Solar Hijri calendar

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The Solar Hijri calendar^[a] is the official calendar of Iran. It is a solar calendar and is the one Iranian calendar that is the most closely aligned with the Gregorian calendar, being astronomically based. It begins on the March equinox as determined by the astronomical calculation for the Iran Standard Time meridian (52.5°E, UTC+03:30) and has years of 365 or 366 days. It is sometimes also called the Shamsi calendar and Khorshidi calendar. It is abbreviated as SH, HS or, sometimes as AHSh, while the lunar based Islamic calendar is usually abbreviated as AH.

The very first day of the Solar Hijri calendar was the day of the Spring equinox, 622 AD. The calendar is named the "Hijri calendar" because the year 622 A.D. was the year that Mohammed is believed to have fled from Mecca to Medina, which event is referred to as the Hijrah. This year is generally considered by Muslims as the first year of Islam. If a Gregorian calendar date falls after the spring equinox, the corresponding year of the Hijri calendar would be the Gregorian year minus 621 years. E.g. a Gregorian date of June, 2024 would fall in the Hijri year of 1403 (2024 - 621 = 1403).

The ancient Iranian Solar calendar is one of the oldest calendars in the world, as well as the most accurate solar calendar in use today. Since the calendar uses astronomical calculation for determining the vernal equinox, it has no intrinsic error.^[2][3][4][5] It is older than the Lunar Hijri calendar used by the majority of Muslims (known in the West as the Islamic calendar); though they both count from the Hijrah, the journey of the Islamic prophet Muhammad and his followers from Mecca to Medina in the year 622.^[6][7] The Hijri calendar uses solar years and is calculated based on the "Year of the Hijrah," and the Islamic calendar is based on lunar months, and dates from the presumed actual "Day of the Hijrah."

Each of the twelve months of the Hijri calendar corresponds with a zodiac sign, and in Afghanistan the names of the zodiacal signs were used for the months;^[b] elsewhere the month names are the same as in the Zoroastrian calendar. The first six months have 31 days, the next five have 30 days, and the last month has 29 days in common years but 30 days in leap years.

The ancient Iranian New Year's Day, which is called Nowruz, always falls on the March equinox. While Nowruz is celebrated by communities in a wide range of countries from the Balkans to Mongolia. Currently the Solar Hijri calendar is officially used only in Iran.

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