## When Is Easter?

Easter is my favorite holiday, because of the bizarre way in which its date is determined. When is Easter? Here is how you can answer that question.

Divide the year by 19, obtaining a remainder (0 through 18). Add one to the remainder, giving you the Golden Number for that year (1 through 19).

From the Golden Number, you can determine when the Paschal Moon (or Paschal Full Moon) is. This Paschal Moon has nothing to do with the real moon. It is just a date, after the first day of Spring (approximately March 21), which you can determine from this table:

 # date # date # date # date 1 Apr. 14 6 Apr. 18 11 Mar. 25 16 Mar. 30 2 Apr. 3 7 Apr. 8 12 Apr. 13 17 Apr. 17 3 Mar. 23 8 Mar. 28 13 Apr. 2 18 Apr. 7 4 Apr. 11 9 Apr. 16 14 Mar. 22 19 Mar. 27 5 Mar. 31 10 Apr. 5 15 Apr. 10

Easter is the next Sunday, after this Paschal Moon date. In other words, if the Paschal Moon is a Sunday, then Easter is the next Sunday.

Note: You can figure out the dates of the Paschal Moon table, like this. Consider all of the dates from March 22 through April 20, a loop. In this loop, March 22 is the day after April 20. This is modular arithmetic, by the way. In the table, April 14 is date #1. Date #2 is eleven days earlier. Date #3 is eleven days earlier than that. Date #4 is eleven days before date #3, except that you have to use this loop of days. All 19 days of the table are determined in the same way, except that if the date is April 18 or April 19, you subtract one more day (April 18 becomes April 17, and April 19 becomes April 18).

Note: Above, I said that the Paschal Moon has nothing to do with the real moon. It comes from a fictitious moon which moves around the earth in a more orderly fashion than the real moon does. The only similarity between this fictitious moon and the real one is that they both orbit the earth in approximately the same length of time.

Addendum: I have been informed that more than one reference book (including The New York Public Library's Book of Answers and The New Columbia Encyclopedia) uses the term "full moon" instead of "Pashal Moon." They are absolutely wrong. The full moon which is used is not a real full moon. It occurs on a different day, usually. No book is free from errors. This year (1999), the Pashal Moon occurs on March 31. By coincidence, this happens to be the day of a real full moon. That ought to cause some confusion.