The modern Persian calendar, adopted in 1925, is a solar calendar based on the Jalālī calendar designed in the eleventh century by a committee of astronomers, including a young Omar Khayyām, the noted Persian mathematician, astronomer, and poet. The Jalālī calendar had 12 months of 30 days each, followed by a 5-day period (6 in leap years), just like the Coptic and Ethiopic calendars described in Chapter 4. In addition to the Jalālī calendar, the Zoroastrian calendar, whose structure is described in Section 1.11, was also used historically in Persia. The lengthy history of Persian calendars is discussed in [3], [5], and [7]; [2] gives a briefer history, together with tables and computational rules for the arithmetic form of the calendar to be discussed in Section 15.3. A calendar identical to the modern Persian calendar, but with different month names, was adopted in Afghanistan in 1957.

Structure

The epoch of the modern Persian calendar is the date of the vernal equinox prior to the epoch of the Islamic calendar; that is, 1 a.p.