Russell Cochran age 14 of Harrisburg, Pa., for his question:

WHAT CAUSES SOLAR AND LUNAR ECLIPSES?

An eclipse is the darkening of any heavenly body. A solar eclipse occurs when the moon's shadow sweeps across the face of the earth. A lunar eclipse takes place when the moon passes through the shadow of the earth.

In a solar eclipse, the shadow usually sweeps from west to east across the earth at a speed of about 2,000 miles per hour. People in the path of the shadow may see one of three kinds of eclipses: a total eclipse, an annular eclipse or a partial eclipse.

A total solar eclipse happens if the moon completely blots out the sun. In an annular eclipse, the moon darkens only the middle of the sun, leaving a bright ring around the edges. In a partial eclipse, the moon covers only part of the sun.

A total lunar eclipse happens if the entire moon passes through the earth's shadow. A partial eclipse occurs if only a part of the moon passes through the shadow.

A total lunar eclipse may last up to one hour and 40 minutes. A lunar eclipse may be seen by most of the people on the night side of the earth. There is no danger in viewing a lunar eclipse.

A total solar eclipse, when the sun is totally darkened, may last as long as seven minutes but it averages about two and a half minutes. A solar eclipse should never be viewed directly. Invisible infrared rays from the sun can damage the eyes. Even the use of darkened film, smoked glass or sunglasses does not eliminate the danger of watching a solar eclipse. Solar eclipses should be viewed indirectly with a pinhole projector.

A total solar eclipse should be seen only in certain parts of the world. These areas lie in the path of totality, or the path along which the moon's shadow passes across the earth. The path of totality is never wider than about 170 miles.

The moon does not become completely dark during most lunar eclipses.

Astronomers can predict eclipses with great accuracy. At least two solar eclipses and as many as three lunar eclipses may be seen each year from various places on the earth.

The earth and the moon always cast shadows into space and the moon orbits the earth about once each moon. But an eclipse, either solar or lunar, does not occur every month. The moon's orbit is tilted about five degrees to the earth's orbit around the sun. For this reason, the moon's shadow generally misses the earth, and so a solar eclipse does not occur.

Likewise, the moon most often escapes being eclipsed by passing above or below the shadow of the earth.

Therefore, a solar or a lunar eclipse can occur only when the earth, sun and moon are in nearly a straight line.

The ancient Chinese thought solar eclipses occurred when a dragon in the sky tried to swallow the sun.