Connaissance de la libration lunaire à l'ère de la télémétrie laser–Lune

Abstract

A renovated knowledge of the lunar librations is exposed in the present paper. This updating derives both from progress of observational techniques of the Moon's motions and from theoretical methods of celestial dynamics. First is presented a summary of classical libration families such as the apparent librations, the physical librations, or the called free librations. Ambiguities and redundancies of this cutting out are discussed. On the one hand, lunar librations are strongly overlapped and datum of their branching is not immediate. On the other hand, new librations have been made into evidence. Starting from a causal analysis of libration nature, the necessary rearrangement of the lunar librations is first based on the modern knowledge of dynamical systems. It takes then into account the post-Newtonian gravitation acquisitions in use of reference systems required for dealing with rotation motions combined with translation ones. By the way of the new families of lunar librations, namely the potential and kinetical librations, the paper gives the libration amplitudes discovered at the joint epoch of the LLR experiment and elaborated methods of numerical integrations of the coupled spin–orbit motion of the Moon. The paper presents also a description of the lunar tides. It takes stock on the relation between the accurate study of the Moon's librations and the knowledge of its internal structure. Finally, it takes into account the lunar spin–orbit interaction whereby the mechanism of the secular acceleration of the Moon is matched by a secular slowing-down of its rotation.