<P> Easter and the holidays that are related to it are moveable feasts which do not fall on a fixed date in the Gregorian or Julian calendars which follow only the cycle of the sun ; rather , its date is determined on a lunisolar calendar similar to the Hebrew calendar . The First Council of Nicaea ( 325 ) established two rules , independence of the Jewish calendar and worldwide uniformity , which were the only rules for Easter explicitly laid down by the council . No details for the computation were specified ; these were worked out in practice , a process that took centuries and generated a number of controversies . It has come to be the first Sunday after the ecclesiastical full moon that occurs on or soonest after 21 March , but calculations vary . </P>
what are the rules for when easter is
the first Sunday after the ecclesiastical full moon on or soonest after 21 March