Research on Lunar Physical Librations Based on Numerical Ephemeris

Lunar librations is a description of the movement of the moon in space. To determine the lunar librations makes it possible to speculate about the excitation and dissipation mechanisms of the libration, such as meteor strikes, moon earthquakes, and viscous friction between the core and mantle. Therefore, the determination of the lunar librations is useful for understanding the origin, evolution, and structure of celestial bodies in the solar system. During the research, the latest INPOP19a ephemeris data is used, the conversion of Euler angle extracted from the ephemeris to the lunar physical librations is completed. The numerical model of the physical librations is compared with the ephemeris INPOP17a and DE430. It is found that the difference in physical librations of different ephemerides has a stable period. It is calculated that there is a maximum difference of 30cm between the center of the earth and the lunar reflector A15. This result has a greater impact on the prediction accuracy of the lunar laser ranging. It provides theoretical support for the high-precision lunar laser ranging. The results show that the accuracy of INPOP19a is significantly higher than INPOP17a and DE430, so INPOP19a is recommended in the research of lunar librations.