Start of month of Kislev on the Hebrew calendar. Kislev (כִּסְלֵו) is the 9th month of the Hebrew year, has 30 or 29 days, and corresponds to November or December 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
https://www.hebcal.com/holidays/rosh-chodesh-kislev-2021?utm_source=js&utm_medium=icalendar