A treasure for anyone interested in early modern India and the history of mathematics, this first English translation of the Siddhantasundara reveals the fascinating work of the scholar-astronomer Jnanaraja (circa 1500 C.E.). Toke Lindegaard Knudsen begins with an introduction to the traditions of ancient Hindu astronomy and describes what is known of Jnanaraja's life and family. He translates the Sanskrit verses into English and offers expert commentary on the style and substance of Jnanaraja's treatise.The Siddhantasundara contains a comprehensive exposition of the system of Indian astronomy, including how to compute planetary positions and eclipses. It also explores deep, probing questions about the workings of the universe and sacred Hindu traditions. In a philosophical discussion, the treatise seeks a synthesis between the cosmological model used by the Indian astronomical tradition and the cosmology of a class of texts sacred in Hinduism. In his discourse, which includes a discussion of the direction of down and adhesive antipodeans, Jnanaraja rejects certain principles from the astronomical tradition and reinterprets principles from the sacred texts. He also constructs a complex poem on the seasons, many verses of which have two layers of meaning, one describing a season, the other a god's activities in that season. The Siddhantasundara is the last major treatise of Indian astronomy and cosmology to receive serious scholarly attention, Knudsen's careful effort unveils the 500-year-old Sanskrit verses and shows the clever quirkiness of Jnanaraja's writing style, his keen use of mathematics, and his subtle philosophical arguments.