Why does the date of Easter change from year to year?
Easter, the annual Christian celebration of the passover of Christ from death to new life, is the oldest Christian annual festival. This celebration grew out of the Jewish annual celebration of passover which celebrated the passing over from slavery under the Egyptians to freedom by which the Jewish people became aware of their special election by God to be His people. The date of Easter is based on the resurrection of Jesus, three days after his crucifixion which occurred on Passover, the fourteenth day of the month of Nisan, according to the Jewish lunar calendar. Much debate and conflict has spawned by efforts to determine this date annually. The difficulty comes in translating an "immovable feast" from a lunar to the Christian solar calendar (Julian, and now Gregorian), on which it becomes a moveable feast. The Council of Nicea in 325 placed Easter on the first Sunday following first full moon after March 20 (which is the vernal equinox when the sun is directly above the earth's equator). This date allowed pilgrims to have moonlight for traveling to the great Easter festivals of that day. Easter may be as early as March 22 and as late as April 25. This dating of Easter reflects its much more ancient origin in the Christian liturgical calendar than the celebration of Christmas. Christmas was dated according to the Roman solar calendar and remains a fixed date from year to year.
[Source: Supplement to the Sunday Bulletin of February 3, 2008; St. Paul Parish, Saskatoon, SK, Canada.]