A feast of the church year that is not celebrated on a fixed date. The date of the movable feast's celebration in each year is determined by other liturgical rules. The church year has two cycles of feasts and holy days, one dependent on the movable date of Easter Day and the other dependent on the fixed date of Christmas, Dec. 25 (BCP, p. 15). Easter Day is the first Sunday after the first full moon after the spring equinox on Mar. 21. This date is fixed in accordance with an ancient ecclesiological computation, and may not correspond to the astronomical equinox (BCP, p. 880). Easter cannot be earlier than Mar. 22, and it cannot be later than Apr. 25. The BCP provides tables and rules for finding the date of Easter Day (pp. 880-883).
The date of Easter determines the date for many feasts (and fasts) of the church year. The date of Easter will determine the number of Sundays in the church year after Epiphany, the dates of Ash Wednesday and the Sundays in Lent, the date of the Feast of the Ascension on a Thursday forty days after Easter, the dates of the Sundays of Easter including Pentecost, and the dates of the Sundays after Pentecost.
The Sundays of Advent are always the four Sundays before Christmas Day, whether Christmas occurs on a Sunday or a weekday (BCP, p. 15). Since Christmas is celebrated on different days of the week, the dates of the four Sundays of Advent preceding Christmas will vary from year to year. The First Sunday of Advent is never earlier than Nov. 27 and never later than Dec. 3. The BCP provides a table to find movable feasts and holy days (pp. 884-885). See Calendar of the Church Year, The.