FRIDAY, DECEMBER 17: It’s the minor fast for the Tenth of Tevet today for observant Jews; unlike most Jewish holidays, today’s observance begins at sunrise and ends at sunset. (Aish.com has related articles and stories.) Although several themes are remembered today, the Tenth of Tevet primarily recalls the siege of Jerusalem by Nebuchadnezzar II of Babylonia—an event that eventually led to the destruction of Solomon’s Temple and the Babylonian exile. (Check out Chabad.org for details and related articles.)
This year’s fast is an unusual one, though, because Jewish fasts traditionally don’t fall on Fridays—only the Tenth of Tevet’s fast can. During a Friday fast, Torah and other readings combine and special prayers are recited at services.
Recently, the Tenth of Tevet was also declared a day to remember victims of the Holocaust whose death anniversaries are unknown. (Wikipedia has more.) Some Jews prefer today as a Holocaust victim remembrance date over Yom HaShoah, since Yom HaShoah falls during the month of Nisan—a time when mourning was traditionally forbidden.