Norouz, also spelled Nowruz or Nawroz, is the Persian New Year celebrated by millions of people worldwide, particularly in Iran, Afghanistan, Tajikistan, and parts of Central Asia. The word "Norouz" means "New Day" and it marks the first day of the Persian calendar, which falls on the spring equinox, usually around March 21st.
Sadeh meaning hundred, is a mid winter feast that was celebrated with grandeur and magnificence in ancient Iran. It was a festivity to honor fire and to defeat the forces of darkness, frost and cold. Two different days were observed for its veneration. One celebration marked the hundred day before the religious No Ruz on the first day of the month Farvardin (religious No Ruz is different from spring No Ruz). The other one was the hundredth day after the gahambar of Ayathrima (one of the six feasts of obligation) held to be the beginning of winter. This day coincides with 10th of Bahman in present calendar. It is not clear why there are two Sadeh Festivals and why different regions have had different dates. Many of Zoroastrian holy days were and are celebrated twice; this is most likely caused by the calendar reform in the 3rd century AD.