Guillaume Le Gentil was born on 11 or 12 September 1725 in
Coutances and first intended to enter the church before turning to astronomy when inspired by a lecture by
Joseph-Nicolas Delisle. By 1753 he was a professional astronomer and he wrote influentially on the subject of estimating the distance from the Earth to the Sun, the
astronomical unit (AU), using
transits of Mercury. After spending some time mapping the eastern coast of
Madagascar, he decided to record the 1769 transit from
Manila in the
Philippines. Due to shipwrecks and wartime attacks on ships, none of the letters he had sent to the academy or to his relatives had reached their destinations. Lengthy litigation and the intervention of the king were ultimately required before he recovered his seat in the academy and remarried. During the time he spent in India, Le Gentil examined local astronomical traditions and wrote several notes on the topic. He reported that the duration of the
lunar eclipse of 30 August 1765 was predicted by a
Tamil astronomer, based on the computation of the size and extent of the earth-shadow, and was found short by 41 seconds, whereas the charts of
Tobias Mayer were wrong by 68 seconds. He died in Paris on 22 October 1792. == Catalogue ==