page_title: Nowruz
section_title: Timing accuracy
hierarchical_section_title: Nowruz / Nowruz / Timing accuracy
context_page_description: Nowruz is the Iranian New Year, also known as the Persian New Year, which is celebrated worldwide by various ethno-linguistic groups.
  Nowruz has Iranian and Zoroastrian origins; however, it has been celebrated by diverse communities for over 7,000 years in Western Asia, Central Asia, the Caucasus, the Black Sea Basin, the Balkans, and South Asia. It is a secular holiday for most celebrants that is enjoyed by people of several different faiths, but remains a holy day for Zoroastrians, Bahais, and some Muslim communities.
  Nowruz is the day of the vernal equinox, and marks the beginning of spring in the Northern Hemisphere. It marks the first day of the first month of the Iranian calendars. It usually occurs on March 21 or the previous or following day, depending on where it is observed. The moment the Sun crosses the celestial equator and equalizes night and day is calculated exactly every year, and families gather together to observe the rituals.
context_section_description: Nowruz's timing in Iran is based on Solar Hijri algorithmic calendar, which is based on precise astronomical observations, and moreover use of sophisticated intercalation system, which makes it more accurate than its European counterpart, the Gregorian calendar.
  Each 2820 year great grand cycle contains 2137 normal years of 365 days and 683 leap years of 366 days, with the average year length over the great grand cycle of 365.24219852. This average is just 0.00000026 (2.6×10⁻⁷) of a day shorter than Newcomb's value for the mean tropical year of 365.24219878 days, but differs considerably more from the current average vernal equinox year of 365.242362 days, which means that the new year, intended to fall on the vernal equinox, would drift by half a day over the course of a cycle. As the source explains, the 2820-year cycle is erroneous and has never been used in practice.
caption: Illumination of the Earth by the Sun on the day of equinox
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