Sunday, 27 March, 2005

Well it's Easter sunday. If you're like me, then you're probably curious about why the data of the festival changes every year. After all, Christmas is the 25^th of December every year so why is it that the marking of Jesus' rebirth changes date every year?

The answer is actually pretty interesting. You see, since people thought Jesus was going to come back pretty soon nobody bothered to capture the date of his death accurately. Around about 325AD, the problem became compounded by the fact that the Christians in the east used a different calendar to the Christians in the West. The westerners used the Julian calendar (devised by Julias Caesar in 45BC) and the easteners used the lunar calendar. Clearly, in the eyes of the church it was important for the all Christians everywhere to observe Easter on the same date. So some calendar independant method for determining the date of Easter needed to be formulated.

In 326AD the Christian chuch sought to rectify the problem by defining Easter as the first Sunday after the Paschal full moon. A lot of internet web-sites say that the Paschal moon is the first full moon after the Vernal equinox; that is, the day in spring when the length of the day is equal to the length of the night. Unfortunately, this is wrong and quite obviously wrong (although it's only today I discovered why ). Think no further than Austrilia for the reason: the first full moon after the Vernal equinox is in September.

The Paschal full moon is actually determined by a table computed in 326AD of future full moons. The date of easter is thus the first sunday after the first full moon in this table after the 20^th of March. So there you go, the date of Easter has absolutely nothing to do with Christ. Gotta love religious dogma.

Simon.