Islamic Hijri calendar
About the Islamic Hijri calendar
The Hijri calendar is purely lunar, with 12 months of 29 or 30 days and no intercalation, so it moves through the seasons in a cycle of about 33 solar years. Caliph Umar instituted it around 638 CE, counting from the Hijra of 622; in the tabular version 1 Muharram AH 1 corresponds to 16 July 622 in the Julian calendar. Religious dates such as Ramadan are usually fixed by sighting of the crescent moon or by national computed calendars such as Saudi Arabia's Umm al-Qura.
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