Tisha B'Av - Sunset August 8, 2011 to Sunset August 9, 2011
Tisha B'Av, the Fast of the Ninth of Av, is a day of mourning to commemorate the many tragedies that have befallen the Jewish people, many of which coincidentally have occurred on the ninth of Av.
This holiday is primarily meant to commemorate the destruction of the first and second Temples, both of which were destroyed on the ninth of Av (the first by the Babylonians in 586 B.C.E.; the second by the Romans in 70 C.E.).