Linda Costello, age 9, of Wayne, Nebraska, for her question:

 What exactly is a gibbous moon?

By itself, the word "gibbous" means a smooth, rounded hump curved in a convex direction. The insides of a hollow cave curve in a concave direction. Its outside may bulge in a convex direction. The golden moon, of course, is forever changing its shape. The outside edge always bulges around in a convex curve. In the quarter moon, the inside curve is con¬cave. At half moon, the outside is convex and the inside forms a straight line. When this phase is over, we begin to see the gibbous moon.

The golden half begins to bulge in the middle and grow bigger. The line down the middle becomes a convex curve. Now we can call it a gibbous moon. Every month, the gibbous moon appears after the half moon. Gradually it grows until we see the round golden circle of the full moon. Some people call the gibbous moon a three quarter moon. This is sensible because it shows us three quarters of the round moon and leaves only one quarter in darkness.