The plane of the Moon's orbit about the Earth rotates with respect to the ecliptic with a period of 18.6 years. This causes the Earth to nod, a motion that is superimposed on the equinoctial precession.
Equinoctial Precession, Precession, Planetary Precession, Variation of Latitude
References
Duffett-Smith, P. "Nutation." §35 in Practical Astronomy with Your Calculator, 3rd ed. Cambridge, England: Cambridge University Press, pp. 60-51, 1992.
