There are several kinds of telescopes, but there are only two kinds I want to make clear to you here; in the first kind the eye sees the object just as it is, that is, standing right side up, or erect. This kind of a telescope is called a spyglass, and is used to look at objects on the surface of the Earth.
In the second kind of telescope the eye sees the object upside down, or inverted, and this kind of telescope, which is called an astronomical telescope, is just as good as the other for looking at the stars.
A Pinhole Telescope.—Before describing how to make and use real telescopes which have lenses I want to tell you of a little scheme to see afar, and though it does not magnify the image of the object that is seen through it, yet it aids the naked eye when you are looking at the Sun and Stars.
To make a pinhole telescope get a pasteboard tube about 1¼ inches in diameter and 5 or 6 inches long. A paper tube for mailing papers and sheet music is just the thing and can be bought at any stationery store.
Fig. 149.—Disk of Cardboard for
Pinhole Telescope.
Fig. 150.—Cross Section of Pinhole Telescope.
Cut out a disk, or circular piece of cardboard just large enough to fit the tube, [see Fig. 149], and push a pin point or needle through the center to make a small, clean hole. Next, glue this cardboard disk in the tube ½ an inch from one end. The disk must be glued in the tube so that no light can leak around the edge.
If, now, you look at the Sun through the pinhole telescope, as shown in [Fig. 150], you will get a better view of it than if you look at it through a pinhole in the cardboard alone, for the tube shuts out all the other rays of light from the eye.