Thanksgiving is the fourth Thursday in November. This year Thanksgiving is on November 28th, which happens to be the first day of Hanukkah (the first "night" of Hanukkah is the night before).
As it happens, November 28th is the latest Thanksgiving can be and the earliest Hanukkah can be.
The Gregorian calendar has Thanksgiving hitting the same date once every 7 years. The Jewish calendar, on the other hand, repeats on a 19 year cycle. 7x19 = 133.
So Thanksgivukkah should happen roughly every 133 years, right?
"Looking back, this is approximately correct - the last time it would have happened is 1861. However, Thanksgiving was only formally established by President Lincoln in 1863," Mizrahi writes. (Caveat: Until 1942 Thanksgiving was the "last" Thursday in November instead of the "fourth," so Thanksgivukkah technically happened once before, in 1888).
So will it happen again?
Because the Jewish calendar is very slowly getting out of sync with the solar calendar, at a rate of 4 days per 1000 years (not bad for a many centuries old calendar!) This means that while presently Hanukkah can be as early as 11/28, over the years the calendar will drift forward, such that the earliest Hanukkah can be is 11/29. The last time Hanukkah falls on 11/28 is 2146 (which happens to be a Monday). Therefore, 2013 is the only time Hanukkah will ever overlap with Thanksgiving.
BUT: If the Jewish calendar is never modified, then it will slowly eek forward through the Gregorian calendar and eventually loop completely around.
So, Hanukkah will again fall on Thursday, November 28th in the year 79811. Jewish law mandates that Passover take place in the spring, so it's likely the calendar intelligentsia will make a change before things get out of hand. Maybe daylight savings time will help, we're not sure.
Also, "For the real nitpickers, it is also true that it is not necessary for Hanukkah to to get all the way back to Thursday, November 28 to hit Thanksgiving again. The actual next time the two will overlap is when the LAST day of Hanukkah falls on the earliest Thanksgiving date, which is in 76695 or 79811.