: Astronomie: precession

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precession

Precession is a slow, periodic conical motion of the rotation axis of a spinning body, most familiar in the wobbling of a toy top or gyroscope. Earth's axis precesses, once around every 25,800 years (a period known as a Platonic year), as a result of it not being perpendicular to the ecliptic (the plane of Earth's orbit around the Sun). Being tipped over at about 23.5°, it is affected by gravitational perturbations from other bodies in the Solar System, including the Sun, Moon, and planets. These bodies pull harder on the part of Earth's equatorial bulge nearest them than on the part farthest away, resulting in a torque that is the underlying cause of precession. (Encyclopedia of Science, by David Darling, https://www.daviddarling.info/encyclopedia/P/precession.html)

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