There is no man in the moon, for the moon is an airless, waterless, dead world. There is no life on it at all. And if there were men there, the moon is so far away we could not see them. Besides, the man's face that we sometimes see, covers the whole, round, bright surface in a good-natured smile thousands of miles wide. That would be a giant! This face is made by the shadows of great mountain ranges, by sunken beds of dried up oceans, and the deep holes of dead volcano craters. It is curious that these hills and holes and shadows should be so placed as to look like a vast face. If you look at the moon through a telescope, or even an opera or field glass, the face disappears, but the things that cause the shines and shadows come out very plainly. Often you can see the mountains on the moon best when it is not full. They stand out, making a jagged or wavy line along the inner edge of the crescent. Astronomers have made maps of the surface of the moon. Knowing the size of the moon, they are able to measure the heights of the mountains by the lengths of the shadows that are cast by them.