Heliocentricity, Aryabhata, and some glimpses of the Indian Astronomy☨
Introduction
Many years ago, a physicist friend posed an interesting question: Had the Indian astronomers or scientists ever pondered on the question of earth’s rotation, earth centric celestial system versus sun centric celestial system? What were their theories and findings? Or did they erroneously postulate that the earth is stationary and the planets and sun just rotate as they appear? I did not have any ready-made answers then, but averred that perhaps some the earlier Indian astronomers probably had addressed the issue at some point in Indian history. After all, one cannot naively presume that Galileo or Kepler were the only scientists to stumble on the right answers to such questions. Somehow, I could not easily accept a priori that intelligence or creativity is the prerogative of some select civilizations. Also, the traditional Indian calendars (both solar and lunar) accurately predict lunar and solar eclipses. In fact, the Hindu calendar is considered even today as perhaps the best rational system. Both Delhi and Jaipur possess astronomical observatories of a bygone era, albeit in a dilapidated condition. Thus, I heuristically intuited that perhaps one of the Indian astronomers had seriously looked into the issue of our solar system, the planets, and their periodic movements. However, I was not then certain which Indian astronomer had tackled this issue and my guess was purely based a bit on the fondness to the ancient Indian civilization and a bit on the “spirit of positivism” (to borrow a phrase from Jean Piaget1).
Elementary and advanced texts in physics and astronomy credit the hypothesis of heliocentric planetary system to Copernicus (1473 – 1543) and Galileo (1564 – 1642). Recently discovered historical evidence2a, 2b refutes this and suggests that the sun centered planetary system ideas originated in the Indian and Arabic regions much earlier, often hundreds of years earlier. Some of the well-known historians of science (ex: Arthur Koestler3, Isaac Asimov4, Jacob Bronowski5) erroneously attributed most of the important scientific discoveries and inventions to regions around Greece, ignoring all the scientific culture that originated in Indian, Chinese, Arabic, and Mayan civilizations with one stroke, which preceded the modern western civilization by hundreds, if not thousands of years. What a terrible moral lapse, historical injustice, and intellectual chicanery!
Effects of (Relative) Motion
To appreciate the difficulties involved with the motion of astronomical bodies, first we have to understand the concept of “frame of reference”. The issue of “frame of reference” is best understood in the context of relativity. In layman’s language, this simply means that what we observe (or what is observed by an instrument) depends on where we are located. One need not invoke the esoteric concepts of relativity (i.e., Einstein’s). The essential ideas about (moving) frames of reference can be gleamed from the common day-to-day experiences. For example, most children notice that while traveling in a train or car the close-by trees on the roadside appear moving away. To a child, the moon and the sun certainly appear moving from east to west. Our visual clues, bodily balance, and senses are conditioned or accustomed to earth’s gravity and earth’s diurnal and annual rotations. Unless we are up in the space and that too on a properly designed laboratory pedestal (in physics lingo, it is called a “frame”), we would not able to see clearly the daily and yearly rotations of our planet earth. The modern space exploration and space vehicles were not available to the early astronomers; they had to contend with the limitation of being tied to the moving frame of earth. Still, they had to decipher the solar system, stars, and the lunar and solar eclipses with precision and postulate a model for all the wonders of our planetary system. Verily, it must have been a stupendous task!
Periodicity
Only the day and night events have the periodicity of 12/24 hour cycles. All other events with longer-term periodic effects cannot be accounted by the simple notion that the sun rotates around the earth. How do we account for the fact that the seasons of spring, summer, and winter occur with regularity that approximates to twelve months rather than 24 hours? Also, many ancient observers or astronomers very likely observed that the stars and some of the nearby planets apparently move in certain pre-determined paths and their positions with respect to earth follows set patterns that retrace periodically. Again, all these observations are difficult to be explained away with a simple hypothesis that everything goes around our “home planet earth”. One can reasonably suppose that these questions surely haunted the early astronomers and physicists in India and other ancient cultures.
Some Clues and Observations
How can we detect that the earth is rotating? Are there some easy experiments or observations that can intimate the motion of earth? For example, it is observed that the cyclones in the North and South have different directions of rotation (clockwise or counter clockwise). This is due to the Coriolis effect, which arises due to the spinning of earth along the North-South vertical axis. The photographs of cyclones with their clear rotation are possible only with modern satellites, balloons, or highflying airplanes. Spinning of the earth can also be observed inside a building by setting up a Foucault’s (1819 – 1868) pendulum. The Coriolis effect is also observed in the flowing river waters; it is observed that one of the banks is eroded more than the other in rivers located in the Northern hemisphere. The effect can be noticed with the motion of a projectile or the drop of a stone in deep mines6. It is not certain whether such effects were ever observed by the early Indian scientists or astronomers in mines (ex: Kolar gold mines, depth approx. 10,000 ft.). We can visually see the earth’s spinning and rotation by watching the night sky7-9. Suppose we leave a camera on a tripod stand focused or aligned along the pole star and leave the shutter open for 10 -30 minutes. What we find on the film is a set of arcs (known as star trails) all arranged as parts of concentric circles; these arcs represent the stars and their (apparent) circular motion as observed by the earth bound viewer.
(to be Contd.) Copyright 2003, 2005, 2021 by the author
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