The Ujjain Observatory, located in the city of Ujjain, Madhya Pradesh, is believed to be the oldest astronomical observatory in the world. It was established around 500 BCE and was a major center for astronomical studies in ancient India.

Varāhamihira, a renowned Indian astronomer and mathematician, is credited with establishing the Ujjain Observatory. He was a pioneer in the field of astronomy and made significant contributions to the development of astronomical knowledge in ancient India.

Jantar Mantar, an astronomical observatory located in Jaipur, Rajasthan, is renowned for its unique sundial, the Samrat Yantra. The Samrat Yantra is a large sundial that accurately measures time and is a testament to the advanced astronomical knowledge of ancient India.

Sawai Jai Singh II, the Maharaja of Jaipur, commissioned the construction of Jantar Mantar. He was a keen astronomer and mathematician and wanted to create an observatory that would help him study astronomy and make accurate astronomical observations.

The Nalanda Observatory is associated with the astronomer Aryabhata. He was a renowned mathematician and astronomer who made significant contributions to the field of astronomy. The Nalanda Observatory was a major center for astronomical studies during Aryabhata's time.

Varāhamihira wrote an astronomical treatise called Brihat Samhita. This treatise covers various aspects of astronomy, including planetary motions, eclipses, and astrology. It is a valuable source of information about ancient Indian astronomy.

Man Mandir is an ancient Indian astronomical observatory located in the city of Varanasi, Uttar Pradesh. It was built by Raja Man Singh I in the 16th century and was used for astronomical observations and studies.

The quadrant is an astronomical instrument used to measure the altitude of celestial bodies. It is a quarter-circle divided into degrees and minutes and is used to measure the angular distance between the horizon and a celestial body.

Jantar Mantar is an ancient Indian astronomical observatory located in the city of Delhi. It was built by Maharaja Jai Singh II in the 18th century and is a UNESCO World Heritage Site.

The sundial is an astronomical instrument used to measure the time of day. It consists of a gnomon, which is a rod or pole that casts a shadow, and a dial, which is a flat surface marked with hour lines. The shadow of the gnomon falls on the dial, indicating the time of day.

Vedhshala is an ancient Indian astronomical observatory located in the city of Mathura, Uttar Pradesh. It was built by Maharaja Jai Singh II in the 18th century and is a UNESCO World Heritage Site.

The sextant is an astronomical instrument used to measure the angular distance between two celestial bodies. It consists of two mirrors and a graduated arc and is used to measure the angle between the horizon and a celestial body.

Mirzam Observatory is an ancient Indian astronomical observatory located in the city of Hyderabad, Telangana. It was built by Nawab Mir Nizam Ali Khan in the 18th century and is a UNESCO World Heritage Site.

The armillary sphere is an astronomical instrument used to measure the position of stars and planets. It consists of a series of concentric rings that represent the celestial sphere and is used to demonstrate the motion of celestial bodies.

Raja Bhoj Observatory is an ancient Indian astronomical observatory located in the city of Bhopal, Madhya Pradesh. It was built by Raja Bhoj in the 11th century and is a UNESCO World Heritage Site.