Recreational math and Easter date calculation

My 6th grade Algebra text (which also happened to be the one that 9th graders used) had a piece of recreational math at the end of every chapter as a sort of entertainment and incentive to finish the chapter. I can't remember all of them but one that I do remember was one that claimed to be a mathematical computation for the date of Easter given any year between 1800 and 4000. I was fascinated enough with the computation rules (we call that an algorithm) that I ran the numbers for every year for which I could find the date of Easter. (Have I told you I was a little crazy about math?)

I've long since lost that algebra book (darn it) but recently found an algorithm that looks very much like the one in that text book. Ready...

This algorithm uses a mathematical operation called "mod" which results in a REMAINDER in a division operation NOT the quotient. With our modern calculators we sometimes forget what a remainder is. It works like this: x mod y = the remainder of x divided by y a whole number of times. That is, 10 mod 5 = 0 and 10 mod 3 = 1. 10 divided by 5 equals 2 with a 0 remainder. And 10 divided by 3 equals 3 with a remainder of 1. With the mod operation we don't care how many times y goes into x just the remainder after it goes a whole number of times.

Now here's the algorithm I promised:

Let Y = the year for which we want to know the date of Easter. Calculate
A = Y mod 4
B = Y mod 7
C = Y mod 19
D = (19C + 24) mod 30
E = (2A + 4B + 6D +5) mod 7
If (D + E) > 9 then Easter is the (D+E-9)th of April otherwise it is the (22 + D + E)th of March.

Let's try this with 2008
A = 2008 mod 4 = 0 (4 goes into 2008 502 time with a remainder of 0)
B = 2008 mod 7 = 6 (7 goes into 2008 286 times with a remainder of 6)
C = 2008 mod 19 = 13 (19 goes into 2008 .... oh, you get the idea)
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
D + E = 1 so Easter is the 22 + 1 + 0 or the 23rd of March.

If you have Microsoft Excel on your computer you can find an Excel version of this algorithm at

http://home.surewest.net/arnoldvl/resources/easter.xls

Here are some facts about when Easter occurs.

Easter this year will be on March 23, 2008. As you may know, Easter is always the first Sunday after the first full moon after the Spring Equinox which is March 20.

This dating of Easter is based on the lunar calendar that Hebrew people used to identify Passover, which is why it moves around on our Roman calendar. Here are a couple of facts which may interest you.

Based on the above, Easter can actually be one day earlier (March 22) but that is rare. This year is the earliest Easter any of us will ever see the rest of our lives. Only the most elderly of our population have ever seen it this early (95 years old or more). None of us has ever, or will ever, see it a day earlier.

Here are the facts:

The next time Easter will be this early (March 23) will be the year 2228 , 220 years from now. The last time it was this early was 1913. So if you're 95 or older, you are the only ones who were around for that. The next time it will be a day earlier, March 22, will be in the year 2285 , 277 years from now. The last time it was on March 22 was 1818. So, no one alive today has ever or will ever see it any earlier than this year, March 23, 2008.