Easter dating system
Why does the date of Easter vary by more than a month?Because the ancient Egyptians and Hebrews used different calendars.Is this why Easter is on a different day in Eastern Europe? That's because the Orthodox church sticks to the calendar promulgated by Julius Caesar but which the West abandoned in the 16th century.But it is all linked to trying to harmonise solar and lunar calendars.The Egyptians had one based on the movement of the sun, which was passed on through the Romans and Christian culture to become the modern world's standard.The Jews had one based on the phases of the moon – as Islam does, which is why the month of Ramadan moves round the calendar and takes places at different times of the year each year, with Muslims waiting for sightings of the moon before they know what day it will begin.
" The Orthodox Easter is still a Julian one and usually follows ours by a week or so and can even stretch into May. Its latest possible date is 25 April but we haven't had that since 1943 and won't again until 2038.
There was a ruling by the First Council of Nicaea in 325 that Easter should be celebrated on the Sunday after the first full moon following the spring equinox but this was ignored for centuries, with even the church in Rome using its own methods until the 6th century. It had been decided that the vernal equinox would occur on 20 March (as it did at Nicaea) but that too varies. So the old church fathers got round this by redefining what a full moon is.
More recently there have been Mallen's Method, Marcos Montes Method, Carter's Method, Oudin's Method... Why are there so many different definitions of a full moon?
Astronomers approximated astronomical full moon dates for the church, calling them Ecclesiastical Full Moon (EFM) dates.
Thus Easter was defined as the Sunday after the first EFM after 20 March.