Jashan-e Tiragan is an annual feast of Zoroastrianism: the feast of Tir or Tishtar. In Zoroastrianism, Tishtar is the yazad, or good spirit, of the star Sirius and the pre-harvest rains. The fourth month of the Zoroastrian calendar, Tir, is dedicated to Tishtar. As the thirteenth day of every month is sacred to Tishtar, 13 Tir is the date of Jashan-e Tiragan.
Jashan-e Tiragan traditionally marked the beginning of the dog days, the hottest days of the summer, evidenced by the helical rising of Sirius. In all but the reworked Fasli calendar, the feast now occurs at a different time of the year. Jashan-e Tiragan occurs in the middle of the ancient midsummer festival, or Maidyoshahem.
The three calendar systems used by Zoroastrians interpret 13 Tir as: