3 - Celestial Motions

Summary

This chapter provides a systematic qualitative overview of the periodicities involved in the motions of the Earth and Moon that are relevant for tides. Key features are the ellipticity of the orbits and the declination. The celestial origin of the different years (sidereal, tropical, anomalistic) is explained, and the same for months (sidereal, tropical, anomalistic, synodic) and days (sidereal, solar, lunar). The long-period variations (lunar apsidal precession and lunar nodal cycle) are also explained. The implications of the solar tide-generating force on the Earth–Moon system are outlined (evection and variation). The chapter ends with a convenient list of all the relevant periods.