Zoroastrians celebrate March 26 as the birthday of the prophet Zarathustra (Zoroaster). His birth date, and even the century in which he was born, are unknown; March 26 is the sixth day after Nau Ruz (New Year). Some call this day "Greater "Nau Ruz." As this site indicates, on Khordad Sal prayers are offered, scriptures read, and parties happen to celebrate the day. "Parsi families come together during the festivities that are put on during Khordad Sal – if families are unable to be together then prayers are offered for those who are not in attendance. It is an important celebration for the Parsi community and because family (and community) is central to the themes of Zoroastrianism guests are invited to participate in the festivities. Parsis also take the time during Khordad Sal to be introspective. They look at ways in which they can improve the lives of others and themselves." See also this site.