Iran's solar calendar and the ancient roots of Nowruz
Introduction
Iran and Afghanistan use the Solar Hijri Calendar, a solar calendar that counts years from the Hijra of the Prophet Muhammad — the same epoch as the Islamic Islamic Calendar — but tracks the sun rather than the moon. The result is a calendar firmly anchored to the seasons, with the year beginning precisely at the moment of the vernal Equinox.
Astronomical Precision
Unlike the Gregorian Calendar, which uses a fixed rule (the 400-year Gregorian cycle), the Solar Hijri calendar determines each year's length by direct astronomical calculation of the tropical year. Years of 365 and 366 days alternate in a pattern that keeps the calendar extraordinarily accurate: its drift against the true astronomical year is less than one day per millennium, significantly better than the Gregorian calendar's drift of roughly one day per 3,030 years.
The Twelve Months
The Solar Hijri calendar divides into twelve months. The first six months each have 31 days, the next five have 30 days, and the last month has 29 days in common years and 30 days in leap years. Month names in the Iranian tradition derive from Zoroastrian religious terminology and ancient Persian names — Farvardin, Ordibehesht, Khordad in the first half; Mehr, Aban, Azar in the autumn months.
Nowruz: New Year at the Equinox
Nowruz ('New Day' in Persian) is the Iranian New Year, celebrated at the exact moment of the vernal Equinox — typically on 20 or 21 March in the Gregorian calendar. It is one of the oldest continuously observed festivals in the world, with roots in Zoroastrian tradition stretching back at least 3,000 years. Nowruz is recognized by UNESCO as an Intangible Cultural Heritage of Humanity.
Celebrations include the Haft-sin table — seven items beginning with the Persian letter 'sin' — spring cleaning, family visits, and outdoor picnics on the thirteenth day (Sizdah Bedar). Nowruz is observed not only in Iran but across Central Asia, the Caucasus, and by Persian diaspora communities worldwide.
Differences from the Hijri Lunar Calendar
Many people confuse the Solar Hijri calendar with the Islamic lunar calendar. The key difference: the Solar Hijri year is 365 or 366 days long, so it does not drift through the seasons. The year 1404 SH in the Solar Hijri calendar began in March 2025 CE, whereas the year 1446 AH in the Islamic lunar calendar began in July 2024 CE. Iran observes both calendars: the Solar Hijri for civil life and the Islamic lunar calendar for religious observances like Ramadan and Eid.
Conclusion
The Solar Hijri calendar is a remarkable achievement of astronomical calendar design — more accurate than the Gregorian system while rooted in the same Islamic historical epoch as the lunar Hijri calendar. Its perfect alignment with the equinox ensures that Nowruz remains a celebration of spring in the truest astronomical sense.