## Archive for November 27, 2013

### The Math of Thanksgivukkah

I know it’s rare that Hanukkah and Thanksgiving coincide. But if one more person tells me that it’ll be another 70,000 years before this happens again, I’m gonna scream.

This may be the single dumbest statistic I’ve ever heard. Here’s why.

Consider some of the reasons that cause Hanukkah and Thanksgiving to coincide this year.

• Jews rely on the Shmuelian calendar for religious holidays, which is why Hanukkah seems to vary so greatly from year to year. It wouldn’t appear to vary quite so much if you followed the Shmuelian calendar, but if you’re like most of the world, you rely on the Gregorian calendar. (On the Shmuelian calendar, by contrast, it would seem that Thanksgiving varies a lot from year to year. For instance, Thanksgiving this year occurs on 25 Kislev, next year on 5 Kislev, in 2015 on 14 Kislev, and in 2016 on 23 Cheshvan.)
• The Shmuelian calendar has a 19-year cycle, while the Gregorian calendar has a (roughly) 7-year cycle. So you might expect that the calendars would coincide about every 133 years. And they sort of do. However, the last time that the first day of Hanukkah fell on November 28 was in 1861, two years before Abraham Lincoln declared Thanksgiving an official U.S. holiday in 1863.
• One year on Earth is approximately 365.25 days — but not exactly. In fact, it’s closer to 365.2422 days. That slight difference is about 11 minutes. Not a big deal, really, but over 400 years, the calendar would incur a discrepancy of about three days. That’s why Pope Gregory, in 1582, decreed that years divisible by 100 but not divisible by 400 would not be leap years. But Rav Shmuel, who organized his calendar in the first century, didn’t have access to such specific solar measurements, so the Shmuelian calendar does not make similar accommodations.

Put all that together and — voila! — an amazing coincidence.

Because the Shmuelian calendar gains one day on the Gregorian calendar every 165 years or so — see the third bullet point above — it’ll be tens of thousands of years before they coincide again.

But here’s the thing. It’ll never happen. Not a chance.

There are lots of reasons why not.

First, Thanksgiving has been around for 150 years, but there’s no reason to think it’ll last another 70,000 years any more than the Romans should have thought we’d still be celebrating Saturnalia today. Countries and empires come and go, and so do their traditions.

Second, smart money says that when the Shmuelian calendar gets far enough out of whack that Passover no longer occurs in spring, there will be an adjustment. Or maybe there’ll be an adjustment to the Gregorian calendar first, for as yet unknown reasons. Or perhaps an entirely new calendar will appear on the scene. Who knows?

Third, zombies. Just sayin’.

Dr. Joel Hoffman gives a more detailed and eloquent description of Why Hanukkah and Thanksgiving Will Never Again Coincide over at Huffington Post.

co·in·cide
verb
1.  what you should do when it starts to rain

Speaking of things that coincide…

Parallel lines meet at infinity — which must make infinity a very noisy place!

An unfortunate coincidence…

The grad student stood up in his cubicle and shouted, “Why do things that happen to dumb people keep happening to me?”

And a funny coincidence…

After a long day of teaching, grading papers, and doing research for a paper, a mathematician headed to the pub where he was supposed to meet his wife. Seeing her across the bar, he walked up behind her, spun her stool around, and kissed her on the lips. She pushed him away violently, at which point he realized the woman wasn’t his wife.

“I’m very sorry,” he said. “I thought you were my wife. You look exactly like her.”

“You rotten, good-for-nothing son-of-a-bitch,” she said, and slapped him across the face.

“Funny,” he said. “You talk like her, too.”

The Math Jokes 4 Mathy Folks blog is an online extension to the book Math Jokes 4 Mathy Folks. The blog contains jokes submitted by readers, new jokes discovered by the author, details about speaking appearances and workshops, and other random bits of information that might be interesting to the strange folks who like math jokes.

## MJ4MF (offline version)

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