The Islamic Calendar

The Islamic Calendar

The Islamic calendar is unique among the major calendars of the world. Unlike the Gregorian calendar and others based on the astronomical solar year—the length of time it takes for the earth to revolve around the sun—the Islamic calendar is based on the lunar year.

The lunar calendar is comprised of 12 lunar months like the calendar based on the solar year. However, since each month begins and ends with the new moon—a period lasting 29 days, 12 hours, 44 minutes, and 2.8 seconds—each lunar year contains only 354 days (or 355 on leap years) as opposed to 365 and 1/4 days for the astronomical year. There are 11 leap years in every cycle of 30 years, the intercalated day always being added to the last day of Dhu al-Hijjah, the last month of the year.

As a consequence of the fewer number of days in the lunar year, the lunar calendar is unrelated to the progression of the seasons. The month of Rajab, for example, could occur in summer in one year and the middle of winter 15 years later. Relative to the solar year, the lunar calendar progresses by 10 or 11 days each year so that 33 Muslim years are approximately equal to 32 Gregorian years.

The difference in the length of the lunar year accounts for some of the difficulty in converting dates from the Islamic (Hijri or "Hijrah") system to the Gregorian and vice versa. The following equation can be used to calculate the Hijrah year in which the corresponding Gregorian year began:

A.D. = 622 + (32/33 x A.H.)

The Islamic calendar was devised in the seventh century in response to the exigencies of governing the far-flung Abbasid empire. It also was created, not incidentally, to glorify the triumph of the new religion. Other calendars in use at the time were tied to other states and religions, and so, the historian al-Biruni tells us, the caliph Umar ibn al-Khattab decided to develop a new calendar based on the advent of Islam, taking July 16, 622 A.D., the date of the Hijrah or the Prophet's sojourn from Mecca to Madina, as the starting point of the calendar of the Muslim era.

The Muslim months are:

Muharram

Jumada al-Awwal

Ramadan

Safar

Jumada al-Thani

Shawwal

Rabi' al-Awwal

Rajab

Dhu al-Qi'dah

Rabi' al-Thani

Sha'ban

Dhu al-Hijjah

The following holidays are observed among Muslim communities throughout the world:
'Id al-Fitr, also known as the Little Feast, marks the end of the great fast of Ramadan. It occurs on the first day of the month of Shawwal.
'Id al-Adha, the Feast of Sacrifice, also known as the Great Feast, falls seventy days after 'Id al-Fitr, on the 10th of the month of Dhu al-Hijjah.
Ra's al-Sannah, New Year's Festival, falls on the first day of the month of Muharram.
Mawlid an-Nabi, the Prophet's Birthday, is celebrated on the 12th day of the month of Rabi' al-Awwal.
Lailat al Isra' wa al-Mi'raj, this festival commemorates the Prophet's miraculous journey, from Mecca to Jerusalem to heaven and then back to Mecca in the same night, is celebrated on the 27th day of the month of Rajab.