Nov. 28 will be a busy day for Jewish Americans this year, but they’d better enjoy every minute of it because the unusual event taking place that day won’t happen again for another 77,798 years — give or take a few millennia.
What is this strange and wondrous occurrence? On Nov. 28, for the first time since 1888 and the last time in any of our lifetimes, the American holiday of Thanksgiving and the Jewish holiday of Hanukkah arrive on the same day.
Of course, Hanukkah is actually eight days long, and the Jewish “day” starts at sundown. So technically the “Festival of Lights” begins the evening of November 27 when Jews celebrate by lighting the first of eight candles. But the first full day of Hanukkah — defined as midnight to midnight — coincides with Thanksgiving.
The date of Thanksgiving changes every year because the holiday is set for the fourth Thursday of November. The date was declared a national holiday by President Abraham Lincoln in 1863. If he had gotten around to it a couple of years earlier, the first Hanukkah-Thanksgiving convergence would have happened in 1861.
Actually, when Lincoln declared Thanksgiving a holiday, he set it for the final Thursday in November. It wasn’t until 1942 that it was specifically designated as the “fourth” Thursday.
A post by math blogger Jonathan Mizrahi figured all of this out back in January. Mathematically, the Gregorian calendar — the one used around the modern world — and the Jewish calendar should align the dates of Hanukkah and Thanksgiving every 133 years.
But there’s a catch. The Jewish calendar is slowly creeping away from its Gregorian counterpart, losing four days every 1,000 years. Because of this date-drift, the next time the two holidays hit the same date will be in the year 79,811, according to Mizarhi’s calculations.
That assumes that Jews do not modify their calendar at any time over the next 79 millenia. But they probably will. By Jewish law, the Passover holiday must take place in the springtime. As the calendar drifts, after a while (a very long while) that will no longer be the case. So the calendar will need to be modified sometime in the next 80,000 years or so.
Sources: Jonathan Mizrahi, Business Insider, USA Today