The Islamic calendar or Muslim calendar or Hijri calendar (Arabic: التقويم الهجري‎; at-taqwīm al-hijrī; Persian: تقویم هجری قمری ‎ taqwīm-e hejri-ye qamari; Turkish: Hicri Takvim) is a lunar calendar based on 12 lunar months in a year of 354 or 355 days. It is the official calendar in Saudi Arabia and it's used to date events in many Muslim countries (concurrently with the Gregorian calendar), and used by Muslims everywhere to determine the proper day on which to celebrate Islamic holy days and festivals. The first year was the year during which the emigration of the Islamic prophet Muhammad from Mecca to Medina, known as the Hijra, occurred. Each numbered year is designated either H for Hijra or AH for the Latin anno Hegirae (in the year of the Hijra).A limited number of years before Hijra (BH) are used to date events related to Islam, such as the birth of Muhammad in 53 BH. The current Islamic year is 1431 AH, from approximately 18 December 2009 (evening) to 6 December 2010 (evening).