Lagadha, who lived around 1400 BCE, is considered to be the first Indian astronomer.

Aryabhata, in his book 'Aryabhatiya', proposed the heliocentric model of the solar system, which places the Sun at the center of the solar system.

Aryabhata, in his book 'Aryabhatiya', calculated the Earth's circumference to be 4967 miles, which is remarkably close to the modern value of 40,075.017 kilometers.

Bhaskara II, in his book 'Siddhanta Shiromani', developed the concept of 'sine' and 'cosine' functions, which are essential in trigonometry.

Brahmagupta, in his book 'Brahma Sphuta Siddhanta', proposed the existence of gravitational force, which he called 'gurutvakarshan'.

Aryabhata, in his book 'Aryabhatiya', developed the theory of planetary motion, which explained the movement of planets around the Sun.

Lagadha, in his book 'Vedanga Jyotisha', observed and recorded a solar eclipse in 1400 BCE.

Aryabhata, in his book 'Aryabhatiya', developed the concept of 'zero' and introduced it to mathematics.

Brahmagupta, in his book 'Brahma Sphuta Siddhanta', developed a method for calculating the time of sunrise and sunset.

Aryabhata, in his book 'Aryabhatiya', developed a method for calculating the positions of planets and stars.

Aryabhata, in his book 'Aryabhatiya', proposed the existence of other galaxies beyond our own.

Aryabhata, in his book 'Aryabhatiya', developed a method for calculating the distance between the Earth and the Moon.

Aryabhata, in his book 'Aryabhatiya', developed a method for calculating the time of lunar and solar eclipses.

Bhaskara II, in his book 'Siddhanta Shiromani', developed a method for calculating the positions of planets and stars using trigonometry.

None of the early Indian astronomers proposed the existence of black holes.