Joyce Pearson, age 12, of Bessemer City, North Carolina, for her question:

How does the brightness of the moon compare with the sun?

A sunbeam is about 650,000 times brighter than the average moonbeam. Astronomers allow for this difference when taking telescope pictures that require time exposures. But the same ratio does not hold true when our human eyes gaze up at the moon. A full moon, shining its best on a clear night, appears to us to be about 450,000 times dim¬mer than the noonday sun. If there were enough full moons to fill the whole sky, they would not shed as much light as the sun. To equal its brilliance, we would need three complete skies crammed to capacity with full moons. And since we can see only one sky at a time, this is downright impossible.

Seen from the. earth, the moon and the sun both occupy the same area of sky space. Both have a diameter of about 1/2 a degree. This is roughly equal to the width of a pencil held at arm's length. Actually the moon is 400 times smaller than the sun but the sun is about 400 times farther away. The moon, of course, shines only with reflected sunlight and it reflects only 7 per cent of the sunlight it gets. The full moon sheds 12 times more brilliance than the quarter new moon.