Tisha B'Av

Tisha B'Av, the ninth of Av, is a full fast day mourning the destruction of both Temples in Jerusalem, along with a list of other catastrophes tradition attaches to the same date. It's the saddest day on the Jewish calendar, marked by sitting low, reading the Book of Lamentations, and skipping the usual greetings people exchange on other fasts. Most Jews who keep little else in the way of fasting still know this one by name.