Gamma (eclipse)

The gamma value (symbol: γ ) of a solar eclipse describes how central the Shadow of the Moon hits Earth. Here, the minimum distance, in which passes the axis of the shadow cone in the center of the earth, expressed as a fraction of the equatorial radius of the earth. The sign of the gamma value that indicates whether the shadow axis north or south of the Erdmittelpunkts passes, a positive value indicates north.

The figure illustrates the gamma value: The red line represents the shortest distance from the center of the earth is, which is approximately 75% of the earth's radius in this figure. Since the umbra passes north at the geocenter, the gamma value in this example is about 0.75.

The amount of the gamma value, allows to distinguish between different types of solar eclipses:

• If the amount of gamma below 0.9972, the darkness is central. The shadow axis strikes the earth and there are places on the earth's surface, from which an observer sees passing by the moon centrally in front of the solar disk. Central eclipses can (if the umbra tip only just reaches the earth's surface, the type even during the darkness of a ring to totally and again to change a ring, then it is a hybrid eclipse ) total or annular be.

• If the amount of gamma 0.9972 to 1.0260, the shadow axis misses though the earth because during a total eclipse of the umbra but has a certain width, yet a part of the umbra cone may interfere with the earth ( in the polar regions ) stripes. In an annular eclipse this similarly applies to the area of annular eclipse (English antumbra ). The result is a non-central total or annular eclipse.

• If the amount of gamma between 0.9972 and about 1.55 and enters the above-mentioned rare special case, not one, so the darkness is partial, the Earth passes through only the penumbra cone.

Because of the flattening of the earth, the limit for a central eclipse not 1, but is 0.9972.

The solar eclipse of 29 April 2014, a gamma value of 1.0001 represents the rare limiting case of an annular, but not central darkness represents the shadow axis misses Earth in the south scarce. Thus, no central line can also be specified for the zone of the annular eclipse.