Tuesday marks the observance of the predawn-to-dusk fast of the 10th of Tevet on the Hebrew calendar. The fast commemorates the start of Babylonia's siege of Jerusalem, ahead of the destruction of the First Temple, as well as the deaths of prophets Ezra and Nechemiah, which happened about the same time, and writing of the Septuagint translation of the Torah into Greek, due to things that got lost in translation.
The Chief Rabbinate of Israel also marks the day of mourning for victims of the Holocaust whose precise anniversaries of death are unknown.