Hijra (in Arabic – eviction, emigration) – this is the name of the Muslim era established by the second caliph of the Arab Caliphate Omar I in 638 AD to honor the Prophet Muhammad’s migration from Mecca to Yathrib (Medina). This event is considered to be the turning point in the history of Islam and 17 years after the great migrations Caliph Omar I used it as a foundation for the Muslim calendar. The first day of the new calendar he chose was Friday, dated July 16, 622 - the very day when the Prophet Muhammad left Mecca. This calendar is lunar, i.e. time periods are calculated according to the moon changing phases; this calculation does not depend on the movement of the Sun. Lunar Hijra calendar is used by all Muslims to calculate the dates of Islamic religious holidays. In some countries, namely Algeria, Iraq, Kuwait, Saudi Arabia and others, Lunar Hijra is adopted as the official national calendar. However, since the astronomical lunar month begins in different countries at different time, the lunar months in these countries do not coincide.

• More on the Muslim calendar

          

Wristwatch "Hijra" with the Muslim calendar

Al-Biruni astronomical clock with the Muslim calendar

Table clock “Lunar Hijra” with the Muslim calendar