During maiðiiö-šam “mid-summer” celebrations, circa two weeks after summer solstice, the festival of ti.štr.iiá or tristar is observed in the Avestan calendar.
Ti.štr.iiá is the brightest and most glorious of the stars in the Zoroastrian sacred lore, and is venerated as a “god being-life-force” ahü and “knower of riddles, most learned master” ratü.
The 8th Yasht (hymn, adoration) in the Avesta is devoted to tristar as a God-star and yazatá. The term yazatá denotes “pure energy, animating force, vital principle and holiness.” It is etymologically the same as Greek hagios.
Bernhard Forssman derives ti.štr.iiá from the Indo European *tri-str-iḭo or *tri-str-iyo literally TRISTAR. By ti.štr.iiá, Sirius as the most brilliant triangle star in the Orion belt is meant.
The epithet of ti.štr.iiá is afš.ciθra “having the brilliance of the waters/rains” (Panaino, 1990, pp. 92-93; cf. Cantera, 1997). The Persian proverb that “waters are luminosity” goes back to the Avestan Yasht devoted to ti.štr.iiá, where the falling of the rains, and flowing of waters is linked to the brilliance/radiance of the stars and constellations specifically Sirius.
Also a clear link to the astral theme of the heavenly “arrow” tigra/tigri is present in the Avestan hymn, in respect to tristar or ti.štr.iiá.
According to Yasht 8th 6-7 and 37-38, ti.štr.iiá flies in the sky as the “arrow” tigra/tigri shot by the most valiant archer of the Aryans, the hero Ereḵša (Kellens 1977).
The name of the most valiant Archer of the Aryans ereḵša literally means “bear,” and is a cognate of Greek árktos, Latin ursa /ursus, all coming from reconstructed Indo-European *hŕ̥ḱtós or*hréḱtes.
The Avestan hymn to ti.štr.iiá contains two narratives, one concerning ti.štr.iiá’s fight with apaôša (drought, literally demise/loss of waters) and the latter battke with the pairikās (mischievous fairies), corresponding to shooting comets (literally worm stars) stárö kərəm.áv.
The first narrative poem (stanzas 13-34) describes the combat of the tristar yazatá (pure energy, god-force) against apaôša (drought) for the liberation of the waters, contained in the cosmic ocean vôúrû.kaša “vast expanse of waters or wide shored sea.”
Ti.štr.iiá assumes three diferent incarnations in the hymn, taking ten days for each; the star successively changes the form of his form into a fifteen-year-old man at the prime of his youth, a bull with golden horns, and finally a splendid white stallion/horse.
These three transformations astronomically cover the period beginning with the heliacal rising of the star Sirius in July and lasting till the first appearance of the meteor showers between August and September (Panaino, 1995, pp. 15-24).
In the shape of a beautiful, white stallion ti.štr.iiá attacks drought, incarnated as a black, dismal and gloomy horse, but after three days and nights, ti.štr.iiá is defeated at first, because the tristar yazatá was not sufficiently worshipped by the Aryans (see Yašt. 8.24).
Yazatás and Immortals are in essence mainiiü “sheer will and the creative power of thoughts/consciousness.” Their powers are unleashed proportional to the amount of concentration/belief in their “mind energy.” Collective belief in and focus on their archetypal ideals releases their vital force and affect the world accordingly.
After a fervent yasná “yearning, fervent desire” (Compare with Greek zelos,) offered by the supreme god Ahûrá Mazdá himself in favor of his star champion, ti.štr.iiá defeats the dismal drought at midday; thus the waters of the cosmic ocean are freed and can be distributed among the seven climes hapta karšvars (Yt. 8.32).
According to the Avestan hymn, other constellations and stars also collaborate with ti.štr.iiá specially the constellation of Canis Minor.
The second narrative poem concerns the struggle of ti.štr.iiá against pairikās (mischievous fairies,) led by duž-yáiriia “the bad/terrible year.” The “bad/horrible year” duž-yáiriia is supported by the stárö kərəm.áv “shooting comets” (literally worm stars) with the purpose of bringing chaos into the energetic radiance of the constellations and stars.
I shall conclude by adding that in the Avesta, Yašt 6 pays homage to the sun, Yašt 7 to the moon, Yašt 8 to ti.štriiá or Sirius, and Yašt 10 to miθra “Lord of the celestial lights and friendship with the Spiritual Immortals.” Also, the 13th day of each Avestan month falls under the patronage of ti.štr.iiá and therefore is considered as an auspicious, lucky day for Zoroastrians, since ti.štr.iiá or tistar is the protagonist of radiance, luminosity, waters/rain and blessings!
Finally, Indo Iranian tigra/tigri “arrow” associated with tri-star in the Avesta, has become the name for the first month of the summer in Persian tīr. The Armenian proper name Tigran/Tigranes comes from the same root. The term has also been borrowed into ancient Greek tígris and Latin tigris “tiger, pointed, sharp.”