Easter is on a different date each year. It can get confusing. How do you keep up with a holiday whose date is always changing? It is especially confusing if you have a calendar that doesn’t list holidays and other important dates on it. So, how can you determine when Easter will be each year, and why does the date change every year, anyway? Here are your answers.
Easter is what is known in early Christian celebrations as a moveable feast. This means it does not fall on a fixed date every year, at least not on the two most commonly used calendars in the past two thousand years… the Gregorian and the Julian calendars. These calendars follow the cycles of the sun and the seasons. Instead, Easter’s date each year is based on a lunisolar calendar, which follows the cycles of the sun and moon. The Hebrew calendar is an example of a lunisolar calendar.
Easter was celebrated by the different early Christian sects on different dates determined to be the most authentic one by each sect. The First Council of Nicaea, which was held in 325 A.D., was the first Christian council to establish any rules for Easter. The council mandated that it be based on the Jewish calendar and that the date for Easter had to be uniform among all the Christian sects worldwide. That was all the council had to say on the matter. It did not give a date on which Easter was to be held, only that all denominations had to celebrate it on the same date. The actual computing of the date for Easter took centuries to work out, and it was not without controversy along the way.
Another thing the council did not specify was that Easter had to take place on a Sunday. This ended up not mattering, because almost all Christian sects at the time already celebrated Easter on Sundays. This tradition was maintained as all of Christianity tried to work out when to celebrate this holiday.
Western and Eastern Christianity ended up coming up with their own calculations for when to have Easter, despite the universality decree of the Council of Nicaea. Western Christianity uses the Gregorian calendar these days, and with this calendar, Easter always falls on a Sunday between March 22 and April 25, usually about seven days after the full moon.
In Eastern Christianity, the Julian calendar is used, at least for religion, if not for civil purposes. There is a thirteen-day difference between the two calendars between 1900 and 2099. Currently, the Julian calendar has Easter falling between April 4 and May 8, usually several days later than the full moon, relative to the Gregorian calendar.
The first official method for computing Easter was written by the Venerable Bede in 725. Bede wrote that the holiday should fall on the “Sunday following the full moon, which falls on or after the Equinox.” Yet, Bede was not following church rules in a precise way when he wrote this. He was referring to something called a Paschal full moon, which is not the astronomical full moon, and it is the astronomical full moon the church recognizes for the purposes of computing Easter. The Paschal full moon is basically the 14th day of a lunar month on a calendar. Also, the church date of the Equinox is always March 21, whereas the astronomical Equinox can fall on that date, or the two days prior to it.
Is this confusing yet? It gets even more convoluted, with different religious, civil, and astronomical calendars involved.
In determining the date of Easter, all Christian churches use the twenty-first of March as their starting point, as it is the church Equinox. They use this date to find the next full moon. The Eastern churches use the Julian calendar to find it, and the Western churches use the Gregorian calendar to find it. Because both calendars are slightly different, March 21 on the Julian calendar is April 3 on the Gregorian calendar.
The lunar cycles are four to five days behind the ones on the Gregorian calendar, further complicating computing Easter between the two church regions. Lunar years contain thirty-day and twenty-nine-day lunar months, alternating, with a slightly different month (similar to February in a Leap Year) to bring the lunar cycle in line with the solar one. January 1 to December 31 is considered a solar year. In each solar year, there is a lunar month that begins with a church new moon which falls between March 8 and April 5 that is designated as the Paschal lunar month for that year.
Easter has been designed over the centuries since the Council of Nicaea to be on the third Sunday in that year’s Paschal lunar month (also sometimes described as the Sunday after the 14th day of the Paschal lunar month).
This is the way the date of Easter is computed today, and has been that way since at least the mid-1700’s. It was a date that was often debated before that. Easter has been celebrated in some form almost since the beginnings of Christianity, and it was an undisputed church tradition by the late second century. Various Christian sects often came into conflict with the church in Rome, once Rome adopted Christianity, over the date of Easter, but these were usually peacefully tolerated by each other, with only a few brief and quickly abandoned attempts by Roman bishops to excommunicate churches using other methods for calculating Easter than the primary church in Rome.
While the method of calculating Easter has changed several times over the centuries, it has always been based in some way on the cycles of the moon, and most importantly, the Paschal full moon.
Beginning in the 20th century, there have been some proposals for a fixed date for Easter, usually being the Sunday after the second Saturday in April. There has been support for this among most denominations, but no proposals have been implemented thus far. Until one is, making Easter a holiday on a fixed date, we will have to continue computing it the old-fashioned way, by calculating the third Sunday in the Paschal lunar month of the year, either on the Julian or Gregorian calendar. Or, you can just consult the Internet, or the calendar on your wall.