Overview

The Solar Hijri calendar is a solar civil calendar used as the official calendar of the Islamic Republic of Iran and also in Afghanistan. Commonly abbreviated SH, it is sometimes rendered as the Solar Hejri calendar. In Persian the name appears as گاه‌شماری هجری خورشیدی and in Pashto as لمريز لېږدیز کلیز. Its year numbering is counted from the Hijra epoch (the migration of the Prophet Muhammad), but the calendar’s months and year length follow the solar cycle and the astronomical vernal equinox rather than the Islamic lunar months.

Structure and general characteristics

Each Solar Hijri year has 365 days in ordinary years and 366 days in leap years. The year begins at the precise instant of the astronomical vernal equinox (Nowruz) as observed at the Iranian standard meridian (52.5°E, UTC+03:30). Because the start of the year is tied to the equinox, Nowruz (the New Year) always falls at the moment of the Sun’s passage into the northern hemisphere, which in the Gregorian calendar most commonly occurs on March 20 or 21, though the exact day may vary with the year and with local observation methods; see the March equinox and the festival of Nowruz.

Months and zodiacal alignment

The calendar has twelve months whose beginnings are aligned roughly with the twelve signs of the zodiac (zodiacal segments). The months and their usual lengths are:

  • Farvardin — 31 days
  • Ordibehesht — 31 days
  • Khordad — 31 days
  • Tir — 31 days
  • Mordad — 31 days
  • Shahrivar — 31 days
  • Mehr — 30 days
  • Aban — 30 days
  • Azar — 30 days
  • Dey — 30 days
  • Bahman — 30 days
  • Esfand — 29 days in ordinary years, 30 days in leap years (intercalated day)

Because months are based on the solar longitude of the Sun, each month corresponds approximately to a single zodiac sign beginning with Farvardin ≈ Aries and ending with Esfand ≈ Pisces. This alignment emphasizes seasonal consistency: months keep roughly the same positions in the agricultural year.

Leap years and intercalation

Intercalation in the Solar Hijri system ensures that the New Year remains on the vernal equinox. Modern practice in civil use relies on astronomical calculation of the equinox for a given meridian, and various tabulations or algorithms are used for practical conversion and administration. Historically different schemes and reform efforts produced tabular approximations; today the practical effect is that Esfand (the final month) gains an extra day in leap years so that the calendar stays synchronized with the tropical year. For an explanation of specific leap-day conventions and their astronomical basis see leap day rules.

History and development

The Solar Hijri calendar has roots in Persian and Islamic calendrical practice and underwent significant reform in medieval times. A prominent early reform known as the Jalali calendar, associated with scholars including the mathematician and astronomer Omar Khayyam in the 11th century, produced an accurate solar calendar tied to the equinox. Later developments adapted and standardized these principles into the modern Solar Hijri civil calendar used in state administration. The calendar preserves the Hijra epoch for year numbering while employing solar, rather than lunar, reckoning for months and days.

Civil use, culture and conversion

The Solar Hijri calendar is used in civil administration, official documents, and cultural observances where seasonal alignment matters, especially for agriculture and the celebration of Nowruz. It contrasts with the Islamic lunar calendar, which moves through the seasons, and with the Gregorian calendar, which uses a fixed leap-year rule. Converting dates between the Solar Hijri and Gregorian calendars requires attention to the instant of Nowruz in a given year and to whether a date falls before or after that instant. A common rule of thumb for year-number conversion is that the Solar Hijri year equals the Gregorian year minus 621 or minus 622 depending on whether the Gregorian date is before or after Nowruz; for precise daily conversion use tabular algorithms, software libraries, or astronomical data.

Further reading and references

For official definitions and civil practice consult national publications of Iran and Afghanistan. General background on the equinox and the festival appears in materials on the March equinox and Nowruz. For comparative context about zodiacal month origins and calendar models see summaries of zodiacal segments and summaries of calendrical reform. Practical notes on intercalation and implementation are discussed in sources addressing leap day rules and in guides to date conversion and New Year observance (New Year observance).