The Ujjain Observatory was built in the 5th century BC and is considered to be the oldest known astronomical observatory in India.

Varahamihira was a renowned Indian astronomer and mathematician who founded the Ujjain Observatory in the 5th century BC.

Ancient Indian observatories were used for a variety of purposes, including studying the stars and planets, predicting eclipses and other celestial events, and creating calendars and almanacs.

Ancient Indian observatories used a variety of instruments, including the astrolabe, sundial, and armillary sphere, to study the stars and planets.

Aryabhata was the first ancient Indian astronomer to develop the concept of the zero in the 5th century AD.

Aryabhata was the first ancient Indian astronomer to develop the heliocentric model of the solar system in the 5th century AD.

Jantar Mantar is an astronomical observatory located in Delhi, India, and was built in the 18th century by Maharaja Jai Singh II.

Nalanda Observatory is an astronomical observatory located in Nalanda, Bihar, India, and was built in the 5th century AD.

Takshashila Observatory is an astronomical observatory located in Takshashila, Punjab, India, and was built in the 5th century BC.

Aryabhata was the first ancient Indian astronomer to develop the theory of planetary motion in the 5th century AD.

Bhaskaracharya was the first ancient Indian astronomer to develop the theory of gravity in the 12th century AD.

The theory of relativity was developed by Albert Einstein in the 20th century AD, and not by any ancient Indian astronomer.

Jantar Mantar is an astronomical observatory located in Jaipur, Rajasthan, India, and was built in the 18th century by Maharaja Jai Singh II.

Brahmagupta was the first ancient Indian astronomer to develop the theory of the precession of the equinoxes in the 7th century AD.

Bhaskaracharya was the first ancient Indian astronomer to develop the theory of the nutation of the Earth's axis in the 12th century AD.