Paris Observatory

Administratively, it is a grand établissement of the French Ministry of National Education, with a status close to that of a public university. Its missions include: • Research in astronomy and astrophysics • Education (four graduate programs, Ph.D. studies) • Diffusion of knowledge to the public It maintains a solar observatory at Meudon and a radio astronomy observatory at Nançay. It remains the source of legal time in France, using multiple atomic fountain clocks maintained by its SYRTE () department.{{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 ==History==

moved to the grounds by Giovanni Cassini, for the mounting of long-tubed telescopes and even longer tubeless aerial telescopes. Under pressure from many scholars—most notably Adrien Auzout, who wrote to the Sun King in 1665 urging the immediate creation of a company dedicated to science and the arts—Louis XIV and its Minister of Finance Jean-Baptiste Colbert established the Royal Academy of Sciences in 1666. The Paris Observatory was proposed in 1665–1666 by the Academy of Sciences. In 1666, King 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, with the Paris meridian exactly bisecting the site north–south. 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. The Paris Observatory predates by a few years the 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." The architect of the Paris Observatory was Claude Perrault whose brother, Charles, was secretary to Jean-Baptiste Colbert and superintendent of public works. 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. The last extension incorporates the Meridian Room designed by Jean Prouvé. Accomplishments In 1671 Saturn's moon Iapetus was discovered from the observatory, followed by Rhea in 1672. The moons Dione and Tethys were also discovered from the observatory in 1684. is traced on the floor. The world's first national almanac, the 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 maps. In 1882, a astrographic lens was constructed, an instrument that catalysed what proved to be the over-ambitious international Carte du Ciel project. In November 1913, the observatory used the Eiffel Tower as an 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. 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. Some of the work is now digitized on the 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. 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. The observatory did not have a recognised Director until 1771, before that each member could do as they pleased. Sometimes 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. The current President of the Observatory is Fabienne Casoli. • 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. In addition to these sites, the Marseilles Observatory became a branch of the Paris Observatory in 1863. In 1873, Marseilles Observatory detached from Paris Observatory. Paris King Louis XIV purchased the land for his new observatory in March 1667. This provided a site for the activities of the Academy of Sciences near to the city of Paris. A dome and terrace was added in 1847. Nançay After the Second World War, French astronomers began designing and building instruments for radio astronomy. A field station was established in 1953, and by the late 1950s several radio instruments were established. 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 (), 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. Nowadays, the AstroQueyras amateur astronomy association operates the facility, using a telescope on loan from the Observatoire de Haute Provence. Numerous asteroids have been discovered there. ==Instruments past and present==

Early telescopes were supplied by the famed craftsman Giuseppe Campani. 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. The Marly tower, moved to the observatory in 1685 for mounting telescopes, was demolished in 1705. The Marly tower was originally made for the Versailles water supply system (see Machine de Marly), but was moved to the southern gardens area near the Paris Observatory. The tower could hold the objective lens for extremely long focal length aerial telescopes. In 1804 a telescope of 8.4 cm aperture, made by Bellet, was established on the roof of the observatory. One of the special telescopes in the collection of the observatory, was the Passy telescope of King Louis XV. In 1835 Arago used this telescope to observe the return of Halley's Comet that year. In 1857 a refracting telescope of aperture objective, the Arago equatorial telescope, was completed. This telescope was proposed by director François Arago in 1846. The transit circle of 1863 was made by Secretan and Eichens. This 120 cm diameter aperture telescope was a silvered glass mirror polished by Martin. 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. • Foucault-Eichens reflector ( aperture) • Foucault-Eichens reflector ( aperture) • Martin-Eichens reflector ( aperture) • Several small refractors The telescopes were mobile and were placed on the terrace for the observations. The Meudon Great refractor is the third largest astronomical refractor of its type in the world. The Meudon refractor is located in the Grande Coupole building, which was renovated in the early 2000s. ==See also==