An eclipse occurs when the Moon moves into alignment with the Sun and the Earth. There are two types of eclipses, lunar and solar.
A Lunar Eclipse
This happens when the Moon passes through the shadow of the Earth. The Sun and the Moon are on opposite sides of the Earth. A lunar eclipse occurs at night and results in the Moon apparently becoming dark in colour. It is a subtle effect.
A Solar Eclipse
A solar eclipse is a much more dramatic evn spectacular sight andoccurs when the Moon passes directly between the Sun and the Earth. In the narrow path of totality swept across the Earth by the Moon's complete shadow (the umbra), daytime briefly turns to an eerie darkness, and during these few minutes the halo of the Sun - the corona -comes into view as the dark disk of the Moon totally obscures the bright Sun. Outside the path of totality, in the Moon's partial shadow (the penumbra), some portion of the Sun's bright disk remains visible and there is not a total eclipse.
Why is a total solar eclipse such a rare event? First of all, eclipses do not occur every month during a new Moon or a full Moon. This is because the orbit of the Moon is tilted by about five degrees with respect to the Earth's orbit, so that usually the Moon passes slightly above or below the line between the Sun and the Earth. Thus at most new and full Moons, the shadows miss their mark and no eclipse occurs. Only about every six months, during an eclipse season, are the conditions right for a lunar or solar eclipse.
And even though solar and lunar eclipses occur with comparable frequency, it is still far more commonplace to experience a lunar eclipse. That's because the darkened full Moon can be seen from anywhere on the nighttime half of the Earth during the eclipse. To see a total solar eclipse, you have to be in the path of totality. This path, sometimes up to 200 miles wide, never covers more than roughly one-half of one percent of the Earth's surface and often traverses open seas or remote regions of the planet. With fewer than 70 total eclipses per century, the chance to see one is for most of us a genuineonce-in-a-lifetime event.
It is quite remarkable that total solar eclipses even occur at all. They are possible because the Sun and the Moon appear from Earth to be about the same size in the sky. The Sun, whose diameter is 400 times that of the Moon, happens to be about 400 times as far away from the Earth. This condition permits the Moon to just barely cover up the Sun. If the Moon were slightly larger then many of the exciting visual effects described below would not occur and if it were slightly smaller then it would not completely obscure the Sun and there would be no total eclipse.
Eclipse 99 World Map |
Eclipse 99 Path Map |
Eclipse 11 August 1999