Zoroastrian festivals

Zoroastrianism has numerous festivals and holy days, all of which are bound to the Zoroastrian calendar. The Shahenshahi and Kadmi variants of the calendar do not intercalcate leap years and hence the day of the Gregorian calendar year on which these days are celebrated shifts ahead with time. The third variant of the Zoroastrian calendar, known as either Fasli (in India) or Bastani (in Iran), intercalcates according to Gregorian calendar rules and thus remains synchronous with the seasons. For details on the differences, see Zoroastrian calendar.

Six irregularly-spaced seasonal festivals, called gahanbars (meaning "proper season"), are celebrated during the religious year. The six festivals are additionally associated with the six "primordial creations" of Ahura Mazda, otherwise known as the Amesha Spentas, and through them with aspects of creation (the sky, the waters, the earth, plant life, animal life, humankind). Due to the peculiarities of the Shahenshahi and Kadmi variants of the Zoroastrian calendar, which do not intercalate and are therefore no longer synchronized with the seasons, the seasonal festivals are actually celebrated many months in advance. The six festivals are:

In the present-day, each of these festivals is celebrated over five days, except Hamaspathmaidyem Gahambar which is held over ten days (two five-day periods, see "other holy days" below).

Originally, these seasonal festivals were celebrated on one day each, and were synchronous with the seasons. The Zoroastrian calendar was originally a 360-day luni-solar calendar, and also without intercalation, with the result that the seasons and the seasonal festivals gradually drifted apart. A first calendar reform (of uncertain date) introduced five epagomenal days at the end of the year, with the result that each festival then had two dates: one in the old 360-day calendar, and one in the new 365-day calendar. These apparently caused some confusion, and at some point the old and new festival days were joined together as six-day-long observations (later reduced to five). Additionally, Hamaspathmaidyem Gahanbar, originally held on the last day of the year, came to be held on the last days of the last month of the year and on the new five epagomena days at the end of the new 360-day year, for a total of ten days. A second reform, in the 4th or 5th century, introduced a one-month intercalation every 120 years, abruptly realigned the calendar such that the year began again on the spring equinox, and the Gahanbars were again in accord with the seasons. However, following the collapse of the Sassanian state, after which Zoroastrianism had no central authority to govern intercalation, the practice was not maintained. As a result, in living Zoroastrianism, the Gahanbar are again no longer synchronous with the seasons.

...
Wikipedia