Iranian Calendar

Iranian Calendars The Iranian calendars or Iranian chronology are a succession of calendars created and used for over two millennia in Iran, also known as Persia. One of the longest chronological records in human history, the Iranian calendar has been modified many times for administrative, climatic, and religious purposes. The most influential person in laying the frameworks for the calendar and its precision was the 11th century Persian polymath, hakim Omar Khayyam. The modern Iranian calendar is currently the official civil calendar in Iran.

The Iranian New Year begins at the midnight nearest to the instant of the northern spring equinox, as determined by astronomic calculations for the meridian (52.5°E). It is, therefore, an observation-based calendar, unlike the Gregorian, which is rule-based. This equinox occurs on or about 20 March of the Gregorian.

https://ar.wikipedia.org/wiki/Iranian_calendars