The Paris Observatory (French: Observatoire de Paris, pronounced [ɔbsɛʁvatwaʁ d(ə) paʁi]), a research institution of the Paris Sciences et Lettres University, is the foremost astronomical observatory of France, one of the largest astronomical centres in the world, and the world’s oldest observatory still in operation. Its historic building is on the 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 established in 1667 as part of a project to create a state-of-the-art astronomical observatory equipped with advanced instruments for mapping the skies and aiding navigation. Complementing the French Royal Academy of Sciences founded the previous year, it became a cornerstone of Western astronomy. It was here that fields such as geodesy, cartography, and meteorology flourished in France. King Louis XIV's minister of finance organized a "scientific powerhouse" to increase understanding of astronomy, maritime navigation, and science in general. 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.
Constitution 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 was also the home to the International Time Bureau until its dissolution in 1987. It remains the source of legal time in France, using multiple atomic fountain clocks maintained by its SYRTE (Systèmes de Référence Temps Espace) department. 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.
History
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. In 1676 the staff concluded that light itself was travelling at a finite speed.
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 33 cm (13 in) 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.
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