About the Solar Hijri calendar
The Solar Hijri calendar counts years from the Hijra like the Lunar Hijri calendar, but its year is solar: it begins at Nowruz, the day of the March equinox, so its months always fall in the same seasons. The first six months have 31 days, the next five 30 days, and the last month 29 days, or 30 in a leap year.
Leap years are not set by a fixed rule but astronomically: a new year starts on the day the equinox occurs before noon in Tehran (52.5° E). This converter applies that rule directly to NASA ephemeris data, so it matches the official calendar even in the years where approximate arithmetic tables differ by a day.