Jean-Baptiste Chappe d'Auteroche (; 23 March 1722 – 1 August 1769) was a French

astronomer An astronomer is a scientist in the field of astronomy who focuses on a specific question or field outside the scope of Earth. Astronomers observe astronomical objects, such as stars, planets, natural satellite, moons, comets and galaxy, galax ...

, best known for his observations of the transits of Venus in 1761 and 1769.

Early life

Little is known of Chappe's early life. He was born into a distinguished family holding administrative posts and coming from

Auvergne Auvergne (; ; or ) is a cultural region in central France. As of 2016 Auvergne is no longer an administrative division of France. It is generally regarded as conterminous with the land area of the historical Province of Auvergne, which was dis ...

, a region of central France. He entered the priesthood, probably as a

Jesuit The Society of Jesus (; abbreviation: S.J. or SJ), also known as the Jesuit Order or the Jesuits ( ; ), is a religious order (Catholic), religious order of clerics regular of pontifical right for men in the Catholic Church headquartered in Rom ...

, 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.

Distance from the Earth to the Sun

In the mid-18th century, the dynamics of the

Solar System The Solar SystemCapitalization of the name varies. The International Astronomical Union, the authoritative body regarding astronomical nomenclature, specifies capitalizing the names of all individual astronomical objects but uses mixed "Sola ...

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 In astronomy, Kepler's laws of planetary motion, published by Johannes Kepler in 1609 (except the third law, which was fully published in 1619), describe the orbits of planets around the Sun. These laws replaced circular orbits and epicycles in ...

. The best candidate for an accurate measurement was the distance between the Earth and

Venus Venus is the second planet from the Sun. It is often called Earth's "twin" or "sister" planet for having almost the same size and mass, and the closest orbit to Earth's. While both are rocky planets, Venus has an atmosphere much thicker ...

, 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 The Seven Years' War, 1756 to 1763, was a Great Power conflict fought primarily in Europe, with significant subsidiary campaigns in North America and South Asia. The protagonists were Kingdom of Great Britain, Great Britain and Kingdom of Prus ...

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 A learned society ( ; also scholarly, intellectual, or academic society) is an organization that exists to promote an academic discipline, profession, or a group of related disciplines such as the arts and sciences. Membership may be open to al ...

Transit of Venus 1761

Chappe was chosen to go to Tobolsk in

Siberia Siberia ( ; , ) is an extensive geographical region comprising all of North Asia, from the Ural Mountains in the west to the Pacific Ocean in the east. It has formed a part of the sovereign territory of Russia and its predecessor states ...

to observe the

transit of Venus A transit of Venus takes place when Venus passes directly between the Sun and the Earth (or any other superior planet), becoming visible against (and hence obscuring a small portion of) the solar disk. During a transit, Venus is visible as ...

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 A lunar eclipse is an astronomical event that occurs when the Moon moves into the Earth's shadow, causing the Moon to be darkened. Such an alignment occurs during an eclipse season, approximately every six months, during the full moon phase, ...

of 18 May, which enabled him to calculate the

longitude Longitude (, ) is a geographic coordinate that specifies the east- west position of a point on the surface of the Earth, or another celestial body. It is an angular measurement, usually expressed in degrees and denoted by the Greek lett ...

of Tobolsk. The spring floods of the

Tobol The Tobol (, ) is a river in Western Siberia (in Kazakhstan and Russia) and the main (left) tributary of the Irtysh. Its length is , and the area of its drainage basin is . History The Tobol River was one of the four important rivers of the S ...

and

Irtysh The Irtysh is a river in Russia, China, and Kazakhstan. It is the chief tributary of the Ob (river), Ob and is also the longest tributary in the world. The river's source lies in the Altai Mountains, Mongolian Altai in Dzungaria (the northern p ...

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 The Cossacks are a predominantly East Slavic languages, East Slavic Eastern Christian people originating in the Pontic–Caspian steppe of eastern Ukraine and southern Russia. Cossacks played an important role in defending the southern borde ...

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 Saint Petersburg, formerly known as Petrograd and later Leningrad, is the List of cities and towns in Russia by population, second-largest city in Russia after Moscow. It is situated on the Neva, River Neva, at the head of the Gulf of Finland ...

(''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.. 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 to

Catherine the Great Catherine II. (born Princess Sophie of Anhalt-Zerbst; 2 May 172917 November 1796), most commonly known as Catherine the Great, was the reigning empress of Russia from 1762 to 1796. She came to power after overthrowing her husband, Peter I ...

herself (although Count Andrey Petrovich Shuvalov is more likely the polemicist).

Longitude measurement

The problem of longitude measurement had been at the heart of astronomical research for a century or more, and

marine chronometer A marine chronometer is a precision timepiece that is carried on a ship and employed in the determination of the ship's position by celestial navigation. It is used to determine longitude by comparing Greenwich Mean Time (GMT), and the time at t ...

s were steadily becoming more accurate. Chappe and physicist

Henri-Louis Duhamel du Monceau Henri-Louis Duhamel du Monceau (; 20 July 170013 August 1782) was a French physician, naval engineer and botanist. Biography Henri-Louis Duhamel du Monceau was born in Paris in 1700, the son of Alexandre Duhamel, lord of Denainvilliers. I ...

(1700–82) were selected to test one such chronometer, made by

Swiss Swiss most commonly refers to: * the adjectival form of Switzerland * Swiss people Swiss may also refer to: Places * Swiss, Missouri * Swiss, North Carolina * Swiss, West Virginia * Swiss, Wisconsin Other uses * Swiss Café, an old café located ...

watchmaker A watchmaker is an artisan who makes and repairs watches. Since a majority of watches are now factory-made, most modern watchmakers only repair watches. However, originally they were master craftsmen who built watches, including all their par ...

Ferdinand Berthoud (1727–1807) on board the corvette ''L'Hirondelle'' in 1764.

Transit of Venus 1769

For the transit of Venus on 3 June 1769, Chappe's destination was the Mission of San José del Cabo at the tip of the Baja California peninsula in modern-day

Mexico Mexico, officially the United Mexican States, is a country in North America. It is the northernmost country in Latin America, and borders the United States to the north, and Guatemala and Belize to the southeast; while having maritime boundar ...

. The journey and observation were uneventful. However, as the expedition was packing to return, an outbreak of fever (possibly yellow 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 colleague César Cassini de Thury. The manuscript is kept at the Library of

Paris Observatory The Paris Observatory (, ), a research institution of the Paris Sciences et Lettres University, is the foremost astronomical observatory of France, and one of the largest astronomical centres in the world. Its historic building is on the Left Ban ...

an
available online

Legacy

As well as the contributions his observations of the transits of Venus gave to solving the problem of the size of the solar system, his nephew,

Claude Chappe Claude Chappe (; 25 December 1763 – 23 January 1805) was a French inventor who in 1792 demonstrated a practical semaphore line, semaphore system that eventually spanned all of France. His system consisted of a series of towers, each within l ...

was greatly inspired by reading ''Voyage en Sibérie''. Claude went on, with his brothers, to create the first optical telegraph network using semaphores and telescopes. Asteroid 14961 d'Auteroche, discovered by

Eric Walter Elst Eric Walter Elst (30 November 1936 – 2 January 2022) was a Belgian astronomer at the Royal Observatory of Belgium in Uccle and a prolific discoverer of asteroids. The Minor Planet Center ranks him among the top 10 discoverers of minor planets ...

La Silla Observatory La Silla Observatory is an astronomical observatory in Chile with three telescopes built and operated by the European Southern Observatory (ESO). Several other telescopes are also located at the site and are partly maintained by ESO. The observato ...

Chile Chile, officially the Republic of Chile, is a country in western South America. It is the southernmost country in the world and the closest to Antarctica, stretching along a narrow strip of land between the Andes, Andes Mountains and the Paci ...

in 1996, was named in his honour.

References

External links

How Far to the Sun? The Venus Transits of 1761 & 1769
{{DEFAULTSORT:Chappe D'auteroche, Jean-Baptiste 1722 births 1769 deaths People from Mauriac, Cantal 18th-century French Jesuits 18th-century French astronomers Jesuit scientists Members of the French Academy of Sciences