How The Solar Eclipse and Lunar Eclipse Occur

An eclipse occurs at those times when the Moon moves into a position of direct alignment with the Sun and the Earth. There are two basic types of eclipses – lunar and solar. Most people have seen at least one total lunar eclipse, when the full Moon passes through the shadow of the Earth. In this case, the Sun and the Moon are on opposite sides of the Earth. If you observe a lunar eclipse (visible only at night at the time of certain full Moons), you’ll see the bright lunar disk turn dark -- sometimes a coppery red color -- for as long as an hour or more.
But the gentle beauty of a lunar eclipse pales in comparison with the truly awesome spectacle of a total solar eclipse, which occurs when the new 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 precious minutes the wispy 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.

Not all solar eclipses are total. During a partial solar eclipse, only the penumbra touches our planet. The umbra passes either just above the North Pole or just below the South Pole, completely missing the Earth. No total eclipse is visible -- only partial phases can be seen.
A third type of solar eclipse occurs when the Moon's umbra passes across the Earth, but is not quite long enough to touch the surface; the shadow cone diminishes to a point before reaching the Earth. This effect happens when the Moon is farther out in its orbit around the Earth. The Moon appears slightly smaller and is not large enough to completely cover the Sun. When the Moon is centered over the Sun, a ring of sunlight remains visible around the edge. This type of eclipse is called an annular eclipse. (Annular comes from the Latin word meaning "ring.") Because the Sun is not completely covered by the Moon, the rare and dramatic effects of a total solar eclipse (onset of darkness and view of the corona) are not present at either annular or partial eclipses of the Sun. (See Effects During a Total Solar 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.