The Iranian Calendar
There are two kinds of calendar, which are available in the Islamic Republic of Iran. First the one which is based on the Arabic calendar (A.H) and the second one which is based on the solar year. The origin of the first one dates back to the time of Holy Prophet’s emigration from Mecca to Medina (which took place in 622 A.D). Till 1344 the Arabic calendar was considered as the basic calendar in Iran. In the same year, which (according to Solar year) 1304 years had passed after the Holy Prophet’s emigration, the solar year was chosen to be the one dedicated to the governmental affairs and was formalized due to the law. Here comes the seventeenth
principle of the Constitution:
“The Holy Prophet’s emigration serves as the basis of Iran’s calendar and the solar year and the Arabic calendar are both valid. However; the solar year will be used as the basis of the governmental affairs…”
The Arabic calendar is shorter than the solar counterpart for about 10 days and 6 hours and 11
seconds. The beginning of the solar year
is the first day of spring which is on March 21 0r 22 (according to Gregorian calendar). In the first half of the year, each month would last 31 days and in the second half each month last 30 days except Esfand, which is 29 days.
Iranian called Farvardin 1, Norooz. In the ancient times, Norooz did not occur in the spring; some times it occurred in the spring or in the summer….
In 471 (AH), by the order of "Sultan Jalal-eddin Malekshah-e Saljuqi", "Hakim Omar Khayam
" along with some other astronomers, prepared Jalali calendar and they allowed Norooz to be at the beginning of the spring (to be more specific the first day). There was another name for spring too, which was "Haml". Therefore; it was arranged so that every four year one day would be added to the total number of the days and therefore the fourth year would last 366 days.
And similarly, every 28 years (7 periods of four -year time) instead of adding a day to the last month of the year, the day would be added to the next period.
Consequently, Jalali Year had been considered as the closest year to the Solar year. The real solar year means a year with 365 days, 5 hours, 48 minutes and 64 seconds.