Yantras are ancient Indian astronomical instruments used to measure the altitude of celestial bodies. They are typically made of brass or copper and have a circular or square shape with a series of concentric circles and lines.

The Nakshatravalaya was a versatile instrument that could be used to measure the altitude of celestial bodies, determine the time of day, and predict eclipses.

The Jantar Mantar in Jaipur is a collection of 19 architectural astronomical instruments built by Maharaja Jai Singh II in the early 18th century.

The Samrat Yantra is located in Jaipur, India, and is the largest sundial in the world.

The Jai Prakash Yantra is located in Jaipur, India, and is a large equinoctial sundial.

The Ram Yantra is located in Jaipur, India, and is a cylindrical sundial.

The Misra Yantra is located in Jaipur, India, and is a combination of a sundial and a quadrant.

The Chakra Yantra is located in Ujjain, India, and is a large stone sundial.

The Nadi Valaya Yantra is located in Ujjain, India, and is a ring sundial.

The Dhruva Darshak Yantra is located in Varanasi, India, and is a pillar sundial.

The Vrihat Samhita was written by Varahamihira, an ancient Indian astronomer and mathematician.

The Surya Siddhanta was written by Aryabhata, an ancient Indian astronomer and mathematician.

The Panchasiddhantika was written by Varahamihira, an ancient Indian astronomer and mathematician.

The Siddhanta Shiromani was written by Bhaskara II, an ancient Indian astronomer and mathematician.

The Lilavati was written by Bhaskara II, an ancient Indian astronomer and mathematician.