Astronomy in Ancient India

Early cultures identified celestial objects with gods and spirits. They related these objects and their movements to predict things like rain, drought, seasons, and tides. The movements of Sun and Moon are used in calendars to measure the day, month and year. It is important to agricultural societies as they need to know the time to plant and harvest. Ancient societies also believed that the position of some celestial bodies have an impact on the human beings. The astronomy and the astrology of India are based upon the stars and the time it takes to make one full orbit around the Sun, relative to the stars.

The earliest references to astronomy are found in the Vedas which are dated around 3000 B.C. to 1000 B.C. By 500 AD, ancient Indian astronomy has emerged as an important part of Indian studies and its affect is also seen in several treatises of that period. In some instances, astronomical principles were borrowed to explain matters, pertaining to astrology, like casting of a horoscope. Apart from this linkage of astronomy with astrology in ancient India, science of astronomy continued to develop independently.

There are astronomical references of chronological significance in the Vedas. Some Vedic notices mark the beginning of the year and that of the vernal equinox in Orion.

Yajnavalkya (estimated 1800 BC) advanced a 95-year cycle to synchronize the motions of the sun and the moon. The Vedanga Jyotisha, a text on Vedic astrology that has been dated to 1350 BC, was written by Lagadha which describes rules for tracking the motions of the Sun and the Moon, and also develops the use of geometry and trigonometry for astronomical uses.

The sun (Surya) was one of the chief deities in the Vedas. He was recognized as the source of light (Dinkara), source of warmth (Bhaskara). In the Vedas sun is also referred to as the source of all life, the center of creation and the center of the spheres.

In Indian languages, the science of astronomy is called Khagola-shastra. The word Khagola perhaps is derived from the famous astronomical observatory at the University of Nalanda which was called Khagola. It was at Khagola that the famous 5th century Indian Astronomer Aryabhatta studied and extended the subject. In 500 AD, Aryabhata presented a mathematical system that took the earth to spin on its axis and considered the motions of the planets with respect to the sun. His book, the Aryabhatya, presented astronomical and mathematical theories in which the Earth was taken to be spinning on its axis and the periods of the planets were given with respect to the sun. Aryabhata wrote that 1,582,237,500 rotations of the Earth equal 57,753,336 lunar orbits which is an extremely accurate calculation.

The lack of a telescope hindered further advancement of ancient Indian astronomy. Though it should be admitted that with their unaided observations with crude instruments, the astronomers in ancient India were able to arrive at near perfect measurement of astronomical movements and predict eclipses. Indian astronomers also propounded the theory that the Earth was a sphere. Aryabhatta was the first one to have propounded this theory in the 5th century.

Another astronomer Varahamihira (476 A.D. – 587 A.D.) recognized that there should be a force which might be keeping bodies stuck to the Earth, and also keeping heavenly bodies in their determined places. Also recognized that this force is an attractive force. The Sanskrit term for gravity is Gurutvakarshan which is an amalgam of Guru-tva-akarshan. Akarshan means to be attracted, thus the fact that the character of this force was of attraction was also recognized. This apart, it seems that the function of attracting heavenly bodies was attributed to the sun.

Brahmagupta (598 A.D -668 A.D.) was the head of the astronomical observatory at Ujjain and during his tenure there wrote a text on astronomy, the Brahmasphutasiddhanta in 628. He was the earliest to use algebra to solve astronomical problems. He also develops methods for calculations of the motions and places of various planets, their rising and setting, conjunctions, and the calculation of eclipses of the Sun and the Moon. Brahmagupta estimated in the 7th century that the circumference of the earth was 5000 yojanas. A yojana is around 7.2 kms. Calculating on this basis we see that the estimate of 36,000 kms as the Earth's circumference comes quite close to the actual circumference known today. Brahmagupta, in the 7th century had said about gravity that ‘Bodies fall towards the Earth as it is in the nature of the Earth to attract bodies, just as it is in the nature of water to flow’.

Bhaskara (1114 A.D -1185 A.D.) was the head of the astronomical observatory at Ujjain, continuing the mathematical tradition of Brahmagupta. He wrote the Siddhantasiromani which consists of two parts: Goladhyaya (sphere) and Grahaganita (mathematics of the planets). He also calculated the time taken for the Earth to orbit the sun to 9 decimal places.

Other important astronomers from India include Madhava, Nilakantha Somayaji and Jyeshtadeva from the 14th century to the 16th century.