Jantar Mantar is a collection of astronomical instruments built by Maharaja Jai Singh II in various cities across India, including Delhi, Jaipur, Ujjain, and Varanasi.

The main purpose of the ancient Indian observatories was to observe celestial bodies, such as the sun, moon, stars, and planets, in order to understand their movements and patterns.

The Ujjain Observatory, established in ancient Ujjain, is renowned for its precise calculations of the Earth's circumference, which were remarkably close to modern measurements.

Aryabhata, a prominent ancient Indian astronomer, proposed a geocentric model of the universe, where the Earth was considered the center of the universe.

The Takshashila Observatory, located in ancient Takshashila, was dedicated to studying the motion of the planets and their positions in the sky.

Bhaskara II, a renowned ancient Indian astronomer, proposed the heliocentric model of the universe, where the sun was considered the center of the universe.

The Nalanda Observatory, located in ancient Nalanda, was used to observe eclipses, comets, and other celestial phenomena.

The ancient Indian observatories played a crucial role in creating accurate calendars, which were essential for agricultural and religious purposes.

Varahamihira, a prominent ancient Indian astronomer, developed a system for calculating the positions of celestial bodies, which was used for astrological purposes.

The Ujjain Observatory was used to study the precession of the equinoxes, which is the gradual shift in the position of the equinoxes over time.

Brahmagupta, a renowned ancient Indian astronomer, developed a theory of gravity, which was later refined by Isaac Newton.

The ancient Indian observatories were used to determine the direction of the North Star, which was essential for navigation purposes.

Varahamihira, a prominent ancient Indian astronomer, developed a system for predicting eclipses, which was based on his observations and calculations.

The Ujjain Observatory was used to study the motion of the moon and its position relative to the Earth.

Aryabhata, a renowned ancient Indian astronomer, developed a system for measuring the distance to celestial bodies, which was based on trigonometry.