Constantine I, Roman emperor, convoked the Council of Nicaea in 325. The council unanimously ruled that the Easter festival should be celebrated throughout the Christian world on the first Sunday after the full moon following the vernal equinox; and that if the full moon should occur on a Sunday and thereby coincide with the Passover festival, Easter should be commemorated on the Sunday following. Coincidence of the feasts of Easter and Passover was thus avoided.
Reform of the Julian calendar in 1582 by Pope Gregory XIII, through adoption of the Gregorian calendar, eliminated much of the difficulty in fixing the date of Easter and in arranging the ecclesiastical year; since 1752, when the Gregorian calendar was also adopted in Great Britain and Ireland, Easter has been celebrated on the same day in the Western part of the Christian world. The Eastern churches, however, which did not adopt the Gregorian calendar, commemorate
at 7:29 PM on Feb. 3, 2010