precession

American  

[pree-sesh-uhn] / 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.

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precession British  

/ prɪˈsɛʃən /

noun

1. the act of preceding

2. See precession of the equinoxes

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

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precession Scientific  

/ prē-sĕsh′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.

3. ◆ 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.

4. See also nutation

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Other Word Forms

• precessional adjective
• precessionally adverb

Etymology

Origin of precession

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

Explanation

Precession is when something comes first in a group or list, like the precession of the kids whose last names start with A in your school's graduation ceremony. You can use this noun as a substitute for precedence, the act of going first in order or time, but it's actually more common as a scientific term meaning "rotating in a wobbly way." The precession of a spinning gyroscope is the usual example a physics teacher gives — a movement that's essentially a rotating object with an axis that's also rotating. In astronomy, precession refers to the changing rotational axis of a planet (or other body).

Example Sentences

As the binary tightens, the planet's precession slows while the stars' precession speeds up.

From Science Daily • Apr. 19, 2026

This subtle difference changes Saturn's precession rate so that it no longer aligns with Neptune's.

From Science Daily • Feb. 27, 2026

The system works by taking advantage of gyroscopic precession, which occurs when a spinning object reacts to an outside force.

From Science Daily • Feb. 18, 2026

This pattern points to a process known as "jet precession," which refers to a gradual shift in the direction of the jets over time, similar to the slow wobble of a spinning top.

From Science Daily • Jan. 10, 2026

But modern astrologers have forgotten about the precession of the equinoxes, which Ptolemy understood.

From "Cosmos" by Carl Sagan