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Nisan-years is an ancient calendar system used around Mesopotamia. Its beginning was from prehistorical era. Ever since Mesopotamia had historical writings, even before the First Babylonian dynasty of Hammurabi, its calendar used the Nisan-years.[1][2][3]

Nisan-years is a lunisolar calendar system, in which the lunar years and the solar years are synchronized by adding in an intercalary month in seven of nineteen years (called the Metonic cycle). Since a tropical year is 365.2422 days,[4] and a synodic month is averaged 29.53059 days,[5] in nineteen years the solar and the lunar calendars will only differ by about two hours, or 1 part in 80,000.

Nisan-years begin in the Spring season. Technically, its New Year's Day is the day after the New Moon closest to (within fifteen days before or after) the 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.


Nisan-years is often called the Jewish religious calendar, in contrast to Tishri-years, which is often called the Jewish civil calendar. The month of Nisan is important since it begins the Spring Feasts of Israel.

The way to determine whether or not an intercalary month should be added was by agricultural observation in Israel. If by the end of a Nisan-year barley did not grow spikes a month was added so that barley can be harvested in the month of Nisan.

Jewish tradition fixed Nisan 16, the second day after Passover (Nisan 15), as the wave offering or omer offering in Israel, when a portion of the harvested barley is dedicated to God as a Thanksgiving. The Torah, however, fixed it on the first day after the Shabbat (Leviticus 23:9-14).


Month Number Babylonian Name Jewish Name Canaanite Name Gregorian Months
First Nisanu Nisan Abib March–April
Second Aianu Iyyar Ziv April–May
Third Simanu Sivan May–June
Fourth Duzu Tammuz June–July
Fifth Abu Av July–August
Sixth Ululu Elul August–September
Seventh Tishritu Tishri Ethanim September–October
Eighth Arahsamnu Heshvan/Macheshvan Bul October–November
Ninth Kislimu Kislev November–December
Tenth Tebetu Tevet December–January
Eleventh Shabatu Shevat Tsakh January–February
Twelfth Addaru Adar February–March

The observation of the New Moon may be influenced by the weather condition, so the Rosh Chodesh may be delayed for one or two days. But over all the errors cancel each other, and the calendar system remains accurate.

The intercalary month could be a second Sixth Month (Ululu II), as often practiced in Mesopotamia, or a second Twelfth Month (Adar II, Adar Sheni, or ve-Adar) as consistently practices in Israel.[6]

See also[edit]


  1. ^ James B. Pritchard, ed. Ancient Near Eastern Texts Relating to the Old Testament (Princeton, NJ: Princeton University Press, 1969), 269-317.
  2. ^ D. J. Wiseman, Chronicles of Chaldean Kings (625-556 B.C.) in the British Museum (London: The Trustees of the British Museum, 1961).
  3. ^ Jack Finegan, Handbook of Biblical Chronology, rev ed. (Peabody MA: Hendrickson Publishers), 25-42.
  4. ^ Colin, Alister Ronan, Measurement of Time and Types of Calendars, from 'Calendar', in Encyclopædia Britannica, vol 3 (Chicago: Encyclopædia Britannica, Inc, 1984), 596
  5. ^ "Month" in Encyclopædia Britannica, vol VI (Chicago: Encyclopædia Britannica, Inc, 1986), 1024.
  6. ^ Richard A. Parker and Waldo H. Dubberstein, Babylonian Chronology, 626 B.C. - A.D. 75 (Providence, RI: Brown University Press, 1956)