1. In the Zoroastrian prayers, there are 5 Nyash and about 20 Yashts. The Nyash may be considered as hymns or songs in praise of a particular creation. They are primarily directed to the creation and then to the divine being (Yazad) presiding over the creation. Each Nyash is dedicated to a radiant creation, as each one of these creations is connected to Khoreh “Divine energy” in one form or the other. All are store houses and conduits of Khoreh.
2. The Nyash are made up of prayers taken from other larger texts. Thus Khorshed Nyash is from Khorshed Yasht and Yasna 68, 33, 36, 43 and 68, the Meher Nyash from Meher Yasht, the Mah Bakhtar Nyash from Mohor Yasht, Avan Nyash from Avan Yasht and Yasna 65 and Atash Nyash from Yasna 33, 34, 62 and the Siroza Yasht.
2. Since the 5 Nyash are for the 5 radiant creations, they are to be preferably prayed facing the creations. Thus the Khorshed and Meher Nyash are to be prayed in presence of the sun, the Mah Bokhtar Nyash in presence of the moon (or in the open, even when one can’t see the moon), the Avan Ardvisur Nyash near waters (preferably flowing waters) and the Atash Nyash near fire or any natural light.
3. The Yashts are invocation prayers, manly for individual Ameshaspands or Yazads. There are two Yashts – the Haptan Yasht and the Siroza Yasht, which are for collective of Ameshaspands and Yazads. Thus the Yashts are directed towards the divine beings and not to the creations.
4. Some of the Yashts are taken from the Yasna too, like the Hom Yasht from Yasna 9,10 and Sarosh Yasht Vadi from Yasna 57.
5. Most Yashts can be recited in any of the five Gehs, the three exceptions being Avan Yasht which can only be recited during day time, Sarosh Yasht Hadokht which can not be recited in Aiwistuthrem Geh and Sarosh Yasht Vadi which can only be recited in the Awisruthrem Geh. Among the Nyash, Khorshed, Meher and Avan Ardvisur Nyash can be recited only during the 3 day time Gehs. Mah Bakhtar and Atash Nyash can be recited in any of the five Gehs.