The
Solar Hijri calendar (, ), also called the
Solar Hejri calendar or
Shamsi Hijri calendar, and abbreviated as
SH, is the official calendar of
Iran and
Afghanistan. It begins on the
vernal equinox as determined by astronomical calculation for the
Iran Standard Time meridian (52.5°E or GMT+3.5h). This determination of starting moment is more accurate than the
Gregorian calendar for predicting the date of the vernal equinox, because it uses astronomical observations rather than mathematical rules.