The Difference Between an Annular & a Total Eclipse

By John Brennan; Updated April 24, 2017
Solar eclipses occur when the moon casts a shadow on Earth.

In 1502, while stranded on the island of Jamaica, Christopher Columbus used an almanac he'd brought from Europe to predict an eclipse would occur in a few days. He used his knowledge to terrify the natives into cooperation. They, like people at many times throughout history, thought solar eclipses signaled the wrath of a higher power. Today, thanks to an improved understanding of science and astronomy, humans find solar eclipses more fascinating than fearsome. Annular and total solar eclipses are the two most interesting kinds you can see.

Characteristics

Just as the Earth has an elliptical orbit around the sun, the moon has an elliptical orbit around Earth. The distance between the Earth and moon, therefore, is not the same at all times. Although the moon on average has the same angular size as the sun, its angular size varies slightly. The moon's orbit is also inclined at a slight angle with respect to the plane of Earth's orbit around the sun. An eclipse only occurs during a new moon and at a time when the moon is close to crossing the plane of the Earth's orbit.

Total Eclipse

When an eclipse occurs, the moon casts a shadow called an umbra. Sometimes an eclipse occurs when the moon is close enough that its umbra falls on Earth. At these times, people located in the path traced by the umbra see the sun completely obscured by the moon. This phenomenon is called a total solar eclipse. These spectacular events are fairly rare because the umbra traces a fairly narrow path. Each total eclipse is only visible from certain locations.

Annular Eclipse

Sometimes the moon's trajectory takes it straight across the center of the sun as seen from the Earth -- just as during a total eclipse. If the moon is too far away for the umbra to fall on the Earth, however, an annular eclipse occurs instead. During these events, the moon leaves a small ring, or annulus, of the sun visible around its edges. These are sometimes called central eclipses.

Penumbra

During both total and annular eclipses, people located too far north or south see a partial eclipse, where the moon partially obscures the sun and seems to take a bite out of it. The region where the sun is only partially covered is called the penumbra, and it's much larger than the actual track of the eclipse. Consequently, partial solar eclipses are more frequent at any one given location than total solar eclipses.

About the Author

Based in San Diego, John Brennan has been writing about science and the environment since 2006. His articles have appeared in "Plenty," "San Diego Reader," "Santa Barbara Independent" and "East Bay Monthly." Brennan holds a Bachelor of Science in biology from the University of California, San Diego.