Jalali calendar
Calendario jalalí de Omar Jayam
- Date
- 1079 · confidence high
- Place
- Isfahan, Iran
- Credited to
- Omar Khayyam and astronomers of the Seljuk sultan Malik Shah
- People
- 👤 Omar Jayam1048–1131
- Field
- Knowledge & symbols
⚠️ Disputed: the sources disagree.
What it is
Solar calendar that fixes New Year at the observed spring equinox, with a mean year of 365.2424 days, more accurate than the Gregorian. Its successor is the calendar currently official in Iran and Afghanistan.
The exact intercalation rule used by Khayyam's team (cycles of 29 or 33 years) does not survive and is debated.
What it led to
- Iranian solar calendar (1925) and Afghan calendar
- astronomical fixing of Nowruz
- precise calendar reforms