Nisan-years

Nisan-years is an ancient calendar system used around Mesopotamia. Its area of usage covers Elam, Persia, Media, Syria and Israel/Judea. Its beginning was from prehistorical era. Ever since Mesopotamia had historical writings, even before the Old Babylonian Empire of Hammurabi, its calendar used the Nisan-years.

Nisan-years is often called the Jewish Religious Calendar, in contrast to Tishri-years, which is often called the Jewish Civil Calendar.

Nisan-years belongs to the Lunisolar calendar system, in which the lunar years and the solar years are synchronized by adding in an intercalary month in a leap year. Three ancient civilizations (Babylonia, China, and Israel) knew that by adding in seven intercalary months in nineteen years (called a Small Mahzor in the Jewish Talmudic Calendar, and the Metonic Cycle in non-Jewish context), the solar and the lunar years are basically synchronized. Since a tropical year is 365.2422 days, and a synodic month is averaged 29.53059 days, in nineteen years the solar and the lunar calendars will only differ by about two hours, or 1 part in 80,000.

Nisan-years begins from the Spring season. Technically, its New Years Day is the day after the New Moon closest to (within fifteen days before or after) the Vernal Equinox (Spring Equinox, when the day and the night is of equal length, set at March 21 in the Gregorian Calendar). It begins the first month, named Nisanu/Nisan/Abib. The month of Nisan is important since it begins the Spring Feasts of Israel.

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