Nowruz runs on a calendar more precise than the Gregorian one
The Persian New Year starts at the exact moment spring does. If the March equinox arrives before noon in Tehran, that day is Nowruz; after noon, it moves to tomorrow. Omar Khayyam helped fix that rule in the 11th century, and the festival behind it is over 3,000 years old.
Nowruz simply means new day, joining the Persian now, new, and ruz, day. Middle Persian said Nogroz and Classical Persian Nawroz, and English spellings range from Norooz and Novruz to Navruz and Newroz. It marks the first day of Farvardin, opening the Solar Hijri calendar, which is official in Iran and was formerly used in Afghanistan, and it usually lands between 19 and 22 March.
The festival grew from Zoroastrianism and has been kept for more than three millennia across West and Central Asia, the Caucasus, the Black Sea region, the Balkans and South Asia. Most people now treat it as a secular holiday, but it remains sacred for Zoroastrians, Baha'is and Ismaili Shia Muslims. In February 2010 the UN General Assembly declared an International Day of Nowruz.
The astronomy is unusually careful. The medieval astronomer Tusi defined the new year as the day the sun entered Aries before noon. Leap years are spread across a vast 2,820-year cycle holding 2,137 ordinary years and 683 leap years, giving an average of 365.24219852 days. That is only about a fiftieth of a second off Newcomb's figure for the mean tropical year, though it differs more from the present vernal equinox year, so the new year can wander by half a day over a full cycle.
Customs differ from one community to another but lean on fire and water, dance, gifts and poetry. In Iran the prelude is Chaharshanbe Suri, festive Wednesday, held on the eve of the final Wednesday before the new year, when people leap over bonfires and set off fireworks. Azerbaijanis begin a month ahead, dedicating each of the four preceding Tuesdays to an element, water, fire, earth or wind, and tending relatives' graves on the eve.
Source: Nowruz
