Hebrew Moon Calendar. Every month is either 29 or 30 days long, beginning (and ending) on a special day known as rosh chodesh (“the head of the month”). A hebrew month begins at the moment of sunset the evening the moon's crescent first becomes potentially visible to the naked eye in jerusalem, assuming ideal sighting conditions without.
The months were once declared by a beit din (rabbinical. Here are some examples of dates in the.