The Islamic calendar is the official calendar in countries around the Persian Gulf, especially Saudi Arabia. But other Muslim countries use the Gregorian calendar for civil purposes and the Islamic calendar for religious purposes.

The Islamic calendar (or Hijri calendar) is a purely lunar calendar. It contains 12 months that are based on the motion of the moon, and because 12 synodic months are only 12 x 29.53= 354.36 days, the Islamic calendar is consistently shorter than a tropical year, and therefore it shifts with respect to the Gregorian calendar.

The Islamic calendar was first introduced in 638 C.E. by the close companion of the Prophet (PBUH) and the second Caliph, Umar ibn Al-KHaTTab (592-644 CE) RAA. He did it in an attempt to rationalize the various, and at times conflicting, dating systems used during his time. Umar consulted with his advisors on the starting date of the new Muslim chronology. It was finally agreed that the most appropriate reference point for the Islamic calendar was the Hijrah. The actual starting date for the calendar was chosen (on the basis of purely lunar years, counting backwards) to be the first day of the first month (1 MuHarram) of the year of the Hijrah. The Islamic (Hijri) calendar (with dates that fall within the Muslim Era) is usually abbreviated A.H. in Western languages from the latinized Anno Hegirae, 'in the year of the Hegira'. MuHarram 1, 1 A.H. corresponds to July 16, 622 (CE).

The Hijrah, which chronicles the migration of the Prophet Muhammad (PBUH) from Mecca to Madina in September AD 622, is the central historical event of early Islam. It led to the foundation of the first Muslim city-state, a turning point in Islamic history.

The Islamic calendar is lunar. Each month must begin with the evening when the new moon is sightable by the unaided naked eye. Muslims are obligated to sight the crescent in every country. Different countries may begin the year at different days based on their own sightings. The calendar is called Hijri calendar. The Arabic word Hijrah means emigration.

The names of the twelve Islamic months are as follows:

Because the Islamic calendar year is about 11 days shorter than the year in the Gregorian calendar, the Islamic years are slowly gaining on the Gregorian years. But it will be many centuries before the two coincide. The 1st day of the 5th month of CE 20874 in the Gregorian calendar will also be the 1st day of the 5th month of A.H. 20874 of the Islamic calendar.

Saudi Arabia doesn't rely on a visual sighting of the crescent moon to fix the start of a new month. Instead, they base their calendar on a calculated astronomical moon. Since 1999 (1420 A.H.) the rule has been as follows: On the 29th day of an Islamic month, the times when the sun and the moon set are compared. If the sun sets before the moon, the next day will be the first of a new month; but if the moon sets before the sun, the next day will be the last (30th) of the current month.

The times for the setting of the sun and the moon are calculated for the coordinates of Mecca.

In the year AD 2004 is the start of the Islamic year A.H. 1425.

Please NOTE that the above information is just a brief explanation of the Islamic calendar. More information can be found at libraries.

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