Abbé Nicolas-Louis de Lacaille (; 15 March 171321 March 1762), formerly sometimes spelled de la Caille, was a French

astronomer An astronomer is a scientist in the field of astronomy who focuses their studies on a specific question or field outside the scope of Earth. They observe astronomical objects such as stars, planets, moons, comets and galaxies – in either obse ...

and

geodesist Geodesy ( ) is the Earth science of accurately measuring and understanding Earth's figure (geometric shape and size), orientation in space, and gravity. The field also incorporates studies of how these properties change over time and equival ...

who named 14 out of the 88 constellations. From 1750 to 1754, he studied the sky at the

Cape of Good Hope The Cape of Good Hope ( af, Kaap die Goeie Hoop ) ;''Kaap'' in isolation: pt, Cabo da Boa Esperança is a rocky headland on the Atlantic coast of the Cape Peninsula in South Africa. A common misconception is that the Cape of Good Hope is t ...

in present-day

South Africa South Africa, officially the Republic of South Africa (RSA), is the Southern Africa, southernmost country in Africa. It is bounded to the south by of coastline that stretch along the Atlantic Ocean, South Atlantic and Indian Oceans; to the ...

. Lacaille observed over 10,000 stars using just a half-inch

refracting telescope A refracting telescope (also called a refractor) is a type of optical telescope that uses a lens as its objective to form an image (also referred to a dioptric telescope). The refracting telescope design was originally used in spyglasses and a ...

Biography

Born at Rumigny in the Ardennes in eastern France, he attended school in Mantes-sur-Seine (now

Mantes-la-Jolie Mantes-la-Jolie (, often informally called Mantes) is a commune in the Yvelines department in the Île-de-France region of north-central France. It is located to the west of Paris, from the centre of the capital. Mantes-la-Jolie is a subprefe ...

). Afterwards, he studied rhetoric and philosophy at the Collège de Lisieux and then theology at the

Collège de Navarre The College of Navarre (french: Collège de Navarre) was one of the colleges of the historic University of Paris, rivaling the Sorbonne and renowned for its library. History It was founded by Queen Joan I of Navarre in 1305, who provided for th ...

. He was left destitute in 1731 by the death of his father, who had held a post in the household of the duchess of Vendôme. However, he was supported in his studies by the

Duc de Bourbon Duke of Bourbon (french: Duc de Bourbon) is a title in the peerage of France. It was created in the first half of the 14th century for the eldest son of Robert of France, Count of Clermont and Beatrice of Burgundy, heiress of the lordship of B ...

, his father's former patron. After he graduated, he did not accept ordination as a priest but took

deacon A deacon is a member of the diaconate, an office in Christian churches that is generally associated with service of some kind, but which varies among theological and denominational traditions. Major Christian churches, such as the Catholic Chu ...

's orders, becoming an

Abbé ''Abbé'' (from Latin ''abbas'', in turn from Greek , ''abbas'', from Aramaic ''abba'', a title of honour, literally meaning "the father, my father", emphatic state of ''abh'', "father") is the French word for an abbot. It is the title for low ...

. He concentrated thereafter on science, and, through the patronage of

Jacques Cassini Jacques Cassini (18 February 1677 – 16 April 1756) was a French astronomer, son of the famous Italian astronomer Giovanni Domenico Cassini. Cassini was born at the Paris Observatory. Admitted at the age of seventeen to membership of the French ...

, obtained employment, first in

surveying Surveying or land surveying is the technique, profession, art, and science of determining the terrestrial two-dimensional or three-dimensional positions of points and the distances and angles between them. A land surveying professional is ...

the coast from

Nantes Nantes (, , ; Gallo: or ; ) is a city in Loire-Atlantique on the Loire, from the Atlantic coast. The city is the sixth largest in France, with a population of 314,138 in Nantes proper and a metropolitan area of nearly 1 million inhabit ...

Bayonne Bayonne (; eu, Baiona ; oc, label= Gascon, Baiona ; es, Bayona) is a city in Southwestern France near the Spanish border. It is a commune and one of two subprefectures in the Pyrénées-Atlantiques department, in the Nouvelle-Aquitain ...

, then, in 1739, in remeasuring the

French meridian arc The Paris meridian is a meridian line running through the Paris Observatory in Paris, France – now longitude 2°20′14.02500″ East. It was a long-standing rival to the Greenwich meridian as the prime meridian of the world. The "Paris meridi ...

, for which he is honoured with a pyramid at

Juvisy-sur-Orge Juvisy-sur-Orge (, literally ''Juvisy on Orge'') is a commune in the Essonne department in Île-de-France in northern France. It is located 18 km south-east of Paris, a few kilometres south of Orly Airport. The site of the town has been o ...

. The success of this difficult operation, which occupied two years, and achieved the correction of the anomalous result published by

in 1718, was mainly due to Lacaille's industry and skill. He was rewarded by admission to the Royal Academy of Sciences and appointment as Professor of mathematics in the Mazarin college of the

University of Paris The University of Paris (french: link=no, Université de Paris), metonymically known as the Sorbonne (), was the leading university in Paris, France, active from 1150 to 1970, with the exception between 1793 and 1806 under the French Revolution. ...

, where he constructed a small observatory fitted for his own use. He was the author of a number of influential textbooks and a firm advocate of Newtonian gravitational theory. His students included

Antoine Lavoisier Antoine-Laurent de Lavoisier ( , ; ; 26 August 17438 May 1794),
CNRS (

Jean Sylvain Bailly Jean Sylvain Bailly (; 15 September 1736 – 12 November 1793) was a French astronomer, mathematician, freemason, and political leader of the early part of the French Revolution. He presided over the Tennis Court Oath, served as the mayor of Pa ...

, both of whom were later guillotined during the

French Revolution The French Revolution ( ) was a period of radical political and societal change in France that began with the Estates General of 1789 and ended with the formation of the French Consulate in November 1799. Many of its ideas are consider ...

Voyage to the Cape of Good Hope

His desire to determine the distances of the planets trigonometrically, using the longest possible baseline, led him to propose, in 1750, an expedition to the

. This was officially sanctioned by

Roland-Michel Barrin de La Galissonière Roland-Michel Barrin de La Galissonière, Marquis de La Galissonière, sometimes spelled Galissonnière (; 10 November 1693 – 6 October 1756), was the French governor of New France from 1747 to 1749 and the victor in the Battle of Minorca ...

. There, he constructed an observatory on the shore of

Table Bay Table Bay ( Afrikaans: ''Tafelbaai'') is a natural bay on the Atlantic Ocean overlooked by Cape Town (founded 1652 by Van Riebeeck) and is at the northern end of the Cape Peninsula, which stretches south to the Cape of Good Hope. It was name ...

with the support of the Dutch Governor

Ryk Tulbagh Ryk Tulbagh (14 May 1699, Utrecht – 11 August 1771, Cape Town) was Governor of the Dutch Cape Colony from 27 February 1751 to 11 August 1771 under the Dutch East India Company (VOC). Tulbagh was the son of Dirk Tulbagh and Catharina Catt ...

. The primary result of his two-year stay were the observations of nearly 10,000 southern stars, the production of which required observing every night for over a year. In the course of his survey he took note of 42 nebulous objects. He also achieved his aim of determining the lunar and solar

parallax Parallax is a displacement or difference in the apparent position of an object viewed along two different lines of sight and is measured by the angle or semi-angle of inclination between those two lines. Due to foreshortening, nearby objects ...

es (

Mars Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System, only being larger than Mercury. In the English language, Mars is named for the Roman god of war. Mars is a terrestrial planet with a thin atmosp ...

serving as an intermediary). This work required near-simultaneous observations from Europe which were carried out by

Jérôme Lalande Joseph Jérôme Lefrançois de Lalande (; 11 July 1732 – 4 April 1807) was a French astronomer, freemason and writer. Biography Lalande was born at Bourg-en-Bresse (now in the département of Ain) to Pierre Lefrançois and Marie‐Anne‐Gab ...

. His southern catalogue, called ''Coelum Australe Stelliferum'', was published posthumously in 1763. He found it necessary to introduce 14 new constellations which have since become standard. One of these was Mons Mensae, the only constellation named after a terrestrial feature (the

Table Mountain Table Mountain ( naq, Huriǂoaxa, lit= sea-emerging; af, Tafelberg) is a flat-topped mountain forming a prominent landmark overlooking the city of Cape Town in South Africa. It is a significant tourist attraction, with many visitors using the ...

). While at the

Cape A cape is a clothing accessory or a sleeveless outer garment which drapes the wearer's back, arms, and chest, and connects at the neck. History Capes were common in medieval Europe, especially when combined with a hood in the chaperon. T ...

, Lacaille performed an

arc measurement Arc measurement, sometimes degree measurement (german: Gradmessung), is the astrogeodetic technique of determining of the radius of Earth – more specifically, the local Earth radius of curvature of the figure of the Earth – by relating the ...

to determine the

radius of the earth Earth radius (denoted as ''R''🜨 or R_E) is the distance from the center of Earth to a point on or near its surface. Approximating the figure of Earth by an Earth spheroid, the radius ranges from a maximum of nearly (equatorial radius, denot ...

in the southern hemisphere. He set out a baseline in the

Swartland The Swartland is a region of Western Cape Province that begins some north of Cape Town and consists of the area between the towns of Malmesbury in the south, Darling in the west, Piketberg in the north, Moorreesburg in the middle and the Rieb ...

plain north of present-day Darling. Using

triangulation In trigonometry and geometry, triangulation is the process of determining the location of a point by forming triangles to the point from known points. Applications In surveying Specifically in surveying, triangulation involves only angle me ...

he then measured a 137 km arc of meridian between Cape Town and

Aurora An aurora (plural: auroras or aurorae), also commonly known as the polar lights, is a natural light display in Earth's sky, predominantly seen in high-latitude regions (around the Arctic and Antarctic). Auroras display dynamic patterns of bri ...

, determining the

astronomical latitude In geography, latitude is a coordinate that specifies the north–south position of a point on the surface of the Earth or another celestial body. Latitude is given as an angle that ranges from –90° at the south pole to 90° at the north pol ...

s of the end points by means of astronomical-geodetic observations. There is a memorial to his work at a location near Aurora, pictured here. His result suggested that the earth was more flattened towards the south pole than towards the north. George Everest, of the Indian Survey, while recuperating from an illness at the Cape nearly seventy years later, suggested that Lacaille's latitude observations had been affected by the deflection of the vertical, caused by

gravitational attraction In physics, gravity () is a fundamental interaction which causes mutual attraction between all things with mass or energy. Gravity is, by far, the weakest of the four fundamental interactions, approximately 1038 times weaker than the strong ...

of Table Mountain at the southern end and by the Piketberg Mountain at the northern. In 1838, Thomas Maclear, who was Astronomer Royal at the Cape, repeated the measurements over a longer baseline ( Maclear's arc measurement) and ultimately confirmed Everest's conjecture.

Maclear's Beacon Maclear's Beacon is a triangulation station used in Maclear's arc measurement for Earth's circumference determination. The beacon is on top of Table Mountain in Cape Town, South Africa. It is situated on the Eastern end on the plateau of the mou ...

was erected on the Table Mountain in Cape Town to help with the verification.

Computing

During his voyage to the southern hemisphere as a passenger on the vessel ''Le Glorieux'', captained by the noted hydrographer Jean-Baptiste d'Après de Mannevillette, Lacaille became conscious of the difficulties in determining positions at sea. On his return to Paris he prepared the first set of tables of the Moon's position that was accurate enough to use for determining time and longitude by the method of 'Lunars' ( Lunar distances) using the orbital theory of Clairaut. Lacaille was in fact an indefatigable calculator. Apart from constructing astronomical

ephemerides In astronomy and celestial navigation, an ephemeris (pl. ephemerides; ) is a book with tables that gives the trajectory of naturally occurring astronomical objects as well as artificial satellites in the sky, i.e., the position (and possibly ve ...

and mathematical tables, he calculated a table of

eclipse An eclipse is an astronomical event that occurs when an astronomical object or spacecraft is temporarily obscured, by passing into the shadow of another body or by having another body pass between it and the viewer. This alignment of three ce ...

s for 1800 years. Lalande said of him that, during a comparatively short life, he had made more observations and calculations than all the astronomers of his time put together. The quality of his work rivalled its quantity, while the disinterestedness and rectitude of his moral character earned him universal respect.

Later life

On his return to Paris in 1754, following a diversion to

Mauritius Mauritius ( ; french: Maurice, link=no ; mfe, label=Mauritian Creole, Moris ), officially the Republic of Mauritius, is an island nation in the Indian Ocean about off the southeast coast of the African continent, east of Madagascar. It incl ...

, Lacaille was distressed to find himself an object of public attention. He resumed his work at the Mazarin College. In 1757 he published his ''Astronomiae Fundamenta Novissimus'', containing a list of about 400 bright stars with positions corrected for aberration and

nutation Nutation () is a rocking, swaying, or nodding motion in the axis of rotation of a largely axially symmetric object, such as a gyroscope, planet, or bullet in flight, or as an intended behaviour of a mechanism. In an appropriate reference frame ...

. He carried out calculations on comet orbits and was responsible for giving

Halley's Comet Halley's Comet or Comet Halley, officially designated 1P/Halley, is a short-period comet visible from Earth every 75–79 years. Halley is the only known short-period comet that is regularly visible to the naked eye from Earth, and thus the on ...

its name. His last public lecture, given on 14 September 1761 at the Royal Academy of Sciences, summarised the improvements to astronomy that had occurred during his lifetime, to which he had made no small contribution. His death, probably caused in part by over-work, occurred in 1762. He was buried in the vaults of the Mazarin College, now the

Institut de France The (; ) is a French learned society, grouping five , including the Académie Française. It was established in 1795 at the direction of the National Convention. Located on the Quai de Conti in the 6th arrondissement of Paris, the institute m ...

in Paris.

Honours

In 1754, he was elected a foreign member of the

Royal Swedish Academy of Sciences The Royal Swedish Academy of Sciences ( sv, Kungliga Vetenskapsakademien) is one of the royal academies of Sweden. Founded on 2 June 1739, it is an independent, non-governmental scientific organization that takes special responsibility for prom ...

. He was also an honorary member of the academies of Saint Petersburg and Berlin, the

Royal Society The Royal Society, formally The Royal Society of London for Improving Natural Knowledge, is a learned society and the United Kingdom's national academy of sciences. The society fulfils a number of roles: promoting science and its benefits, re ...

of London and the

Royal Society of Göttingen Royal may refer to: People * Royal (name), a list of people with either the surname or given name * A member of a royal family Places United States * Royal, Arkansas, an unincorporated community * Royal, Illinois, a village * Royal, Iowa, a cit ...

, and the Institute of Bologna. Lacaille has the honor of naming 14 different constellations: *

Antlia Antlia (; from Ancient Greek ''ἀντλία'') is a constellation in the Southern Celestial Hemisphere. Its name means "pump" in Latin and Greek; it represents an air pump. Originally Antlia Pneumatica, the constellation was established by N ...

Caelum Caelum is a faint constellation in the southern sky, introduced in the 1750s by Nicolas Louis de Lacaille and counted among the 88 modern constellations. Its name means “''chisel''” in Latin, and it was formerly known as Caelum Sculptorium ( ...

Circinus Circinus is a small, faint constellation in the southern sky, first defined in 1756 by the French astronomer Nicolas-Louis de Lacaille. Its name is Latin for compass, referring to the drafting tool used for drawing circles (it should not be co ...

Fornax Fornax () is a constellation in the southern celestial hemisphere, partly ringed by the celestial river Eridanus. Its name is Latin for furnace. It was named by French astronomer Nicolas Louis de Lacaille in 1756. Fornax is one of the 88 modern ...

* Horologium * Mensa *

Microscopium Microscopium ("the Microscope") is a minor constellation in the southern celestial hemisphere, one of twelve created in the 18th century by French astronomer Nicolas-Louis de Lacaille and one of several depicting scientific instruments. The n ...

Norma Norma may refer to: * Norma (given name), a given name (including a list of people with the name) Astronomy *Norma (constellation) * 555 Norma, a minor asteroid * Cygnus Arm or Norma Arm, a spiral arm in the Milky Way galaxy Geography *Norma, Laz ...

Octans Octans () is a faint constellation located in the deep Southern Sky. Its name is Latin for the eighth part of a circle, but it is named after the octant, a navigational instrument. Devised by French astronomer Nicolas Louis de Lacaille in 175 ...

Pictor Pictor is a constellation in the Southern Celestial Hemisphere, located between the star Canopus and the Large Magellanic Cloud. Its name is Latin for painter, and is an abbreviation of the older name Equuleus Pictoris (the "painter's easel"). ...

Pyxis Pyxis is a small and faint constellation in the southern sky. Abbreviated from Pyxis Nautica, its name is Latin for a mariner's compass (contrasting with Circinus, which represents a draftsman's compasses). Pyxis was introduced by Nicolas-Lo ...

Reticulum Reticulum is a small, faint constellation in the southern sky. Its name is Latin for a small net, or reticle—a net of crosshairs at the focus of a telescope eyepiece that is used to measure star positions. The constellation is best viewed be ...

Sculptor Sculpture is the branch of the visual arts that operates in three dimensions. Sculpture is the three-dimensional art work which is physically presented in the dimensions of height, width and depth. It is one of the plastic arts. Durable sc ...

Telescopium Telescopium is a minor constellation in the southern celestial hemisphere, one of twelve named in the 18th century by French astronomer Nicolas-Louis de Lacaille and one of several depicting scientific instruments. Its name is a Latinized for ...

The crater " La Caille" on the

Moon The Moon is Earth's only natural satellite. It is the fifth largest satellite in the Solar System and the largest and most massive relative to its parent planet, with a diameter about one-quarter that of Earth (comparable to the width of ...

is named after him.

Asteroid An asteroid is a minor planet of the inner Solar System. Sizes and shapes of asteroids vary significantly, ranging from 1-meter rocks to a dwarf planet almost 1000 km in diameter; they are rocky, metallic or icy bodies with no atmosphere. ...

9135 Lacaille (AKA 7609 P-L and 1994 EK6), discovered on 17 October 1960 by

Cornelis Johannes van Houten Cornelis Johannes van Houten (18 February 1920 – 24 August 2002) was a Dutch astronomer, sometimes referred to as Kees van Houten. Early life and education Born in The Hague, he spent his entire career at Leiden University except for a brief pe ...

, Ingrid van Houten-Groeneveld and

Tom Gehrels Anton M.J. "Tom" Gehrels (February 21, 1925 – July 11, 2011) was a Dutch–American astronomer, Professor of Planetary Sciences, and Astronomer at the University of Arizona, Tucson. Biography Youth and education Gehrels was born at Ha ...

Palomar Observatory Palomar Observatory is an astronomical research observatory in San Diego County, California, United States, in the Palomar Mountain Range. It is owned and operated by the California Institute of Technology (Caltech). Research time at the observa ...

, was also named after him. In honor of his contribution to the study of the southern hemisphere sky, a 60-cm telescope at

Reunion Island Reunion may refer to: * Class reunion * Family reunion Reunion, Réunion, Re-union, Reunions or The Reunion may also refer to: Places * Réunion, a French overseas department and island in the Indian Ocean * Reunion, Commerce City, Colorado, ...

will be named the Lacaille Telescope.(French)

Main works

La Caille - Leçons elementaires d'astronomie géométrique et physique, 1755 - 1437831

*''Leçons élémentaires de Mathématiques'' (1741), frequently reprinted *ditto ''de Mécanique'' (1743), &c. *ditto ''d'Astronomie'' (1746); 4th edition augmented by Lalande (1779) * 2nd edition *Calculations by him of eclipses for eighteen hundred years were inserted in ''L'Art de vérifier les dates'' by

Benedictine , image = Medalla San Benito.PNG , caption = Design on the obverse side of the Saint Benedict Medal , abbreviation = OSB , formation = , motto = (English: 'Pray and Work') , found ...

historian Charles Clémencet (1750) *He communicated to the Academy in 1755 a classed catalogue of forty two southern nebulae, and gave in t. ii. of his ''Ephémérides'' (1755) practical rules for the employment of the lunar method of longitudes, proposing in his additions to

Pierre Bouguer Pierre Bouguer () (16 February 1698, Croisic – 15 August 1758, Paris) was a French mathematician, geophysicist, geodesist, and astronomer. He is also known as "the father of naval architecture". Career Bouguer's father, Jean Bouguer, one ...

's ''Traité de Navigation'' (1760) the model of a nautical almanac. *''Tabulae Solares'' (1758)

Star catalogue

*"Remarques sur le Catalogue suivant des principales Étoiles du Ciel",
Éphémérides des mouvemens célestes
pour dix années, depuis 1755 jusqu'en 1765, et pour le meridien de la ville de Paris'' (1755), pp. xlix-lxiii. *"Table des Ascensions Droites et des Declinaisons Apparentes des Etoiles australes renfermées dans le tropique du Capricorne..."
''Memoires Academie Royale des Sciences'' pour 1752
(1756), pp. 539–592. (describing fourteen new constellations) *"Stellarum ascensiones rectae verae & declinationes verae ad Epocham anni ineuntis 1750",
Astronomiae fundamenta
novissimis solis et stellarum observationibus stabilita, Lutetiae in Collegio mazarineo et in Africa ad Caput Bonae-Spei'' (1757), pp. 233–237. (containing a standard catalogue of 398 stars) *"Stellarum longitudines & latitudines verae ad annum ineuntum 1750, Earum praecipue quae Zodiacales sunt", ''Astronomiae fundamenta'' (1757), pp. 238–239. *"Stellarum Australium Catalogus
''Coelum australe stelliferum''
''seu, Observationes ad Construendum Stellarum Australium Catalogum Institutae: in Africa ad Caput Bonae-Spei'' (1763), (edited by J. D. Maraldi), pp. 139–158. *"Catalogue suivant des principales Étoiles du Ciel, pour le commencement de l'Anee 1750",
Éphémérides des mouvemens célestes
pour dix annees, depuis 1765 jusqu'en 1775, et pour le meridien de la ville de Paris'' (1763), pp. lvii-lxiv. *"Observations sur 515 étoiles du Zodiaque", ''Éphémérides des mouvemens célestes, pour dix annees, depuis 1765 jusqu'en 1775'', (1763) pp. lxv-lxxvii.
''A catalogue of 9766 stars in the southern hemisphere,''
'for the beginning of the year 1750: from the observations of the Abbé de Lacaille, made at the cap of Good Hope in the years 1751 and 1752; with a preface by Sir J. F. W. Herschel'' (1847), giving zone observations of about 10,000 stars, re-edited by F. Baily

Star map

* "Planisphere contenant les Constellations Celestes comprises entre le Pole Austral et le Tropique du Capricorne", ''Mem. de l'Ac. R. des Sc.'' 1752 (1756), p. 590, plate 20. (French) *
Coelum Australe
, ''Coelum australe stelliferum'' (1763). (Latin) * "Planisphere des Etoiles les Australes dressé par M. i'Abbé de la Caille", ''Atlas Celeste de Flamsteed'' (1776), 2nd ed., plate 29. (French)* "Planisphere des Etoiles les Australes dressé par M. i'Abbé de la Caille", ''Recueil de Planches de l'Encyclopédie par ordre de matieres'' (1789), vol. 7, plate 3. (French) * "Planisphere des Etoiles les Australes dressé par M. i'Abbé de la Caille", ''Atlas Celeste de Flamsteed'' (1795), 3rd ed., plate 29. (French)

Notes

References

*Jean-Baptiste Joseph Delambre, Histoire de l'astronomie au Dix-Huitième siècle, Paris, Bachelier, 1827. * David S. Evans: ''Lacaille: astronomer, traveller; with a new translation of his journal''. Tucson: Pachart, 1992 * I.S. Glass: ''Nicolas-Louis de La Caille, Astronomer and Geodesist''. Oxford: Oxford University Press, 2013 *N.L. de La Caille: ''Travels at the Cape, 1751–53: an annotated translation of Journal historique du voyage fait au Cap de Bonne-Espérance ...''; transl. and ed. by R. Raven-Hart. Cape Town: A.A. Balkema for the Friends of the South African Library, 1976 *Journal historique du voyage fait au Cap de Bonne-Espérance par feu M. l'abbé de La Caille..., Paris, Guillyn, 1763. This work was edited by Abbé Carlier, who attached a discourse on La Caille's life. *
Virtual exhibition on Paris Observatory digital library
{{DEFAULTSORT:Lacaille, Nicolas Louis De 1713 births 1762 deaths People from Ardennes (department) University of Paris faculty 18th-century French astronomers Members of the French Academy of Sciences Members of the Royal Swedish Academy of Sciences Fellows of the Royal Society Honorary members of the Saint Petersburg Academy of Sciences Catholic clergy scientists French geodesists