"But even as it is," said his sister, "you can see some of these colors. Look at white Sirius, that sometimes seems to me tinged with blue, and then at red Aldebaran in the eye of the bull, and a creamy star called Capella just near the Twins. So you can see some of the colors. And now a few more words about Castor, which is a double star. That is, it is made up of two bright stars, and they go around each other. "Professor Ball was once showing the stars through his telescope to some friends, when he pointed out this double star to them. First of all, he told them to note the different colors of the stars, for one was white, the other green. All double stars are of complementary colors. One may be green and the other red, one blue and the other orange. "Then Professor Ball told his visitors that the stars went round each other. "'Oh, yes!' said one of the visitors. 'I saw them going round in the telescope.' "But it was the twinkling that made the stars appear to dance around each other. In reality, he would have had to remain with his eye at the telescope more than a hundred years before he could have seen the stars go completely around each other." NUMBER OF THE STARS. "I wonder how many stars there are in the sky, sister," said Harry. "Do you think we could count them?" "I read somewhere," replied his sister, "that the stars are as plentiful as the sands on the seashore. Still, in the whole sky, the number bright enough to be seen without a telescope is only from six to seven thousand in a clear, moonless sky. With an opera glass you can bring the number up to one hundred thousand. A small telescope can show about three hundred thousand, while with a telescope such as the one at the Lick Observatory the number would be nearly one hundred million. But it is possible to photograph the stars, and millions of stars have had their pictures taken. Probably we would never have known anything about them but the camera caught them, and now they are being named and labeled, so that they cannot escape us again. In fact, some of the stars are so far away that if we had not captured them in this way they would have remained hidden to us forever." "What do you mean, sister?" said Harry, his eyes filled with surprise. "I mean, dear, that some stars are so far away that their light has not yet reached us. Don't you remember what I told you about Jupiter's moons: that they are so far away that light takes about half an hour in coming from them to the earth. Well, the stars are hundreds of times as far away as Jupiter's moons. So far away are they that even from the nearest--a star seen in the southern hemisphere--light takes four years and four months in reaching us, although light travels more than 186,000 miles a second." DISTANCE OF THE STARS.