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 similar to the Gregorian calendar, being based on the Earth's orbit around the Sun. 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 Hijri calendar (commonly known in the West as the 'Islamic calendar', although both calendars are Islamic) is usually abbreviated as AH. The solar Hijri calendar predominates in Shia Islam whereas the lunar Hijri calendar predominates in Sunni Islam.

The first day of the Solar Hijri calendar was the day of the spring equinox, March 18, 622 CE. The calendar is named the "Hijri calendar" because that was the year that Mohammed is believed to have left 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.

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.^[6][7] The solar Hijri calendar uses solar years and is calculated based on the "year of the Hijrah," and the lunar Hijri 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. 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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