As directed by the Koran, this is an entirely lunar calendar. It ignores the solar year (being about 11 days shorter), so months will change seasons over the years, cycling about every 33 solar years and making it one more year ahead of solar calendars. Thus, currently around 40 more lunar years have passed than corresponding solar years (e.g. 1996 AD is around 1418 AH).
Months (moons):
In a leap-year, Thw al-Hijjah has 30 days. The leap-years go through a 30-year cycle, with the leap-day occurring in years 2, 5, 7, 10, 13, 16, 18, 21, 24, 26, and 29.
Being a religious calendar, it holds great importance to Muslims. The months do not start at the exact time of a new moon, but are based on the first physical sighting of a new crescent. Due to various methods of observance, and differences in confirmation on local, regional, and global levels, specific dates of festivals can vary.
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