As Venus tracks slowly across the face of the Sun on Tuesday, it may be fitting to remember one of the most unlucky astronomers in the history of the science.
The Frenchman Guillaume Joseph Hyacinthe Jean-Baptiste Le Gentil de la Galaisiere risked death in the 18th century to travel halfway across the world to observe a pair of transits of Venus.
But despite the eleven-and-a-half years he was on the job — in what has been described as the longest lasting astronomical expedition in history — first war, and then a ”fatal cloud” deprived him of his goal.
In the days before rockets and satellites, careful timing of the transit of Venus coupled with geometric calculation was the most reliable way of determining the distance from the Earth to the Sun, which in turn gave an idea of the scale of the solar system. As the visionary English astronomer Edmund Halley put it, this was the way the ”immensities of the celestial spheres [could be] compelled to more precise boundaries”.
Transits have for the past few hundred years occured in close pairs, roughly every century; in the 18th century, they were predicted for 1761 and 1769.
Le Gentil was one of 120 distinguished astronomers from several nations who were dispatched to sites across the globe to conduct scientific observations of the 1761 transit, which was to take place on June 6.
His destination was Pondicherry off the east coast of India, and he gave himself more than enough time to get there by leaving in March 1760.
He reached Mauritius in July, but in the meantime war had broken out between England and his native France, and he had to wait five months on the island, at times stricken with dysentery, before a French vessel ventured to brave the enemy’s warships.
After an infuriatingly slow voyage up the African coast, his vessel, the Sylphide, crossed to Ceylon.
There, with only six days to go before the transit, it was discovered that the English had captured Pondicherry. The Sylphide turned back for Mauritius, and was still at sea on June 6.
To Le Gentil’s despair he was forced to watch the transit ”as best I could” from the rolling deck of the ship.
Without absolute certainty of his latitude and longitude, or of the timing of his observations, the measurements he did manage were useless.
But he was not easily discouraged: rather than return home, he decided to stay in the East and wait for the next transit in 1769. He spent much of this time on Mauritius and Madagascar making ”all the observations I could on geography, natural history, physics, astronomy, navigation, winds and tides”.
He also used the opportunity to calculate the best spot for observing the next transit, deciding on Manila in the Philippines.
However when he arrived there he was given a hostile reception by the Spanish governor, who suspected him of being a spy. Instead he decided to head for his original destination, Pondicherry, which had been handed back to France at the end of hostilities.
He reached Pondicherry in March 1768, where he was warmly welcomed and given permission to set up his observatory on the site of a palace which had been destroyed in the war.
Masons spent a year preparing the building for his use, while the governor decided at one point to house the colony’s main gunpowder magazine in the basement.
The transit was to occur early on the morning of June 3. The skies were clear for the whole of May, and for the first two days of June, but as was inevitable, on the morning of the transit it clouded over.
The clouds remained firmly in place for the duration of the phenomenon; all he could see of the sun was a fuzzy white blob.
Two hours after the transit was over, the skies cleared. It had of course been sunny in Manila.
”This is the fate which often awaits astronomers,” wrote a devastated Le Gentil.
”I had gone more than ten thousand leagues; it seemed that I had crossed such a great expanse of seas, exiling myself from my motherland, only to be the spectator of a fatal cloud which arrived in front of the Sun at the precise moment of my observation, to snatch from me the fruits of my pains and of my fatigues…
”I was unable to recover from my astonishment. I had difficulty in realising that the transit of Venus was finally over.”
He fell into a depression, barely able to summon the courage to write a letter to France reporting the failure of his mission. During his wait for a passage back to France he fell ill with dysentery and a fever that nearly killed him.
He secured a place in 1770 on a French vessel which was nearly dismasted by a gale off the Cape and limped back to Mauritius. There he transferred to a Spanish warship which was blown off course north of the Azores before docking at Cadiz. On his return to Paris he learned he had been declared dead, and that his estate had been looted by relatives.
In addition the Academy, also believing he had passed on, had given his post to someone else.
However things began to look up when the Academy created a special Chair for him and he married a wealthy heiress, with whom he set up a happy home at the Paris Observatory.
The observatory’s records contain a complaint that Madame Le Gentil hung out nappies to dry in the observatory gardens.
His memoirs of his epic journey, Voyage dans les mers de l’Inde, were published in two volumes in 1779 and 1781 and his scientific studies of Mauritius, Madagascar, and India met with critical acclaim.
A contemporary wrote of him praising his character but allowed that ”in his sea voyages he had contracted a little unsociability and brusqueness”.
Le Gentil died quietly at home in October 1792 at the age of 67. He was honoured in 1961 by having a crater of the Moon named after him. – Sapa