Once and For All

Do do do, dusting off the cobwebs, couple of tumbleweeds, aaanndd... we're back. Rorry for the bear bit. (For "rorry," refer to Jetson, Astro. And by bear bit, I mean that I am sorry for the big paws, erm, pause.) Anyway, I figured I'd just turn over the ol' engine just to keep the wheels of this well-oiled machine a-tranglin'. I don't really have anything important to say, but since I'm one-dimensional, and I like to go out of my way to appear even smarter than I actually am, I'm going to jot down the Doomsday Calendar method so that people don't keep asking me how it's done. For those of you who are unfamiliar with my brilliance (read: for those of you who have never eaten a Shabbat meal with me), one of my many talents is the ability to determine the day of the week for any date. I can usually figure this out in roughly five seconds. Pay close attention; here's how it works:

1. This is called the Doomsday Calendar method, so for our purposes, "Doomsday" is defined as the last day of February in any given calendar year, be it the 28th or 29th. The first step is to determine what day of the week the Doomsday is for the year in question. This requires some memorization: The Doomsday for every century year, e.g. 400, 1900, 3000, can only be Sunday, Tuesday, Wednesday, or Friday. For argument's sake, let's use the year 1900. The Doomsday for 1900 is Wednesday. Going backwards in centuries, the Doomsday for 1800 is Friday, for 1700 it's Sunday, for 1600 it's Tuesday, and for 1500 it's back to Wednesday. The cycle continues like this, with those four days in exactly that order as you go backwards in time.

2. Now we must determine the Doomsday for a specific year in that century. Here's how we do it. Firstly, we know that there are 365 days in a non-leap year. Just to use some mathematical terminology for a moment, when you divide 365 by seven you get 52 with a remainder of 1. Or, in math-talk: 365 modulo 7 = 1. Another words, the year is exactly 52 weeks and one day long, az the same calendar date next year will be exactly one day of the week later. For example, if the Doomsday of 1900 is Wednesday, then the Doomsday for 1901 is Thursday. Obviously, in a leap year you would gain two days, so 1902 is Friday, 1903 is Saturday, and 1904 is Monday. Good.

3. But let's say you wanted to figure out the Doomsday for my birth year, 1982. It's extremely tedious to have to add 82 days plus 20 leap years onto the Wednesday from 1900. Az, in order to make it easier, we divide everything by twelve. Why twelve you ask? Listen closely: in twelve years you would gain one day for each of the twelve years plus three additional days for the three leap years contained in those twelve years. Az in twelve years you actually gain 15 days, which is really just two weeks and one day, which for our purposes is just one weekday. Just like tomorrow is Thursday, two weeks and one day from today is also Thursday. For example, the Doomsday for the year 1972, is just six days after the Doomsday for 1900, because 72 divided by twelve is six. So the Doomsday for 1972 is six days after Wednesday, or just Tuesday.

4. Now we need to deal with the remainders, because not all years are divisible by twelve. Let's continue using 1982. To determine the Doomsday for the year 1982, we need to divide 82 by twelve and take note of the remainder. Az 82 divided by twelve is six with a remainder of ten (82 mod 12 = 10). Now, for the ten remaining years we need to add ten more days, and in those ten years there are two leap years, so we need to add two more days. To sum up: for 1982 we add SIX days plus TEN days plus TWO days (Six because 82/12 = 6, 10 because it's the remainder, and 2 because there are 2 leap years in 10 years). Now, six plus ten plus two equals 18. Az to determine the Doomsday for the year 1982, we must add 18 days to the Doomsday of 1900, which is Wednesday. Az the Doomsday for 1982 is 18 days after Wednesday, or just Sunday. Great, that's the hard part.

5. Now that we know the Doomsday for our year, we need to determine the day of the week for any other date in that year. Here's how we do it: all you need to do is remember certain key dates. There are many easy-to-remember dates throughout the year that are the same day of the week as the Doomsday: 4/4, 6/6, 8/8, 10/10, and 12/12 are all the same day of the week as the last day of February. Additionally, for the odd months: 5/9, 9/5, 7/11 and 11/7. Finally, July 4th and Halloween are also the same day as the Doomsday. For example, if the Doomsday is Sunday, then April 9th is Friday, because it's five days after 4/4. November 25th is Thursday, because it's two weeks and four days after 11/7. Great, we're done.

Just to leave you with an arbitrary example, let's see what day of the week the Declaration of Independence was signed:

1. The Doomsday for 1700 is Sunday.
2. 76 divided by twelve is six remainder four, so you add six plus four plus one, or eleven days to Sunday, so the Doomsday for 1776 is Thursday.
3. July 4th is the same day of the week as February 29th 1776, so America declared its independence on a Thursday.

If anyone has any questions, fire them over; I'll be sure to correct your spelling and grammar, I mean answer them.