Because of the tragic events of this period, semi-mourning is observed. On Lag B'Omer, however, marriages are performed and other mourning observances relaxed. It is known as 'The Feast of Weeks' because it falls seven weeks after Passover. In Jewish tradition it commemorates the giving of the Torah on Mt. Sinai which took place on this date. This led to the capture of the city and the destruction of the Temple by the Babylonians, under Nebuchadnezzar, three weeks later and the exile of the Jews to Babylonia.
Differences of opinion exist as to how much time elapses between sunset and nightfall.
Specific times may be set in Preferences from the Main Menu. If the previous month has 30 days, the thirtieth day is celebrated as the first day of Rosh Hodesh, and the actual first day of the new month, as the second day of Rosh Hodesh. However, the beginning of the month is always counted from the second day of Rosh Hodesh if Rosh Hodesh is observed for 2 days.