Full moon full moon on 15 Nisan of the Hebrew calendar. The date of the Jewish Rosh Hashana and Sukkot festivals along with all other Jewish holidays are dependent on the dates of the new moons. In lunisolar calendars, an intercalary month occurs seven times in the 19 years of the Metonic cycle, or on average every 2.7 years (19/7). In the Hebrew Calendar this is noted with a periodic extra month of Adar in the early spring. In the modern system of "traditional" full moon names tied to the solstice and equinox points, a supernumerary full moon in such a period
Tishri-years the years from the Autumn season, around the Autumn Equinox (Gregorian September 22/23). The New Years Day of the Tishri-years is called "Rosh Hashanah" ("Head of the Year"); it begins the Fall Feasts of Israel. Tishri 1, however, is not determined directly by its relationship to the Autumn Equinox. It depends on the determination of Nisan 1, which is the day after the New Moon closest to the Spring Equinox (within fifteen days before or after). Tishri 1 is the first day of the seventh month. Although the month number is always counted from Nisan, in the Tishri-years, the year