A solar eclipse occurs when our view of the Sun is partially or totally blocked by the Moon. This happens when the Moon, Sun, and Earth are directly in line with one another. A solar eclipse can only happen during a new or full Moon.
Our Sun undergoes three types of eclipses: partial, annular, and total.
Watch the video below from Nasa explaining and demonstrating solar eclipses:
Both partial and annular eclipses occur when the Moon isn't quite in line with the Earth and the Sun. Therefore, it can't totally block out our view of the Sun. This happens because the Moon's orbit is elliptical and so it doesn't always line up directly in front of our view of the Sun.
You will also see a partial eclipse on the way to what will become a total eclipse because the Moon doesn't block out the Sun for the entire time during a total eclipse. Instead, the Moon gradually moves across the sky until the Sun is completely blocked from our view for a short period of time.
Both partial and annular eclipses occur when the Moon is further from the Earth than the length of its shadow. The Moon's shadow consists of the umbra (the center of the Moon's shadow) and the penumbra (the remainder of the Moon's shadow). During a solar eclipse, if the Moon to too far from Earth then the umbra doesn't reach us. This causes the Moon to appear smaller than the Sun and we can still see a portion of the Sun during the eclipse. During an annular eclipse all we can see of the Sun is its outer ring (called the annulus).
Because a portion of the Sun remains visible during both an annular and a partial eclipse we can't see the Sun's corona (the glow around the Sun).
A total eclipse happens with the Moon blocks out our entire view of the Sun. This happens when the moon is closer to Earth than the length of its shadow. This makes the Moon appear larger than the Sun. During a total eclipse the umbra reaches Earth and blocks out our view of the Sun. Everything darkens, and the only thing visible is the Sun's corona, as shown in the photo.
The longest a total eclipse can last is 7.5 minutes, although many don't last that long.
The next total solar eclipse is predicted to occur on November 13, 2012.
Safety When Viewing a Solar Eclipse
You can't look directly at a solar eclipse without seriously damaging your eyes. You also don't want to look at a solar eclipse through binoculars or a telescope. You can damage and even lose your eyesight. However, there are some companies that sell solar filters designed for viewing a solar eclipse.
For more information on solar eclipses please see the NASA Eclipse Website.
Photo of Solar Eclipse: © The Corel Corporation - may not be copied.