The reason for its destruction was the relentless pursuit of immorality - whether idol worship or sexual impropriety.
The Second Temple was destroyed for one reason only, "Sinat Chinam", or causeless hatred. The Jewish people at the time simply hated one another for no reason, and had absolutely no compassion for each other.
What happens on this day?
Traditionally, one fasts from sunset to sunset, 25 hours in total. In the synagogue we read the book of Lamentations (Eichah), which details the destruction of the First Temple.
In addition, we abstain from activities such as listening to music, sitting on comfortable chairs and sexual relations.
Jan. 9th - 10th
14th Tevet
Begins: 15:57
Ends: 17:06
Sedra: Vayechi