A Brief Introduction to the Islamic Calendar:
The Islamic calendar is based on lunar months, which begin when the thincrescent Moon is actually sighted in the western sky after sunset a day or so afterNew Moon. For Islamic calendar purposes, the sighting must be made with the unaidedeye.
The names of the 12 months of the Islamic calendar, transliterated into the Romanalphabet, and their formal tabular lengths are:
| Name | Length | Notes |
|---|---|---|
| Muharram | 30 | Holy month |
| Safar | 29 | |
| Rabi' I | 30 | |
| Rabi' II | 29 | |
| Jumada I | 30 | |
| Jumada II | 29 | |
| Rajab | 30 | Holy month |
| Shaabán | 29 | |
| Ramadân | 30 | Month of fasting |
| Shawwál | 29 | |
| Dhú'l-Q'ada | 30 | Holy month |
| Dhú'l-Hijjab | 29 | Holy month; in a leap year Dhú'l-Hijjab has 30 days. |
Since 12 lunar months are, on average, 11 days shorter than the (Gregorian) civilyear, the Islamic year shifts earlier in each civil year by about this amount. The countof years for the Islamic calendar begins with 1 Muharram A.H. 1 (Anno Hegira), whichcorresponds to Friday, 16 July 622 C.E. (Julian calendar).
Tabular Islamic Calendar:
A tabular Islamic calendar has been established for some non-religiouspurposes in which the lengths of the months alternate between 29 and 30 days. Thiscalendar consists of a 30-year cycle in which 11 of the 30 years are leap years. In leapyears, an extra day is added to the last month, Dhú'l-Hijjab. Civil datescorresponding to important Islamic dates in this tabular calendar are available here.
For further information on calendars, see Richards, E.G. 2012,"Calendars," from the Explanatory Supplement to the Astronomical Almanac, 3rd edition, S.E Urban and P.K. Seidelmann eds., (Mill Valley, CA: University Science Books), Chapter 15, pp. 585-624.
Related information on these web pages includes:
Phases of the Moon and Percent ofthe Moon Illuminated in the Information Center
Dates of Primary Phases of the Moonin Data Services
Sun or Moon Rise/Set Table for One Year in Data Services
Complete Sun and Moon Data forOne Day in Data Services
Crescent Moon Visibility in the Information Center
