View source for Paris Observatory

{{short description|Foremost astronomical observatory of France}}
{{Infobox observatory
| name = Paris Observatory - PSL
| logo = Observatoire de paris-comarquage-noir.svg{{!}}class=skin-invert-image
| established = {{start date|1667}}
| telescope1_name = East Tower 38 cm (15 in)
| telescope1_type = Equatorial refractor
}}

The '''Paris Observatory''' ({{langx|fr|Observatoire de Paris}}, {{IPA|fr|ɔbsɛʁvatwaʁ d(ə) paʁi|pron}}), a research institution of the [[Paris Sciences et Lettres University]], is the foremost [[Astronomy|astronomical]] observatory of France, and one of the largest astronomical centres in the world. Its historic building is on the [[Rive Gauche|Left Bank]] of the [[Seine]] in central Paris, but most of the staff work on a satellite campus in [[Meudon]], a suburb southwest of Paris.

The Paris Observatory was founded in 1667 as the first public observatory.<ref name="r840">{{cite web | title=The first observatories | website=Esposizioni on-line - Istituto e Museo di Storia della Scienza | url=https://brunelleschi.imss.fi.it/galileopalazzostrozzi/section/TheFirstObservatories.html | access-date=2025-07-27}}</ref><ref name="Widemann2">{{Cite journal|issn=0003-9810|title = Aux origines d'une science et d'une sociabilité européennes: l'Observatoire de Paris à 350 ans|journal = Archives Internationales d'Histoire des Sciences|volume = 72|issue = 189|pages = 6–23|last1 = Widemann|first1 = Thomas|last2 = Knobloch|first2 = Eberhard|year = 2022| doi=10.1484/J.ARIHS.5.133702 |url=https://www.brepolsonline.net/toc/arihs/2022/72/189|url-access = subscription}}</ref> Construction was completed by the early 1670s and coincided with a major push for increased science, and the founding of the [[French Academy of Sciences|Royal Academy of Sciences]].<ref name=":1">{{Cite book|url=https://books.google.com/books?id=y3CODwAAQBAJ&q=Paris+Observatory+history&pg=PA109|title=History of Indian Astronomy: The Siamese Manuscript|last=Narayanan|first=Anil|date=2019-03-08|publisher=Lulu.com|isbn=9781483496320}}{{self-published source|date=June 2020}}</ref> King Louis XIV's minister of finance organized a "scientific powerhouse" to increase understanding of astronomy, maritime navigation, and science in general.<ref name=":1" />

Through the centuries the Paris Observatory has continued in support of astronomical activities, and in the 21st century connects multiple sites and organizations, supporting astronomy and science, past and present.<ref>{{Cite web|url=https://www.obspm.fr/-observatoire-de-paris-.html?lang=en|title=Paris Observatory – Observatoire de Paris – PSL Centre de recherche en astronomie et astrophysique|website=www.obspm.fr|access-date=2019-11-19}}</ref><ref>{{Cite book|url=https://books.google.com/books?id=12CnfM1u32kC&q=Paris+Observatory+founded&pg=PA1|title=Women in Early British and Irish Astronomy: Stars and Satellites|last=Brück|first=Mary|date=2009-07-25|publisher=Springer Science & Business Media|isbn=9789048124732}}</ref>

==Constitution==

Administratively, it is a ''[[grand établissement]]'' of the French [[Ministry of National Education (France)|Ministry of National Education]], with a status close to that of a public university. Its missions include:<ref name="home">{{ cite web | url=http://www.obspm.fr/presentation.en.shtml | title=The Paris Observatory | publisher=l'Observatoire de Paris | access-date=2007-08-27 | url-status=dead | archive-url=https://web.archive.org/web/20070824063505/http://www.obspm.fr/presentation.en.shtml | archive-date=2007-08-24 }}</ref>
* Research in astronomy and [[astrophysics]]
* Education (four graduate programs, [[Doctor of Philosophy|Ph.D.]] studies)
* Diffusion of knowledge to the public

It maintains a solar observatory at [[Meudon, France|Meudon]] and a radio astronomy observatory at [[Nançay Radio Telescope|Nançay]].<ref name="home"/> It was also the home to the [[International Time Bureau]] until its dissolution in 1987.<ref>Guinot (2000)</ref> It remains the source of legal time in France,<ref>[https://heurelegalefrancaise.fr/ French legal time] "French legal time is generated and provided by Observatoire de Paris as part of its missions and in agreement with Decree No. 2017-292 of March 6, 2017 defining French legal time.  Legal time is constructed from UTC(OP), which is the real-time realization of UTC at Observatoire de Paris."</ref> using multiple [[atomic fountain]] clocks maintained by its '''SYRTE''' ({{lang|fr|Sytèmes de Référence Temps Espace}}) department.<ref>{{cite journal
 |title=Atomic fountains and optical clocks at SYRTE: status and perspectives
 |author1=M. Abgrall |display-authors=etal
 |journal=[[Comptes Rendus Physique]] |volume=16 |issue=5
 |date=June 2015 |pages=461–470
 |doi=10.1016/j.crhy.2015.03.010
 |arxiv=1507.04623
|bibcode=2015CRPhy..16..461A }}</ref>  The Paris Observatory Library, which was founded in 1785, provides the researchers with documentation and preserves the ancient books, archives, and heritage collections of the institution. Many collections are available online.{{fact|date=March 2024}}

==History==

[[File:La Hire 1682.jpg|thumb|upright=1.25|A 1682 map shows corrections to the coast of France]]
[[File:Paris Observatory XVIII century.png|thumb|upright=1.25|left|The Paris Observatory at the beginning of the eighteenth century, with the wooden "Marly Tower" on the right, a remnant of the [[Machine de Marly]] moved to the grounds by [[Giovanni Cassini]], for the mounting of long-tubed telescopes and even longer tubeless [[aerial telescope]]s.]]

The Paris Observatory was proposed in 1665–1666 by the [[French Academy of Sciences]], which had recently been founded by the Minister of Finance [[Jean-Baptiste Colbert]]. In 1666, King [[Louis XIV of France|Louis XIV]] authorized the building of the Observatory. On [[Midsummer's Day]] 1667, members of the Academy of Sciences traced the future building's outline on a plot outside town near the [[Port-Royal Abbey, Paris|Port Royal abbey]], with the [[Paris meridian]] exactly bisecting the site north–south.<ref>{{Cite book|url=http://gallica.bnf.fr/ark:/12148/bpt6k9773412z|title=Histoire de l'Observatoire de Paris, de sa fondation à 1793 / par C. Wolf,...|last=Wolf|first=Charles (1827–1918) Auteur du texte|date=1902|publisher=Gauthier-Villars|location=Paris|pages=1–12}}</ref> The meridian line was used as a basis for navigation and would be used by French cartographers as their [[prime meridian]] for more than 200 years.{{cn|date=August 2025}}

The Paris Observatory predates by a few years the [[Royal Observatory, Greenwich|Royal Greenwich Observatory]] in England, which was founded in 1675. The English philosopher [[John Locke]] visited the Paris Observatory on 28 August 1677, which he recorded in his journal: "At the Observatory we saw the Moon in a twenty-two foot glass, and Jupiter, with his satellites, in the same. The most remote was on the east, and the other three on the west. We also saw Saturn and his ring, in a twelve-foot glass, and one of his satellites. Monsieur Cassini told me, that the declination of the needle at Paris is about two and a half degrees to the west."<ref>{{cite book |last1=King |first1=Peter |title=The Life and Letters of John Locke |date=1858 |publisher=Henry Bohn |location=London |page=73}}</ref>

The [[architect]] of the Paris Observatory was [[Claude Perrault]] whose brother, [[Charles Perrault|Charles]], was secretary to Jean-Baptiste Colbert and superintendent of public works.<ref>[Anon.] (2001) "Perrault, Claude", ''[[Encyclopædia Britannica]]'', Deluxe CDROM edition</ref>  Optical instruments were supplied by [[Giuseppe Campani]]. Construction of the Observatory was completed in 1671, though the buildings were extended in 1730, 1810, 1834, 1850, and 1951.<ref name="eb">[Anon.] (2001) "Paris Observatory", ''[[Encyclopædia Britannica]]'', Deluxe CDROM edition</ref> The last extension incorporates the Meridian Room designed by [[Jean Prouvé]].<ref>[Anon.] (2001) "Prouvé, Jean", ''[[Encyclopædia Britannica]]'', Deluxe CDROM edition</ref>

[[File:Destruction incendie chateau neuf archives departem 92.jpg|thumb|upright=1.25|The Château-Neuf at Meudon in 1871, after the fire.]]
[[File:Projet non réalisé de restauration du chateau neuf vers 1880.JPG|thumb|upright=1.25|Project for a dome in the heart of the Château-Neuf, never built. Circa 1880]]

===Accomplishments===
In 1671 Saturn's moon [[Iapetus (moon)|Iapetus]] was discovered from the observatory, followed by [[Rhea (moon)|Rhea]] in 1672.<ref name=":4">{{Cite book|url=https://books.google.com/books?id=-ePHSCLOMvwC&q=paris+observatory+discoveries&pg=PA66|title=Cosmic Discoveries: The Wonders of Astronomy|last=Levy|first=David H.|date=2010-09-09|publisher=Prometheus Books|isbn=9781615925667}}</ref> The moons [[Dione (moon)|Dione]] and [[Tethys (moon)|Tethys]] were also discovered from the observatory in 1684.<ref name=":4" /> In 1676 the staff concluded that light itself was travelling at a finite speed.<ref>{{Cite journal|last=Abbott|first=Alison|date=January 2009|title=Hidden treasures: the Paris Observatory|journal=Nature|volume=457|issue=7225|pages=33|doi=10.1038/457033a|issn=1476-4687|doi-access=free}}</ref>

[[Image:Obs-Paris-meridienne.jpg|thumb|upright=1.1|The Meridian Room (or Cassini Room) at the Paris Observatory. The [[Paris Meridian]] is traced on the floor.]]
The world's first national almanac, the ''[[Connaissance des Temps|Connaissance des temps]],'' was published by the Observatory in 1679, using eclipses in [[Jupiter]]'s satellites to aid sea-farers in establishing [[longitude]]. In 1863, the observatory published the first modern [[weather map]]s. In 1882, a {{convert|33|cm|abbr=on}} [[astrograph]]ic [[lens (optics)|lens]] was constructed, an instrument that catalysed what proved to be the over-ambitious international ''[[Carte du Ciel]]'' project.{{Citation needed|date=August 2007}}

In November 1913, the observatory used the [[Eiffel Tower]] as an [[Antenna (radio)|antenna]], exchanged sustained radio signals with the [[United States Naval Observatory]] in [[Washington, D.C.]] to determine the exact difference of longitude between the two institutions.<ref>"Paris Time By Wireless," ''New York Times,'' Nov 22, 1913, pg 1.</ref>

=== Heritage ===
The Paris Observatory library preserves a great number of original works and letters of the Observatory and well known astronomers. The entire collection has been inventoried in an online archive called Calames.<ref>[https://calames.abes.fr/pub/obs.aspx Calames]</ref> Some of the work is now digitized on the [https://bibnum.obspm.fr digital library] such as those of [[Johannes Hevelius]], [[Jérôme Lalande]] and [[Joseph-Nicolas Delisle]].

==Directors and staff==
The title of Director of the Observatory was officially given for the first time to [[César-François Cassini de Thury]] by a Royal brevet dated November 12, 1771.<ref>Archives nationales, O1 117, fol. 991–993. See also Charles Wolf, ''Histoire de l'Observatoire de Paris de sa fondation à 1793'', Paris : Gauthier-Villars, 1902, p. 194 and following.</ref> However, the important role played by his grandfather and father in this institution during its first century actually gave them somewhat the role of Director.{{cn|date=August 2025}}

The observatory did not have a recognised Director until 1771, before that each member could do as they pleased.<ref>{{Cite journal |bibcode = 1971JBAA...81..479F|title = Cassini and the Paris Observatory|journal = Journal of the British Astronomical Association|volume = 81|pages = 479|last1 = Friedjung|first1 = M.|year = 1971}}</ref> Sometimes [[Giovanni Domenico Cassini|Giovanni Cassini]] (1671–1712) and  [[Jacques Cassini]] (1712–1756) are listed as "Directors" retrospectively. The same goes for François Arago, who also was not actually a Director although he did have a ''de facto'' position of leadership and is often credited as such.{{cn|date=August 2025}}

The current President of the Observatory is [[Fabienne Casoli]].<ref>{{Cite web|title=Fabienne Casoli élue Présidente de l'Observatoire de Paris – PSL – Observatoire de Paris – PSL Centre de recherche en astronomie et astrophysique|url=https://www.obspm.fr/fabienne-casoli-elue.html?lang=en|website=www.obspm.fr| date=4 February 2020 |access-date=2020-05-09}}</ref>
* [[César-François Cassini de Thury]] (1756–1784)
* [[Dominique, comte de Cassini]] (1784–1793)
* [[Joseph Jérôme Lefrançais de Lalande]] (1795–1800)
* [[Pierre Méchain]] (1800–1804)
* [[Jean Baptiste Joseph Delambre]] (1804–1822)
* [[Alexis Bouvard]] (1822–1843)
* [[François Arago]] (1843–1853)
* [[Urbain Le Verrier]] (1854–1870)
* [[Charles-Eugène Delaunay]] (1870–1873)
* [[Urbain Le Verrier]] (1873–1877)
* [[Amédée Mouchez]] (1878–1892)
* [[Félix Tisserand]] (1892–1896)
* [[Maurice Loewy]] (1896–1907)
* [[Benjamin Baillaud]] (1908–1926)
* [[Henri-Alexandre Deslandres]] (1926–1929)
* [[Ernest Esclangon]] (1929–1944)
* [[André Danjon]] (1945–1963)
* [[Jean-François Denisse]] (1963–1967)
* [[Jean Delhaye]] (1967–1971)
* Raymond Michard (1971–1976)
* Jacques Boulon (1976–1981)
* Pierre Charvin (1981–1991)
* Michel Combes (1991–1999)
* Pierre Couturier (1999–2003)
* Daniel Egret (2003-2011)
* Claude Catala (2011–2020)
* [[Fabienne Casoli]] (2020–present)

== Facilities ==
The first site was the Paris headquarters established in 1667 by King Louis XIV of France. This facility had various work done on it over the centuries, and in 1927 the Meudon Observatory was added, which included a new site and facilities. It was built in 1891.{{cn|date=August 2025}}

In addition to these sites, the [[Marseille Observatory|Marseilles Observatory]] became a branch of the Paris Observatory in 1863.<ref name=":02">{{Cite book|url=https://books.google.com/books?id=cWBDAAAAQBAJ&q=Marseille+Observatory&pg=PA121|title=Le Verrier—Magnificent and Detestable Astronomer|last=Lequeux|first=James|date=2013-03-15|publisher=Springer Science & Business Media|isbn=9781461455653|language=en}}</ref> In 1873, Marseilles Observatory detached from Paris Observatory.<ref>{{Cite journal|last1=Prévot|first1=Marie-Louise|last2=Caplan|first2=James|date=1998|title=History of the Marseille Observatory|journal=Acta Historica Astronomiae|language=en|volume=3|pages=78|issn=0003-2670|bibcode=1998AcHA....3...78P}}</ref>

=== Paris ===
[[File:Observatoire Paris 20030404.jpg|thumb|upright=1.25|Paris Observatory]]
King Louis XIV purchased the land for his new observatory in March 1667.<ref name="1971JBAA...81..479F Page 479">{{Cite journal|title=1971JBAA...81..479F Page 479|bibcode = 1971JBAA...81..479F|last1 = Friedjung|first1 = M.|journal = Journal of the British Astronomical Association|year = 1971|volume = 81}}</ref> This provided a site for the activities of the Academy of Sciences near to the city of Paris.<ref name="1971JBAA...81..479F Page 479"/> The original buildings was designed by Claude Perrault.<ref name=":3">{{Cite journal|last=Lequeux|first=James|date=January 2017|title=The Paris Observatory has 350 years|journal=L'Astronomie|volume=131|pages=28|issn=0004-6302|bibcode=2017LAstr.131a..28L}}</ref> A dome and terrace was added in 1847.<ref name=":3" />

{{anchor|LESIA}}
=== Meudon ===
[[File:Le chateau neuf en observatoire meudon 2014.JPG|thumb|upright=1.25|The great refractor of [[Meudon]] overlooking the facilities' gardens.]]

The Meudon site was constructed in the late 19th century by [[Jules Janssen]], one of the discoverers of [[helium]]. With a million francs and permission to build on the ruins of the old royal palace, he constructed one of the grandest observatories of its day, with a focus on astronomy and solar physics. After World War I, the observatory was integrated with the nearby Paris Observatory and  became an important campus for that observatory. Even into the 21st century solar observations are conducted at the Meudon site, and the preserved Great Refractor (Grande lunette) and astronomical gardens overlooking the city of Paris have delighted visitors for decades. The site includes:
* [[Solar Observatory Tower Meudon]]
* [[Chateau de Meudon]]
* LESIA space and astrophysics instrumentation research laboratory<ref name=COROTPR2005>{{cite press release
 |title=Completion and delivery of equipment bay and camera to CNES mark major project milestone
 |publisher=Released jointly by [[Observatoire de Paris]], [[CNES]] and [[CNRS-INSU]] |date=2005-06-30 |access-date=2008-08-03
 |url =http://www.cnes.fr/web/3820-pr52-2005-joint-press-release-corot-observation-satellite-cnes-mission-completion-and-delivery-of-equipment-bay-and-camera-to-cnes-mark-major-pr.php
 }}</ref>

=== Nançay ===
[[File:Nançay Plan 02.jpg|thumb|Nançay radar antenna]]
After the Second World War, French astronomers began designing and building instruments for radio astronomy.<ref name=":2">{{Cite journal|title=2010JAHH...13...29L Page 29|journal = Journal of Astronomical History and Heritage|volume = 13|issue = 1|pages = 29|bibcode = 2010JAHH...13...29L|last1 = Lequeux|first1 = James|last2 = Steinberg|first2 = Jean-Louis|last3 = Orchiston|first3 = Wayne|year = 2010 | doi=10.3724/SP.J.1440-2807.2010.01.03 }}</ref> A field station was established in 1953, and by the late 1950s several radio instruments were established.<ref name=":2" />
In 1965 the [[Nançay radio telescope]] was established, a design equivalent to an almost 100-metre dish.<ref>{{Cite book|url=https://books.google.com/books?id=9MTbtJJ0vycC&q=Nan%C3%A7ay+Radio+Observatory&pg=PA229|title=High-Sensitivity Radio Astronomy|last1=Davis|first1=R. J.|last2=Jackson|first2=N.|date=1997-01-28|publisher=Cambridge University Press|isbn=978-0-521-57350-4|language=en}}</ref>

=== Saint-Véran ===
Also known as the Observatoire du Pic de Château Renard, the [[Observatoire de Saint-Véran]] was built in 1974 on top of the Pic de Château Renard ({{convert|2900|m|abbr=on|disp=or}}), in the commune of [[Saint-Véran]] in the Haut Queyras ([[Hautes Alpes]] ''département''). A [[coronograph]] was in operation there for ten years; the dome was moved there from the Perrault building of the Observatoire de Paris.{{cn|date=August 2025}}

Nowadays, the AstroQueyras amateur astronomy association operates the facility, using a {{convert|60|cm|abbr=on}} telescope on loan from the [[Observatoire de Haute Provence]]. Numerous [[asteroid]]s have been discovered there.<ref>{{ cite web| url=http://www.obspm.fr/histoire/saintveran/saintveran.fr.shtml | title=L'Observatoire du Pic de Château Renard (2900 m) | work=Histoire | publisher=l'Observatoire de Paris | language=fr | access-date=2007-08-27 | url-status=dead | archive-url=https://web.archive.org/web/20070915043839/http://www.obspm.fr/histoire/saintveran/saintveran.fr.shtml | archive-date=2007-09-15}}</ref>

==Instruments past and present==
[[File:Observatoire de Paris - coupole 1.JPG|thumb|upright=1.25|The Arago equatorial telescope (38 cm/ 15 inch aperture)]]
[[File:Observatoire Paris lunette meridienne du jardin.jpg|thumb|A meridian instrument of the Observatory]]
Early telescopes were supplied by the famed craftsman Giuseppe Campani.<ref>{{Cite book|url=https://books.google.com/books?id=hMgXh8jMSGgC&q=Giuseppe+Campani+paris+observatory&pg=PA116|title=Planetary Astronomy from the Renaissance to the Rise of Astrophysics, Part A, Tycho Brahe to Newton|last1=Taton|first1=R.|last2=Wilson|first2=C.|last3=Hoskin|first3=Michael|date=2003-09-18|publisher=Cambridge University Press|isbn=978-0-521-54205-0}}</ref> Cassini, an astronomer who worked in the early days of the Observatory, had used Campani's telescopes in the 1660s, and continued to do so when he moved to the Paris Observatory.<ref>{{Cite book|url=https://books.google.com/books?id=E8f7gERE4rMC&q=Giuseppe+Campani+paris+observatory&pg=PA2|title=From Earth-Bound to Satellite: Telescopes, Skills and Networks|last=Morrison-Low|first=Alison D.|date=2011-11-11|publisher=BRILL|isbn=978-90-04-21150-6}}</ref>

The Marly tower, moved to the observatory in 1685 for mounting telescopes, was demolished in 1705.<ref>{{Cite web|url=https://sites.google.com/site/histoireobsparis/a-short-history-of-paris-observatory|title=A short Story of Paris Observatory – Histoire de l'Observatoire de Paris|website=sites.google.com|access-date=2019-11-20}}</ref> The Marly tower was originally made for the [[Palace of Versailles|Versailles]] water supply system (see [[Machine de Marly]]), but was moved to the southern gardens area near the Paris Observatory.<ref name=":8">{{Cite book|url=https://books.google.com/books?id=YfyWBQAAQBAJ&q=The+Marly+tower+paris+observatory&pg=PA56|title=New Insights From Recent Studies in Historical Astronomy: Following in the Footsteps of F. Richard Stephenson: A Meeting to Honor F. Richard Stephenson on His 70th Birthday|last1=Orchiston|first1=Wayne|last2=Green|first2=David A.|last3=Strom|first3=Richard|date=2014-11-24|publisher=Springer|isbn=978-3-319-07614-0|language=en}}</ref> The tower could hold the [[Objective (optics)|objective lens]] for extremely long focal length aerial telescopes.<ref name=":8" />

In 1732 a quadrant instrument made by Langlois was established at the Observatory.<ref>{{Cite book|url=https://books.google.com/books?id=KAWwzHlDVksC&q=paris+observatory+instruments&pg=PA106|title=The History of the Telescope|last=King|first=Henry C.|date=2003-01-01|publisher=Courier Corporation|isbn=978-0-486-43265-6|language=en}}</ref>

In 1804 a telescope of 8.4&nbsp;cm aperture, made by Bellet, was established on the roof of the observatory.<ref name=":7" /> In 1807 a [[James Short (mathematician)|Short reflector]] telescope was acquired, and there were several instruments available including a 9&nbsp;cm aperture [[Dollond & Son|Dollond]] telescope, and a telescope by Lerebours.<ref name=":7">{{Cite book|url=https://books.google.com/books?id=ikqGCgAAQBAJ&q=Fran%C3%A7ois+Arago+director&pg=PA180|title=François Arago: A 19th Century French Humanist and Pioneer in Astrophysics|last=Lequeux|first=James|date=2015-09-08|publisher=Springer|isbn=978-3-319-20723-0|language=en}}</ref>

One of the special telescopes in the collection of the observatory, was the Passy telescope of King [[Louis XV]].<ref name=":7" /> This telescope was built by Dom Noel in the late 18th century, and was a reflecting telescope with a 61&nbsp;cm aperture bronze mirror.<ref name=":7" /> In 1805 the mirror was re-polished, but it was tarnished again within two years; it remained at the Observatory until it was dismantled in 1841.<ref name=":10"/>

A Lerebours telescope of 24.4&nbsp;cm aperture was installed in 1823, at a cost of 14,500 francs.<ref name=":6">{{Cite book|url=https://books.google.com/books?id=ikqGCgAAQBAJ&q=paris+observatory+24.4+cm&pg=PA180|title=François Arago: A 19th Century French Humanist and Pioneer in Astrophysics|last=Lequeux|first=James|date=2015-09-08|publisher=Springer|isbn=978-3-319-20723-0}}</ref> In 1835 Arago used this telescope to observe the return of [[Halley's Comet]] that year.<ref name=":6" />

In 1837 the Gambey [[mural circle]] was installed, and also a transit instrument, also by Gambey.<ref name=":5">{{Cite book|url=https://books.google.com/books?id=MIZBDgAAQBAJ&q=paris+observatory+gambey%27s+circle&pg=PT285|title=British University Observatories 1772–1939|last=Hutchins|first=Roger|date=2017-03-02|publisher=Routledge|isbn=9781351954525}}</ref>

In 1857 a [[refracting telescope]] of {{convert|38|cm|in|sigfig=4}} aperture [[Objective (optics)|objective]], the [[Arago telescope|Arago equatorial telescope]], was completed. This telescope was proposed by director François Arago in 1846.<ref name=":3"/> It was installed in the east tower and was made by Lerebours.<ref name=":5" /> This instrument is known to have conducted photometry measurements of Jupiter's moons (there were only four known at that time) in the late 1880s.<ref name=":5" />

In 1863 a large [[transit circle]] was installed, and in 1878 a meridian instrument.<ref>{{Cite book|url=https://books.google.com/books?id=9jyExgmZxBoC&q=paris+observatory+tower&pg=PA388|title=History of Astronomy: An Encyclopedia|last=Lankford|first=John|date=2013-03-07|publisher=Routledge|isbn=9781136508349}}</ref> The transit circle of 1863 was made by Secretan and Eichens.<ref name=":5" />

In 1875 a 120&nbsp;cm aperture silver-on-glass reflecting telescope was built, for 400,000 francs.<ref>{{Cite book|url=https://books.google.com/books?id=vps3AQAAMAAJ&q=paris+observatory+reflector&pg=RA1-PA103|title=Astronomical and Meteorological Observations Made at the United States Naval Observatory During the Year ...|last=Observatory|first=United States Naval|date=1891|publisher=U.S. Government Printing Office}}</ref>

This 120&nbsp;cm diameter aperture telescope was a silvered glass mirror polished by Martin.<ref name=":9">{{Cite book|url=https://books.google.com/books?id=ZX7-nyXyy_cC&q=paris+observatory+telescopes&pg=PA135|title=Popular Astronomy|last=Newcomb|first=Simon|date=2011-10-24|publisher=Cambridge University Press|isbn=978-1-108-03773-0|language=en}}</ref> However, when it was mounted it was realized the gravity altered its shape because of the mirror's weight, thus causing an image quality issue.<ref name=":9" />

In 1886 a Henry astrograph with 13-inch objective was acquired.<ref name=":5" />

For the 1907 [[Transit of Mercury]], some of the telescopes used at the Paris Observatory included:<ref name=":10">{{Cite book|url=https://books.google.com/books?id=cWBDAAAAQBAJ&q=grand+telescope+of+Passy%2C&pg=PA111|title=Le Verrier—Magnificent and Detestable Astronomer|last=Lequeux|first=James|date=2013-03-15|publisher=Springer Science & Business Media|isbn=978-1-4614-5565-3|language=en}}</ref>
* Foucault-Eichens reflector ({{convert|40|cm|in|abbr=on}} aperture)
* Foucault-Eichens reflector ({{convert|20|cm|in|abbr=on}} aperture)
* Martin-Eichens reflector ({{convert|40|cm|in|abbr=on}} aperture)
* Several small refractors

The telescopes were mobile and were placed on the terrace for the observations.<ref name=":10" />

===Meudon 83-cm Great Refractor===
{{main|Meudon Great Refractor}}
[[File:Grande Lunette de l'Observatoire de Meudon.jpg|thumb|upright=1.25|The ''Grande Lunette'' of Meudon Observatory (France), is a double refractor with both an 83 cm and 62 cm aperture objective lenses on one shaft. It was installed in 1891.]]
The Meudon [[great refractor]] (Meudon 83-cm) is an {{convert|83|cm|abbr=on}} aperture refractor, which, with September 20, 1909 observations by [[E. M. Antoniadi]], helped disprove the [[Mars canals]] theory. It is a double telescope completed in 1891, with a secondary {{convert|62|cm|abbr=on}} aperture lens for photography. It was of the largest refracting telescopes in Europe and was active for a century until 1991. In the 21st century, it was renovated and supports public education and visitation.{{cn|date=August 2025}}

The Meudon refractor was built at [[Meudon Observatory]]. It is one of three sites of the Paris Observatory; Meudon Observatory became part of the Paris Observatory in 1926.<ref name=":0">{{Cite web|url=https://www3.astronomicalheritage.net/index.php|title=UNESCO Astronomy and World Heritage Webportal – Home|website=www3.astronomicalheritage.net|access-date=2019-10-21}}</ref> The Meudon Great refractor is the third largest astronomical refractor of its type in the world.<ref>{{Cite web|url=https://www3.astronomicalheritage.net/index.php|title = UNESCO Astronomy and World Heritage Webportal – Home}}</ref> The Meudon refractor is located in the ''Grande Coupole'' building, which was renovated in the early 2000s.<ref name=":0" />

==See also==
* [[Bureau des Longitudes]]
* [[List of astronomical observatories]]
* [[List of largest optical refracting telescopes]]

==References==
{{reflist}}

==Bibliography==
* [Anon.] (2001) "Paris Observatory", ''[https://www.britannica.com/topic/Paris-Observatory Encyclopædia Britannica]'', Deluxe CDROM edition
* {{ cite journal | title=The fading star of the Paris Observatory in the nineteenth century: astronomers' urban culture of circulation and observation | author=Aubin, D. | journal=Osiris | volume=18 | date=2003 | pages=79–100 | doi=10.1086/649378 | bibcode=2003Osir...18...79A | s2cid=143773138 }} [https://web.archive.org/web/20071129105436/http://www.institut.math.jussieu.fr/~daubin/publis/2003c.pdf]
* {{cite conference | author=Guinot, B. | title = History of the Bureau International de l'Heure | book-title=Polar Motion: Historical and Scientific problems | pages=175–184 | date = 2000 | bibcode = 2000ASPC..208..175G }}
* Widemann, T., Knobloch, E. (2022). "Aux origines d'une science et d'une sociabilité européennes: l'Observatoire de Paris à 350 ans", 'Archives Internationales d'Histoire des sciences, Vol. 72, N°189, 2022 {{ISBN|978-2-503-59736-2}} [https://www.brepolsonline.net/toc/arihs/2022/72/189]

==External links==
{{commons category|Observatoire de Paris}}
* [http://www.obspm.fr/?lang=en Paris Observatory] (official site, in English)
* [https://maps.google.com/maps/ms?hl=en&ie=UTF8&msa=0&msid=103015796427039682952.00046ac5940f4335f749d&ll=48.836009,2.336934&spn=0.007231,0.015557&z=16 Location in Paris]
* [https://alidade.obspm.fr/ Inventory of astronomy heritage] {{Webarchive|url=https://web.archive.org/web/20191210213902/https://alidade.obspm.fr/ |date=2019-12-10 }}
* [https://bibnum.obspm.fr/ Digital library for astronomy archives]
* [http://gallica.bnf.fr/Search?idArk=&n=15&p=1&lang=FR&adva=1&adv=1&reset=&urlReferer=%2Fadvancedsearch%3Flang%3DFR&enreg=&tri=&catsel1=f_title&cat1=&ope2=MUST&catsel2=f_creator&cat2=observatoire+de+paris&ope3=MUST&catsel3=f_tdm&cat3=&date=daTo&daFr=&daTo=&t_typedoc=periodiques&biblio=Biblioth%C3%A8que+nationale+de+France&sel_source=toutSources&biblioSpecifique=Gallica&sel_provenance_Part=toutPartenaires&sel_provenance_Edist=toutSNE&dateMiseEnLigne=indexDateFrom&firstIndexationDateDebut=&firstIndexationDate Publications of the Observatoire de Paris] in [[Gallica]], the digital library of the [[BnF]] (in French)

{{Établissement public à caractère scientifique, culturel et professionnel}}
{{Portal bar|France|Astronomy|Stars|Spaceflight|Outer space|Solar System|Education|Science}}
{{Authority control}}

[[Category:Paris Observatory| ]]
[[Category:Grands établissements]]
[[Category:Astronomical observatories in France]]
[[Category:Buildings and structures in the 14th arrondissement of Paris]]
[[Category:1671 establishments in France]]