The Hebrew calendar is a lunisolar calendar made up of solar years, lunar months, and seven-day weeks beginning on Sunday and ending on Saturday, the Shabbat day. As a starting point, he refers to Genesis (“Bereshit”: “beginning”), the first book of the Bible, whose beginning he corresponds to the year -3761 of the Gregorian (proleptic) calendar.
Today January 21, 2022 is Shevat 19, 5782 in the Hebrew calendar.
While the religious year began in the spring, in the month of Abib or Nisan, the biblical account reports that before that the Israelites began the year in the fall. In fact, a double calendar was used: the religious and the civil or agricultural (Ex 23:16; 34:22; Le 23:34; Dt 16:13). After the Exile, the 1st of Tishri, in the second half of the year, marked the beginning of the civil year, and the Jewish New Year or Rosh ha-Shana (“head of the year”) is always celebrated in that date.
Each new month begins with the new moon. The calendar is aligned with a solar year and with lunations of 29 days 12 hours 44 minutes and 3 seconds + ⅓ of a second and alternates months of twenty-nine and thirty days. A lunar year of twelve months is 354.367 days. As a solar year is 365.2468 days, nearly eleven days are lost each year. To make up for these lost days, the years successively comprise twelve or thirteen lunar months, according to a metonic cycle.
A letter from a Gamaliel—either Gamaliel the Elder or Gamaliel of Yavne—testifies that until at least the 1st or 2nd century AD the Metonic cycle was not in effect and that the timing of the addition of a extra month (embolism) in order to make the calendar year coincide as well as possible with the tropical year, belonged to the Sanhedrin.[insufficient source] According to tradition, Yohanan ben Zakkai received permission from the Emperor Vespasian to establish an academy in the city of Yabneh (Jamnia), after leaving Jerusalem, during the siege of the city. “By this coup de force consisting in bringing together an assembly of the most famous Pharisee sages of his time and taking over its presidency, Rabban Yohanan ben Zakkai (died ca. 80-85) succeeded, in the eyes of the members of the rabbinical movement, in to replace the ancient authority of the high priest, that of the priesthood and that of the Sanhedrin. He had previously requested authorization from the Roman authorities, who must have “appreciated this takeover, even limited, of part of the Judeans by the rabbinical movement. »
Yohanan ben Zakkaï takes nine decrees, takkanot (“improvements”), “which are presented as essential for worship, because they concern the dates of auspicious days, fasted days, feast days and the beginnings of months. This task previously fell to the high priest and the Sanhedrin, but the destruction of the Temple in Jerusalem—and probably the Roman ban—left these institutions vacant. This recovery of the liturgical calendar at the expense of the priesthood probably met with opposition from priests, scribes and notables in general. However, because of the unquestionable authority that Yochanan enjoyed in the Pharisee movement and because these were the essential measures that had to be taken at that time for the continuation of worship outside Jerusalem, these measures probably found some legitimacy. “Especially since the liturgical calendar is still one of the keys to legitimacy in religious matters, even if the authority of these measures has probably not gone beyond the borders of the rabbinical movement. »
Until the 4th century, it was the rabbinical authorities attached to the court of the patriarch established in the land of Israel who fixed the dates of the calendar.