Epigraphia Indica Vol 14

Author(s): Sten Konow, F W Thomas
Publisher: Archaeological Survey of India

Page 14

EPIGRAPHIA INDICA.
VOLUME XIV.
No. 1.-THE TRUE LONGITUDE OF THE SUN IN HINDU ASTRONOMY. BY ROBERT SEWELL (I.C.S., RETIRED).
(A continuation of the author's "Indian Chronography," continued from Epig. Ind. XIII. p. 103.) 234. The exact position of the true or apparent sun at sunrise of each civil day, taken for tabular purposes as mean sunrise, is one of the essential elements of Hindu chronography, and the exact position of the true moon is another. From these positions are calculated the beginning and end of each tithi and nakshatra, with the currency of these at sunrise. All over India for many centuries the civil day has been coupled with the true tithi current at sunrise, the nakshatra in which the true moon stands at sunrise being stated in the local almanacks and constantly mentioned in the dates of historical inscriptions. In southern India the nakshatra was considered of such importance that from as early as the tenth century it has regularly given its name to the day. For the proper verification of historical inscriptiondates, therefore, it is of the highest importance that we should know the precise position of the true sun at any moment and more especially at the moment of mean sunrise.1
235. Now the process adopted for this purpose in "The Indian Calendar" (Sewell and S. B. Dikshit, 1896), though resulting in a fair approximation, did not, for critical examinations of dates, give a sufficiently close result, as I have already explained in my "Indian Chronography," §§ 119, 120, pp. 42-43); something more accurate was required. We want, for each of the Indian astronomical authorities separately, extremely accurate determination of the sun's true longitude each day of the year; and there is only one way to obtain this. For each day a calculation must be made of the exact equation of the sun's centre on the basis of the sun's mean anomaly, according to the Hindu method of computation. This was a formidable undertaking; but it has now been accomplished for the two principal authorities, and the Tables are published herewith. It is to be hoped that they are final. They are intended to fix the true longitude of the sun on any day or at any moment of the day, with an accuracy extending to the hundredth part of a second, the calculation having been each separately carried to eight or nine decimals of a second so as to ensure correctness. I give the result in degrees and parts, and in ten-thousandths of the circle. The former, converted as desired, can be adapted to any system of reckoning; the latter are for use by the Indian Calendar system,"
1 For calculation affecting all parts of India the basis has to be mean sunrise, and this is always taken as mean sunrise at Lanka, or Ujjain.
1 The Indian Calendar System is the system adopted by Prof. Jacobi (of Bonn) in 1888 (Indian Antiquary, Vol. XVII) itself founded on Largetesu (Connaissance des Tempe, 1845).