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World Space Week: How India’s Siddhantic Era Shaped Our Understanding of Astronomy

Author: Dr Aniket Sule and Prof. Mayank Vahia
Publication: The Weather Channel
Date: October 8, 2020
URL:      https://weather.com/en-IN/india/space/news/2020-10-08-space-week-how-india-siddhantic-era-shaped-astronomy?s=03

Ask any child in India, who is the first astronomer, he would say Aryabhata I (born 476 CE). However, globally, the answer to this question will most likely be Copernicus (born 1473 CE). There, one could have the testimony to the long history of Indian astronomy.

The Indian Astronomy in the Middle Ages looks very different from astronomy in prehistoric times. Before Aryabhata, we knew about astronomy mostly as a list of observations recorded or facts listed. However, for nearly 1000 years starting since Aryabhata, Indian astronomers wrote specialised books about the mathematics behind the motion of planets and stars.

We know this era as the Siddhantic Astronomy era (500 CE to 1400 CE).

Siddhanta means principle or rule. The word Siddhantic astronomy is associated with the formulation of Mathematical rules of calculations of various astronomical aspects. It formally begins with the book Aryabhatiya (~499 CE) written by Aryabhata, which is a very compact (121 verses) but very complex text.

Aryabhata: the humble astronomer

In just 121 verses, he covers calendrical system, large units of time, ratios of orbital periods of planets, tables of sines and cosines (needed for positions of planets), methods for measuring areas, arithmetic and geometric progressions, gnomon based timekeeping devices, linear, quadratic, simultaneous and indeterminate equations, cause of day and night, rising of different zodiac signs, the shape of the earth, etc. He also argued that the movement of stars and planets that we see is just an effect of the earth’s rotation.

Was Aryabhatiya the first text of its kind and was Aryabhata truly the first Siddhanta astronomer? Aryabhata says that he is merely codifying what he learnt from the ancestors and it is also reasonable to argue that it is very unlikely that a 23-year-old would have discovered all this knowledge on his own in the limited time available to him after his studies. Hence it is possible that at least some of the things which he wrote were indeed passed to him from previous generations.

On the other hand, we should also remember that Indian tradition teaches humility and it was a common practice to give the credit for one’s own scholarly work to the ancestors. So when Aryabhata says he was taught all this, it may just be him being humble.

Early texts

In terms of books, there is Suryasiddhanta, a book which was written between 4th to 8th century CE. Early Siddhantic astronomers also mention another compilation called Garga Samhita. But sadly, no copy of Garga Samhita is available today and large uncertainty in the exact date of Surya Siddhanta would mean that it might have been written after Aryabhatiya.

Varahamihira was almost a contemporary of Aryabhata and he wrote his own treatise called Brihad Samhita (~505 CE). Although he was the first Indian to give rules of astrological predictions, he himself did not think that it is necessary for a good astronomer to believe in astrology.

The split

After this, the Siddhantic Astronomers of India almost split into two branches. Many accomplished astronomers followed Aryabhata in toto and wrote commentaries on Aryabhatiya e.g. his disciple Bhaskara I (Bhashya, c. 600 CE) or Nilakantha Somayaji (Aryabhatiya Bhasya, 1465 CE). Most of the Astronomers of Kerala School of Mathematics (12th to 15th century CE) were part of this tradition. They all developed better and better techniques to calculate positions of planets with high precision.

Towards the end of Kerala School, they were using numerical methods, which we now teach under calculus. The 15th-century mathematician Nilakantha, in fact, proposed an alternate model of the solar system (later independently proposed by Tycho Brahe) which gave the most accurate positional predictions for all planets till the invention of the Heliocentric model of Copernicus.

Astronomers like Brahmagupta (~600 CE), Lalla and Sripati agreed with Aryabhata on timekeeping systems but were not in favour of his ideas like rotating earth. They mostly followed rules given in Surya Siddhanta and Brahmasphutasiddhanta (of Brahmagupta).

Hits and misses of Siddhantic Era

Where do we place all these works in the overall development of Astronomy? As far as positional calculations of planets or calculation of eclipses are concerned, these methods were far superior to any other civilisation at that time. They could be accurately applied for about a couple of centuries on either side of the time of the respective astronomer, beyond that the precession of the earth would introduce noticeable errors.

All of them, starting from Aryabhata, were aware of this limitation and they always maintained that the numerical calculations must be backed up by observations and suitable corrections should be made. The numerical methods developed in the process were again ahead of their times.

On the other hand, their obsession with planetary positions and mathematical rules also led to their willful omission of all other celestial events which kept happening in their lifetimes. Comets came by and went away, a few very bright supernovae appeared in the sky. But these events find no mention in any of the Siddhanta texts. This was the biggest shortcoming of this era of highly advanced mathematical astronomy.

* This article is a part of a series of eight articles on the World Space Week 2020, published each day from October 4 to 10. The previous four articles in the series can be found here:

1. Applying Astronomical Dating Methods to Ancient Indian Epics Mahabharata and Ramayana

2. How Study of Ancient World Can Shed Light on Beginning of Astronomy in India

3. Ancient Astronomy in Vedic and Post-Vedic Literature

4. Sneak Peek at Indian and Vedic Calendars and Astronomy Behind Them

* This series was produced in collaboration with the Astronomical Society of India, a society dedicated to Astronomy and related branches of science in India. Dr Aniket Sule and Prof. Mayank Vahia are from the Homi Bhabha Centre for Science Education (HBCSE-TIFR), Mumbai and the NMIMS School of Mathematical Sciences, Mumbai, respectively.

* This article is a guest column reflecting the author’s opinions and does not necessarily represent the official views of The Weather Channel.


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