When is Easter?

According to the New Testament, Christ was crucified on the eve of and shortly afterward rose from the dead. In consequence, the Easter festival commemorated Christ’s resurrection. In time, a serious difference over the date of the Easter festival arose among Christians. Those of Jewish origin celebrated the resurrection immediately following the Passover festival, which, according to their Babylonian lunar calendar, fell on the evening of the full moon (the 14th day in the month of Nisan, the first month of the year); by their reckoning, Easter, from year to year, fell on different days of the week.
Christians of Gentile origin, however, wished to commemorate the resurrection on the first day of the week, Sunday; by their method, Easter occurred on the same day of the week, but from year to year it fell on different dates. An important historical result of the difference in reckoning the date of Easter was that the Christian churches in the East, which were closer to the birthplace of the new religion and in which old traditions were strong, observed Easter according to the date of the Passover festival. The churches of the West, descendants of Greco-Roman civilization, celebrated Easter on a Sunday.
Rulings of the Council of Nicaea on the Date of EasterConstantine 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.
The Council of Nicaea also decided that the calendar date of Easter was to be calculated at Alexandria, then the principal astronomical center of the world. The accurate determination of the date, however, proved an impossible task in view of the limited knowledge of the 4th-century world. The principal astronomical problem involved was the discrepancy, called the epact, between the solar year and the lunar year. The chief calendric problem was a gradually increasing discrepancy between the true astronomical year and the Julian calendar then in use.
Later Dating MethodsWays of fixing the date of the feast tried by the church proved unsatisfactory, and Easter was celebrated on different dates in different parts of the world. In 387, for example, the dates of Easter in France and Egypt were 35 days apart. About 465, the church adopted a system of calculation proposed by the astronomer Victorinus (fl. 5th cent.), who had been commissioned by Pope Hilarius (r. 461–68) to reform the calendar and fix the date of Easter. Elements of his method are still in use. Refusal of the British and Celtic Christian churches to adopt the proposed changes led to a bitter dispute between them and Rome in the 7th century.
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 Easter on a Sunday either preceding or following the date observed in the West. Occasionally the dates coincide; the most recent times were in 1865 and 1963.
Because the Easter holiday affects a varied number of secular affairs in many countries, it has long been urged as a matter of convenience that the movable dates of the festival be either narrowed in range or replaced by a fixed date in the manner of Christmas. In 1923 the problem was referred to the Holy See, which has found no canonical objection to the proposed reform. In 1928 the British Parliament enacted a measure allowing the Church of England to commemorate Easter on the first Sunday after the second Saturday in April. Despite these steps toward reform, Easter continues to be a movable feast.