Jean-Baptiste Chappe d'Auteroche
| Jean-Baptiste Chappe d'Auteroche | |
|---|---|
| Born |
23 March 1722 Mauriac, Cantal, France |
| Died | 1 August 1769 (aged 47) San José del Cabo, Baja California, Mexico |
| Nationality | French |
| Fields | astronomy |
| Institutions | Royal Academy of Sciences |
| Known for | transits of Venus |
Jean-Baptiste Chappe d'Auteroche (23 March 1722 – 1 August 1769) was a French astronomer, best known for his observations of the transits of Venus in 1761 and 1769.
Little is known of Chappe's early life. He was born into a noble family in the Auvergne region of central France. He entered the priesthood, probably as a Jesuit, and devoted himself to the study of astronomy. He was appointed assistant astronomer at the Royal Observatory and admitted to the Royal Academy of Sciences on 14 January 1759.
In the mid-18th century, the dynamics of the Solar 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 from Kepler's laws of planetary motion. The best candidate for an accurate measurement was the distance between the Earth and Venus, which could be calculated from observations of transits 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 the Seven 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 various learned societies.
Chappe was chosen to go to Tobolsk in Siberia to observe the transit 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 the lunar eclipse of 18 May, which enabled him to calculate the longitude of Tobolsk. The spring floods of the Tobol and Irtysh 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 armed Cossacks to make his observations. Fortunately, the weather conditions were excellent, and Chappe was able to observe the entire transit. He published his results from Saint 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.
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