Islamic (Hijri)

Purely lunar · Umm al-Qura

A purely lunar calendar of 12 months totalling about 354 days, so it slips ~11 days earlier against the seasons each year. It counts from the Hijra, Muhammad’s migration to Medina in 622 CE; shown here in the Umm al-Qura tabular reckoning, which fixes the months by calculation in advance. Traditionally a month opens instead on the first crescent sighted after the new moon, which is why an observed date can fall a day either side of this one.

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