Jalali Calendar
The Iranian, or Persian, calendar is solar, with the particularity that the year is defined by two successive, apparent passages of the Sun through the vernal (spring) equinox. It is based on precise astronomical observations, and moreover uses a sophisticated intercalation system, which makes it more accurate than its younger European counterpart, the Gregorian calendar. It is currently used in Iran as the official calendar of the country.
The Iranian calendar has a long, multi-millennial history with deep roots in the Persian culture, in particular the Zoroastrian heritage. The present version of the calendar results from a reform led by the famous astronomer, mathematician, and poet Omar Khayyâm which took place at the vernal equinox of A.D. 1079 (Friday, 21 March), corresponding to the 1st of Farvardin of A.P. (Anno Persico) 458. The calendar was also called Jalâli, from the name of the ruler who ordered the reform. In modern times, its principles were officially adopted by the Iranian parliament on 31 March 1925 (11 Farvardin A.P. 1304).