Muslims around the world use the Islamic calendar (also known as the Lunar or Hijri calendar) to determine the dates of religious events and observances. The Islamic calendar is based on 12 lunar months – a new month begins when a new moon is sighted.
Lunar cycle is consisting of 354 or 355 days and 12 months. Islamic Calendar depends on the movement of the moon. The beginning of each month is marked by the observance of a new moon seen for the first time.