Image: This is a model of the oldest known Jewish calendar, known as the Gezer Calendar, which was found at this site, Tel Gezer. Some date it as early as the 10th c. BCE. Photo by Mujadara via Wikimedia.
שָׁמוֹר֙ אֶת־חֹ֣דֶשׁ הָאָבִ֔יב וְעָשִׂ֣יתָ פֶּ֔סַח לַיהוָ֖ה אֱלֹהֶ֑יךָ כִּ֞י בְּחֹ֣דֶשׁ הָֽאָבִ֗יב הוֹצִ֨יאֲךָ֜ יְהוָ֧ה אֱלֹהֶ֛יךָ מִמִּצְרַ֖יִם לָֽיְלָה׃Deuteronomy 16:1
Observe the month of Aviv and offer a Passover sacrifice to the LORD your God, for it was in the month of Aviv, at night, that the LORD your God freed you from Egypt.
These words fall near the end of Parashat Re’eh, and they are confusing to many people who know a bit about the Jewish calendar. One of them might well ask, “Rabbi, isn’t Passover in the month of Nisan? What’s this about Aviv? There is no month of Aviv in my calendar at home.”
Absolutely right! That’s because the Jewish calendar we are familiar with was still a work in progress when the book of Deuteronomy was written. We have had the current Jewish calendar since sometime prior to 450 BCE, when the Jews brought it back with them from Babylon. In the chart below, the modern Jewish name of the month is listed first, the older Biblical name is listed in parentheses, and I have listed a few major holidays underlined.
- Tishri – (Ethanim in 1 Kings 8:2) Rosh Hashanah, Yom Kippur, Sukkot
- Cheshvan – (Bul in 1 Kings 6:38)
- Kislev – (“the ninth month”) Chanukah
- Tevet – (“the tenth month”)
- Shvat – (“the eleventh month”)
- Adar – (“the twelfth month”) Purim
- Nisan – (Aviv in Exodus 13:4, 23:15, 34:8, and Deut. 16.1) Passover
- Iyyar – (Ziv in 1 Kings 6:1, 6:37)
- Sivan – (“the third month”) Shavuot
- Tammuz – (“the fourth month”)
- Av – (“the fifth month”)
- Elul – (“the sixth month”)
As you see above, the Jewish calendar differs from the Biblical calendar in a couple of ways: (1) The names of the months are different and (2) the new year is counted from a different month. In Biblical times the month of Nisan was the first month of the year. After the return from Babylon, the Jews counted the year from the first of Tishri, and called Rosh Chodesh Tishri “Rosh Hashanah,” [Head of the Year,] a term that does not appear in Torah.
What happened? As always happens when our community lives in a place for a while, they took on and Judaized some local ideas. In this case, they took on several month-names similar to the names of the Babylonian months.
As for the matter of the date of the new year, that took on a very interesting wrinkle. The opening verse of Mishnah Rosh Hashanah informs us:
There are four new years:The first of Nisan is the new year for kings and for festivals. The first of Elul is the new year for the tithe of beasts. Rabbi Elazar and Rabbi Shimon say: the first of Tishri. The first of Tishri is the new year for years, for shmitta and jubilee years, for planting and for [tithe of] vegetables. The first of Shevat is the new year for trees, according to the words of Bet Shammai. Bet Hillel says: on the fifteenth of that month.Mishnah Rosh Hashanah 1:1
FOUR New Years? That’s right, there are four Jewish New Years. Rosh Hashanah, the first of Tishri, is the new year for years (meaning, that is the day we get a new number for the year) and for other laws that apply only inside the land of Israel. There are also three other new years, which I explain in Four New Years Every Year?! We don’t know for sure how or why the first month switched from Nisan to Tishri, but Dr. Uri Gabbay writes about the possibilities in Babylonian Rosh Hashanah.
If you are curious as to the numbering of Jewish years, read The Jewish Calendar: Why 5779? If you are looking for an explanation of Jewish leap years and the doubling of Adar, see Why 2 Months of Adar?