Constellations · Physics · History
Precession
Say it: pree-SESH-un IPA: /priˈsɛʃən/ noun
Precession: A gradual change in the direction of a rotation axis or the orientation of an orbit.
Earth's spin axis slowly changes its pointing direction, rather like the axis of a spinning top. An orbit's long axis can also change direction, which is orbital precession.
- Example
- Axial precession gradually changes which stars lie near Earth's celestial poles.
- Why astronomers use it
- It matters for accurate sky coordinates and the long-term geometry of planetary systems.
- Tiny cosmic connection
- Precession is a change in orientation, not the ordinary daily rotation of Earth.
Observatory Constellations Physics History
Where to check it
Written for Cool Moon Facts in its own words; the sources cover the same idea in more depth.