Why does Easter fall on different dates each year?
In Western Christianity, Easter is always celebrated on the Sunday immediately following the Paschal Full Moon date of the year. I had previously, and somewhat erroneously stated, “Easter is always celebrated on the Sunday immediately following the first full moon after the vernal (spring) equinox.” This statement was true in 325 AD, when it was established by the Council of Nicea. However, the course of history has modified the meaning of this instruction, and therefore, a clearer, more accurate explanation is necessary today. There are, in fact, as many misunderstanding about the calculation of Easter dates, as there are reasons for confusion about Easter dates. What follows is an attempt to clear up at least some of the confusion. In actuality, the date of the Paschal Full Moon is determined from historical tables, and has no correspondence to lunar events. In the year 325 AD astronomers approximated the dates of all the full moons in the year for the Western Christian churches. The
It’s what’s known as a moveable feast. In Christianity, a moveable feast or movable feast is a holy day—a feast or a fast—whose date is not fixed to a particular day of the calendar year but moves in response to the date of Easter, the date of which varies according to a complex formula. The ecclesiastical rules are: Easter falls on the first Sunday following the first ecclesiastical full moon that occurs on or after March 21 (the day of the ecclesiastical vernal equinox). This particular ecclesiastical full moon is the 14th day of a tabular lunation (new moon).
