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Jean-Baptiste Chappe d'Auteroche | |
|---|---|
.jpg) Jean Chappe d'Auteroche by J. B. Tilliard | |
| Born | (1722-03-23)23 March 1722 |
| Died | 1 August 1769(1769-08-01) (aged 47) |
| Known for | transits of Venus |
| Scientific career | |
| Fields | astronomy |
| Institutions | Royal Academy of Sciences |
Jean-Baptiste Chappe d'Auteroche (French pronunciation:[ʒɑ̃batistʃapdotʁɔʃ]; 23 March 1722 – 1 August 1769) was a Frenchastronomer, best known for his observations of thetransits of Venus in 1761 and 1769.
Little is known of Chappe's early life. He was born into a distinguished family holding administrative posts and coming fromAuvergne, a region of central France. He entered the priesthood, probably as aJesuit, and devoted himself to the study of astronomy. He was appointed assistant astronomer at theRoyal Observatory and admitted to theRoyal Academy of Sciences on 14 January 1759.[1]
In the mid-18th century, thedynamics of theSolar System were reasonably well understood, but astronomers only had an approximate idea of its scale. If the distance between two planets could be measured, all the other distances would be known fromKepler's laws of planetary motion. The best candidate for an accurate measurement was the distance between the Earth andVenus, which could be calculated from observations oftransits of Venus, when Venus passes directly between the Earth and the Sun, appearing as a small black dot moving across the face of the Sun.
However, transits of Venus are very rare. Before 1761, the previous transit had been in 1639; after 1769, the next transit would be in 1874. The importance of the measurement led to an unprecedented international effort to obtain as many observations as possible from different points in the world – points as far apart from one another as possible. Despite theSeven Years' War which was raging throughout most of the world, astronomers were given letters of introduction and safe passage to enable them to reach their observation points and make their observations under the coordination of the variouslearned societies.
Chappe was chosen to go toTobolsk inSiberia to observe thetransit of Venus expected for 6 June 1761. The trip was arduous and Chappe arrived in Tobolsk with little time to spare, although he was able to observe thelunar eclipse of 18 May, which enabled him to calculate thelongitude of Tobolsk. The spring floods of theTobol andIrtysh rivers had been particularly severe that year, and some of the local peasants blamed the foreigner with his strange equipment who was "messing with the Sun": Chappe had to be protected by a cordon of armedCossacks to make his observations. Fortunately, the weather conditions were excellent, and Chappe was able to observe the entire transit. He published his results fromSaint Petersburg (Mémoire du passage de Vénus sur le soleil, avec des observations sur l'astronomie et la déclinaison de la boussole faites à Tobolsk, en Sibérie), and didn't return to France until 1763.[2]
Chappe published an account of his travels through Russia (Voyage en Sibérie fait en 1761 (avec la description du Kamtschatka, trad. du russe de Khracheninnikow)) in 1768. The text is hardly a flattering description of the country, and an anonymous pamphlet (Antidote ou Réfutation du mauvais livre superbement imprimé intitulé : Voyage en Sibérie, etc.) was soon circulating whose authorship is often attributed toCatherine the Great herself (although CountAndrey Petrovich Shuvalov is more likely the polemicist).[2]
Theproblem of longitude measurement had been at the heart of astronomical research for a century or more, andmarine chronometers were steadily becoming more accurate. Chappe and physicistHenri-Louis Duhamel du Monceau (1700–82) were selected to test one such chronometer, made bySwisswatchmakerFerdinand Berthoud (1727–1807) on board the corvetteL'Hirondelle in 1764.
For the transit of Venus on 3 June 1769, Chappe's destination was theMission ofSan José del Cabo at the tip of theBaja California peninsula in modern-dayMexico. The journey and observation were uneventful. However, as the expedition was packing to return, an outbreak of fever (possiblyyellow fever) hit the area. Chappe stayed to tend the sick, but was infected and died on 1 August. Only one member of the expedition made it back to Paris alive with Chappe's observations and notes. Chappe's account of his journey (Voyage en Californie, pour l'observation du passage de Vénus sur le disque du soleil) was published posthumously by his colleagueCésar Cassini de Thury.[2] The manuscript is kept at the Library ofParis Observatory andavailable online.
As well as the contributions his observations of thetransits of Venus gave to solving the problem of the size of the solar system, his nephew,Claude Chappe was greatly inspired by readingVoyage en Sibérie. Claude went on, with his brothers, to create the first optical telegraph network using semaphores and telescopes.[3] Asteroid14961 d'Auteroche, discovered byEric Walter Elst atLa Silla Observatory inChile in 1996, was named in his honour.
