Joe McCarry, age 9, of Spokane, Wash., for his question:
Why isn't the lunar eclipse black?
Joe has seen both a lunar eclipse and a partial solar eclipse. In the solar eclipse, the sun, or part of it, was blotted out with the jet black disc of the moon. In the lunar eclipse, the moon turned only a dull, coppery color. It is natural to wonder why the moon was not also eclipsed with a jet black shadow.
When any eclipse occurs, the sun and the moon and the earth are in a direct line. In a solar eclipse, the moon is between the earth and the sun. In a ,lunar eclipse, the earth is between the sun and the moon. The eclipse is caused by the shadow of a heavenly body falling upon another heavenly body. In the solar eclipse, the moon's shadow falls upon the earth. In the lunar eclipse, the earth's shadow falls upon the moon.
The moon and its shadow can blot out the dazzling sun. But the earth, four times as big as the moon and just as solid, casts only a dusky shadow on the face of the moon. There are two reasons why this is so. One is the earth's atmosphere, the other is the positions of the sun, moon and earth during an eclipses
In a solar bclipse, the new moon is directly between us and the sun. The moonts long shadow falls upon the earth and the moon itself gets directly between us and the sun. The moon's solid body passes across the da;zling face of the sun, blotting it out. At total eclipse, the sun is exactly hidden by the disk of the moon, though the sun's diameter is 400 times greater than that of the moon. The two disks fit exactly because the sun, 400 times bigger, is 400 times further away from us. In a lunar eclipse, the earth is directly between the full moon and the sun.
If we stood on the moon, we would see the dark disk of our globe pass across the dazzling face of the sun and blot it out just as the moor blots out the sun during a solar eclipse.But as we stand on earth during a lunar eclipse, all we see is the earth's shadow passing over the face of the moon. The shadow is dark, but not nearly so dark as the solid disk of the moon.
The earth's shadow is a pointed cone, some 859,000 miles long. It points away from the sun and its wide base fits on the night half of the solid globe like a tall hat. Around the base of the shadow, the high atmosphere glows with sunlight from the other side of the earth. Some of this sunlight is bent and scattered into the shadow, giving it a reddish glow. This is the shadow, glowing faintly with borrowed sunlight, which falls upon the moon during the lunar eclipse. The earth's shadow is dark enough to dim the full moon, but it is not dark enough to hide its face.