Zarthost No Deeso takes place in June, on Khorshed roz, Dae mah (11th day, 10th month) of the Zoroastrian calendar.

This is the day on which the death anniversary of the prophet symbolically falls.

Special prayers are recited and Zoroastrians go to the Fire Temple to pray. There aren't any elaborate celebrations on the day since it is a solemn occasion.

There are many versions of the legend of how Zarathushtra died. One says that in his 77th year, he was killed in a fire-temple by the Turanian army. A variation says that the person who was killed was not Zarathushtra but someone else; Zarathushtra himself ascended the skies.

There are also versions which say that the murderer was also killed on the spot by divine intervention, or that Zarathushtra was killed by a thunderbolt. Another legend says that Zarathushtra died in his sleep.

Rituals
There are no public functions to mark the day. Ceremonies and services are confined to either the home or to the temple. Special prayers are recited, and lectures and discourses are held on the life and works of the prophet.

Celebrated in
Zarthost No Deeso is observed in Mumbai and Gujarat particularly, and in other pockets which have a Parsi population.