Justin du Coeur (jducoeur) wrote,
Justin du Coeur

Okay, it's not just me...

One thing that has always mystified me is, "When the heck is Easter?". The date has always seemed -- well, arbitrary to me. But I figured that that was just because I was raised in a secular Jewish household, and it just didn't impact our lives enough to talk about it.

Maybe not so much, though. Thanks to Gundormr for pointing out this article on the subject. The main thrust of the article is about the fact that the very early Easter this year has screwed up British families' holiday plans, but it also includes this delicious formula, showing how Easter is calculated:
((19*t+u-w-(u-(u+8)\25)+1)\3)+15)mod30)+(32+2*x+2*y-(19*t+u-w- (u-(u+8)\25)+1)\3)+15)mod30)-z)mod7)-7*(t+11*(19*t+u-w(u- (u+8)\25)+1)\3)+15)mod30)+22*(32+2*x+2*y-(19*t+u-w-(u- (u+8)\25)+1)\3)+15)mod30)-g)mod7)+114)\31
No, I don't know what the variables are, but if this is correct, it's pretty insanely complex regardless. This wikipedia article discusses the rules in broad strokes, and this long and detailed one actually gives the algorithms. (The formula above looks like a variation of the "Meeus/Jones/Butcher Gregorian algorithm".) *Surely* the entire concept of the date of Easter must have been invented by geeks, as a way to pass the time before the invention of the slide rule.

Footnote: he also sent along this picture, of the only mechanical watch in the world sophisticated enough to calculate the date of Easter. (Which, given how much high-end watchmakers love to put in every imaginable gadget, tells you something about how messy the problem is.)

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