About Tishtar:

 

Tishtar, one of my most favorite names, is the name of the brightest star, Sirius, in the night sky of our planet, the Earth, in ancient Persian!

 

In addition, there is a historical story behind this name:

Tiregan or Jashn-e Tiregan is an ancient Iranian rain festival, observed on the first of July. This festival is one of the four most widely celebrated feasts (along with Mehregan, Yalda and Norooz) amongst Iranians.
This event is celebrated in July (the Tir Month of the Persian calendar) and refers to the archangel Tir (arrow) or Tishtar (lightning bolt) who appeared in the sky to generate thunder and lightning for much needed rain. Tir in modern Persian; Tishtar in Middle Persian or Pahlavi; and Avestan Tishtrya, is the Yazad presiding over the Star Sirius, the brightest star in the night-time sky, and of rain, and thus Tir Yazad especially invoked to enhance harvest and counter drought (Av. Apaosha).
Legend says that Arash-e Kamangir was a man chosen to settle a land dispute between two leaders, Iran and Turan. Arash was to shoot his arrow on the 13th day of Tir and where the arrow landed, there would lie the border between the two kingdoms.
Turan, who had suffered from the lack of rain, and Iran rejoiced the settlement of the borders, the peace and rain poured onto the two countries. Today, some Iranians celebrate this occasion with dancing, singing, reciting poetry and serving spinach soup and Sholeh-zard. It has also been observed that during this celebration children rejoice by swimming in streams and splashing water around. The custom of tying rainbow-colored bands on their wrists, which are worn for ten days and then thrown into a stream, is also a great way to rejoice for kids.