Astrometric effect

Nutation

The small, shorter-period nodding of the Earth's axis superimposed on the steady precessional wobble, caused mainly by the changing orientation of the Moon's orbit, with a dominant period of about 18.6 years. Nutation must be added to precession to compute a body's true position of date to arcsecond precision.

Highlights

›The axis's 18.6-year nod on top of precession

Precession
The International Celestial Reference System
Earth Orientation Parameters

Across the reference systems

Precession

Knowledge connections

Associated withPrecession
Associated withPrecession
Associated withThe International Celestial Reference System
Associated withEarth Orientation Parameters

Sources

The primary and reference sources this topic draws on.

IAUInternational Astronomical Union
Official naming, definitions, constellation boundaries, and astronomical nomenclature.