15.5.78.5 Islamic Calendar

The Islamic calendar is a strict lunar calendar. The beginning of a new month is tied to the first sighting of the lunar crescent in the evening after a New Moon. Because the beginning of the month is determined by observation, it cannot be accurately predicted. However, for secular use a tabular calendar is available that is determined by fixed rules. This tabular calendar is described below.

The Islamic tabular calendar has 12 months per year, that each have 29 or 30 days, starting at sunset. The month names and lengths in days are listed in the following table.

Number  Month Name   Length
  1       Muharram     30
  2          Safar     29
  3       Rabi`a I     30
  4      Rabi`a II     29
  5       Jumada I     30
  6      Jumada II     29
  7          Rajab     30
  8        Sha`ban     29
  9        Ramadan     30
 10        Shawwal     29
 11  Dhu al-q`adah     30
 12  Dhu al-Hijjah     29 (30 in a leap year)

There are 11 leap years in a fixed cycle of 30 years. In a leap year, the extra day is added at the end of the month of Dhu al-Hijjah. The epoch of the calendar is sunset of 15 July 622 C.E. and "year of the Era of the Hegira" may be abbreviated to A.H. (= Anno Hegirae). The epoch coincides with the migration of the Prophet Mohammed from Mecca to Medina. The calendar function takes an A.H. date to refer to the date that is current at noontime. The first noon after the epoch was the noon of 16 July 622 C.E., so the calendar function equates 1 Muharram 1 A.H. with 16 July 622 C.E.