Nutation power spectrum

FFT of Earth's pole motion in J2000 ecliptic coordinates over a 200-year window, with the linear precession trend removed. Periodic frequencies emerge directly from the Newton-integrated dynamics — the dotted vertical lines mark the canonical IAU 1980 nutation terms for reference. The 18.6-yr lunar-nodal term should dominate; the 1-yr and ½-yr peaks come from solar geometry; sub-monthly peaks come from the lunar orbit.