Solar Hijri calendar

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The Solar Hijri calendar^[a] is a solar calendar and one of the various Iranian calendars. 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 the modern principal calendar in Iran and Afghanistan and is sometimes also called the Shamsi calendar and Khorshidi calendar. It is abbreviated as SH, HS or, by analogy with AH, AHSh.

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] one uses solar years and the other lunar years.

Each of the twelve months 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, the Solar Hijri calendar itself remains only in official use in Iran.

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