Traditional study of Jyotiṣa is derived from śloka from the Bṛhat Parāśara Horā Śāstra. This most comprehensive text on Vedic natal astrology was written by Sage Parāśara, father of Vedavyāsa. You can find an online version of Bṛhat Parāśara Horā Śāstra or BPHS here: https://archive.org/details/BPHSEnglish