Dating Easter

Religious Origins and Background

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Although the dating of Easter is a little complicated, it still seems like it should be a rather straightforward process. Appearances can be deceiving, however - because this date is supposed to commemorate the resurrection of Jesus Christ, Christians have always placed a high emphasis on getting it "right," and that means that they have endured many disagreements over just which date it should fall on. Currently, the biggest division lies between the Western churches and the Eastern Orthodox churches - their Easter celebrations are often separated by many weeks.

Before 325 CE, Christian communities celebrated Easter on a variety of different days of the week; but the Council of Nicea, called together by Emperor Constantine, issued the "Easter Rule" which standardized Easter observance to the first Sunday after the first full moon (known as the paschal moon) on or after the vernal equinox (but never on the same date as the Jews celebrated Passover).

This "full moon" is not defined in a scientific manner, however - it is an "ecclesiastical full moon" and the "ecclesiastical vernal equinox" is always on March 21st. This means that Easter always occurs on a Sunday between March 22nd and April 25th, signaling the end of the season of Lent. Each year, the date moves progressively later in April until the year before leap-year is reached. On leap-year, the date moves back to an earlier time and the four-year cycle is then repeated. 

Calculations for Easter in Eastern Orthodox churches are slightly different because even those which otherwise use the Gregorian calendar for most purposes still use the Julian calendar for dating the equinox. Thus, while their Easter can fall on the same date as Easter for Western churches, it can also be one, four, or even five weeks later.

At one time, there were also the Quatrodecimens, a group of Christian whose churches in Asia Minor celebrated Easter on the 14th day of the Jewish month of Nisan, essentially making Easter a Christian Passover. Important Quatrodecimens included Polycarp of Smyrna and Apollinaris of Hierapolis. Although the Council of Nicea was supposed to settle the date of Easter for all Christians, there is evidence of Quatrodecimens continuing their tradition down through the 5th century.

There are also secular interests at work when it comes to dating Easter. Because Easter has long been a cultural as well as religious holiday, businesses have developed a vested interest on what happens on that date. People take vacations, businesses close, and many retailers bring out Spring fashions. Marketing forecasts and spring sales depend heavily upon Easter.

Unfortunately, a lot of that can be upset by the fact that Easter moves around so much. People travel less and sales are slower if Easter falls March than if it falls in late April. As a consequence, some have urged that an "official" date for Easter be permanently set in the calendar some time late in April and regardless of when the full moon occurs. Religious leaders have naturally recoiled from the suggestion.