Saros (astronomy)
The saros (/ˈsɛərɒs/ ⓘ) is a period of exactly 223 synodic months, 18 years 11 days 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. Every eclipse has an associated saros series and all succeeding or preceding eclipses have a different saros series associated with them - as the eclipse of the same series occurs or occurred with a gap of one saros only. Solar and lunar eclipses have different saros series.
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 of 173.31 days)
- 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 solar eclipse can occur.