By Katie Reilly
Passover begins this Friday, later than usual and almost a month after the Christian celebration of Easter, which fell on March 27 this year.
The Jewish holiday falls on the same day in the Jewish calendar every year, but because that calendar is based on the lunar cycle, the celebration of Passover varies according to the Gregorian calendar.
In order to keep the Hebrew year aligned with the seasons of the solar calendar, the Jewish calendar regularly includes leap years that add an extra month—and 2016 is one of them. Leap years occur seven times in a 19-year cycle, and this year pushed Passover into late April.
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Write to Katie Reilly at Katie.Reilly@time.com