A Mission Delayed by War and Weather
In 1760, French astronomer Guillaume Le Gentil set sail from Paris with one goal: to observe the rare 1761 transit of Venus from Pondicherry, India. The scientific world believed that measurements from such transits could help calculate the astronomical unit—the distance between Earth and the Sun.
The expedition, part of a global collaboration, was disrupted when war between France and Britain made access to the intended observation site impossible. Though the skies were clear on the transit day, Le Gentil’s ship was still at sea, and he missed the event entirely.
A Second Chance, Lost Again
Rather than return home, Le Gentil decided to remain abroad and await the next transit in 1769. He spent the intervening years conducting scientific observations in Madagascar and the Philippines.
He faced resistance from Spanish authorities in Manila and eventually returned to Pondicherry, now back under French control. He built an observatory and prepared for the second transit. On June 4, 1769, after eight years of preparation, clouds obscured the sky, and Le Gentil missed the event again.
Return to a New Life
His journey back to France was delayed by illness and storms. After shipwrecks and a stop at Île Bourbon, he secured passage on a Spanish ship.
When Le Gentil finally arrived in Paris in 1771—eleven years after his departure—he discovered he had been declared dead, removed from the Royal Academy of Sciences, and had lost his property. None of his correspondence had arrived during his travels. After legal struggles and royal intervention, he regained his position and eventually remarried.
Work in India and Final Years
During his stay in India, Le Gentil studied Tamil astronomy and recorded its accuracy. He reported that a local astronomer’s calculation of a lunar eclipse in 1765 was accurate within 41 seconds—better than European charts.
Despite his setbacks, Le Gentil made significant astronomical contributions, including cataloguing nebulae and participating in a pioneering international scientific effort. He died in Paris on October 22, 1792.
In 1760, French astronomer Guillaume Le Gentil left for India to observe the rare Venus transit.
What followed was an 11-year ordeal of delays, storms, and war. His mission, meant to measure the Earth–Sun distance, became one of science’s most frustrating journeys…🧵👇 pic.twitter.com/zwXRocknbo
— Detective Tiger’s Stories (@TigerDetective) May 26, 2025