Astronomical nutation

Astronomical nutation is the periodic variation in Earth’s rotation-axis orientation, caused chiefly by changing gravitational torques from the Moon and Sun. It is superimposed on the slower precession of the equinoxes.

Connect

Lunisolar precession: The gradual change in Earth’s rotation-axis direction caused mainly by gravitational torques from the Moon and Sun. Nutation is the periodic variation superimposed on this slower axial motion.
Earth's rotation axis: The imaginary line through Earth’s poles around which the planet rotates. Nutation is defined by periodic changes in this axis’s orientation.
James Bradley: An English astronomer who discovered stellar aberration and identified nutation in the eighteenth century. His observations established nutation as a real variation in Earth’s axis.
Earth orientation parameters: Measured quantities describing Earth’s rotation, pole position, and orientation relative to celestial reference frames. Nutation is one part of the orientation data represented by these parameters.
Polar motion: The movement of Earth’s rotation pole relative to its crust. Polar motion is measured in the terrestrial frame, unlike nutation’s celestial-axis variation.
Ecliptic: The apparent annual path of the Sun on the celestial sphere, lying in Earth’s orbital plane. The changing angle between the ecliptic and equator helps set the nutation torques.
Celestial sphere: An imaginary sphere centered on an observer, used to map the apparent positions of celestial objects. Astronomical nutation describes changes in Earth’s orientation relative to this sky-mapping framework.
Nutation (astronomy): A periodic oscillation superimposed on the precession of an astronomical body's rotation axis. Earth’s astronomical nutation is the best-measured case of this broader phenomenon.
Very-long-baseline interferometry: A radio-astronomy technique combining widely separated telescopes to achieve high angular resolution. It measures celestial-source directions precisely enough to constrain nutation.
Chandler wobble: A free oscillation of Earth’s rotation pole with a period of roughly 14 months. It is a terrestrial pole motion, not the forced celestial oscillation called nutation.