- On this day the Hebrew spies came back from Canaan and reported that the land was unconquerable, the Hebrew cried and told God they would rather go back to Egypt than be killed by the Canaanites. God, reasonably so, is upset with their distrust and he sentences them to wander in the desert for another 38 years, so that the distrustful generation would not see the promised land.
- The first and second Temples were destroyed on the same day, the 9th of Av, five hundred years apart.
- In 134 AD (note here, Jews who do not believe that Jesus is the Moshiach say CE or "common era" instead of "anno domini" or "in the year of our Lord", for obvious reasons), the Romans plowed over the Temple Mount.
- The Jews were expelled from England in 1290 AD on the Tisha B'Av and from Spain in 1492 on, well, you get the picture.
The main observance for this date is the destruction of the temple, and secondarily the exile into the wilderness. They fasted from sunset on the 19th on June through the 20th. They read the book of Lamentations, do not wash or use oils and creams, abstain from sex, and do not wear shoes made with leather.
As a Jew who believes that Jesus is the Moshiach (Messiah), it was more a day to remember and less of a day to mourn. God has already rebuilt his church in Christ and has spread it to the Gentiles so that the Temple is now the soul of every believer. And of course, the physical temple will be rebuilt when Jesus comes back.
Sometimes the second coming sounds crazy, but I guess that's the point. It's gonna be a crazy day.
Rosh Hashanah is the next celebration; check back in September!