The Islamic Calendar.
The Islamic (Hijri) calendar is purely lunar. There are 12 lunar months in the calendar year. This is an average of 354.36 days in a year (about 11 days short of the solar year), so this puely lunar calendar revolves through the seasons about once every 33 years.
The epoch of the Islamic calendar dates from the Hijri (the journey of Mohamed from Mecca to Medina). According to the Explanatory Supplement to the Astronomical Almanac, astronomers consider this first Islamic New Year date, 1 A.H. (Anno Higerae, or the Year of Hijri) Muharram 1, to be 16 July 622 (Julian Calendar). According to the Explanatory Supplement, the astronomical New Moon occurred (assuming ΔT=1.0 hour) on 14 July 622 (Julian) at 04:44 Universal Time. The Crescent Moon was therefore probably observed on the evening of 16 July 622 (Julian).
The Quran, Sura IX, 36-37 is the basis of the Islamic calendar:
| 36. Surely the number of months with Allah is twelve months in Allah's ordinance since the day when He created the heavens and the Earth, of these four being sacred; that is the right reckoning; therefore be not unjust to yourselves regarding them, and fight the polytheists all together as they fight you all together, and know that Allah is with those who guard (against evil).
37. Postponing (of the sacred month) is only an addition in unbelief, wherewith those who disbelieve are led astray, violating it one year and keeping it sacred another, that they may agree in the number (of months) that Allah has made sacred, and thus violate what Allah has made sacred; the evil of their doings is made fairseeming to them; and Allah does not guide the unbelieving people. |
The practice in the Middle East at that time was to insert intercalary (leap) months to keep the Lunar months synchronized with the Solar seasons (and in fact the month names, dating to the days of Babylon, denote seasons). By his statement above, Mohamed forbade these intercalary months.
In the year 17 A.H. (638 Julian), Caliph `Umar I defined the Hijra Era and laid out the Islamic calendar.
The months in the Islamic calendar are:
1. Muharram
2. Safar
3. Rabi' al-awwal (Rabi' I)
4. Rabi' al-thani (Rabi' II)
5. Jumada al-awwal (Jumada I)
6. Jumada al-thani (Jumada II)
7. Rajab
8. Sha'ban
9. Ramadan
10. Shawwal
11. Dhu al-Qi'dah
12. Dhu al-Hijjah
The days of the seven-day week are numbered. They are:
1. Yawm al-'ahad (Sunday, the first day)
2. Yawm al-'ithnayn (Monday)
3. Yawm ath-thalaathaa' (Tuesday)
4. Yawm al-'arba`a' (Wednesday)
5. Yawm al-khamiis (Thursday)
6. Yawm al-jum'a (Friday)
7. Yawm as-sabt (Satturday, the Sabbath Day)
The early Islamic community became keenly interested in accurate methods to predict the Crescent Moon. Circa 760 C.E., Caliph al-Munsur had the Indian astronomical text Surya Siddhanta translated into Arabic. The famous ninth-Century astronomer-mathematician al-Khwarizimi of Baghdad calculated tables of astronomical phenomena including phases of the Moon and the Crescent Moon using methods from the Surya Siddhanta. According to the Surya Siddhanta, the Crescent Moon becomes visible when it is at least 78° behind the Sun at sunset.
Around 900 C.E., several translations were made of Ptolemy's Almagest into Arabic.
These translations of the Surya Siddhanta and Almagest became the foundation of astronomical science in the early Islamic world. However, Islamic astronomers were keen observational astronomers and realized that the techniques in these older texts were not perfect. They endeavored to improve astronomical theory.
The most famous of these Islamic astronomers was the eleventh-Century astronomer al-Biruni. He named his treatise Canon. He accurately solved the problem of Qibla — the direction to face the kaaba in Mecca for prayers, creating tables for longitudes and latitudes in the Islamic world.
In Saudi Arabia, the government adopted astronomical calculations in 1999 C.E. In Saudi Arabia, on the 29th day of each month, the times of the setting Sun and the setting Moon at Mecca are compared. If the Moon sets before the Sun, the month is given a 30th day. If the Sun sets before the Moon, the month ends on this 29th day. This method generated some controversy, as the times of Moonset and sunset do not guarantee the visibility of the crescent Moon.
Effective 16 March 2002, Saudi Arabia added the refinement that in addition to the Moon setting after the Sun in Mecca, the geocentric New Moon also had to occur before sunset at Mecca. This is an improvement over the previous method, but still does not gurantee the visibility of the crescent Moon, and so there is still some controversy about this in the Muslim community.
Mecca is located in Saudi Arabia, at 39°45' East Longitude and 21°29' North Latitude.
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