There are six fast days during the Jewish Calendar Year
1. Yom Kippur- The Torah demands that we fast on the tenth day of the Seventh month. On this day Moshe descended Sinai with the second set of tablets, signifying G-d's forgiving the nation for worshiping the golden calf. Yom Kippur begins at nightfall on September 18th, 2018.
2. Tisha B'av- The ninth of Av is the worst day in the Jewish year. It marks the destruction of the two ancient temples (Beit Hamikdash) in Jerusalem by the Babylonians in the year 586 BCE, and the Romans in the year 70. Like Yom Kippur we are prohibited from eating and drinking for an entire 24 hour period. Tisha B'av begins at nightfall on July 21st, 2018.
3. Asarah B'tevet-On the tenth of Tevet, in the year 589 BCE, the Babylonians laid siege to Jerusalem, ultimately leading to its destruction some three years later. This fast takes place in the winter, just one week after Chanukah. On this day, and the others below, one is only obligated to fast from dawn until dusk. Asarah B'tevet begins at dawn on December 18th, 2018.
4. Shiva Asar B'tamuz- On the seventeenth of Tamuz the walls of Jerusalem were breached. This fast, which takes place in the summer, begins the most solemn time in the Jewish year, the three weeks. The three weeks culminate with Tisha B'av. Shiva Asar B'tamuz begins at dawn on July 1st, 2018.
5. Tzom Gedalyah- on the third day of Tishrei we commemorate the murder of Gedalyah Ben Achikam. Following the destruction of the temple, the Babylonians appointed Gedalyah as the governor of the remaining Jewish community in Judea. When Gedalyah was murdered by a fellow Jew, the remaining Jews fled to Egypt due to fear of reprisal attacks. Tzom Gedalyah begins at dawn on September 12th, 2018.
6. Taanit Esther- on the thirteenth of Adar, prior to the joyous holiday of Purim, we mark the fast of Esther, the heroine of the Purim story. The origins of the fast are unclear. Two of the more common explanations are: 1. It is a fast in solidarity with Esther, who fasted prior to her approaching King Achashverosh. 2. It recalls the fasting of the Jewish warriors who went out to battle our enemies on the day originally picked by Haman for the Jewish People's destruction. The warriors fasted in order to receive special Divine protection. Taanit Esther begins at dawn on March 20th, 2019.