so is the base-line formed by our whole yearly journey to thousands of distant stars. We _might_ measure how far away they are, only the longest base-line within our reach is too short for our purpose. The planet Neptune has a wider orbit than ours. But even his orbit, seen from the greater number of the stars, would shrink to a single point. After all, how useless to talk of two hundred and seventy-five thousand times ninety-three millions of miles! What does it mean? We can not grasp the thought. Let us look at the matter from another view. Do you know how fast light travels--this bright light shining round us all day long? Light, so far as we know, does not exist everywhere. It travels to and fro, from the sun to his planets, from the planets to one another; from the sun to the moon, from the moon to the earth, and from the earth to the moon again.