Eclipses

In astronomy, the word "eclipse" can be used to describe two different things: an eclipse of the sun or the eclipse of the moon.

An eclipse of the sun is called a solar eclipse. This happens when the moon passes directly in front of the sun. As seen from different points on the earth, the moon blocks out the sun.

When the whole moon or the whole sun is eclipsed, we speak of a total exiles. When only part of the moon or the sun is exposed, we will call it a partial eclipse.

When the moon moves directly between the earth and the sun, it will cast a shadow on the earth. At the center of the shadow is a darkness circle called the umbra. Surrounding the umbra is a wider circle of semi darkness. This is called the penumbra.

During a total solar eclipse the umbra will make a dark circle of about 100 kilometers in diameter somewhere on earth. This is a circle of about 60 miles. As the earth continues to rotate, the umbra sweeps across the surface from west to east at a speed of about 1,600 kilometers an hour. This is about 1,000 miles an hour. It is only the people who are in the path of the umbra that will see the total eclipse. They will see the moon's dark shape move slowly across the face of the sun. The sun becomes hidden for a brief time. This is usually not longer than 7 1/2 minutes. Then, the moon will gradually move on. A crest of the sun will begin to appear until the whole sun is seen again.

The penumbra spreads itself over a much larger area. It extends about 4,000 kilometers or 2,500 miles beyond the umbra. People who are in the area of the penumbra will see a partial eclipse of the sun.

Sometimes, when the moon is at its greatest distance from the earth, the umbra will not quite reach the earth. The moon does not entirely cover the face of the sun. A bright rim will be visible all around the dark disk. This is called an annular or ring shaped exile.

People who are observing an eclipse should protect their eyes from the intense light of the sun. You should always remember to never look directly at an eclipse.

The earth will always cast a shadow on the side opposite of the sun. As the earth then orbits the sun, its shadow will sweep around through space. The moon, at the same time, orbits the earth. About once every twenty-nine days, the moon will overtake the earth's shadow. Sometimes the moon passes through the shadow. Other times it passes above or below the shadow. When the moon passes through the earth's shadow, a lunar eclipse will occur.

If the moon passes through the umbra of the earths shadow, this would be called an umbral eclipse. This type of an eclipse can be total or partial. If it misses the umbra all together, the eclipse is called a penumbral.

An eclipse will occur more often than most people think. There can be as many as seven eclipses in a year. There are never more than seven or less than two. If there are only two eclipses in a one year time period, both of them will be solar eclipses.

Eclipses are of big interest to astronomers. The reason is because so much can be learned about objects in space during an eclipse. The blinding light of the sun will hide the nearby stars. But, during a total solar eclipse, astronomers can observe the stars near the sun and therefore study the light that these stars produce. Astronomers learned that the sun's gravity will bend the light of nearby stars.

A solar eclipse can also provide a rare view of the sun's atmosphere. The long jets of glowing gases that extend out from the sun make up its corona. A look at the corona will provide a view of the spread of the suns energy toward it's planets.

The influence of solar energy on the earth is of huge interest to scientist. During an eclipse the earth is, for a while, shielded from at least some of the suns energy. This gives scientists the chance to study this influence. Measurements of the energy in the atmosphere are made before and during and eclipse. These measurements are then compared. They will give information about the suns effect.

In addition to solar and lunar eclipses, many other kinds of eclipses can occur. One planet may pass in front of another planet, thus causing an eclipse of a planet. The moon and planets can eclipse stars. The moon eclipses planets. Eclipses of this kind are called occulations.

Occulations also give opportunities for learning more about objects in space. An example would be the rings of the planet Uranus were discovered during the planets occultation of a star.

Eclipses are amazing to watch, but as you can see, there is also so much to be learned from them. So, next time you look into the sky, see what new things you might see and learn.