What Is a Solar Eclipse?

This image shows the Aug. 1, 2008, solar eclipse at the point of totality, when the moon completely blocks out the body of the sun, revealing the normally hidden, halo-like corona. NASA/courtesy of nasaimages.org

As seen from the Earth, a solar eclipse occurs when the Moon passes between the Sun and the Earth, and the Moon fully or partially covers the Sun as viewed from a location on Earth. This can only happen during a new moon, when the Sun and Moon are in conjunction as seen from Earth. At least two, and up to five, solar eclipses occur each year; no more than two can be total eclipses. Total solar eclipses are nevertheless rare at any particular location because totality exists only along a narrow path on the Earth's surface traced by the Moon's umbra.

Some people, sometimes referred to as "eclipse chasers" or "umbraphiles", will travel to remote locations to observe or witness a predicted central solar eclipse. The solar eclipse of August 11, 1999 in Europe helped to increase public awareness of the phenomenon, which apparently led an unusually large number of journeys made specifically to witness the annular solar eclipse of October 3, 2005, and of March 29, 2006.

A total solar eclipse is a natural phenomenon. Nevertheless, in ancient times, and in some cultures today, solar eclipses have been attributed to supernatural causes or regarded as bad omens. A total solar eclipse can be frightening to people who are unaware of their astronomical explanation, as the Sun seems to disappear during the day and the sky darkens in a matter of minutes.