In the Zoroastrian religious calendar, the celebration of autumnal equinox is closely associated with Mehregán and the Old Avestan paitiš.hahaiia festival. Mehregán is a celebration of Miθrá, the god-force of “reciprocity, friendship” who is embodied in the first appearance of light in the sky before sunrise. The celebration of Miθrá reminds us of our duties and responsibilities toward Immortals and our sacred contract with Godhood. In the Zoroastrian Jurisprudence, our duties and responsibilities are the decisive factor that establish our role and identity.
In the Váršt.mánsar commentary of Yasna 46.5 of the gathas or poetic songs of Zarathustra, Miθrá is associated with the “light of knowledge, awareness and understanding of things”. Accordingly, it is our contract with the Gods and our duties and responsibilities that define us.
The celebration of equinoxes are among the most important festivals in the Zoroastrianseasonal calendar. The Avestan name of the festivals that correspond to the two equinoxes are hamas.paθ.maædhya (when the celestial paths are at a midpoint and stand at the same or an equal distance from each other, pertaining to Vernal Equinox and/or Nauvrooz) and paitiš.hahaiia (Festival of harvest and fruits, pertaining to Mehregán and/or Autumnal Equinox.)
The autumnal festivities in the Zoroastrian Iran were so elaborate and joyous that the term Mehergán has been borrowed into Arabic where the Arabic version of it or Mehreján refers to any joyous festival or festivity in general.
Paitiš.hahaiia literally means the “Lord/Master of Harvest and Fruits.” The second compound hahiia, means “harvest, crop, fruit.” Hittite še-e-šå “fruit, harvest, crop” is a cognate of Avestan hahaiia and the reconstructed Indo-European form is se-sh1-o- (sh1-es-o-) “crop, fruit, harvest.”
Paitiš.hahaiia is honored on 180th day of the seasonal calendar and is a celebration of “healthy abundance and wealth.” hahaiia comes in the poetic songs/gathas of Zarathustra in the form of haŋhüs referring to the “sunny fruits of good/superb mind.” (See Yasna 53.4, 3rd rhymed verse line.)
The celebration of paitiš.hahaiia emphasizes that Zoroastrianism greatly praises “prosperity and material wealth” based on “happiness and positive, peaceful mental attitude.”
There are two months in the Zoroastrian calendar that start with the equinoxes: the month of the Fravašịs (Archetypes, Heroic Ancestors) starting after the vernal equinox and the month of Miθrá starting after the autumnal equinox with the month of the waters (ábán) following the month of Miθrá.
Interestingly, the longest Avestan hymns or Yašts preserved in the sacred lore of the Zoroastrians (Avesta) are dedicated respectively to the Fravašịs (Archetypes, Heroic Ancestors,) Miθrá and Anáhita, the (Fair Mighty Lady of the Undefiled Waters.) The mention of Miθra and Anāhitā in the Old Persian inscriptions from Artaxerxes II could be an echo of this prominence of Miθrá and the Waters.