Nutation
Article
Nutation is a small periodic variation superimposed on the slower precession of a rotating body's axis. For Earth, it causes the celestial poles and equinoxes to move through a series of small oscillations rather than following a perfectly smooth precessional path.
The largest component of Earth's nutation has a period of about 18.6 years and is caused by the regression of the Moon's orbital nodes. Numerous smaller terms arise from the changing positions of the Moon, Sun, and planets.
Nutation changes Earth's axial direction by small angles that must be included in precise astronomical calculations. It affects apparent star positions, celestial coordinate systems, Earth-orientation measurements, and navigation.
The phenomenon is predicted using models of gravitational torques, Earth's internal structure, oceans, atmosphere, and rotational response. Modern observations use very-long-baseline interferometry and other high-precision geodetic techniques.
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- Source / publisher: Wikipedia
- URL type: WWW
- Credits: Wikipedia
- URL: https://en.wikipedia.org/wiki/Nutation