Sherry Lee Robinson, Age 7 Of Eugene, Ore., for her question:

How do they measure the mountains of the moon?

The moon's mountains cast their shadows over the sunlit lunar landscape, and, all things being equal, the tallest mountains cast the longest shadows. Their shadows, of course, are shortest at noon when the sun is highest in the lunar sky. They must be measured under many conditions to form an estimate of their true height.

Astronomers know the size of the moon and the ratio between the shadows of the lunar mountains and the landscape. There is another way to check the estimated height of the mountains at the edge of the moon. Sometimes these ragged peaks stand out like shining teeth against the black sky, and their height can be compared with the ratio of the circumference of the moon.