Magnitude of eclipse

The size ( and magnitude) of a solar eclipse is a measure for the area covered by the moon part of the solar diameter at a specific place and time. For a partial or annular eclipse, this value is smaller than 1, in total darkness greater than 1 During a solar eclipse takes place on a the size of the darkness slowly, reaches a maximum and decreases again. The for an observer at a suitable place maximum attainable size is an important parameter and can be found as " size of Darkness" in the relevant tables.

For the size, there are in addition to the usual used also by NASA definition of the Bureau des Longitudes another in Paris, which provides for the partial phase matching sizes, but not during an annular and total eclipse.

Another way to describe the extent of the eclipse, is the degree of coverage, which expresses the proportion of the area covered by the Moon surface of the solar disk and is expressed as a percentage (see eclipse ).

Partial eclipse

The size of a partial solar eclipse is the ratio between the area covered by the moon part of the solar diameter, and all the apparent diameter of the sun. Since the moon does not completely cover the sun during the partial phase, the value is less than 1

Total or annular eclipse

After the usual definition of the size of a total or annular eclipse is the ratio of the apparent diameters of the Moon and the Sun. The value is greater than 1 at a total solar eclipse, an annular eclipse in less than 1

However, this definition leads during the transition from partial to total or annular phase to a discontinuity in the course of the size: In the moment in which the totality begins, the size reaches the value of 1.0 and then jumps to example 1.05.

Alternative definition of the Bureau des Longitudes

According to the definition of the Bureau des Longitudes, the size of the length of that route, which passes through the centers of the sun and moon, and extends from the center of the sun the nearest edge of the moon to the moon middle of the nearest solar limb, expressed as a ratio to the solar diameter ( see figure). This definition provides during the partial phase, the same numerical values ​​as the first definition, but avoids the discontinuity at the beginning of totality.

The size of this definition also provides an indication of how centrally lunar and solar disc lie on each other. The maximum value is greater, the central lunar and solar disc lie on each other.

Comparison of the two definitions

Both definitions lead during the partial phase to the same numerical value, but provide for the central phase different values. Since the standard definition in total darkness represents the full diameter of the lunar disk into account the alternative, however, by the two protruding edges only one, the size of the darkness according to the alternative definition of which is smaller than after the usual. In an annular eclipse, it is vice versa. This must be considered when data from different sources to be compared. So used by NASA for their darkness tables the standard definition, the French IMCCE ( Institut de Mecanique Celeste et de Calcul des Ephemerides ) the alternative.

In the case of partial darkness both numbers are the same ( the slight difference is due to the ephemeris and astronomical constants used in each case ). In the case of the other two eclipses, the information in the sense mentioned differ. According the alternative definition, the difference of the maximum value to 1 is only half as large as the difference between the constant value to 1 in the standard definition.