Thursday, the third day of the Hebrew month of Tishrei, is the Fast of Gedaliah, marking the assassination of the leader of the small remaining Jewish community in the Land of Israel after the destruction of the First Temple.
Some 2,500 years ago, the Babylonian King Nebuchadnezzar - who had just destroyed the First Holy Temple in Jerusalem and slaughtered or exiled most of the Jewish population - appointed Gedaliah ben [son of] Achikam to serve as Jewish governor of those who remained.
Gedaliah was soon murdered, however, by Yishmael ben Netaniah, commissioned by the king of neighboring Ammon. As a result, the final vestiges of Jewish autonomy in the Holy Land were destroyed, many more thousands of Jews were slain, and the rest were driven into exile. Only 70 years later would the Jews return and build the Second Temple.
The events are described in the Bible in Kings II 25 and Jeremiah 40-41.
The fast day began at dawn and ends at sundown. The special penitential prayers, known as Selichot, that are recited from before Rosh HaShanah until Yom Kippur, are augmented on this day. Passages are recited on the concepts of Teshuvah (repentance), G-d's acceptance of repentance, the special Ten Days of Repentance between Rosh HaShanah and Yom Kippur, Abraham's near-sacrifice of his son Isaac, the destruction of the Temple, Israel's longing for Redemption, and more.