How often does the first day of Hanukkah fall on Christmas?

This year, the first day of Hanukkah falls on Christmas Day, for the first time in nearly two decades.

In just over a century, the first day of Hanukkah, which begins at sundown, has coincided with Christmas Day four other times, the last instance in 2005. The two holidays also happened on the same day in 1959, 1921 and 1910.

The Hebrew calendar is different from the Gregorian calendar, which is the primary dating system of the Western world.

The Hebrew calendar is lunisolar, which means it uses the moon’s phases to determine dates. A new moon marks the beginning of each month. Getting through all the moon’s phases takes just under 30 days, and 12 months are about 354 days long. Every few years, an extra month is added to keep seasonal celebrations roughly at the same time each year.

The eight days and nights of Hanukkah are fixed, starting on the 25th day of Kislev, one of the months of the Hebrew calendar. However, because of the difference in year lengths, Hanukkah can occur any time from late November to late December on the Gregorian calendar.

The Gregorian calendar is a solar calendar determined by the movement of the sun. Christmas always falls on December 25 on the Gregorian calendar.

Although the two holidays orbit each other during the winter season, they have different origins.

Hanukkah, also known as the Celebration of Lights, is an eight-day holiday that marks the rededication of the Temple in Jerusalem in the 2nd century BC after Jewish fighters liberated it from occupying foreign forces.

Meanwhile, Christmas is a festival that celebrates the birth of Jesus Christ by many Christians and non-Christians worldwide.

Hanukkah stretches into January

Because of how late Hanukkah is occurring this year, the eight days of Hanukkah will stretch into January, also overlapping with the Gregorian calendar’s New Year.

While it’s been almost 20 years since the two holidays were aligned in this way, the wait will be shorter before it happens again.

After this year, the next time the first day of Hanukkah and Christmas overlap will be in 2035.