Sunday Nibble #69: Let’s get doomed!


One hundred years ago today, on July 11, 1921, William Howard Taft was sworn in as the 10th Chief Justice of the U.S. Supreme Court, becoming the first and only person to hold both that office and the Presidency.

He became Chief Justice eight years after leaving the presidency, but was most likely a one-term President because Teddy Roosevelt ran as a third-party candidate, splitting the vote, so that noted racist Woodrow Wilson was elected instead.

Taft was probably the fattest U.S. President ever — although that’s arguable — and was also the namesake for several schools, including my own High School.

Taft’s elevation to Chief Justice on July 11 is commemorated by Free Slurpee Day. Okay, not really. July 11 is so-designated because the date is 7/11 and it’s a publicity stunt by the chain of convenience stores that is actually named 7-Eleven.

Originally called “Tote’m,” the name was changed to 7-Eleven in 1946 to reflect the new extended hours, from 7:00 a.m. to 11:00 p.m. Once the stores started staying open 24/7/365, the name did not change again.

Of course, the numbers 7 and 11 are naturally associated for a couple of reasons. One is the obvious: In English, they rhyme. But they’re also connected in the game of craps, in which they can either make you win or lose instantly, depending on what number you’re rolling for.

Remember that pair as well as 9 to 5 — as in the working hours that no one works any more or the old movie — and you’re most of the way to being able to say what day of the week any day of the year falls on almost instantly without looking at a calendar.

It’s called the Doomsday Rule, and while there’s an extended method wherein you can pretty quickly determine in your head what day of the week any day in any given year fell, it’s generally only useful for dealing with the current year, or maybe just the one before or after.

So the convenient cheat is this: take a look at the calendar, and remember what day of the week the last day of January falls on. This is considered the year’s “Doomsday” — and don’t blame me for the name.

As long as it’s not a leap year, then that day is consistent, and for February and March it will always be the 7th of the month. If it is a leap year, it only applies to January and February, then jumps ahead a day for March and the rest of the year.

So, in other words, if a year’s Doomsday is Tuesday and it’s not a leap year, then January 31, and February and March 7 will be Tuesdays. If it is a leap year, then January 31 and February 7 will be Tuesdays, while March 7 and all successive Doomsdays will be on Wednesday.

But let’s start with 2021, which is not a leap year.

January 31, 2021 was a Sunday. You may have noticed that today, July 11, 2021, is also a Sunday. That’s not a coincidence, and it’s where the 7/11 and 9/5 rules come into play. We already know January and March. For all other odd numbered months, then they work in pairs like that. July 11 and November 7 will both be Doomsdays. So will May 9 and September 5 — 7/11, 11/7, 5/9, and 9/5.

Reverse these if you’re British, of course. Or don’t actually, because they still work, just out of order.

Now, as for the rest of the even months except February, the month number very conveniently works out to be its Doomsday. For this year, April 4 was a Sunday, as were June 6. So will be August 8, October 10, and December 12.

This does some interesting things to holidays. Pi Day (March 14), July 4, and Halloween will always fall on a Doomsday — 3/7 plus a week, 7/11 minus a week and 10/10 plus three weeks. Christmas and New Year’s Day will always happen the day before Doomsday.

Now, if the following year is not a leap year, then its Doomsday will be one day later. For example, January 31, 2022 will be a Monday, 2023 will be a Tuesday, and 2024 will be a Wednesday for the first two months before jumping to Wednesday.

When I worked in actual jobs in offices with people, I used to use this trick all the time whenever someone wondered what day of the week a date was. While people scrambled for their phones, I’d just calmly announce something like, “April 15 is a Wednesday this year” or “the 4th of July is on a Saturday.”

And then people would check, see that I was right, and just nod and be amazed. So it’s a good superpower to have, and you can even turn it into a party trick — especially if you learn the full method to account for any given year.

Except that the full method is just ridiculous. But there is a modified “odd + eleven” method that seems to work brilliantly, and all you need to remember is the “anchor day” for the century. For the 21st century, for example, it’s Tuesday.

TL;DR version of the “odd + eleven,” take the two-digit year. If it’s odd, add 11. If it’s even, don’t. Divide that result by two. Repeat one more time — add 11 if odd, nothing if even, then divide by seven and take the remainder (“modulo 7,” if you know the term.)

Subtract this number from 7, then count up that many days from the century’s anchor year. Ta-da!

So, for 2021, it works like this. The anchor day is Tuesday. The year 21 is odd, so add 11 to get 32. Divide by 2 to get 16, and add nothing since it’s now even. Divided 16 by seven. The answer it 2, with a remainder of 2. Subtract that from 7 to get 5.

Now count up five days from Tuesday and you get… Sunday, which we’ve already seen is the actual Doomsday.

So next time you want to impress people at parties, tell them you can guess which day of the week they were born on just by knowing their birthdates, and you’re sure to make a few new friends. You’re welcome!

Oh, in case you’re wondering — Taft was sworn in on a Monday, and I did not look that up.

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