Template:AH

AH Gives Julian years for a given Hijri year. Use only in cases where Hijri year is known, but not the month or day (common for birth/death dates of medieval people). The given AH year usually results in two possible adjacent AD years. Example:

results in: (death year of Ibn al-Muqaffa').

Does not take into account the Gregorian calendar reform of 1582, but:
 * use of this template is predominantly for medieval dates, before 1582, as for later dates the exact dates will typically be known
 * for most years post-1582 the result will still be accurate

The arithmetical or tabular calendar was introduced by Muslim astronomers in the 9th century CE to predict the approximate begin of the months in the Islamic lunar calendar. This calendar is sometimes referred to as the Fātimid calendar but this is in fact one of several almost identical tabular Islamic calendars.

The months in the tabular Islamic calendar are assumed to be alternately 30 and 29 days in length resulting in a normal calendar year of 354 days (sanā basīta). In order to keep the calendar in step with the lunar phases every two or three years an extra day is added at the end of the year to the last month resulting in a calendar year of 355 days (sanā kabīsa). According to the most commonly adopted method 11 intercalary days are added in every 30 years (the historical origin for this scheme is explained below).

Four slightly different intercalary schemes have been described in the literature The Fātimid calendar (also known as the Misri or Bohra calendar) inserts intercalary years with 355 days in each 30-year cycle	as follows:
 * 2, 5, 8, 10, 13, 16, 19, 21, 24, 27 & 29

Of each intercalary scheme two variants are possible depending on whether the epoch of the Islamic calendar (1 Muharram, 1 AH) is assumed to be 15 July, 622 CE (known as the ‘astronomical’ or ‘Thursday’ epoch, Julian day 1948439) or 16 July, 622 CE (the ‘civil’ or ‘Friday’ epoch, Julian day 1948440).

Robert Harry van Gent