In AD 638, Umar ibn Al-Khattab (592-644 C.E.) Raa introduced the calendar as a way of consolidating the various calendars then in common usage among Muslim peoples. The years are measured from the date when Muhammad migrated to the city of Medina, on July 16th, A.D. 622. The calendar is also called the Hijri Calendar as this migration is called the Hegira. The first day of the first month (1 MuHarram) is this day. Dates in this calendar are usually abbreviated using A.H. from the latinized phrase Anno Hegirae, "in the year of the Hegira".
The predecessor to the Islamic calendar was similar to the Hebrew calendar in that it was primarily lunar but was kept synchronized with the tropical year (that is, based on the motion of the sun) by the insertion of an additional month when required. In the 9th year after the Hejira or migration to Medina, Muhammad forbade the insertion of the additional months.
This is expressed in the 9th chapter and 37th verse of the Quran as:
- Verily the transposing (Of a prohibited month) is an addition to Unbelief: The Unbelievers are led to wrong thereby: for they make it lawful one year, and forbidden another year, of months forbidden by Allah and make such forbidden ones lawful. The evil of their course seems pleasing to them. But Allah guideth not those who reject Faith.
This means that the Islamic calendar is always shorter than the Gregorian year by about 11 days, and the days of the calendar are not tied to a specific season of the year. It takes a 33 year cycle of lunar months until a complete traversal of the seasons occurs so that a month will fall again during the same season.
Of all the months in the Islamic calendar, Ramadan is the most sacred, and all Muslims are required to fast during the daytime.
the Islamic months are named as follows:
- Muharram ul Haram (or shortened to Muharram)
- Rab-ul-Akhir (or Raby` al-THaany)
- Jamadi-ul-Akhir (or Jumaada al-THaany)
- Dhul Qadah (or Thw al-Qi`dah)
- Dhul Hijja (or Thw al-Hijjah)
The Holy Quran, in the fifth chapter and 36th verse mentions the calendar (translated into English) states: "The number of months with Allah has been twelve months by Allah's ordinance since the day He created the heavens and the earth. Of these four are known as sacred; That is the straight usage, so do not wrong yourselves therein, and fight the Pagans. "
These four sacred months are: Muharram, Rajab, Dhul Qadah and Dhul Hijja. It is from this verse that it is commonly believed that fighting during sacred months is a sin.
Extremely important dates in the Islamic (Hijri) year are:
- 1 MuHarram (Islamic new year)
- 27 Rajab (Isra & Miraj)
- 1 RamaDHaan (first day of fasting)
- 17 RamaDHan (Nuzul Al-Qur'an)
- Last 10 days of RamaDHaan which include Laylatu al-Qadar
- 1 SHawwal (`iyd al-fiTr)
- 8-10 Thw al-Hijjah (the Hajj to Makkah)
- 10 Thw al-Hijjah (`iyd al-'aDHHaa').
The Islamic Calendar years of 1421 and 1422 occur in the Gregorian calendar year of 2001. January 1st 2001 is the day of 6 Shawwal of 1421 AH. 1 MuHarram 1422 AH is March 26th, 2001.