India’s contribution to the science of astronomy stretches way back in time, with the earliest written mention of astronomy appearing in the Rigveda, believed to have been composed between 1700 and 1100 BCE making it the oldest religious text still in use. However, it is speculated that the astronomical data reported in this Vedic text goes back as far as 4500 BCE, and perhaps much further.
As in most ancient cultures, India’s advancement of astronomy was driven by the practice of astrology, in which a relationship is believed to exist between astronomical phenomena and human affairs. During this period Indian astrologers developed an understanding of the movements of stars, planets, constellations, eclipses, lunar month and solar months in order to devise astronomical charts. In the 5th millenia BCE, Egypt produced the first calendar known to use a year of 365 days, and similarly the ancient Indian year was divided into 366 days with adjustments made to maintain 12 months of 30 days.
It has also been suggested that the idea of a heliocentric solar system first found its voice in Vedic literature, with the Sun often referred to as the “centre of spheres.” The Aitareya Brahmana (9th century BCE) also states:
“The Sun never sets nor rises. When people think the sun is setting, it is not so; they are mistaken. It only changes about after reaching the end of the day and makes night below and day to what is on the other side.”
Influence Of Ancient Greece (330BCE)
The period from Alexander the Great’s foray into India (327 BCE) until the end of Indo-Greek rule of northwestern India (1st century BCE) subsequently saw Ancient Greek astronomy first influence its Indian counterpart. However, Greek astronomers, too, enjoyed further insights gained from the Indian Vedas with the two great ancient civilizations mostly glad to learn from each other in the interest of scientific progress. Nevertheless, Indo-Greek astronomical knowledge studied during this period had a visible affect on post-Vedic tradition.
Testimony to the Greek’s influence on Indian astronomy can be found in various testimonies, such as the Indian astronomer and mathematician Varahamihira (505–587 AD), who wrote: ”The Greeks, though impure, must be honored since they were trained in sciences and therein, excelled others” or the sage Garga, who wrote; “The Yavanas are barbarians, yet the science of astronomy originated with them and for this they must be reverenced like gods.”
According to Sailendra Nath Sen in his book ‘Ancient Indian History And Civilization,’ features that were introduced to India through the Greeks included the idea of parallax and methods of calculating it; methods of calculating ellipses; the idea of heliacal settings and risings of heavenly bodies; and correct rules for calculating the length of day, night and the year.
Siddhanthic Era (500AD): A Golden Era of Indian Astronomy
The Golden Era of Indian Astronomy, known as the Siddhanthic era started in the 5th century, when detailed and precise mathematical solutions to astronomical problems were compiled into astronomical texts called the ‘Siddhantas.’ This period produced such influential astronomers as Aryabhatta (476 AD), Varahamihira (505 AD), Brahmagupta (598 AD) and Bhaskara II (1114 AD).
As referenced in the Paitamaha Siddhantas: “Their (Greeks) details reflect a rather chaotic mix of (among other things) Babylonian and Aristotelian notions invoked by various early Hellenistic theories that fell into oblivion after Ptolemy. Indian astronomers combined these concepts with other parameters and techniques in their astronomical tradition to produce the cosmological and computational models that became standard in siddhantas.”
During this period, Aryabhatta (476-550 AD) was the first of the great mathematician-astronomers, and made some remarkable advances on ancient Greek astronomy, including calculating the Earth’s circumference as 24,835 miles (actual 24,902 miles), an improvement on the 24,662 miles computed by Greek mathematician Eratosthenes (276–195 BCE).
Aryabhatta also calculated the rotation of the earth relative to the fixed stars (sidereal rotation) as 23 hours 56 minutes and 4.1 seconds (actual 23:56:4.091) and his length of the sidereal year at 365 days 6 hours 12 minutes 30 seconds was only 3 minutes 20 seconds out over the length of a year.
However, various discoveries which have been attributed to Aryabhatta have been overstated somewhat and have their origin in ancient Greece. For instance, it was Anaxogoras (510-428 BCE) who was the first person to explain that the moon shines due to reflected sunlight and Philolaus (480-405 BCE) that the Earth spins. In addition, it has been suggested Aryabhatta proposed a heliocentric model of the solar system, something originally advanced by Greek astronomer Aristarchus (310– 230 BCE).
Nevertheless, contributions made to the astronomic sciences by such Indian astronomers as Aryabhatta and Brahmagupta were invaluable and, historically, second only to those of the ancient Greeks.