Robin Silva, age 13, of New Bedford, Mass., for her question:
WHAT CAUSES AN ECLIPSE?
An eclipse is a complete or partial darkening of one heavenly body by another. It is caused when one body casts its shadow on the other. The kind of eclipses that are best known are those that affect the sun and the moon.
A solar eclipse is when the moon lies between the sun and the Earth and the moon blots out the view of the sun from an area on Earth. The coon's shadow then falls on Earth.
A lunar eclipse is when the Earth lies between the sun and the moon and the Earth blots out the moon's view of the sun. The Earth's shadow then falls on the moon.
Some years there are no eclipses of the moon and in other years there may be from one to three. Every year, however, at least two solar eclipses take place, and there may be as many as five. The total of solar and lunar eclipses never exceed seven in one year.
An eclipse of the sun happens only when the moon is new because then the moon and the sun are on the same side of the Earth. If the path of the moon were always in line with the orbit of Earth around the sun, a solar eclipse would take place at every new moon. But in the moon's trip around Earth, the moon sometimes passes above and sometimes below the path of the Earth.
If the moon hides the sun completely, it is called a total eclipse and none of the sun's light can be seen. A total eclipse can last just a few seconds or as long as about 7 1/2 minutes.
When the moon is too far from Earth to hide the sun completely, the moon is seen as a dark disk imposed on the sun. This is an annular eclipse. The name comes from the Latin word "annulus," which means "ring."
A total eclipse of the sun is visible only from a narrow strip on the surface of the Earth. This strip, the path of total eclipse, is never more than 167 miles wide, but it may be thousands of miles in length. Outside this narrow strip, the sun appears to be only partially covered.
An eclipse of the moon may last for as long as an hour and 40 minutes. A partial eclipse of the moon takes place when the moon enters only partly into the shadow of the Earth.
Back in ancient times people in all parts of the world feared the darkness of an eclipse. Some believed that it was caused by a dragon trying to eat up the sun or the moon. As recently as 400 years ago, people in Europe used to hide in cellars during eclipses because of fear.
Today most people have no fear of eclipses because they understand the events are a normal part of nature's way.
In 1931 a French astronomer named Bernard Lyot developed a camera like instrument called the coronagraph. It can photograph certain features of the sun's corona normally seen only to an eclipse.