"Look at the Pole Star some night, and you will not see it as it is now, but as it was more than sixty-two years ago. All this time its light has been on its way to Planet Earth. If a planet travels around the Pole Star, or Polaris, as it is sometimes called, and an astronomer on that planet looked at the earth he would not see it as it is now, but as it was more than sixty-two years ago. There are other stars so far away that light takes hundreds of years in coming here. Perhaps they faded out long ago, but the message is still on its way. It does seem strange to think of people who may be living on distant worlds in space, watching our little world, but we need not fear. The earth is so small that it could not be seen at all, even from the nearest star. At that distance Giant Sun would not look quite as bright as Sirius does to us, and giant Planet Jupiter would only appear as a faint speck of light near the sun." "How far away everything seems to be!" said Harry. "Yet you said just now that we could tell what the stars are made of. How can we do that?" WHAT ARE THE STARS MADE OF? "The stars are made of iron, copper, zinc, and other such metals, but the heat is so intense that these metals are turned into vapor. You have seen the steam coming from the spout of a kettle when water is boiling, and you know then that the water is scalding hot. But imagine heat so great that masses of iron and copper are not only melted but turned into vapor. Then you have some idea of the intense heat that prevails on the stars. The rains that fall on earth are made up of drops of water, but the rainfalls on the stars must be drops of melting iron, while the clouds that form are sheets of molten metal." "How wonderful!" said Harry; "and how do we know this, as the stars are so far away?" "By means of a little instrument known as the spectroscope, or light-sifter. But you must wait till you are a little older before I can explain that to you, as it is something very difficult to understand. At any rate, I can tell you this, that when we want to find out what a star is made of we catch a ray of its light and examine it with the light-sifter. As Professor Ball quoted in one of his lectures: "'Twinkle, twinkle, little star, Now we find out what you are, When unto the midnight sky We the spectroscope apply.'" "And can you tell how old the stars are?" asked Harry; "because when you were talking about the planets you said some are old and some are young." "This same little spectroscope tells us that as well, and we can recognize the stars that are in their infancy, and others that are middle-aged or nearly worn-out." "How strange to think of worn-out stars," said Harry; "yet I suppose they must grow old sometime, just as we do; only I suppose they take ever so much longer growing up."