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Friday, March 21, 2008

something for easter eggheads

just in case you're one of the few who still hasn't heard, let me be the first to break it to you:

easter sunday is THIS SUNDAY, march 23rd.

and yes, it's really early this year. how did that happen, you ask?

basically, it boils down to this: after much wheeling and dealing among christian church heads many, many centuries ago, they came up with the following general rule (with some exceptions, of course):

Easter falls on the first Sunday following the first ecclesiastical full moon that occurs on or after the day of the vernal equinox, where this particular ecclesiastical full moon is the 14th day of a tabular lunation (new moon), and the vernal equinox is fixed as March 21. This means that Easter can never occur before March 22 or later than April 25.

so since today is the first full moon after the vernal equinox, it then follows that this sunday is easter sunday.

however, if you're a math geek (like me), a fairly straightforward algorithm can be used to calculate the exact date of this moveable feast.

ready? here it is:

a = Y mod 19
b = Y mod 4
c = Y mod 7
d = (19a + M) mod 30
e = (2b + 4c + 6d + N) mod 7

where Y is the year and the values for M and N are determined as follows:
if Y is 1900 through 2099, M=24 and N=5
if Y is 2100 through 2199, M=24 and N=6
if Y is 2200 through 2299, M=25 and N=0

finally, after you've solved for a through e, if d + e is less than 10, then easter falls on march x (where x = d + e + 22). otherwise, easter falls on april x (where x = d + 3 - 9).

and if that weren't complicated enough, there's more...

if the resulting date is april 26th (which is outside the valid range), easter is moved back a week to april 19th. and if the result is april 25th (which is valid) but d = 28, e = 6, and a is greater than 10, the date should be changed to april 18th. don't ask me why.

so just for fun, let's solve for easter 2008:

a = 2008 mod 19 = 13
b = 2008 mod 4 = 0
c = 2008 mod 7 = 6
d = [(19 x 13) + 24] mod 30 = 271 mod 30 = 1
e = [(2 x 0) + (4 x 6) + (6 x 1) + 5] mod 7 = 35 mod 7 = 0

since d + e = 1 + 0 = 1 which is less than 10, then easter in 2008 falls on march x, where x = 1 + 0 + 22 = 23. ta da... march 23rd!

and to throw in some trivia you can impress your friends with, check out this entry from earthsky.org:

This upcoming Easter on March 23 will be the earliest date for Easter in all of the 21st century.
The last time Easter fell on March 23 was in 1913, and the next time won’t be till 2160.
The earliest possible date for Easter is March 22. This last happened in 1818 and won’t happen again until 2285.
The latest possible date for Easter is April 25, which happened most recently in 1943 and will happen next in 2038.


anyway, the point of this exercise wasn't to find out if you were paying attention in math class; rather, it's a heads-up:

some yoga studios will have modified schedules and/or special events this weekend, so before you show up for class on saturday or sunday, be sure to check ahead!

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