THE BUREAU DES LONGITUDES FROM 1795 TO TODAY

The Bureau des longitudes was founded by a law of the Convention Nationale (French national assembly) on June 25, 1795 (7 messidor year III of the republican calendar). The main goals were to solve the astronomical problems involved in the determination of longitude at sea, strategic at that time (its name comes from this activity), to calculate and publish the ephemerides (la Connaissance des Temps) and an almanac suitable to regulate those of the Republic ”, to organize scientific expeditions in the geophysical and astronomical fields and to be a consultative committee for some scientific problems. The Observatoire de Paris was under its direction until 1854.

Since its foundation, the structure and the activities of the Bureau des longitudes changed considerably. The initial structure was a committee of ten scientists : Lagrange, Laplace, Méchain, Lalande, Cassini, Delambre, Borda, Bougainville, Buache et Caroché. Five other members were associated for calculations. In 1802 the Service of Calculations was founded and was in charge of the ephemerides computation.

The structure of this service was reshaped several times and in 1961, A. Danjon and J Kovalevsky created a modern research laboratory, replacing the old service des calculs, which became the Service des Calculs et de Mécanique Céleste du Bureau des longitudes. Besides its missions of ephemerides computation, an intense research activity was developed in the dynamical and celestial mechanic fields. In 1979 it was associated to the Centre National de la Recherche Scientifique. In 1998, it becomes the Institut de mécanique céleste et de calcul des éphémérides (IMCCE) within the theObservatoire de Paris.

The bicentenary of the Bureau des longitudes was celebrated in Paris on July 3, 1995. (symposium 172).

THE ORGANIZATION OF THE BUREAU DES LONGITUDES AND THE INSTITUT DE MÉCANIQUE CÉLESTE ET DE CALCUL DES ÉPHÉMÉRIDES

Since 1998, two entities contribute to the development of the national ephemerides: Institut de Mécanique Céleste et de Calcul des Éphémérides (IMCCE) and the Bureau des Longitudes.

• The IMCCE, named Service des calculs et de mécanique céleste du Bureau des longitudes until 1998, is in charge to build and publish ephemerides. It is a research laboratory since 1961 and of which Jean Kovalevsky was the first director (1961-1970) followed by Bruno Morando (1971-1984), Jean Chapront (1985-1992), Jean-Eudes Arlot (1993-2002) and of W Thuillot (2003-2010). D Hestroffer is the director since 2011.
  
• This laboratory is composed of 17 researchers, lecturers, professors and astronomers, 16 engineers and technicians and about 15 students and trainees each year. It is a unit of research associated to the Centre National de la Recherche Scientifique since 1979 (Unité Mixte de Recherche UMR 8028), the director of which is also D Hestroffer.
• In 1992 the multi-field team of research: " Dynamical Astronomy and Systems " which includes researchers astronomers, and mathematicians was created. This team joined the UMR 8028 since 1996. The laboratory also include in 1997 lecturers and professor of the observatory of Lille who continue to teach at the university of Lille.
• The Bureau des longitudes is an academy of 16 members and 32 correspondents (astronomers, geophysicists and physicists), working in their own laboratories, they guarantee and define the missions of public utility entrusted to the Institut de Mécanique Céleste et de Calcul des éphémérides.