Chasing Mercury: Transit tales from India

Abstract

Planets passing across the disk of the Sun are among the most uncommon and fascinating phenomena in the Solar System. From the Earth, the transits of only Mercury and Venus can be seen. Early on, the transits of Venus were important for precisely determining the scale of the Solar System whereas the transits of Mercury were used to accurately ascertain its orbit and variations in the size of the Sun. This paper presents observations of transits of Mercury made in India from 1651 until 1927 (the last one before Independence in 1947). The observers were East India Company engineers and British officials, European missionaries and geographers and professional and amateur astronomers. In our quest, we stumbled across brief references to the transits of 1753 and 1756 observed by the Jesuit Gaston-Laurent Coeur-doux in Puducherry, and of 1815 by John Hodgson of the East India Company's Bengal Infantry in Dalmau. We also present the unpublished observations of the transit of 1861 made by Norman Pogson at Madras Observatory. Finally, we report on photographs of the 8 May 1924 and 10 November 1927 transits taken at Kodaikanal Observatory as part of their on-going solar physics research.