If you think enough of the stars to try to photograph them with your little camera, I should say there is a very good chance of your being able to photograph them sometime through an equatorial telescope for all things come to the boy who wants them hard enough.
What the Stars Are Made of.—To know what the stars are made of is to know more about them than men knew of the Earth a few hundred years ago.
But just think of looking at a star like Aldebaran, which is so far away that it takes 45 years for its light to reach the Earth—light travels eleven million miles a minute—and then saying it is made of iron, and mercury and hydrogen and sodium and half a dozen other substances!
Now you ask, “How is it done?” And I’ll say with a glass prism, and then we’ll have made a flying start. Now a glass prism is a three-sided piece of glass—the ends don’t count—as shown in [Fig. 144], and it is just as wonderful in its way as a lens is wonderful in its way.
If you will hold a prism to your eye and look at the flame of a candle through it, you will see the flame in all the brilliant colors of the rainbow, and these bright colors form what is called a spectrum.
Now make another experiment; cover a window, on which the Sun shines, with a sheet of cardboard, in the middle of which you have cut a horizontal slit with a sharp knife, about 1 inch long and ¹/₂₅ inch wide. Make the room perfectly dark except for the light which comes in through the slit in the cardboard, and set a prism in front of the slit, as shown in [Fig. 145]. The beam of sunlight which passes through the prism will be split up, or decomposed, as it is called, into the seven colors of the rainbow, but the colors will be much brighter.
If you will fix another sheet of white cardboard in a vertical position so that the colors will shine on it in a band, the colors, beginning with red at the bottom, next orange, then yellow, green, blue, indigo and violet, will follow each other to the top bright and beautiful. These rainbow colors, spread out in a band on the screen, form what is called the solar spectrum, that is, the spectrum which is produced by sunlight.
This beautifully colored spectrum is really made up of a great many images of the slit in the cardboard, one for each wave-length of the light. If the slit is made very narrow, the images of the slit will not overlap much and you can tell whether any of the wave-lengths are missing by looking for fine black lines crossing the spectrum. Such dark lines are very important in finding out what the Sun and Stars are made of.
Fig. 182.—Boy Looking through Prism at Slit in Cardboard.