Chrismukkah, the portmanteau holiday made famous by The O.C., is rapidly approaching. Hanukkah begins Saturday at sundown, and Christmas is Sunday. Just how rare is this two-for-one holiday?

Chrismukkah actually happens pretty frequently. (It helps that Hanukkah lasts eight days.) The two holidays coincided with one another 31 times in the last century. The last time was in 2011, and it happens again in 2019. This year, the first Hanukkah candle is lit on Christmas eve and the holiday lasts through New Year’s Day.

The name for the holiday was coined back in 2003 on an episode of The O.C., when Seth Cohen introduces the holiday as a way to celebrate with both his Jewish father and Protestant mother. But families have been celebrating both Christmas and Hanukkah together for years, in part because of the rise in inter-faith marriages. For some Jewish families, Christmas is celebrated as a secular holiday. Plus, having a Christmas tree and a menorah is a great way to maximize the festive vibe.

chrismukkah
Chrismukkah!

Both Christmas and Hanukkah land on the same date every year, but they don’t always line up because those dates are on different calendars. Christmas is on the 25th day of December on the Gregorian calendar, and Hanukkah is on the 25th day of Kislev on the Hebrew calendar.

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The Gregorian calendar is a solar calendar, so its length is determined by the number of days it takes Earth to make a full trip around the sun. The Hebrew calendar is a hybrid lunar-solar calendar. Most of the calendar is determined by the lunar cycle, with adjustments from the solar cycle. Neither calendar precisely matches the exact time in a year — 365 days, 5 hours, 48 minutes, and 46 seconds — so they both have to add in extra time, like leap days, to compensate. The Hebrew calendar adjusts more often than the Gregorian calendar, so Hanukkah seems to jump around.

Both the Gregorian and Hebrew calendars are slowly shifting (even with leap year and leap second adjustments), so yearly events like solstices are moving around. Eventually, thousands of years from now, the summer solstice, currently in late June, will be in May, and Sukkot, a Jewish holiday celebrating the fall harvest, won’t actually take place in the fall.

chrismukkah sweeps the nation
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Hanukkah occasionally overlaps with other holidays, too. Back in 2013, we had Thanksgivukkah, which won’t happen again until 2070. Hanukkah overlaps with New Year’s Eve and Day next in 2025. But another Chrismukkah is only three years away, so there’s something to look forward to after this year’s celebration.

Photos via Giphy (1, 2, 3)