Aryabhata is widely regarded as the father of Indian astronomy due to his significant contributions to the field. He lived in the 5th century CE and is known for his work on astronomy, mathematics, and physics.

Aryabhata was the first astronomer to propose the heliocentric model of the solar system, where the Earth and other planets revolve around the Sun. This concept was revolutionary for its time and challenged the prevailing geocentric model.

The gnomon was the primary instrument used by ancient Indian astronomers for observing celestial bodies. It is a simple device consisting of a vertical rod or pillar that casts a shadow. By measuring the length and direction of the shadow, astronomers could determine the time of day, the altitude of celestial objects, and the position of the Sun and stars.

Aryabhata developed a method for calculating the circumference of the Earth using trigonometry. He estimated the Earth's circumference to be approximately 24,835 miles, which is remarkably close to the modern value.

Maharaja Jai Singh II constructed five astronomical observatories known as Jantar Mantar in various cities across India. These observatories were equipped with large instruments for observing celestial bodies and were used to study astronomy, astrology, and timekeeping.

Varahamihira wrote the astronomical treatise 'Surya Siddhanta,' which is considered one of the most important works in ancient Indian astronomy. It covers various topics, including planetary motions, eclipses, and the calculation of time.

The quadrant was an astronomical instrument used by ancient Indian astronomers to measure the altitude of celestial bodies. It consisted of a quarter-circle arc with markings for measuring angles.

Brahmagupta developed a method for calculating the time of eclipses, which was a significant achievement in ancient Indian astronomy. His method involved using mathematical calculations to predict the occurrence of eclipses.

The sundial was an astronomical instrument used by ancient Indian astronomers to measure the time of day. It consisted of a rod or pillar with markings that indicated the time based on the position of the Sun.

Varahamihira wrote the astronomical treatise 'Panchasiddhantika,' which is a compilation of five astronomical treatises from different schools of thought. It covers various topics, including planetary motions, eclipses, and the calculation of time.

The Yasti Yantra was an astronomical instrument used by ancient Indian astronomers to measure the distance between celestial bodies. It consisted of a long rod or pole that was used to sight celestial objects and determine their angular separation.

Bhaskara II developed a method for calculating the position of planets using mathematical calculations. His method involved using trigonometric functions to determine the position of planets in the sky.

The Dhruva Yantra was an astronomical instrument used by ancient Indian astronomers to measure the time of sunrise and sunset. It consisted of a vertical rod or pillar with markings that indicated the time based on the position of the Sun.

Bhaskara II wrote the astronomical treatise 'Lilavati,' which is a comprehensive work on mathematics and astronomy. It covers various topics, including arithmetic, geometry, algebra, and astronomy.