Wednesday, April 20, 2011

Passover & the Moveable Easter

Easter's never had the same mass popularity as Christmas, even though it's theoretically the bigger holiday religiously speaking. One simple reason for that is timing. Easter moves around. It's not on a set date every year, which makes it harder for greeting card companies to market it.

Why does Easter move around so much, and how do they decide when it is every year? Good questions. First you have to realize that Easter isn't just one holiday, but a series of them. Palm Sunday was last Sunday. Then we have Holy Thursday and Good Friday and finally Easter Sunday. The key to all this date moving around shenanigans lies with Holy Thursday, the evening of the famed Last Supper. You know the one. The one where Jesus grossed everyone out by turning the wine and bread into his body and blood and where Judas became the most infamous snitch of all time. The wild party where Peter lost an ear.

All that epic zaniness happened on Passover (and you thought your family seders were crazy) or maybe the day before if you believe a new biblical/historical analysis. As a result, the mystery of Easter's date placement is related to Passover. (Jesus was Jewish, remember?)

Now Passover does have a set date. It just happens to be a set date on the Jewish Calendar, the 15th of Nisan to be precise. The Jewish Calendar doesn't sync up with the Gregorian Calendar we all know and love today (the same one that moved George Washington's birthday around). Instead, it's based on the phases of the moon. Thus, Passover starts the night of the first full moon after the vernal equinox (the first day of spring).

Easter, therefore, is set to be the first Sunday after the first full moon after the vernal equinox. (I suppose technically it should be three days after Passover, but Christianity is more concerned with it being a Sunday every year.)

Except of course that Christianity, being the bastion of scientific accuracy that it is, defines the vernal equinox as March 21, even though astronomically speaking sometimes it's the 20th. Combine that with other subtle differences between the Gregorian and Jewish Calendars, and every now and then Passover is actually about a month after Easter. And since Passover isn't allowed to start on a Monday, Wednesday, or Friday anymore, the seder never lines up with Holy Thursday.

This year the vernal equinox fell the day after a full moon (or two days after if you're Christian). So we've had to wait almost an entire month for Passover and Easter to come around. April 24 is almost as late as Easter can possibly be. It can only be one day later and won't be this late again until April 25, 2038.

In case you're wondering, the earliest it can be is March 22, but you'll have to wait until 2285 for that. April 19 is the most common date for Easter. The cycle of Easter dates repeats itself every 5,700,000 years. Like I said... hard to market that.

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