The ancients believed that an eclipse was an event only explainable through the actions of their gods. Modern man has the benefit of not only knowing what an eclipse is caused by, but of being able to support these beliefs through scientific fact.
An eclipse is “the partial or total blocking of light of one celestial object by another.” While this does not occur solely on planet Earth, I shall limit this discussion to the ones that do.
There are two major types of eclipses that occur on Earth. These are the solar eclipse and the lunar eclipse. In a solar eclipse, the Sun becomes partially or totally covered by the Moon. This is an active process, in which the Moon gradually moves across the Sun. During a lunar eclipse, the Moon has a dark shadow slowly moving across it. Each of these two categories there are three subtypes: penumbral, partial, and total.
To understand what an eclipse is, it is important to understand a few terms. The word penumbra refers to the faint outer shadow cast by either the earth or the moon. The umbra is the dark inner shadow. The antumbra is the negative shadow.
It is also important to be aware that a given eclipse does not occur everywhere on earth, and that it can be viewed to a greater or lesser extent in different locations
During a solar eclipse the moon’s shadow is cast on the earth’s surface. This occurs when the moon passes between the Earth and the Sun during a new moon. At this time, all or part of the sun is covered by the moon. A partial eclipse occurs when the Moon’s penumbral shadow (faint outer shadow) falls upon the earth; a total eclipse occurs when the darker umbral (inner) shadow is cast. Typically, the totally eclipsed Sun can only be seen in a 10,000 by 100 mile swath. During a total eclipse, the phase during which the Sun is completely covered only last a few minutes.
In contrast to the total eclipse of the Sun, during an annular solar eclipse, the Sun appears larger than the Moon. When the Moon is directly in front of the Sun, there is still a ring of light from the Sun around the Moon.
A lunar eclipse occurs when the moon moves into the shadow of the earth. This can only happen during a full moon. When the Moon’s orbit brings it through the Earth’s penumbral shadow (faint outer shadow), there is a penumbral lunar eclipse. These are very subtle. A partial eclipse of the Moon occurs when the Moon passes through the Earth’s umbral (inner) shadow. A total lunar eclipse occurs when the Moon passes through the Earth’s umbral (inner) shadow at an angle that causes it to completely cover the Moon. Depending on the degree of eclipse, a lunar eclipse can last anywhere from 51 minutes to 3 hours and 29 minutes. In a total eclipse the time in which the Moon is completely covered can last up to 1 hour and 31 minutes.
When we think of an eclipse, we think of an event that occurs in the sky. However,
it also has a dramatic effect on life on the Earth.
In May of 1984 my husband and I were moving from Boston to Tucson in a rented U-Haul. As we hit I-95 we were dismayed to learn that our U-Haul would not go faster than 53 miles per hour. Driving at this slow pace, with no radio or air conditioning to distract us (another surprise), we had long, uninterrupted periods to meditate on the wonders of nature. When we reached Knoxville, Tennessee we turned west, beginning the long trek across the state. Suddenly we sensed a change in our environment. The birds had stopped singing. The light had a curious aura. The world felt different and we didn’t know why. Later, we found out that there had been a nearly total solar eclipse.
Though we resisted the urge to take a nap, our innate senses were not that different from other animals. During a solar eclipse, animals normally active in the daytime prepare for sleep, and nocturnal ones begin to move about.
By understanding what an eclipse is, combined with scientist’s ability to predict when future ones will occur, humans have the unique ability to not only cope with its effects, but to appreciate its drama and beauty.
http://www.mreclipse.com
http://sunearth.gsfc.nasa.gov/eclipse/LEcat/LEdecade2001.html
http://dictionary.reference.com
