Technical Notes on the Great "Thannukahsgiving" Convergence This Year

Most of my American readers probably know this already, but my foreign readers (even my Canadian readers who celebrate Thanksgiving in mid-October and on a Monday to boot for reasons understood only north of the 49th parallel) may not be aware of it yet, but this year the US Thanksgiving holiday coincides with the first day of Hannukah. This has not happened since 1888 and this precise combination may or may not ever occur again in the foreseeable future depending on some variables. (Our present rules for dating Thanksgiving only date from 1942, and before that the variables were different. Under the present rules, even 1888 wouldn't count.)

As this post at chabad.com, in an explanation called "Chanukah and Thanksgiving: A Brief History,"
puts it: 

Question:

Is it true that . . .

• Thanksgiving falls on Chanukah this year,
• it’s never happened before, and
• it will never happen again?

Answer:

Yes, no, and maybe.

Now, Chabad is a Lubavitcher  Hasidic ultra-Orthodox Jewish movement, and my Irish Catholic self is not about to argue with them on the finer points of the Jewish calendar. Nor do I think more liberal Jewish movements would disagree. and I know I should stay away from calendar issues. In 2012 I did a post called "Why are Eastern and Western Easter on Different Dates? Don't Expect to Figure it Out from this Post."

Despite the obvious caveat in the headline, I was taken to task in the comments, one beginning with

The Zonaras proviso is not a rule. It is an after-the-fact explanation for the inaccuracies of the Julian lunar calendar. If it were a rule, it would have precise mathematical content which would enter into the computation of Julian Easter. It has no such mathematical content.

And it went on from there. I have no doubt the commenter was right, and I will never try to sound authoritative about the Zonaras Proviso again. (Even if I still remembered what it was.) So I know I am risking abject humiliation if I pontificate about calendars, so I'm just going to assume the Chabad folks have the Jewish one more or less right (see another of their articles here and there are many others to be found around the Internet) and will talk more about the date of Thanksgiving. I'm fairly sure on that I can talk turkey.

I will throw in one clarification: The statement that this has not occurred since 1888 and cannot be certainly predicted in the coming thousands of years is technically true of the exact coincidence occurring tomorrow.when Thanksgiving exactly coincides with the first day of Hannukah. But Hannukah is an eight-day feast and Jewish religious days do not coincide with midnight-to-midnight Western days. Apparently, in 1899 Thanksgiving coincided with the fourth day of Hannukah, and in 1918 it coincided with the eve of Hannukah. Because Jewish days begin at sundown the night before and days are short in November, in 1918 the first candle could have been lighted before the turkey was carved. That coincidence is predicted to recur in 2070 and 2165, but there is no predicted recurrence of tomorrow's exact coinciding of Thanksgiving with the first day. Or so the Chabad folks say: complain to them if they're wrong; I couldn't even get the Zonaras Proviso right.

Thanksgiving also complicates matters. The date has moved around. In 1777 the Continental Congress proclaimed a Thanksgiving on December 18 after the victory of Saratoga. (December 18 is unthinkable today as it would leave only a week for Christmas shopping!) Various dates were celebrated thereafter.

Abraham Lincoln established the tradition of the last Thursday in November. But Thanksgiving still had to be proclaimed by a Presidential proclamation; it was not set in law. In 1939 Franklin D. Roosevelt used the fact that there were five Thursdays that November to proclaim it on the fourth Thursday instead of the last. With the country emerging from the Great Depression, Roosevelt hoped to extend the Christmas shopping season. In 1940 and 1941, each of which had the usual four Thursdays instead of five, Roosevelt declared Thanksgiving on the third Thursday.  His Republican opposition acted as if he'd moved Christmas to July; he was insulting the memory of Lincoln (Republicans still were proud of Lincoln then) and they dubbed the new date "Franksgiving."

Finally in 1942, Congress split the difference and passed a law making Thanksgiving the fourth Thursday of every November, which differs from the traditional date only when five Thursdays occur in the month. It was also the first legal codification of the date. A few states held out and Texas (always marching to a different drummer) celebrated the fifth Thursday as late as 1956 (accorfing to the Chabad calculations, giving it two more coincidences of Thanksgiving with the eve of Hannukah in 1945 and 1956).

To clarify, until 1942 Thanksgiving could occur as late as November 30 under certain circumstances. Since 1942 it cannot occur later than November 28, tomorrow's date.

Now the punchline: the only previous time tomorrow's exact coincidence of Thanksgiving with the first day of Hannukah happened, in 1888, it was on November 29, 1888, a date that would be impossible under the 1942 law!

So, unless the date of Thanksgiving changes again (retailers would probably welcome a longer shopping season: but the vagaries of the Jewish calendar mean Hannukah will occur later and later into the Gregorian year), enjoy tomorrow's "Thannukahsgiving" convergence: you (probably if the calendars don't change) will not gaze upon its (precise) like again.