Persian Calendar

Omar Khayyam Calendar

In XI century C.E. the commission of astronomers under the leadership of Persian mathematician, astronomer and poet Omar Khayyam under instructions of Seljuq sultan Malik-Shah the solar calendar was elaborated, which was based on the 33 years cycle, consisting of 25 ordinary years (365 days each) and 8 leap years (366 days each).

Omar Khayyam

1st, 5th, 9th, 13th, 17th, 22nd, 26th and 30th were the leap years. The year started from the day of Vernal equinox and consisted of 12 months. Omar Khayyam calendar commission fixed original Vernal equinox for the epoch of March 15, 1079 C.E. according to the Julian calendar.

Ordinal number
of the month		 Name
of the month		 Number of days in the months
of the non leap year		 Number of days in the months
of the leap year
1 Farvardin 31 31
2 Ordibehesht 31 31
3 Khordad 31 31
4 Teer 31 31
5 Mordad 31 31
6 Shahrivar 31 31
7 Mehr 30 30
8 Aban 30 30
9 Azar 30 30
10 Day 30 30
11 Bahman 30 30
12 Esfand 29 30
Total days in the year: 365 366

Medium length of the Omar Khayyam calendar year was:

(365 * 25 + 366 * 8) / 33 = 365.24242 days.

This quantity was only the 0.00022 part of the day more than a tropical year (365.24220 days). Thus, Khayyam's calendar is more accurate than the Gregorian one and makes the mistake of one day for 4500 years!

For unknown reasons Omar Khayyam's calendar was not brought into life by Malik-Shah, but Omar Khayyam's project is so good that it is impossible not to mention it.

Modern Persian Calendar

Persian calendar, introduced in Iran in 1925 C.E. is based on the Omar Khayyam solar calendar. According to the Law of 1925 C.E. the day of the new year beginning and the length of the year is determined not on the basis of alterations of ordinary and leap years, as was suggested by Khayyam, but on the basis of astronomical calculations. When the Vernal equinox occurs before true noon (midday), than this day becomes the first day of the new year, but if it happens after the true noon, than next day becomes the first day of the new year. The epoch of the calendar becomes the date of the Vernal equinox, occurred before the epoch of the lunar Islamic calendar, i.e. Friday March 19, 622 A.D. of Julian calendar.

Try converting dates using the Calendar Converter.