Aryabhata, in his book 'Aryabhatiya', proposed the heliocentric model of the solar system, where the Earth and other planets revolve around the Sun.

Ancient Indian observatories were used for various purposes, including astrological predictions, timekeeping, and navigation.

The Ujjain Observatory, built around the 5th century BCE, is considered the oldest astronomical observatory in the world.

Varahamihira, a renowned Indian astronomer and astrologer, is credited with founding the Ujjain Observatory.

The gnomon, a simple vertical rod, was the primary instrument used for astronomical observations in ancient Indian observatories.

Maharaja Jai Singh II constructed the Jantar Mantar observatory in Jaipur, India, in the 18th century.

The Jantar Mantar observatory in Jaipur consists of 20 instruments for astronomical observations.

The Samrat Yantra, a large sundial, is the largest instrument in the Jantar Mantar observatory.

The Nalanda Observatory was located in the ancient city of Nalanda, which was a renowned center of learning in ancient India.

The Nalanda Observatory was used for various purposes, including astrological predictions, timekeeping, and navigation.

The Takshashila Observatory was located in the ancient city of Takshashila, which was a renowned center of learning in ancient India.

The Takshashila Observatory was used for various purposes, including astrological predictions, timekeeping, and navigation.

Aryabhata wrote the book 'Surya Siddhanta', which is considered one of the most important texts in ancient Indian astronomy.

The main theme of the book 'Surya Siddhanta' is the geocentric model of the solar system, where the Earth is considered the center of the universe.

Brahmagupta wrote the book 'Brahma Sphuta Siddhanta', which is considered one of the most important texts in ancient Indian astronomy.

The main theme of the book 'Brahma Sphuta Siddhanta' is the geocentric model of the solar system, where the Earth is considered the center of the universe.