Step 1:
Bṛhatsamhitā is a celebrated Sanskrit encyclopedic work.
Step 2:
It was composed by Varāhamihira.
Step 3:
The text mainly deals with astronomy, astrology, omens, and related sciences.
Step 4:
Hence, the correct answer is:
\[
\boxed{\text{(3) Jyotiṣaśāstra}}
\]