pre·ces·sion / prəˈseshən/ • n. Physics the slow movement of the axis of a spinning body around another axis due to a torque (such as gravitational influence) acting to change the direction of the first axis. It is seen in the circle slowly traced out by the pole of a spinning gyroscope.DERIVATIVES: pre·cess / prēˈses; ˈprēˌses/ v.pre·ces·sion·al / priˈseshənl/ adj.

precession Wobble of the axis of a spinning object. It occurs as a result of the torque on the spin axis, which increases as the angle of precession increases. The Earth precesses about a line through its centre and perpendicular to the plane of the ecliptic extremely slowly (a complete revolution taking 25,800 years) at an angle of 23.5°. The motion of a gyroscope is another consequence of precession, because the entire ring containing the spinning wheel and its axle precesses around the support pivot.

precession The action of a couple whose axis is perpendicular to the rotational axis (a torque) on a rotating body causing its axis of rotation to trace out a path about an average position, instead of having a constant alignment, i.e. the axis of rotation itself revolves conically about a central point. The Earth's axis of rotation precesses as a result of several forces, e.g. changes in mass distribution on its surface, changes in the gravitational field due to changes in the relative positions of the Moon, Sun, and planets, etc.

precession (astron.) of the equinoxes. XVI. — late L. præcessiō, -ōn-, f. præcēdere PRECEDE.