Easter, by the numbers

Jay Ryan from Classical Astronomy gives a good overview of why we celebrate Easter when we do.   You'll learn such intricacies as:

[...] every 19 years, the Moon's phases will recur on the same dates of the solar year.  This 19 year "luni-solar" cycle was the basis for the calendar used in Babylon. In the west, its discovery is attributed to the Greek philosopher Meton, who may have learned it from the Babylonians. The 19 year cycle was generally well known and understood in antiquity, and was apparently used by the Persian rulers of Babylon after the restoration of Israel.

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