In addition to the normal Islamic lunar
calendar, various important adaptations of it have been used in various areas of the Islamic world
. These were mainly used in the past but some are still significant today.
Because the Hegira calendar is purely lunar, it was inconvenient for fiscal and administrative purposes, especially during the pre-modern era, when most of the taxes collected were agricultural products. Remember, lunar calendar is not constant - for example, currently the fasting month of Ramadan falls roughly around late December or early January, but in a decade or so, it is going to take place during our summer. This of course presented some problems for the ruler: how are you supposed to levy agricultural taxes every year if your harvest times don't match your calendar? To undermine this problem, Muslim governments from early times worked out a series of solar adaptations of the Hegira year with Iranian, Christian and other months. The most important of these are:
1. The Turkish financial year (maliyye)
This was an adaptation of earlier fiscal calendars combining the Hegira date with solar year, and was introduced into the Ottoman revenue administration in 1789 CE. The Maliye was a Julian year, with most of the old Syrian month names retained. However, this new calendar presented another problem: since the Islamic year is shorter than the Julian one, the counting of taxational years lagged behind the years of the religious calendar and had to be corrected from time to time. For this purpose, a practice of siwish ('changing') was adopted, whereby one solar year could be jumped over altogether.
At first, the Ottomans retained the old Byzantine New Year on 1 September, but later on they moved the beginning of the year to 1 March. After this, each maliyye year had, in theory, the same number as the Hegira year during which it began, with the omission of one year every 33 years, i.e. whenever the 1st of March did not fall within the religious Hegira year (please refer to schmOOnkie pOOnks' write-up above). However, even this was not enough to avoid further problems, which mostly arose from the fact that the Ottomans collected taxes according to the Julian year but paid salaries according the the lunar year. This obviously led to difficulties with the bookkeeping whenever siwish became necessary.
Eventually the system broke down: the maliyye year 1287 (1871-2 AD) should have been followed by maliyye 1289 (1872-3), but for some reason the year 1288 was not left out, with the result that for the remainder of its history the maliyye calendar was out of step with the religious year. It was officially abolished with the adoption of the Western-style Christian era in 1927.
2. The Persian solar year
This was introduced in 1925 in Iran and is based on the Hegira, except it is calculated in solar years, using an adaptation of the old Iranian month names. To convert Gregorian solar years to Iranian, subtract 622 from dates 1 January-21 March; and 621 from dates 21 March-31 December. The New Year (nowruz), 1 Farvardin, falls in the third week of March. This calendar is currently used in Iran for all but purely religious purposes.
As stated above, the year begins at the spring equinox. The first six months have 31 days each, the next five have 30 and Esfand has 29 in an ordinary year and 30 in a leap year, giving 365 or 366 days in total. The inevitable difficulties arise when one tries to determine which years should be leap years. The rule, unlike that used with the Gregorian calendar, is quite complicated - there is no consistent method of calculation, or at least I have yet to see one.
The months of the solar calendar are as follows:
Farvardin (March 21- April 20)
Ordibehesht (April 21-May 21)
Khordad (May 22-June 21)
Tir (June 22-July 22)
Mordad (July 23-August 22)
Shahrivar (August 23-September 22)
Mehr (September 23-October 22)
Aban (October 23-November 21)
Azar (November 22-December 21)
Dey (December 22- January 20)
Bahman (January 21-February 19)
Esfand (February 20-March 20)
For information about the old Persian calendar from which this system borrows both the names of its months and its function, see Zoroastrian Calendar.
3. The Turco-Mongol Calendar
Before coming to contact with Islam, the ancient Turks adopted a form of the Chinese luni-solar calendar, which then passed from the Uyghur Turks to the Mongols, who in turn introduced it in their medieval empire in Persia, where it was quite widely used alongside the Islamic calendar.
If you are familiar with the Chinese zodiac, you will already know that the Chinese lunar months begin not with the sighting of the new crescent, as in the Middle East, but a couple of days earlier with the calculated time of conjunction between the sun and the moon. The year begins while the sun is in Aquarius. The year is kept in pace with the solar year by the periodic intercalation of a thirteenth month, which is inserted whenever two new moons fall during the time that the sun is in one and the same zoological sign.
The Turkish names for the first (aram ay) and last (djakhshabat ay) months derive from Sanskrit or Iranian, the other ten months have no names but are merely counted, as in Chinese ("second moon" etc).
Years were counted according to the twelve-year cycle of Chinese astrology, where each year of the cycle takes the name of an animal. The Turkish and Mongol forms are as follows:
Year 1: sicghan / kulughana (rat)
Year 2: udh / üker (ox)
Year 3: bars / bars (tiger)
Year 4: tawishghan / tawlay (hare)
Year 5: lu / luu (dragon)
Year 6: yilan / moghay (snake)
Year 7: yunt / morin (horse)
Year 8: kon / konin (sheep)
Year 9: becin / becin (monkey)
Year 10 takighu / takiya (rooster}
Year 11: it / nokay (dog)
Year 12: tonuz / ghakay (pig)
The intercalary month was called shün ay, a borrowing from the Chinese run.
The animal cycle continued to be used in Persia until the beginning of the 20th century, generally in connection with other calendars.
Encyclopedia of Islam
B. Lewis: The Middle East. (London, 1995)
E.W. Lane: Arabian Society in the Middle Ages (London, 1883)