Sylvia Francis, age 11, of Chicago, I11., for her question:
What is an eclipse?
Our big round earth has a shadow which is 900,000 miles long. It extends out into space with a long tapering finger, always pointing in the opposite direction from the sun. The moon too has a shadow and it too points a tapering finger out into space. The moons shadow, however, is only about 232,000 miles long. An eclipse occurs when the earth's shadow falls upon the moon and when the moon's shadow falls upon the earth.
The solar eclipse takes place when the moon's little shadow falls on some spot on our globe. At this time, the round moon is exactly between this eclipse region and the sun. The dazzling face of the sun is completely blotted out by the dark moon. The sun is totally eclipsed.
We wonder how this can happen when we realize that the sun is some 400 times wider than the moon. The sun, however, is about 400 times farther away from us which reduces them visually both zc the same size. The moon, 400 times smaller and 400 times closer, is just big enough to blot out the sun.
The moon varies in its distance from the earth. Sometimes its orbit brings it nearer than others. At its average distance, the eclipsing moon does not quite cover the face of the sun. There is a golden band visible around the outer rim. We call this an annular eclipse.
A solar eclipse can take place only when the moon is new. For then it is between us and the sun and its shadow can fall upon the earth. We have, of course, a new moon every month. Then why not an eclipse every month? Because the moon varies slightly on its orbit.
Usually it is too far away for its shadow to reach the earth. It can eclipse the sun only when it wobbles a little closer to the earth as it sometimes does. There are two to five solar eclipses each year. There are about two total eclipses every three years. Each eclipse is seen over a very small part of the earth.
When the long shadow of the earth fads upon the full moon, we have a lunar eclipse. This must happen when the moon is full, because the earth must be directly between the sun and the moon. As the time approaches, the earth's shadow takes a bite out of the golden moon. The bite grows and grows, maybe through hours. For one and a half hours or more, the moon may be all inside the earth's shadow. This is the total lunar eclipse.
The earths shadow does not black out the moon as the moon blacks out the face of the sun in a total solar eclipse. In the lunar eclipse, the golden moon turns a coppery red, dusky and dim. The moon may be totally eclipsed for one hour and 40 minutes. The total eclipse of the sun lasts but a few minutes.