EASTER

Easter is the most important festival in Christianity. Without the crucifixion and - especially - the resurrection of Jesus, much of the religion would be reduced to the sayings of a nice guy. So it is surprising that Christians rarely celebrate Easter on the same day. This year the west will do so on Sunday, 31 March; the Orthodox Christians of the east will not do so until 5 May.

This is not a new phenomenon. Much of the tensions in early Christianity in Britain between the Irish tradition, which had converted the north of England and the Roman, which had converted the south, hinged on the date of Easter. These tensions were decisively resolved in favour of the latter at the Council of Whitby in 664.

The Irish tradition was in fact already an anomaly. According to the Bible, Jesus held the Last Supper on a Thursday, was crucified the next day and resurrected on the Sunday. But the Last Supper took place as part of the Jewish festival of Passover, which depends on the first full moon on or after the vernal equinox. This can be on any day of the week; so, in order to ensure that the celebration of the resurrection always takes place on a Sunday, the Council of Nicaea decided in 325 that Easter would be on the first Sunday after the first full moon on or after the vernal equinox. Furthermore, the vernal equinox was fixed as 21 March, which it was back in 325, though it now takes place on 20 March. The Council's decision makes the earliest possible date for Easter 22 March, when the full moon is on 21 March and that date is a Saturday; that last happened in 1818 and will next take place in 2285. Similarly, the latest possible date is when there is a full moon on 20 March, so you have to wait until the next one, 29 days later, on 18 April. If 18 April is itself a Sunday, then you have to wait a week until the next Sunday, giving the latest date for Easter as 25 April. This last happened in 1943 and will next happen in 2038.

Since all Christians signed up to the Council of Nicaea, how come there are differences today? The answer lies in the change from the Julian to the Gregorian calendar promulgated by the Pope in 1582, and gradually introduced to Western Europe over the following centuries. The Orthodox church, which didn't recognise the Pope, still uses the Julian calendar, which is currently 13 days behind. If a new moon appears during that 13 day period, as is the case this year, then you can get a large variation in the dates for Easter between west and east.

Many people have argued for finding a date which is the same the world over, and which doesn't depend on the moon; indeed, in 1928, the British Parliament passed such a law, fixing Easter as the Sunday after the second Saturday in April (though the law has never been implemented). However, one of the enduring features of Christianity is the fact that its various strands have a habit of arguing with each other about various doctrinal and other issues. Don't expect there to be agreement on this one any time soon.

Walter Blotscher