Roger Billard

The Astronomy in India Roger Billard

Introduction The astronomy of the ancient Indian can be broadly divided into two kinds. One deals mainly with the Sun and the Moon and the node of the Moon called Rahu. The apogee of both the Sun and the Moon is also implicitly included in the consideration as the period of the Moon phase cycle varies on account of these, but these are general corrections to the cycle. The apogees are not finding place directly in the computations. The other deals with the motion of the planets and the positions in the sky where they appear, as seen from the earth from time to time. The Sun, Moon and Rahu are also included as are the apogees of the Sun and the Moon. The first astronomy is generally known as the Vedanga Jyotisa under several different names. The motion of the planets is given in several different treatises or astronomical Siddhantas, in several hand- books of computations or Karana and in many Bija Siddhanta which give small specific corrections to be applied to some other computation method. All these have received attention of the western scholars and in the process have received very adverse assessment of the capability of the ancient Indians in the field of mathematics and astronomy. Some of them grudgingly concede the competence of the ancient Indians in mathematics to some extent but do not accept their astronomical proficiency. The Indian astronomers have been accused of having made no observations on their own but having drawn up their treatises from the astronomical knowledge drawn from the Greek or Babylonian sources. They have also been accused of having forged these documents and they have been accused of having used Greek or Iranian astronomical manual for draft- ing their treatises. Of these various charges against the ancient Indian astronomers the charge of having not made any observations at all but having prepared their astronomica treatises already in use in other countries is the most serious one. Other charges, in effect, attribute such mathematical prowess to the ancient Indians ability to draw up mathematical theories based on treatises of an earlier date and adapt them to their current astronomical realities, which in any case require a substantial amount of accurate observations. In this backdrop the correct thing would appear to be to compute the difference between the positions of the planets as given in the ancient Indian astronomical texts and compare them with what their positions would be as projected from the modern astronomical science. From such comparisons it would become possible to judge, if such a judgement is at all possible, whether there is any connection between the astronomical reality assigned to the text and that projected by the text. The main objective of Billard's work The objective of the work done by Billard, as has already been stated earlier, is to examine the astronomical reality of the ancient period, to compare it with the astronomy as reflected in the various texts under study, to compute the difference between the two, and to plot the difference chronologically to see if such a plot has any significance. Further he has also examined, when the plot has some meaningful contribution, to find out the likely period when there was agreement between the text and the astronomical reality and assess, using statistical methods, the likely error in the determination of the such period of agreement. These are quite formidable objectives and for this, in addition as already mentioned, he had also to collect and sort out the various available texts of the ancient astronomy and decide on the astronomical elements which they represent which are to be taken for the study. Having done that he went about his work in a methodical way.