Saros (astronomy)

The saros (/ˈsɛərɒs/ ^ⓘ) is a period of exactly 223 synodic months, approximately 6585.321 days, or 18 years, 10, 11, or 12 days (depending on the number of leap years), and 8 hours, that can be used to predict eclipses of the Sun and Moon. One saros period after an eclipse, the Sun, Earth, and Moon return to approximately the same relative geometry, a near straight line, and a nearly identical eclipse will occur, in what is referred to as an eclipse cycle. A sar is one half of a saros.

A series of eclipses that are separated by one saros is called a saros series. It corresponds to:

6,585.321347 solar days
18.029 years
223 synodic months
241.999 draconic months
18.999 eclipse years (38 eclipse seasons)
238.992 anomalistic months
241.029 sidereal months

The 19 eclipse years means that if there is a solar eclipse (or lunar eclipse), then after one saros a new moon will take place at the same node of the orbit of the Moon, and under these circumstances another eclipse can occur.

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