Also on these boards
The months and years of the Jewish calendar are established by the cycles of the moon and the sun. Though the months follow the lunar cycle, the lunar months must always align themselves with the seasons of the year, which are governed by the sun. Thus, the Jewish calendar is "Luni-Solar." In the fourth century a fixed calendar was instituted based on the Sanhedrin's guarded secrets of calendric calculation. This is the calendar according to which the New Moons and festivals are calculated.