Here’s Why Christmas and First Night of Hanukkah Overlap This Year for the First Time Since 1978

Seth Rogen, Joseph Gordon-Levitt and Anthony Mackie star in Columbia Pictures' "The Night Before." Columbia Pictures

The only thing better than one holiday is two holidays, right? Christmas and the first night of Hanukkah will overlap this year for the first time since 1978, and experts believe the rare occurrence will happen more often in the future.

Hanukkah begins at sundown on Christmas Eve (December 24) this year — and ends on New Year's Day (January 1) — because of the difference between the civil, solar Gregorian calendar and the lunar Jewish calendar. A solar year lasts 365 and a quarter days, while a lunar year lasts approximately 354 days, requiring a leap or "intercalary" month, according to Time.

In 2016, the intercalary month was added to the Hebrew calendar and started in late February, causing Hanukkah to appear later on the Gregorian calendar. The Jewish calendar is presently on the year 5777, as Jews count years from Creation (3761/3760 BCE).

Calendar expert Philipp Nothaft, who is a fellow at All Souls College at the University of Oxford, told Time that observers can expect a Christmas-Hanukkah overlap more often because of the difference between the two calendars. Nothaft told the news outlet that Hanukkah "will eventually be associated with December and January," rather than the usual November or December, causing a more frequent overlap.

The December holidays haven't overlapped in nearly four decades, and will not overlap again until 2027. Sacha Stern, a Rabbinic Judaism professor at University College London, told Time that the occurrence currently happens roughly every 30 years.

Merry Chrismukkah!

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