The Saros Cycle and Prediction of Eclipses

A long time ago, Babylonians carefully maintained records of the occurrence of eclipses and used these records to predict future eclipses. To honor that, in 1691, Edmund Halley named the interval in a cycle of eclipse using a Babylonian unit of time: the “Saros”.

NASA explained the Saros in a web page titled Eclipses and the Saros, and the unscrupulous flat-Earthers were quick to devise a conspiracy theory. They invented the scenario that NASA —a space agency with billions of dollars of a budget— are somehow using ancient technology to predict the occurrences of an eclipse. They are wrong. NASA does not use the Saros Cycle to predict eclipses.

A Saros is 6585⅓ days between two occurrences of an eclipse. These two eclipses and the subsequent ones have similar characteristics.  Today, the Saros Cycle is used to group eclipses. The eclipses in the same Saros Cycle are grouped in the same “Saros Series”. A Saros Series has a number to identify it, not unlike the way we identify a year with a number.

These days, predicting eclipses are not done using the Saros Cycle. The Saros Cycle cannot be used to predict the time and duration within the accuracy of a second. It also can never be used to determine the path of totality in a solar eclipse.

At any moment, there are multiple active Saros Series. During a Saros Series, unrelated eclipses from the different Saros Series will occur many times. An eclipse cannot be predicted from the occurrence of another eclipse that belongs to the different Saros Series.

Eventually, a Saros Series will end, and there will not be another eclipse from the same Saros Series. On the other hand, an eclipse that marks the beginning of a Saros Series cannot be predicted using the Saros Cycle.

Some features of an eclipse can’t be determined from the Saros Cycle. And the Saros Cycle can’t predict all eclipses and certainly can’t predict them with sufficient accuracy. The assumption flat-Earthers made that an eclipse can only be predicted using the Saros Cycle is wrong.