Vivian Shimp, age 11, of deliver, Pa., for her question:
Where is the rest of a quarter moon?
Our yellow moon waxes and wanes. In a little less than four weeks it grows from a slender crescent to a golden coin and shrinks back again to a thin crescent. Or so it seems. Actually the moon merely seems to wax and wane, to grow and shrink. It remains the same.
The changeable moon is dust fooling us. It is a solid globe, even when we see only a thin sliver of it. It is a solid globe when it looks like a section of an orange, half a yellow saucer or a shiny golden coin. The same side of the round moon is always facing the earth, but as a rule we see only the part of the disk that is washed in golden sunshine.
Once in a while, when the earth's blanket of air is very clear, we get a glimpse of the un7.ighted face of the moon. If you stars hard at the new moon, you may see that a ghostly round shadow is cradled in the shining crescent. Old timers say that the old moon is sleeping in the new moon's arms. This dim, pearly shadow which falls upon the dark area of the moon is also called earthshine and for a very good reason.
The moon, like the earth, has a day and a night. The lunar day, however, is equal to 27 1/3 earth days. All sides of the moon have a day which lasts almost two earth weeks and a night which lasts almost two earth weeks. Every lunar month, a day and a night creep across the half of the moon which faces the earth. The sunlit area shines with golden sunlight, but the night area is usually too deep in shadow for us to see.
But the earth also shines With daylight sunshine. Same of our sunshine bounces back into space, and once in a while a small fraction of this reflected light of ours falls upon the night side of the moon. This is the earthshine which shows us that all of the round moon is still there, even though we see only the sunny area. The moonlight which spills a soft glow upon the earth is sunshine reflected from the moon. On our side of the moon, the long lunar night is often washed with sunshine from the earth. If we were there, we might call it earthlight.
The moon's rotation on its axis is equal to one revolution around its orbit which is why the same half of the round ball always faces the earth. In one lunar month, a lunar day follows a lunar night across our side of the moon. Sometimes earthshine adds a dim glow to the lunar night, but as a rule this shadowy area is invisible against the night sky.