In the Gupta age, Varahamihira wrote the famous book, Brihat Santhita. It was a treatise on—

Varahamihira was a prominent mathematician, astronomer, and astrologer who lived in Ujjain during the Gupta period [1]. His encyclopedic work, the Brihat Samhita, is a comprehensive treatise that integrates scientific observation with traditional knowledge [1]. While the text covers a vast array of subjects including architecture, meteorology, agriculture, and gemology, its core foundation lies in astronomy and astrology (Jyotisha) [1]. It serves as a critical resource for understanding ancient Indian cosmology and astronomical calculations, such as planetary positions and eclipses. Varahamihira is credited with synthesizing Indian, Greek, and Roman astronomical knowledge, making the Brihat Samhita a landmark text in the history of science. Other notable works by him include the Pancha-Siddhantika, which summarizes five earlier astronomical systems [2]. Therefore, among the given options, astronomy is the most accurate description of the treatise's primary focus.

Sources

1. [1] Exploring Society:India and Beyond ,Social Science-Class VII . NCERT(Revised ed 2025) > Chapter 7: The Gupta Era: An Age of Tireless Creativity > New Ideas and Wonders: The Classical Age > p. 158
2. [2] History , class XI (Tamilnadu state board 2024 ed.) > Chapter 7: The Guptas > Mathematics and Astronomy > p. 100