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precession

[pree-sesh-uh n] /priˈsɛʃ ən/
noun
1.
the act or fact of preceding; precedence.
2.
Mechanics. the motion of the rotation axis of a rigid body, as a spinning top, when a disturbing torque is applied while the body is rotating such that the rotation axis describes a cone, with the vertical through the vertex of the body as axis of the cone, and the motion of the rotating body is perpendicular to the direction of the torque.
3.
Astronomy.
  1. the slow, conical motion of the earth's axis of rotation, caused by the gravitational attraction of the sun and moon, and, to a smaller extent, of the planets, on the equatorial bulge of the earth.
  2. precession of the equinoxes.
Origin
1300-1350
1300-50; < Late Latin praecessiōn- (stem of praecessiō) a going before, advance, equivalent to Latin praecess(us) (past participle of praecēdere to precede) + -iōn- -ion; see cession
Related forms
precessional, adjective
Dictionary.com Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2014.
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British Dictionary definitions for precessional

precession

/prɪˈsɛʃən/
noun
1.
the act of preceding
3.
the motion of a spinning body, such as a top, gyroscope, or planet, in which it wobbles so that the axis of rotation sweeps out a cone
Derived Forms
precessional, adjective
precessionally, adverb
Word Origin
C16: from Late Latin praecessiō a going in advance, from Latin praecēdere to precede
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition
© William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins
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Word Origin and History for precessional

precession

n.

1590s, from Late Latin praecissionem (nominative praecissio) "a coming before," from past participle stem of Latin praecedere "to go before" (see precede). Originally used in reference to calculations of the equinoxes, which come slightly earlier each year.

Online Etymology Dictionary, © 2010 Douglas Harper
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precessional in Science
precession
  (prē-sěsh'ən)   
  1. The rotational motion of the axis of a spinning body, such as the wobbling of a spinning top, caused by torque applied to the body along its axis of rotation.

  2. The motion of this kind made by the Earth's axis, caused mainly by the gravitational pull of the Sun, Moon, and other planets. The precession of Earth's axis has a period of nearly 25,800 years, during which time the reference points on the equatorial coordinate system (the celestial poles and celestial equator) will gradually shift their positions on the celestial sphere. ◇ The precession of the equinoxes is the slow westward shift of the autumnal and vernal equinoxes along the ecliptic, resulting from precession of the Earth's axis. See also nutation.


The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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