Different calendars determine dates
The reason Eastern Orthodox churches celebrate Easter on a different date from Catholics and some Protestant faiths is mind-bending.
Catholic and Orthodox churches agree Easter should be celebrated on the first Sunday after the first full moon after the vernal equinox.
Orthodox churches follow the Julian calendar, introduced by Julius Caesar in 46 B.C., and Catholics follow the Gregorian calendar, introduced by Pope Gregory XIII in 1582 and followed in most countries, including the U.S.
And, unlike Catholics, Orthodox churches honor the fourth-century decree that Easter always comes after Passover.
As for the full moon, Catholics determine it using church tables, while Orthodox churches use astronomical charts. The churches also calculate the vernal equinox differently.
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