The Jewish Calendar is a lunisolar calendar used primarily for religious observances in Judaism. It consists of 12 months in a common year and 13 months in a leap year, which occurs seven times in a 19-year cycle. Each month begins with the sighting of the new moon, making it different from the Gregorian calendar, which is purely solar. The months of the Jewish Calendar include Nisan, Iyar, Sivan, Tammuz, Av, Elul, Tishrei, Cheshvan, Kislev, Tevet, Shevat, and Adar. Important holidays, such as Passover and Yom Kippur, are observed according to this