Count Bjornstjerna proves conclusively that Hindu astronomy was far advanced even at the beginning of the Kaliyug or Iron Age of the Hindus, about 5000 years ago.
They knew about the precession of the equinoxes anti about the diurnal revolution of the earth on its axis which the priests (Brahmins) discussed in the 5th century B.C.
The above quotations give some idea of the antiquity of the astronomical science of the ancient Hindus. There are numerous treatises written by famous scientists on astronomy and also astrology which was considered equally important. Some of the well known scientists were Parashar (12th century B. C.), Aryabhata and Varahamihira.
“The Hindu astronomers knew about and practiced .the division of the ecliptic into lunar mansions, the precession of the equinox, the earth’s self support in space the revolution of the moon on her axis, her distance from the earth, the dimensions of the orbits of the planet and the calculation of the eclipses.
The ancients knew about the roundness of the earth. In Aryabhateeya we read: ‘The earth, situated in the middle of the heaven and composed of five elements, is spherical in shape.
The theory of gravity is thus described in the Siddhanta Sirornani: ‘The earth, owing to its force of gravity, draws all things towards itself, and so they seem to fall towards the earth.
Another ancient scientist, Gargya, was the first enumerator of constellations and divided the zodiacalbeli into 27 equal parts. Varahamihira, son of Gautania is said to be the first person to identify Jupiter (Brihaspati), reference to which is to be found in the Rig-Veda.
Towards our time, A. D. 1727, we have Maharaja Jai Singh II, the builder of Jaipur, one of the earliest planned cities and of the famous observatories in Jaipur, Delhi, Varanasi, Mathura and Ujjain. A number of the instruments in these observatories are still working accurately. The sun—dial in Jaipur still gives the time with an accuracy of two seconds! Sawai Jai Singh corrected the Indian almanac also.