Iranian Calendar is based on the movement of the earth around the sun.A mathematician and poet “Omar Khayyam” formulated the present calendar. The Iranian year begins on the first day of spring, when the length of day and night is equal. It has 4 seasons and every season has 3 months. The first 6 months have 31 days. The next 5 months are 30 days long and the lost has 29 days except every 4 years (leap year) when it has 30 days. It must be noted that because Iranians are Moslem (mostly Shia) they also use the Islamic calendar, which is based on the movement of the moon around the earth.This calendar has a 355 or 354-day year.
The national Iranian holidays are:
1- No.rooz* (the New Year days): Farvardeen 1st = March 21st up to 25th (4 days holiday). 2- Farvardeen 12th (the Islamic republic day) = April 2nd. 3- Sizdah-be-dar (Farvardeen the 13th) = April 3rd. 4- Khordad 14 th (imam khomaini (RH) passed away) =June 4th. 5- Khordad 15 th (the uprising of the citizens of Qum) = June 5th. 6- Bahman 22 nd (the day of victory of the Islamic revolution) = 11th February. 7- Esfand 29th (the day of the nationalization of the oil industry) = March 20th.
*A brief about No.Rooz: No.Rooz festival has associated with Zoroastrianism and Parsiism. It begins on March 21st, which is the first day of spring. It also is the significant of seasonal renewal, which is the change in climatic conditions, weather phenomena, mountains, rivers, vegetations and animals. For this reason the U.N. has named the Iranian New Year's Day “The day of the Earth.