The Jalali calendar, also known as the Persian calendar, is a solar calendar used primarily in Iran and Afghanistan. It was established in 1079 AD by the astronomer Omar Khayyam and is based on the Earth's revolutions around the Sun. The calendar consists of 12 months, with the first day of the year, known as Nowruz, occurring at the vernal equinox in March. The Jalali calendar is highly accurate, with a year length of about 365.2425 days. It includes a leap year system that adds an extra day every four years, similar to the Gregorian calendar. This calendar is widely used for civil purposes and cultural celebrations in regions where it is recognized.