How does a solar and lunar eclipse form?

   The Moon does not give off any light of its own. It would not shine if the Sun did not shine on it. Quite often— sometimes as often as three times in one year—the Moon travels into the Earth's shadow. With the Earth shutting off the sunlight, the Moon stops shining brightly. We say, when this happens, that there is a total eclipse of the Moon.

   Sometimes the Moon travels across just one edge of the Earth's shadow. Then only a part of the Moon is darkened. We say that there is a partial eclipse.

   Even during a total eclipse the Moon does not completely disappear. The air around the Earth bends some of the Sun's rays so they strike the Moon. Instead of disappearing, the Moon looks dull red.

There cannot be an eclipse of the Moon unless the Moon is on the opposite side of the Earth from the Sun—when the Moon is full. The Moon cannot get into the Earth's shadow at any other time.

   There are eclipses of the Sun, too. An eclipse of the Sun occurs when the Moon moves between the Earth and the Sun and shuts off the view of the Sun from part of the Earth. The Moon is too small to ever hide the sun from the whole Earth.

   If the Sun's entire disk is hidden by the Moon, we say that there is a total eclipse. If only a part of the Sun's disk is hidden, we say that there is a partial eclipse. There are always at least two eclipses of the Sun in a year, and there may be as many as five. But most of the eclipses are only par­tial eclipses.

   An eclipse of the Sun does not last nearly as long as an eclipse of the Moon. A total eclipse of the Moon lasts for about two hours. A total eclipse of the Sun never lasts for more than eight minutes.

   During a total eclipse of the Sun, the whole round disk of the Sun is hidden. But the bright band of light around the Sun— the "corona," it is called—still shows. So do some of the flames that shoot up from the Sun. So much sunlight, however, is shut off that darkness falls just as if the Sun had set. Chickens often go to roost, and other animáis go to their barns. But in a very few minutes the "night" is over.

   An eclipse of the Moon can be seen from half the Earth, but an eclipse of the Sun can be seen only in the narrow path where the Moon's shadow falls. Astronomers of­ten make long trips to see a total eclipse of the Sun. They are willing to go a long way because there are many problems about the Sun and the stars that they can study best during a total eclipse.

   People of long ago were frightened by eclipses. But today we are not afraid of them. Scientists now understand eclipses so well that they know all the eclipses there will be in the next several thousand years.