Ancient Indian astronomers used a variety of instruments to measure the positions of celestial bodies, including the astrolabe, sundial, and quadrant.

The Jantar Mantar is an observatory that was built by Maharaja Jai Singh II in the 18th century. It consists of a collection of architectural structures designed for astronomical observations.

The armillary sphere was primarily used to observe the motion of planets and understand their positions in the sky.

Varāhamihira, a renowned astronomer and astrologer, is credited with developing the concept of the zodiac and the system of 12 zodiac signs in ancient India.

Ancient Indian astronomers recognized 27 Nakshatras, or lunar mansions, which are significant in astrology and astronomy.

The Surya Siddhanta is primarily concerned with the Sun and its motion, providing detailed information about its position, movement, and eclipses.

Aryabhata, a brilliant astronomer and mathematician, proposed the theory of the Earth's rotation on its axis, challenging the prevailing belief of a stationary Earth.

The Yantra Raj Yantra is an equatorial sundial, designed to accurately measure time based on the Sun's position in the sky.

Varāhamihira, in his astronomical treatise, proposed the concept of the nine planets, including Rahu and Ketu, which are significant in Hindu astrology.

The Brihat Samhita by Varāhamihira covers topics such as astronomy, astrology, and architecture, but it does not include medicine.

The Lilavati by Bhaskara II is primarily focused on arithmetic and provides detailed explanations of various mathematical operations and concepts.

Aryabhata, through his astronomical observations, recognized and described the phenomenon of the precession of the equinoxes.

The Siddhānta Shiromani by Bhaskara II is divided into four chapters, each covering different aspects of astronomy and mathematics.

Aryabhata devised a method for calculating the circumference of the Earth based on the angle of depression of a star.