Why is Easter such a movable feast?
Whether you are a believer or not, Easter is one of those points in the calendar that seems to give us a psychological lift. Summer is on its way and, if we are lucky, it might even bring some warmer weather with it. But unlike Christmas which is fixed rigidly on December 25th, irrespective of what day of the week it falls on, the date of Easter is movable, much to the consternation of those who like certainty in such matters. Why is that and what are the rules which determine the date of Easter?
The starting point in our enquiries is the Gospels. All four disciples (Matthew 26.2, Mark 14.1, Luke 22.1, and John 18.39) agree that the crucifixion of Christ took place in conjunction with the Jewish feast of Passover. The first three describe the Last Supper, traditionally placed as taking place on the Thursday, as a Passover meal whereas John’s account suggests that on the morning of Christ’s death the Jewish authorities hadn’t yet eaten their Passover meal. Our story is complicated enough that we will quickly pass over that little discrepancy.
The festival of the Passover, commemorated to celebrate the liberation of the Jews from slavery in Egypt, begins at sundown of the fourteenth day of Nisan. Its date is determined by the first full moon after the vernal equinox. The early Christians wanted to maintain the link between the death and resurrection of their Lord with the dating of the Jewish festival. As the latter was movable, based on lunar and solar cycles, so too was Easter.
By 325 CE, however, the Church authorities decided to add some intellectual rigour to the dating of Easter. At the Council of Nicaea they laid down the basic rules which are still used today. They took as their starting point the vernal equinox. They also wanted Easter to fall on a Sunday. The understanding of the celestial spheres and the orbit of the moon had advanced sufficiently that astronomers could estimate the date of all future full moons. So, an algorithm was developed which fixed Easter as the first Sunday after the first full moon following the vernal equinox. If the calculated Ecclesiastical Full Moon (EFM) falls on a Sunday, Easter will be the following Sunday. That means that Easter will always be between one and seven days after the EFM.
There was a tiny bit of a problem, though.
The vernal equinox itself is not a fixed date. The Nicaean Council used March 20th as the cornerstone for their calculation, it is known as the Paschal equinox, simply because it happened to be the date of the vernal equinox in the year of their deliberations. This means that the calculated EFM dates can be out of whack by as much as two days with the actual full moon we see in the night sky.
The next complicating factor was the introduction of the Gregorian calendar by Pope Gregory XIII in October 1582 to replace the Julian calendar, replacing ten dates in that month to realign the Paschal Equinox with the seasons. By that time, of course, we in Britain had split with the Catholic church and not having truck with foreign ways (where have we heard that before?) did not adopt the new calendar until 1752. So for near on two centuries our Easters were out of line with those celebrated by the Catholic church.
The Eastern Orthodox churches were also having nothing to do with the Gregorian calendar reforms and to this day they still use the Julian calendar. Although they use the methodology established by the Council of Nicaea the date ranges in which their Easter celebrations fall can differ markedly. The last time the two festivals coincided on the same date was as recently as 2017 and they will do again in 2025.
The upshot of all this is that Easter can fall between March 22nd and April 25th using the Gregorian calendar whereas the Eastern churches can celebrate Easter between April 4th and May 8th. Easter this year is quite late but not as late as it will be in 2038, when it will fall on the latest possible date, April 25th. The last time Easter fell on March 22nd was way back in 1818 and it won’t settle on that date again until 2285. I don’t think I will be around to see it.
There have been attempts to pin Easter down. The Second Vatican Council agreed to a fixed date in 1963, provided agreement could be reached amongst all the Christian churches. A further attempt to resolve matters was made at the meeting of the Council of World Churches in 1978 in Aleppo where it was proposed that the latest scientific methods for calculating the full moons would replace that developed in 325CE.
Nothing has come of that initiative and for me, that’s no bad thing. Easter would lose some of its charm if it was a fixed date in the calendar.
If you enjoyed this, check out Fifty Curious Questions by Martin Fone