Based on the overview from the previous chapter, the main tidal constituents are understood intuitively when their frequencies are derived. This involves the three species of long-period, diurnal, and semidiurnal tides. The corrections needed for the lunar nodal cycle are discussed. The effect of the main constituents on the tidal signal are illustrated (modulation due to elliptic orbit, diurnal inequality, spring-neap, and related cycles). The principle of the method of harmonic analysis is explained. For the tidal signal as a whole, the notion of the tidal period is discussed, including its variability and long-term mean, as well as the presence of circa-tidal clocks in marine organisms.

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.