On Thursday, November 28, 2013, the American holiday of Thanksgiving and the Jewish holiday of Hanukkah will converge (overlap). Hanukkah will begin at sundown on Wednesday, November 27 and at sundown on Thanksgiving day, the second day of Hanukkah will begin. The convergence happens because the Hebrew calendar reflects both the solar year and the phases of the moon; it can have 353–385 days. The Gregorian calendar has 365–366 days, depending on whether or not it is a leap year. Because the calendars are calculated differently, the dates of Hanukkah appear at a different time each year on the Gregorian calendar.
Some sources claim that this is the first Thanksgiving–Hanukkah convergence, but it’s not. In 1863, President Lincoln proclaimed a national day of Thanksgiving to be celebrated on the last Thursday of November, meaning it would fall in the date range of November 24–30. This made the Thanksgiving days of November 29, 1888 and November 30, 1899—which coincided with the first and fourth days of Hanukkah, respectively—later in the year than was possible after 1939, and this is possibly the source of the erroneous claims.
Thursday, November 28, 1918 was the first night of Hanukkah, meaning that a Thanksgiving–Hanukkah convergence occurred that year, but only a partial convergence, since Hanukkah begins at sundown. In other words, the first Hanukkah candle was lit at sundown on Thanksgiving day. A similar partial convergence will also occur on Thursday, November 27, 2070—Thanksgiving with Hanukkah beginning at sundown.
In 1939, there were five Thursdays in November and President Roosevelt changed the date of Thanksgiving to the fourth Thursday (the 23rd) to allow another week of shopping before Christmas. In 1940 and 1941, when November had four Thursdays, Roosevelt declared the third Thursday to be Thanksgiving (the 21st and the 20th, respectively). In late 1941, both houses of Congress passed a joint resolution declaring Thanksgiving be observed annually on the fourth Thursday of November, giving a range of November 22–28, the current Thanksgiving day.
The Jewish calendar and the Gregorian calendar drift out of sync with each other due to the differences in the number of days in the year. The Jewish calendar—created more than 2,000 years ago—has 12 months of roughly 30 days, a little more than 354 days in the year. This causes the Jewish year to move earlier and earlier in the Gregorian year. Since some Jewish holidays are tied to a specific season, the Jewish calendar adds a complete month in 7 out of every 19 years. This year is a leap year (the extra month will occur in 2014), so all the Jewish holidays are extra early on the Gregorian calendar. Next year, Hanukkah will be back in December.
After 2013, Thanksgiving will not appear completely within Hanukkah again until Thursday, November 28, 79811—that’s 77,798 years from now, in case you wanted to wait. And that assumes that there are still Americans and Jews at that time and that the Jewish calendar has not been revised.