History and Heritage

The history of the IMCCE is similar to the history of ephemerides in France and thus the history of the Academy of Sciences, the Observatory of Paris and the Bureau des longitudes. It is within these organizations that ephemerides have been designed and constantly improved for the needs of society, researchers and, more recently, for the space exploration. Below is a brief history with links to further studies, historical documents and archives that provide information on the evolution of the laboratory.

The Académie des sciences and the ephemerides

Soon after the creation of the french Académie des sciences in 1666, Colbert proposed to Louis XIV to provide a new building for the members of the academy of sciences. This building will become the Paris observatory housing the astronomers. The goal was not simply observing the sky in order to understand the motion of celestial bodies but also to use astronomy to be able to travel on Earth and to map the territories of France. The problem of determining longitudes is crucial for strategic reasons. In 1679, the first French “official” ephemerides will be published under the title Connaissance des temps, ephemerides always published today. The French Revolution changed the hierarchy over the ephemerides, and the Academy of Sciences was divested of its prerogative to the benefit of the Bureau des longitudes, created in 1795 (Law of 7 messidor, year III of the Republican Calendar).

The Bureau des longitudes from 1795 to nowadays

The Bureau des longitudes (BDL) was founded by a law of the National Convention (French National Assembly) of June 25, 1795 (7 messidor, year III of the Republican Calendar). The main goals were to solve astronomical problems related to the determination of longitude at sea, strategic at that time (its name comes from this activity), to calculate and publish the ephemerides (the Connaissance des temps) and a yearbook “to regulate those of the Republic”, to organize scientific expeditions in the geophysical and astronomical fields and to be an advisory committee on certain scientific problems. The Observatory of Paris was under his direction until 1854.

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

The structure of this service has been reworked several times and in 1961, A. Danjon and J. Kovalevsky created a modern research laboratory, replacing the former computing department, which became the Service des calculs et de mécanique céleste du Bureau des longitudes. In addition to its mission of calculating ephemerides, intense research activity developed in the fields of dynamics and celestial mechanics. In 1979, it was associated with the CNRS (Centre national de la recherche scientifique). In 1998, it became the Institut de mécanique céleste et de calcul des éphémérides (IMCCE) inside the Observatoire de Paris.

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

The Institut de mécanique céleste et de calcul des éphémérides

The Institut de mécanique céleste et de calcul des éphémérides (IMCCE) is the successor of the Service des calculs et de mécanique céleste du Bureau des longitudes. It was created by decree of June 2, 1998 and installed as an autonomous institute within the Paris Observatory (similar status to the schools and institutes of the universities).

Since 1998, two entities have contributed to the development of the national ephemerides: Institut de mécanique céleste et de calcul des éphémérides (IMCCE) and Bureau des longitudes.

The Connaissance des temps

The Institut de mécanique céleste et de calcul des éphémérides is in charge of the official French ephemerides whose Connaissance des temps is the reference book published annually. It has evolved enormously since its first publication in 1679 in precision as well as in volume and form since the needs of today (with the Internet) are very different from those of yesterday when calculations were done by hand.

All volumes of the Connaissance des temps have been digitized and are now accessible to all. They are available on Gallica: from 1679 to 1803, from 1804 to 1979 and from 1980 to 2004.

Some topics and some detailed studies of specific aspects of Connaissance des temps are presented on a dedicated website (in french).

Historical researches have been made on the volumes of CDT in order to help readers to understand the evolution of CDT and its ephemerides.

The Annuaire du Bureau des longitudes

The Bureau des longitudes is also obliged to publish a “yearbook suitable for settling those of the Republic”. This is a work intended for a wider audience giving simple ephemerides and astronomical phenomena as well as very diverse data that go far beyond the field of astronomy. These volumes, published annually, are also digitized and available on Gallica: from 1797 (first volume) to 1969, from 1970 to 1977, from 1978 to 1984, from 1985 to 2004 and from 2005 to 2016. The yearbook is still published today but contains only astronomical data since 1977.

An history of the Annuaire du Bureau des longitudes (1795-1932) has been published in April 2021 by Colette Lelay.

History and Archives

We propose historical documents on the events related to the scientific works of the IMCCE and the old French makers of ephemerides since the first issue of the Connaissance des temps in 1679. Note that all the yearly issues of Connaissance des temps are available as quoted above.

Numerous documents and archives are proposed in the specific page.

IMCCE has a huge amount of archives on past activities and works. Interested researchers may contact us for more information.

  • The IMCCE (and formerly the Service des calculs et de mécanique céleste du Bureau des longitudes) is responsible for building and publishing ephemerides. It is a research laboratory since 1961 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), William Thuillot (2003-2010) and Daniel Hestroffer (2011-2017). Jacques Laskar is the director at the present time.

    This laboratory is made up of researchers, teacher-researchers and astronomers, engineers and technicians and also students and trainees each year. It is a research unit associated with the CNRS since 1979 (the associated unit UMR 8028), whose director is also Jacques Laskar.

    In 1992, he hosted the multidisciplinary research team: Astronomy and Dynamic Systems which includes astronomers, researchers and mathematicians. This team has joined the UMR 8028 since 1996. The laboratory also welcomed in 1997 researchers from the observatory of Lille, who continue to teach at the university of Lille.

    The institute was organized into research teams at the request of the CNRS and currently the Institute is home to three research teams:

    • ASD (Astronomy and Dynamic Systems)
    • ACME (Asteroids, Comets, Meteors and Ephemerides)
    • PEGASE (Dynamic planetology and astrometry)

  • The Bureau des longitudes is an academy of 16 members and 32 correspondents (astronomers, geophysicists and physicists) working in their own laboratories, who guarantee and define the public service missions entrusted to the Institut de mécanique céleste et de calcul des éphémérides

Last update Wednesday 23 March 2022