Physical Libration of the Moon: An Extended Problem

Abstract

The work is devoted to the study of the physical libration of the Moon. Interest in the traditional topic related to the rotation of the Moon is stirred up by the activity of many countries regarding the development of circumlunar space. Scientifically, the main agenda is to consider the viscosity of the core. At this stage of the theory development, such effects as indirect and direct perturbations from the planets were considered, the 4th order harmonic was included in the gravitational potential of the Moon, and the mean tidal potential was also considered. The inclusion of the described effects in the equations of the Moon’s rotation led to a significant improvement in the solution when compared with the corresponding data from the DE421 theory, although the residual differences still remain greater than the 1 ms accuracy required by the theory. The influence of the direct effect from the planets was milliseconds. The influence of the 4th harmonic manifested itself as a systematic shift of the order of 0.85$''$ in the residual differences in libration in longitude. Considering the tide made it possible to reduce the residual differences in latitude by almost an order of magnitude. In this case, the main factor that reduces the residual differences is changes in the second-order Stokes coefficients. The calculations were carried out using the DE421 ephemeris built at NASA Jet Propulsion Laboratory.