ANALYSIS OF THE TAMIL PARALLAX PROCEDURES IN LE GENTIL'S REPORT OF 1776

Abstract

: The Tamil procedures for computing the circumstances of eclipses were reported by the French astronomer Guillaume Le Gentil from his visit to India in the 1760's. This paper investigates these Tamil procedures for a solar eclipse, focusing on the procedures for finding the eclipse parallax which are needed to describe the local appearance of an eclipse. These procedures constitute the essential difference between a solar and lunar eclipse. The procedures are compared with the parallax procedures in Sūryasiddhānta and give similar results. It is found that there seems to be little theoretical background to the Tamil procedures, although they work rather well in practice. There are parallels with parallax procedures in Southeast Asian traditional astronomy. The Tamil calculations of the circumstances of the lunar eclipse 13 December 1769 have earlier been analyzed by Otto Neugebauer in a paper in Isis .