March 20 eclipse and the Saros

March 20 eclipse and the Saros
by Fred Espenak in Blogs » Astronomy Essentials, Space

There are currently 40 different Saros series in progress, each with its own assigned number. The total solar eclipse of March 20, 2015 belongs to Saros 120.

The total solar eclipse of March 20, 2015 belongs to a family of eclipses known as Saros 120. A Saros series is composed of a group of eclipses in which each eclipse is separated from the next (or previous) eclipse by 6,585.3 days. This equals 18 years 10 days 8 hours (or 18 years 11 days 8 hours, depending on the number of leap years over this interval).

The Saros period is special because any two eclipses separated by one Saros are very similar to each other. The moon is nearly at the same position with respect to its node (the point where the moon’s orbit crosses Earth’s orbit) and is also at almost the same distance from Earth. Not only that, the eclipse occurs at virtually the same time of year.

These coincidences arise because three of the moon’s orbital periods repeat after one Saros period of 18 years 10.3 days. ...

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