The Rigveda, one of the four Vedas, contains hymns and verses that mention astronomical observations and celestial bodies.

Astronomy was primarily used to determine the auspicious times for religious ceremonies and festivals.

Varahamihira, in his work 'Brihat Samhita', described the zodiac and its 12 signs.

Maharaja Jai Singh II built five Jantar Mantars in different cities, including Delhi, Jaipur, Ujjain, Varanasi, and Mathura.

Aryabhata, in his work 'Aryabhatiya', proposed that the Earth rotates on its axis and the planets revolve around the Sun.

The quadrant was a quarter-circle instrument used to measure the altitude of celestial bodies above the horizon.

Aryabhata, in his work 'Aryabhatiya', developed a method for calculating the circumference of the Earth using the concept of the Earth's shadow.

The sundial was the most common instrument used to measure time in ancient India.

Bhaskara II, in his work 'Siddhanta Shiromani', developed a theory of planetary motion based on elliptical orbits.

The heliostat was an instrument used to reflect sunlight onto a fixed surface for observation.

Brahmagupta, in his work 'Brahmasphuta Siddhanta', developed a method for calculating the position of the Moon.

The Jacob's staff was an instrument used to measure the distance between celestial bodies.

Ptolemy, a Greek astronomer, developed a theory of planetary motion based on epicycles and deferents, which was adopted by some ancient Indian astronomers.

The armillary sphere was an instrument used to observe the stars and their positions.

Varahamihira, in his work 'Brihat Samhita', developed a method for calculating the time of sunrise and sunset.