Instead, they returned to a fixed-length calendar that had 12 months of 30 days each, but with five days added at the end.10 Usually at a date later than the mid-eighth century B. E., many other peoples who had previously considered the year to be 360 days in length reluctantly returned to a calendar of twelve 30-day months, but added five days to the end of their year. with the birth of their founder, the prophet Zoroaster, use a calendar of 365 days.This is still done for the Islamic Calendar, but a new moon’s date is calculated for traditional lunar calendars that are currently used in China and India.During the period when month lengths were not fixed, new moons were usually sighted after either 29 or 30 days.These two calendars are identical except for year number. One of Alexander the Great’s generals, Seleucus Nicator, founded (late 4th Century BCE and early 3rd century BCE) an empire that stretched from Asia Minor to India.
E., civilizations all over the world either discarded or modified their old 360 day calendars.These additional days were considered to be very unlucky or unpropitious. Both of them observe three 365 day years followed by one 366 day year. It consists of twelve 30-day months with five "gatha days" added at the end of the year.