The Ujjain Observatory, established in the 5th century BCE, is believed to be the oldest astronomical observatory in the world.

Varāhamihira, a renowned astronomer and mathematician, is credited with establishing the Ujjain Observatory.

Ancient Indian observatories were used for various purposes, including observing celestial bodies, predicting eclipses, and measuring the Earth's circumference.

Aryabhata, a renowned astronomer and mathematician, developed a geocentric model of the universe, where the Earth was considered the center of the universe.

The gnomon, a simple yet effective instrument, was used by ancient Indian astronomers to measure the altitude of celestial bodies.

Maharaja Jai Singh II constructed five Jantar Mantars, astronomical observatories, in various cities across India, including Delhi, Jaipur, Ujjain, Varanasi, and Mathura.

Stone was the primary material used in the construction of ancient Indian observatories, ensuring their durability and longevity.

Aryabhata, in his treatise 'Aryabhatiya,' proposed that the Earth rotates on its axis, a revolutionary concept at the time.

The sundial, a simple yet effective instrument, was used by ancient Indian astronomers to measure the time of day.

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

The quadrant, a quarter-circle instrument, was used by ancient Indian astronomers to measure the angular distance between celestial bodies.

None of the ancient Indian astronomers mentioned developed a heliocentric model of the universe.

The astrolabe, a versatile instrument, was used by ancient Indian astronomers to observe celestial bodies and make various astronomical calculations.

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

Ancient Indian astronomers did not have instruments capable of measuring the distance between celestial bodies.