Easter Approacheth...

and with it, comes the perennial discussion about the determination of the date on which Easter will fall each year. Now, I'm a pragmatist from way back. So when, as a youngster, I got to wondering about the determination of Easter, I pulled out that year's calendar, and one from the previous year, and attempted to figure it out. I'd heard that it had something to do with the full moon, and with the start of spring, but no matter how I tried, I couldn't make the dates on those calendars obey a fixed rule.

Fast forward a dozen or so years, and I'm dealing with the comparison between the Western and Eastern (or Orthodox) church calendars. For most holidays (Christmas and New Year's, for example), you simply add 13 days to the Western date to get the Eastern date. This, I knew, was due to the different versions of the calendar the assorted churches used. Western churches used the Gregorian calendar, Eastern churches, the Julian calendar. No biggie. After all, if you use the appropriate calendar, Christmas falls on December 25th. The argument is over when December 25th is.

But Easter isn't so simple. At first it seems like it should be. After all, if Easter is determined based on Full Moons and the start of spring, it shouldn't matter which calendar you use. Spring is spring and a moon is full whether the calendar you use if Gregorian, Julian, Hebrew, Coptic, Mayan or Fischer Universalist, right?

Well, this is where we hit trouble. For it seems that the Western church stopped paying attention to the sky when figuring spring and full moons about 1500 years ago. Instead, of using the actual full moon and actual equinox, they used the ecclesiastical full moon and ecclesiastical equinox(March 21st) when calculating the date of Easter. The Eastern Orthodox churches, however, base the date of Easter on the actual Full Moon and actual equinox.

The long and the short of it is that the dates vary. So, in 2007, both systems produced the same date for easter, April 8th. This year, on the contrary, the dates differ wildly, giving March 23rd in the Western Church, and April 27th in the Eastern church. There's a useful table of dates here, if you're interested in planning your easters-yet-to-come.

Thanks to infoplease for filling me in on the details of this puzzling situation.

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