Persian Calendar (Iran)
- solar calendar with starting point that matches Islamic Calendar
- modern calendar adopted 1925 and supplanted eleventh century calendar
- origin traced to 11th century when group of astronomers created Jalaali calendar
- 12 months:
31 days |
Farvardin |
30 days |
Mehr |
31 days |
Ordibehesht |
30 days |
Aban |
31 days |
Khordad |
30 days |
Azar |
31 days |
Tir |
30 days |
Day |
31 days |
Mordad |
30 days |
Bahman |
31 days |
Shahrivar |
29/30 days |
Esfand |
- Esfand has 19 days in ordinary year 30 days in leap year
- Persian year starts at vernal equinox at reference longitude for Iran Standard Time (52°30’E)
- If the astronomical vernal equinox falls before noon (Tehran true time) on a particular day, then that day is the first day of the year. If the astronomical vernal equinox falls after noon, the following day is the first day of the year
- Years counted since Mohammed’s emigration to Medina (like Islamic Calendar) AD 622
- Vernal equinox of that year, AP (Anno Persico/Anno Persarum=Persian year) 1 started
- Years in which there are 366 days between two Persian new year’s days
- Due to how year is defined by astronomical vernal equinox
- Calendar divided into periods of 2820 which is divided into 88 cycles
- Lengths follow pattern: 29, 33, 33, 33, 29, 33, 33, 33, 29, 33, 33, 33, ...37
- Grand cycles: 128 years (29, 33, 33, 33) or 132 years (29, 33, 33, 37)
- Last cycle extended by 4 years
- Great Grand Cycle: 21 consecutive 128 year grand cycles and 132 year grand cycle for total of 2820 years
- Number the years within each cycle starting with 0, then leap years are years divisible by 4
- Year 0 is not a leap year
- 683 leap years every 2820 years, average year length of 365+683/2820=365.24220
- error of 1 day in 3.8 million years
- better approximation to tropical year than Gregorian calendar
- current 2820 year period started in year AP 475 (AD 1096)
- Problem: years between AP 1244 and 1531 (AD 1865 and 2152) one day discrepancy seen twice, namely in AP 1404 and 1437 (starting at vernal equinox of AD 2025 and 2058)