Nowruz, historically and in contemporary times, is the celebration of the traditional Iranian new year holiday and is celebrated throughout the countries of the Middle East and Central Asia such as in Iran, Azerbaijan, Turkey, Iraq, Armenia, Georgia, Russia, Afghanistan, Pakistan, Syria, and Tajikistan Kurdistan. Since ancient times it has been a national holiday in Iran and was celebrated by more than one religious group. The Báb, the founder of Bábism, and then Bahá'u'lláh, the founder of the Bahá'í Faith, adopted the day as a holy day and associated it with the Most Great Name of God.
The Báb, the founder of Bábi religion, instituted the Badí' calendar composed of 19 months, each of 19 days. The first month, and the first day of each month, are both named Bahá, an Arabic word meaning splendour or glory. Thus Naw-Rúz, the first day of the year, is the day of Bahá in the month of Bahá. The day was called the Day of God by the Báb, and was associated with He whom God shall make manifest, a messianic figure in the Báb's writings.
Bahá'u'lláh, the founder of the Bahá'í Faith who is recognized as the messianic figure expected by the Báb, adopted the new calendar and the use of Naw-Rúz as a holy day. The day follows the Bahá'í month of fasting, and he explained that Naw-Rúz was associated with the Most Great Name of God, and was instituted as a festival for those who observed the fast.
The symbolic notion of the renewal of time in each religious dispensation was made explicit by the writings of the Báb and Bahá'u'lláh and the calendar and the new year made this spiritual metaphor more concrete. `Abdu'l-Bahá, Bahá'u'lláh's son and successor, explained that significance of Naw-Rúz in terms of spring and the new life it brings. He explained that the equinox is a symbol of the Manifestations of God, who include Jesus, Muhammad, the Báb and Bahá'u'lláh among others, and the message that they proclaim is like a spiritual springtime, and that Naw-Rúz is used to commemorate it.
Bahá'u'lláh, in the Kitáb-i-Aqdas, defines Naw-Rúz as the day on which the vernal equinox occurs. The exact timing of Naw-Rúz for Bahá'ís worldwide depends on the choice of a particular spot on the Earth and was left to the Universal House of Justice, the governing body of the Bahá'ís to decide. In 2014, the Universal House of Justice chose Tehran as the particular spot. Since Bahá'í days start at sundown, if the equinox occurs just before sunset, the day which started on the previous sunset is Naw-Rúz. Thus Naw-Rúz could fall on either March 20, 21st or 22nd of the Gregorian calendar, though these dates are pre-calculated years in advance. All dates in the Bahá'í calendar are set in relation to Naw-Rúz and thus may shift on the Gregorian calendar by a day or two depending on the timing of the vernal equinox.
Naw-Rúz is one of nine Bahá'í holy days where work and school must be suspended; the only one that is not associated with an event in the lives of either the Báb or Bahá'u'lláh. It is usually a festive event observed with meetings for prayer and music and dancing. Since the new year also ends the Bahá'í month of fasting the celebration is often combined with a dinner. As with all Bahá'í holy days, there are few fixed rules for observing Naw-Rúz, and Bahá'ís all over the world celebrate it as a festive day, according to local custom. Persian Bahá'ís observe many of the Iranian customs associated with Nowruz such as the Haft Sîn, but American Bahá'í communities, for example, may have a potluck dinner, along with prayers and readings from Bahá'í scripture.