Rosh Hashanah is the birthday of the universe, the day G‑d created Adam and Eve, and it’s celebrated as the Jewish New Year. Rosh Hashanah 5785 begins at sundown on the eve of Tishrei 1 (Oct. 2, 2024) and ends after nightfall on Tishrei 2 (Oct. 4, 2024). (See here for special info for this year.)
The central observance of Rosh Hashanah is blowing the shofar (ram’s horn) on both mornings of the holiday (except on Shabbat), which is normally done in synagogue as part of the day’s services.
Rosh Hashanah feasts traditionally include round challah bread (studded with raisins) and apples dipped in honey, as well as other foods that symbolize our wishes for a sweet year.
Other Rosh Hashanah observances include candle lighting in the evenings and desisting from creative work.
Together with Yom Kippur (which follows 10 days later), it is part of the Yamim Nora'im (Days of Awe, or High Holidays).
