Fortunately for us the Sun and the Moon each appear to be about .5 degrees in angular size when view from the Earth. This means that the Moon just barely covers the Sun as viewed from any position on the Earth. 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 and the Moon each appear to be about .5 degrees in angular size. 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. In fact, if the Moon's diameter (2,160 miles) were just 140 miles less, it would not be large enough to ever completely cover the Sun so a total solar eclipse could never happen anywhere on Earth.

Like lunar eclipses, there are different type of solar eclipses. If you are interested in more details about when and where a solar eclipse will occur The Astronomical Almanac has detailed listings for future eclipses.

Total solar eclipse

Here the Moon is in exactly the right position just cover the Sun. During a total eclipse, the Earth's rotation, coupled with the Moon's orbital motion , causes the Moon's umbra to zip along at speeds of over 1,700 kilometers/hour (1060 miles/hour), so the length of time that any single location observes totality is limited to only a few minutes at most. In fact the longest that any single location can observe totatiliy is only 71/2 minutes! The path that the Moon's umbra traces across the Earth's surface is called the eclipse path.

Partial Solar Eclipse

If the Earth enters the Moon's penumbra then the Sun's surface appears only partially covered by the Moon. During a partial solar eclipse, the Moon's penumbra covers a large part of the Earth's suface. The Sun will appear to be dimmer that it normally does. However, partial solar eclipses, like penumbral eclipses of the Moon can be difficult to observe since the Sun can only be slighltly dimmer than usual.

Annular Eclipse

These are perhaps the most spectactular of all the eclipses. Here the Moon is too far away, due to its elliptical orbit (the moon is at apogee), from the Earth. In this case the Moon's umbral shadow does not even reach the Earth! At mid-eclipse what is observed is a thin ring of light surrounding the edge of the Moon. Annular Eclipses are slightly more common than total eclipses.

Which do we see more of Solar or Lunar Eclipses?

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 once-in-a-lifetime event.