The modern astronomical usage is attributed to Edmond Halley, who based it on the word σάρος, defined in the Suda as "a measure and a number among Chaldeans. For 120 saroi make 2222 years according to the Chaldeans' reckoning, if indeed the saros makes 222 lunar months, which are 18 years and 6 months."
It may come from the Babylonian word "sāru" meaning the number 3600.
- (historical, Babylon) A period of 3600 years.
- (astronomy) A period of 223 synodic months (approximately 18 years 11 days 8 hours), after which the relative positions of the earth, sun and moon recur, used to predict eclipses.