Bahá'u'lláh was born in Tehran in 1817. The first and second days after the eighth new moon following Naw-Rúz, so they move from year to year. Work is suspended. The Festivals of the Twin Birthdays or the Twin Holy Birthdays refers to two successive holy days in the Baháʼí calendar that celebrate the births of two central figures of the Baháʼí Faith. The two holy days are the birth of the Báb on the first day of Muharram in the Islamic calendar (20 October 1819) and the birth of Baháʼu'lláh on the second day of Muharram (two years prior, on 12 November 1817). Wiki link Dates computed on the Badí' calendar from Tehran's equinox, sunsets and new moons (before 2015, the West's fixed dates). Text: Wikipedia (CC BY-SA).