Iran is a four season country and different seasons are sometimes experienced at the same time in different regions of the country. Bahar (spring), Tabestan (summer), Pa-yeez (fall) and Zemestan (winter) are the names of the four seasons in the Persian language.
The official calendar of Iran is the Shamsi (Solar) Hijri calendar abbreviated SH. Iranian astronomers created the solar calendar used in Iran today in the 11th century and named it Taqvim-e Jalali (Jalali Calendar).
Just like the lunar calendar, the starting point of the solar calendar is the March equinox of the year (622 AD) in which Prophet Mohammad (PBUH) immigrated to Medina from Mecca.
Each of the 12 months corresponds with a zodiac sign. The first six months have 31 days, the next five have 30 days, and the last month has 29 days in ordinary years and 30 days in leap years. The New Year's Day always falls on the March equinox.
Persian months are named after 12 Zoroastrian deities Amshaspandan, Yazdans and Forouhars. Persian calendar months are:
Farvardin (Far-Var-Deen): Begins March 19 or 22, and ends on April 18 or 21
Ordibehesht (Or-Dee-Behesht): Begins April 19 or 22, and ends on May 18 or 21
Khordad (Khor-Dad): Begins May 19 or 22, and ends on June 18 or 21
Tir (Teer): Begins June19 or 22, and ends on July 18 or 21
Mordad (More-Dad): Begins July 22 or 23, and ends on August 21 or 22
Shahrivar (Shah-Ree-Var): Begins August 22 or 24, and ends on September 21 or 22
Mehr (Mih-r): Begins September 22 or 23, and ends on October 21 or 22
Aban (Aa-Baan): Begins October 22 or 23, and ends on November 21 or 22
Azar (Aa-Zaar): Begins November 22 or 23, and ends on December 21 or 22
Dey (Day): Begins December 22 or 23, and ends on January 20 or 21
Bahman (Bah-Man): Begins January 21 or 22 and ends on February 19 or 20
Esfand (Es-Fand): Begins February 20 or 21 and ends in March 20 or 21
In Iran, the lunar calendar is only used to determine religious occasions and holidays.