The Iranian calendar or Solar Hejri (Persian: تقویم هجری شمسی؛ سالنمای هجری خورشیدی, Taqwim Hejri Shamsi, Salanmay Hejri Khurshidi) is an astronomical solar calendar and one of the longest chronological records in history and is currently used in Iran and Afghanistan as the main official calendar. Beginning each year on the vernal equinox as precisely determined by astronomical observations from Tehran (or the 52.5°E meridian, which also defines IRST), this makes it more accurate than the Gregorian Calendar in being synchronized with the solar year, but harder to work out when a particular date would occur before the New Year preceding that date.