The Solar Hijri Calendar, also known as the Persian Calendar, is a solar calendar used primarily in Iran and Afghanistan. It begins on the vernal equinox, marking the first day of spring, and consists of 12 months, totaling 365 days in a common year and 366 days in a leap year. The calendar is based on the Earth's revolutions around the Sun, making it highly accurate for seasonal changes. Each month in the Solar Hijri Calendar has either 29 or 30 days, with the first six months having 30 days and the remaining months alternating. The calendar is widely used for civil purposes and is important for cultural and religious observances in the region, including the celebration of Nowruz, the Persian New Year.