Theresa May’s recent defence of Easter egg hunts as a Christian ritual has provoked many responses pointing at the complex origins of the festival: the name in English is thought to refer to a pagan goddess Eostre, Easter eggs may imply fertility, while whatever their intended role Easter bonnets have all but disappeared.
The mish-mash of traditions represents the fact that most cultures have spring festivals, no doubt because winter is hard and we all welcome the return of longer days and rising temperatures. Yet, there is at least one thing that is undeniably Christian about Easter, and that is when it is celebrated – because Easter moves!
As we all know, any conversation about Easter contains the ubiquitous question: ‘why can’t they fix the date?’ Even the archbishop of Canterbury waded in last year suggesting the date could be set. The reality is discussions on how to date Easter are as old as the celebration itself. The Synod of Nicaea in AD 325 attempted to resolve these ambiguities, and, while that didn’t really work, the principles they agreed underlie the calculation of Easter today.
For Easter, as all students of medieval history learn, is the first Sunday after the first full moon after the vernal equinox. And that simple statement contains the crux of the matter, because the Christian celebration of Easter attempts to synchronize three independent and unrelated calendrical systems.
Let’s take these one at a time:
- Easter must fall on a Sunday, because Jesus rose from the dead on the first day of the week. This proscription is the most obvious difference between the Christian Pasch and the Jewish Passover, and means that Easter must subscribe to the rules of the seven-day week, an artificial division of time.
- Easter is linked to the full moon. Our culture pays little attention to phases of the moon but lunar ‘months’ were a common measure of time in the ancient world, as the moon’s waxing and waning was a useful way to organise communal life. Several cultures continue to use lunar calendars today, for example, Islamic religious festivals are based on the moon as is the Jewish celebration of Passover. Following the Gospel accounts, Jesus was crucified at Passover (though John differs slightly from the other three), and the Church, which regards Passover as the antecedent for Easter (Christ is the paschal lamb), is committed to continuing its lunar association.
- Easter falls after the vernal equinox. Equinox, when day and night are of equal length, occurs twice a year: 20 March and 23 September – the dates vary slightly as planetary orbits are elliptical not circular . The vernal equinox marks the beginning of day’s increase over night and, for the Church, symbolises Christ’s resurrection which is the ultimate victory of light over dark and life over death.
These three criteria are not naturally reconcilable. The solar year is 365 days, 5 hours, 48 minutes and 45 seconds; a lunar month (though the more correct astronomical term is year) is 29 days, 12 hours, 44 minutes and 3 seconds; and neither of these is easily matched to the 7-day week. To synchronise solar, lunar and weekly cycles the Church uses a complex mathematical formula based on the 19-year Metonic cycle, which was invented by Meton of Athens in the fifth century BC.
The Metonic cycle was employed by the Church of Alexandria to calculate Easter at an early stage in Christian history and from there spread all over the known world, substantially helped in the western Church by the English monk, the Venerable Bede.
Easter is ‘late’ this year because we had full moon on 12 March, a week before the vernal equinox, so must wait for the next full moon on 11 April and Easter is the following Sunday, 16 April – as the rule dictates, the first Sunday after the first full moon after the vernal equinox.
Of all the traditions associated with Easter, its moveable nature is the most ancient and most authentic. While this may inconvenience secular calendars, it is essential for the integrity of the Church’s greatest festival. And, as we are increasingly removed from the natural world and see less and less of the night sky due to light pollution, why not embrace the fact that once a year we find ourselves bending – just a little – to the advanced mathematics of an ancient luni-solar cycle.
Máirín MacCarron is a Lecturer in Medieval History at the University of Sheffield. Her research centres on the early medieval period, with a particular interest in time, chronology and the writing of history. She is is currently completing a monograph on Bede and Time and has recently co-edited a collection on the use of maths in the study of history called Maths meets Myths (Springer, 2016). You can find her on twitter @.
Image: Easter calendar years 532-632 A.D. [via Wikicommons].