Varahamihira is an ancient astronomer. He was a renowned Indian mathematician, astronomer, and astrologer who lived during the 6th century AD. Varahamihira made significant contributions to the field of astronomy and astrology in ancient India. He is best known for his work in the field of mathematical astronomy, where he developed mathematical formulas and calculations to accurately predict celestial movements and events. His major work, the Brihat Samhita, covers various subjects including astrology, astronomy, architecture, and more. Varahamihira`s teachings and works have greatly influenced the development of astronomy and astrology not only in India but also across the world. Therefore, option 4, "an ancient astronomer," is the correct answer.