We see that the Soma (plant and its extract) is one of the chiefly mentioned subjects in the Vedic literature. Especially in the rig veda there are many mantras and hymns dedicated to soma and its extraction and related rituals.
How many hymns are there in the vedas (rig veda or other) which are exclusively dedicated to soma?
115 Hymns of the Rig Veda. Chandra the moon god, aka Soma, was an important Vedic god because he is the god of the Soma drink, which is vital to many Yagnaas. In any case, Rishis and Devatas of the hymns of the Rig Veda are given in my answer here. As per your specifications, I'm excluding hymns that are partially addressed to Chandra and partially addressed to some other god or gods. So here are the hymns of the Rig Veda that are entirely addressed to him:
111 of the hymns of Book 9, known as the Soma Mandala, praise Chandra as Soma Pavamana or the clear-flowing form of Soma. Book 9 consists of 114 hymns, but three of them are either not addressed to Chandra at all, or only partially addressed to Chandra: Hymn 5, Hymn 66, and Hymn 67. In any case, the hymns of Book 9 were heard by a variety of different sages.
Book 10 Hymn 25, which was heard by either Vimada Aindra, Vimada Prajapatya, or Vasukrit Vasukra.
As a point of comparison, there are 1028 hymns in the Rig Veda Samhita. So it's over 11% of the total number of hymns.
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