Start of month of Tevet on the Hebrew calendar. Tevet (טֵבֵת) is the 10th month of the Hebrew year, has 29 days, and corresponds to December or January on the Gregorian calendar. רֹאשׁ חוֹדֶשׁ, transliterated Rosh Chodesh or Rosh Hodesh, is a minor holiday that occurs at the beginning of every month in the Hebrew calendar. It is marked by the birth of a new moon
Torah: Numbers 28:1-15, 7:42-47
https://hebcal.com/h/rosh-chodesh-tevet-2031?uc=ical-jewish-holidays-all