The Institut de mecanique celeste et de calcul des ephemerides provides and publishes ephemerides of solar system bodies. It serves as the official and public source of ephemerides devoted to regulate calendars.

It performs theoretical research activities in the fields of celestial mechanics, planetology and mathematics. It initiates and coordinates observing campaigns of rare and specific celestial events.
 

Discovery of a strong tidal dissipation in Saturn -Why our vision of the Saturnian system could change-

Astrometry is the discipline that focuses on determining the position of celestial bodies in space with highest precision. For some of the main satellites of Saturn, the first measurements date back to the middle of the seventeenth century. But one needed to wait the advent of large instruments equipped with micrometers and early photographic plates for obtaining a precision of the order of a thousand kilometers on their position. Today, the most accurate astrometric observations of this system are given by the Cassini spacecraft (in orbit around Saturn since 2004) and can constrain the position of Saturn's moons in a range of about ten kilometers. That could raise some doubts on the usefulness of very old observations. However the international team ENCELADE - named after the second main Saturnian satellite - demonstrated that old observations made far in the past could significantly complete the data from Cassini. This has made possible the quantification of tides raised by Enceladus, Tethys, Dione and Rhea on their primary.

Indeed just like the Earth-Moon system that gets its distance increased by 3 to 4 centimeters per year, the tidal effects push away the satellites from their primary. As a consequence, each moon decelerates in its orbit. So far assumed negligible, such tidal effects appear ten times stronger than expected. This could be the mysterious cause of the observed geysers of Enceladus South Pole may have found a natural explanation. But in the mean time, this shakes our knowledge of the Saturnian system. In particular, the origin of such strong tidal dissipation in Saturn, or even the formation process of the satellites may have to be reconsidered.

An artist picture representing the high tidal dissipation within Saturn induced by each satellite (© IMCCE-Observatoire de Paris / CNRS / Y.Gominet).

 

Agenda 2013

For several years, the Observatoire de Paris and IMCCE publish this unique astronomical calendar.
Explore the sky until these distant galaxies, read about the scientific advances that have revealed the mysteries of the universe, find these men and women who have pushed the boundaries of knowledge! You will also find, this year, the latest advances in radio astronomy.

L'observatoire de la marine et du Bureau des longitudes au parc Montsouris 1875-1914

Why a marine observatory in Paris, in Parc Montsouris?

The answer is contained in this story, so far forgotten, that Guy Boistel has patiently reconstructed from the extensive archives of the Bureau des Longitudes, among others.

Caution : This Website was created with the Ministère de l'Education Nationale, the CNRS and the CNES support. Any use of the data published on this website requires the IMCCE agreement..