Around 300-400 B.C. Mesopotamian astronomers developed numerical methods to predict the position of the Sun, Moon and known planets based on careful observations of these objects. At about the same time Greek astronomy was beginning. The Greek Apollonius (around 200 B.C.) developed the theory of epicyclic circular motions for the planets. He proposed that the planets did not move in circles around the Earth at a uniform rate but instead they moved at a uniform rate on a small circle called an epicycle and the center of the epicycle moved at a uniform rate around the Earth. This model successfully mimicked retrograde motion of the planets where the planets appear to slow, stop, precede backwards and then more forward again against the back ground stars in the course of several months. Hipparchus (around 150 B.C.) used observational data attributed to the Mesopotamians to refine the calculations and two hundred years later Ptolemy, during the Roman imperial period, published the monumental
Almagest in which he described somewhat more elaborate numerical models, still based on epicycles, which were used for the next 1400 years to predict the positions of the Sun, Moon and planets.
During the first century A.D astronomers in India were influenced by Greek astronomical texts, and their Mesopotamian arithmetical methods. Following this contact Indian astronomy seems to have developed in near isolation. Thus, a look at ancient Hindu astronomy, which was based on the pre-Ptolemy contact, affords an interesting glimpse at very early methods of astronomical calculations.
The oldest Sanskrit astronomical texts to survive were written around 600 A.D. One of the most notable of these text is the
Surya Siddhanta which survives in a much revised version. In 1858 Ebenezer Burgess published an annotated English translation of this text, available now as
Surya-Siddhanta; a text-book of Hindu astronomy, Ebenezer Burgess, Kessinger Publishing Company (
http://www.kessinger-publishing.com/), 1998. Hindus believe that the
Surya Siddhanta was produced by devine revelation and came from
Surya the Sun God.
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