Editing Nicolas-Louis de Lacaille

{{Short description|French astronomer and geodesist}}
{{Use dmy dates|date=May 2024}}
{{Infobox scientist 
 |name              =Nicolas-Louis de Lacaille
 |image             =Lacaille.jpg
 |image_size        = 250
 |birth_date        ={{birth date|df=yes|1713|03|15}} 
 |birth_place       = [[Rumigny, Ardennes|Rumigny]], France
 |death_date        = {{death date and age|df=yes|1762|3|21|1713|03|15}}
 |death_place       = Paris, France
 |residence         =
 |citizenship       = [[Kingdom of France|French]]
 |nationality       =
 |ethnicity         =
 |field             = [[Astronomy]]
 |work_institutions =
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 |doctoral_advisor  =
 |doctoral_students =
 |known_for         =
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Abbé '''Nicolas-Louis de Lacaille''' ({{IPA|fr|nikɔla lwi də lakaj|lang}}; 15 March 1713{{snd}}21 March 1762),{{refn|The traditional birth date of 15 March 1713 has been questioned due to many infants of the Catholic Church being baptised on the day of their birth in the 17th and 18th centuries.<ref>{{cite book |first=Thomas|last=Hockey |display-authors=etal |title=The Biographical Dictionary of Astronomers |publisher=[[Springer Publishing]] |year=2007 |isbn=978-0-387-31022-0 |page=665}}</ref> His baptism date is 15 December 1713; babies were normally baptised on the day that they were born.<ref>{{cite journal |last=Boquet|first=F. |title=Le Bicentenaire de Lacaille |journal=[[L'Astronomie (magazine)|L'Astronomie]] |year=1913 |volume=27 |pages=457–473 |bibcode=1913LAstr..27..457B |url=http://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?bibcode=1913LAstr..27..457B&db_key=AST&page_ind=2&plate_select=NO&data_type=GIF&type=SCREEN_GIF&classic=YES}} (See page 459.)</ref>}} formerly sometimes spelled '''de la Caille''', was a [[kingdom of France|French]] [[astronomer]] and [[geodesist]] who named 14 out of the [[IAU designated constellations|88 constellations]]. From 1750 to 1754, he studied the sky at the [[Cape Colony|Cape of Good Hope]] in present-day [[South Africa]]. Lacaille observed over 10,000 stars using a [[refracting telescope]].<ref>{{cite web |url=http://www.astro.wisc.edu/~dolan/constellations/extra/Lacaille.html |title=Abbé Nicolas Louis de Lacaille |publisher=[[University of Wisconsin–Madison]] |website=astro.wisc.edu |access-date=18 February 2019}}</ref>

==Biography==

Born at [[Rumigny, Ardennes|Rumigny]] in the [[Ardennes]] in eastern France, he attended school in Mantes-sur-Seine (now [[Mantes-la-Jolie]]). Afterwards, he studied rhetoric and philosophy at the [[:fr:Collège de Lisieux|Collège de Lisieux]] and then theology at the [[Collège de Navarre]]. 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 [[Louis Henri, Duke of Bourbon|Duc de Bourbon]], his father's former patron.<ref>{{cite book|title=Nicolas-Louis de La Caille. Astronomer and Geodesist|author=Glass, I.S.|publisher=[[Oxford University Press]]|location=Oxford|date=2013|isbn= 978-0-19-966840-3}}</ref>

After he graduated, he did not accept ordination as a priest but took [[deacon]]'s orders, becoming an [[Abbé]]. He concentrated thereafter on science, and, through the patronage of [[Jacques Cassini]], obtained employment, first in [[surveying]] the coast from [[Nantes]] to [[Bayonne]], then, in 1739, in remeasuring the [[French meridian arc]], for which he is honoured with a pyramid at [[Juvisy-sur-Orge]]. The success of this difficult operation, which occupied two years, and achieved the correction of the anomalous result published by [[Jacques Cassini]] in 1718, was mainly due to Lacaille's industry and skill. He was rewarded by admission to the [[French Academy of Sciences|Royal Academy of Sciences]] and appointment as Professor of mathematics in the [[College des Quatre-Nations|Mazarin college]] of the [[University of Paris]], 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]] and [[Jean Sylvain Bailly]], both of whom were later guillotined during the [[French Revolution]].{{Citation needed|date=April 2025}}

==Voyage to the Cape of Good Hope==
[[File:A memorial to the Abbe de la Caille, at Aurora in the Western Cape of South Africa (cropped).JPG|thumb|A memorial to the Abbé de Lacaille and [[Thomas Maclear]], at Aurora in the Western Cape of South Africa.  The English portion of the inscription reads: "This is the site of the Maclear Beacon positioned in 1838 near the original North Terminal of the Arc of Meridian positioned by Abbé de Lacaille, the first surveyor to introduce Geodetic Surveying into South Africa." Open the image to see the Afrikaans portion.]]

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 [[Cape of Good Hope]]. This was officially sanctioned by [[Roland-Michel Barrin de La Galissonière]]. There, he constructed an observatory on the shore of [[Table Bay]] with the support of the Dutch Governor [[Ryk Tulbagh]]. The primary result of his two-year stay was 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]]es ([[Mars]] serving as an intermediary). This work required near-simultaneous observations from Europe which were carried out by [[Jérôme Lalande]].

His southern catalogue, called ''Coelum Australe Stelliferum'', was published posthumously in 1763. He found it necessary to introduce 14 new [[constellation]]s which have since become standard.<ref>{{cite web| url = http://www.ianridpath.com/startales/startales1d.html#lacaille14| title = Star Tales – Lacaille's southern survey| access-date = 24 January 2009| first = Ian| last=Ridpath}}</ref> One of these was [[Mensa (constellation)|Mons Mensae]], the only constellation named after a terrestrial feature (the [[Table Mountain]]). An 1890 study of this catalogue by [[Benjamin Apthorp Gould|B. A. Gould]] found a considerable number of errors.<ref>{{citation | postscript=.
 | title=Investigation of errors in Lacaille's Coelum Australe Stelliferum, I
 | last=Gould | first=B. A. | author-link=Benjamin Apthorp Gould
 | journal=Astronomical Journal
 | volume=9 | issue=211 | pages=145–152 | date=February 1890
 | doi=10.1086/101322 | bibcode=1890AJ......9..145G
}} Note that there are three other parts to this study. Cf. {{bibcode|1890AJ......9..169G}}, {{bibcode|1890AJ.....10....1G}}, and {{bibcode|1890AJ.....10...17G}} .</ref>

{{anchor|Arc measurement}}While at the [[Cape of Good Hope|Cape]], Lacaille performed an [[arc measurement]] to determine the [[radius of the Earth]] in the southern hemisphere. He set out a [[baseline (surveying)|baseline]] in the [[Swartland]] plain north of present-day [[Darling, Western Cape|Darling]]. Using [[triangulation (surveying)|triangulation]] he then measured a 137&nbsp;km [[meridian arc|arc of meridian]] between [[Cape Town]] and present-day [[Aurora, Western Cape|Aurora]], determining the [[astronomical latitude]]s of the end points by means of [[astro-geodesy|astronomical-geodetic]] observations. There is a memorial to his work at a location near Aurora, pictured here.  His result suggested that the Earth was lengthened (prolate) instead of [[Earth's flattening|flattened (oblate)]] towards the south pole. [[George Everest]],<ref>{{cite journal|last=Everest|first=George|title=On the Triangulation of the Cape of Good Hope|journal=Memoirs Roy. Astr. Society|year=1821|volume=I, pt. II|pages=255–270}}</ref> 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 [[Gravity of Earth|gravitational attraction]] of Table Mountain at the southern end and by the [[Piketberg|Piketberg Mountain]] at the northern.<ref>{{cite web
 |url=http://assa.saao.ac.za/sections/history/expeditions/arc_meridian
 |title=Arc of the Meridian
 |publisher=Astronomical Society of South Africa
 |access-date= 27 August 2020
}}</ref> 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.<ref>{{cite journal
 |title=Lacaille 250 years on
 |last=Warner
 |first=Brian
 |journal=Astronomy and Geophysics
 |date= 1 April 2002
|volume=43
 |issue=2
 |pages=2.25–2.26
 |doi= 10.1046/j.1468-4004.2002.43225.x
 |doi-access=free
 }}</ref>  [[Maclear's Beacon]] was erected on the Table Mountain in [[Cape Town]] to help with the verification.<ref>{{cite book|last=Maclear|first=T.|title=Verification and Extension of Lacaille's Arc of Meridian at the Cape of Good Hope|date=1866|volume=I|publisher=Lords Commissioners of the Admiralty}}</ref>

==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 distance (navigation)|Lunar distances]]) using the orbital theory of [[Alexis Claude Clairaut|Clairaut]]. Lacaille worked hard at astronomical calculations; apart from constructing astronomical [[Ephemeris|ephemerides]] and mathematical tables, he calculated a table of [[eclipse]]s for 1800 years. [[Jérôme Lalande|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.{{Citation needed|date=April 2025}}

==Later life==

On his return to Paris in 1754, following a diversion to [[Mauritius]], 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 of light|aberration]] and [[astronomical nutation|nutation]]. He carried out calculations on comet orbits and was responsible for giving [[Halley's Comet]] 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. His death, probably caused in part by over-work{{Citation needed|date=April 2025}}, occurred in 1762. He was buried in the vaults of the Mazarin College, now the [[Institut de France]] in Paris.

==Honours==

In 1754, he was elected a foreign member of the [[Royal Swedish Academy of Sciences]]. He was also an honorary member of the academies of Saint Petersburg and Berlin, the [[Royal Society]] of London and the [[Göttingen Academy of Sciences and Humanities|Royal Society of Göttingen]], and the Institute of Bologna.<ref>Thomas Hockey et al. The Biographical Dictionary of Astronomers, Springer, 2007, {{ISBN|978-0-387-31022-0}}, p666</ref>

Lacaille has the honor of naming [[IAU designated constellations|14 different constellations]]:

* [[Antlia]]
* [[Caelum]]
* [[Circinus]]
* [[Fornax]]
* [[Horologium (constellation)|Horologium]]
* [[Mensa (constellation)|Mensa]]
* [[Microscopium]]
* [[Norma (constellation)|Norma]]
* [[Octans]]
* [[Pictor]]
* [[Pyxis]]
* [[Reticulum]]
* [[Sculptor (constellation)|Sculptor]]
* [[Telescopium]]

The crater "[[La Caille (crater)|La Caille]]" on the [[Moon]] is named after him. [[Asteroid]] [[9135 Lacaille]] (AKA 7609 P-L and 1994 EK6), discovered on 17 October 1960 by [[Cornelis Johannes van Houten]], [[Ingrid van Houten-Groeneveld]] and [[Tom Gehrels]] at [[Palomar Observatory]], was also named after him.

In honor of his contribution to the study of the southern hemisphere sky, a 60-cm telescope at [[Réunion|Réunion Island]] will be named the Lacaille Telescope.<ref name=imcce-o-t60>{{cite web|title=TÉLESCOPE LACAILLE DE 60CM DES MAKES (ILE DE LA RÉUNION)|url=http://www.imcce.fr/en/observateur/t60.php|publisher=IMCCE|access-date=1 December 2011|archive-url=https://web.archive.org/web/20111212125310/http://www.imcce.fr/en/observateur/t60.php|archive-date=12 December 2011|url-status=dead}}(French)</ref>{{Verify source|date=April 2025|reason=As of 2025, the current URL for the observatory, https://www.observatoiredesmakes.com/l-observatoire/le-mat%C3%A9riel, seems to make no mention of the 60cm telescope being named after Lacaille.}}

==Main works==
[[File:La Caille - Leçons elementaires d'astronomie géométrique et physique, 1755 - 1437831.jpg|thumb|''Leçons elementaires d'astronomie, géométrique et physique'', 1755 edition]]
[[File:Messier 55 VISTA.jpg|thumb|[[Messier 55]] is a globular cluster discovered in 16 June 1752.<ref>{{cite book |first1=Robert |last1=Thompson |first2=Barbara Fritchman |last2=Thompson |title=Illustrated guide to astronomical wonders |series=DIY science |publisher=[[O'Reilly Media, Inc.]] |year=2007 |isbn=978-0-596-52685-6 |page=413 | url=https://books.google.com/books?id=ymt9nj_uPhwC&pg=PA413}}</ref>]]

*''Leçons élémentaires de Mathématiques'' (1741), frequently reprinted
*ditto ''de Mécanique'' (1743), &c.
*ditto ''d'Astronomie'' (1746); 4th edition augmented by Lalande (1779)
* {{Cite book|title=Leçons élémentaires d'optique|volume=|publisher=Hippolyte Louis Guérin & Louis François Delatour|location=Paris|year=1764|language=fr|url=https://gutenberg.beic.it/webclient/DeliveryManager?pid=7154759}} 2nd edition
*Calculations by him of eclipses for eighteen hundred years were inserted in ''L'Art de vérifier les dates'' by [[Benedictine]] historian [[Charles Clémencet]] (1750)
*He communicated to the Academy in 1755 a classed catalogue of forty&nbsp;two southern nebulae,<ref>{{cite web |url=http://www.messier.obspm.fr/xtra/history/lacaille.html |title=Lacaille's "Catalog of Nebulae of the Southern Sky" |work=SEDS' Messier Database |date=18 September 2007 |access-date=1 May 2019 |archive-url=https://web.archive.org/web/20180626220837/http://messier.obspm.fr/xtra/history/lacaille.html |archive-date=26 June 2018}}</ref> 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]]'s ''Traité de Navigation'' (1760) the model of a nautical almanac.
*''Tabulae Solares'' (1758)

===Star catalogues===
*"Remarques sur le Catalogue suivant des principales Étoiles du Ciel", ''[https://books.google.com/books?id=CGHtdxdcc5UC 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 [[Tropic of Capricorn|tropique du Capricorne]]...", [http://www.atlascoelestis.com/88%20lacaille.htm ''Memoires Academie Royale des Sciences'' pour 1752] (1756), pp.&nbsp;539–592. (describing fourteen new constellations)
*"Stellarum ascensiones rectae verae & declinationes verae ad Epocham anni ineuntis 1750", ''[https://books.google.com/books?id=LXm0RAf6fk0C Astronomiae fundamenta] novissimis solis et stellarum observationibus stabilita, Lutetiae in Collegio mazarineo et in Africa ad [[Cape of Good Hope|Caput Bonae-Spei]]'' (1757), pp.&nbsp;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.&nbsp;238–239.
*"Stellarum Australium Catalogus",[https://books.google.com/books?id=ijEVAAAAQAAJ ''Coelum australe stelliferum''],''seu, Observationes ad Construendum Stellarum Australium Catalogum Institutae: in Africa ad Caput Bonae-Spei'' (1763), (edited by [[Giovanni Domenico Maraldi|J. D. Maraldi]]), pp.&nbsp;139–158.
*"Catalogue suivant des principales Étoiles du Ciel, pour le commencement de l'Anee 1750", ''[https://books.google.com/books?id=8Y9uW-OVAOsC 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.
*[https://archive.org/details/bub_gb_hbEvAQAAMAAJ ''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 [[Francis Baily|F. Baily]]
=== Star maps===
* "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.&nbsp;590, plate 20. (French)
* "[https://www.repository.cam.ac.uk/bitstream/handle/1810/245247/img722.jpg?sequence=4&isAllowed=y 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==
{{reflist}}

==References==
*Jean-Baptiste Joseph Delambre, Histoire de l'astronomie au Dix-Huitième siècle, Paris, Bachelier, 1827.
*[[David Stanley Evans|David S. Evans]]: ''Lacaille: astronomer, traveller; with a new translation of his journal''. Tucson: Pachart, 1992  {{ISBN|0-88126-284-6}}
*[[Ian Glass|I.S. Glass]]: ''Nicolas-Louis de La Caille, Astronomer and Geodesist''. Oxford: Oxford University Press, 2013 {{ISBN|978-0-19-966840-3}}
*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  {{ISBN|0-86961-068-6}}
*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 [[Claude Carlier|Abbé Carlier]], who attached a discourse on La Caille's life.
*{{EB1911|wstitle=Lacaille, Nicolas Louis de|volume=16|page=35}}
*[https://bibnum.obspm.fr/exhibits/show/la_caille Virtual exhibition on Paris Observatory digital library]

{{ConstellationsNLDLAltered}}
{{ConstellationsByLacaille}}

{{Authority control}}

{{DEFAULTSORT:Lacaille, Nicolas Louis De}}
[[Category:1713 births]]
[[Category:1762 deaths]]
[[Category:People from Ardennes (department)]]
[[Category:Academic staff of the University of Paris]]
[[Category:18th-century French astronomers]]
[[Category:Members of the French Academy of Sciences]]
[[Category:Members of the Royal Swedish Academy of Sciences]]
[[Category:Fellows of the Royal Society]]
[[Category:Honorary members of the Saint Petersburg Academy of Sciences]]
[[Category:Catholic clergy scientists]]
[[Category:French geodesists]]