39th Festal Letter

Wikipedia extract

Extract is from the broader Wikipedia page "Easter letter", not about this record specifically

The Festal Letters or Easter Letters are a series of annual letters by which the Bishops of Alexandria, in conformity with a decision of the First Council of Nicaea, announced the date on which Easter was to be celebrated. The council chose Alexandria because of its famous school of astronomy, and the date of Easter depends on the spring equinox and the phases of the moon.

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