Pre-cĕs'sion, n.

(-sĕsh'ŭn), n. [Fr. précession, Sp. precesion, It. precessione, fr. Lat. præcedere, præcessum, to go before. See PRECEDE.] The act of going before, or forward.

Luni-solar precession, that part of the precession which depends on the sun and moon alone.—Planetary precession, that part which depends on the action of the planets alone.—Precession of the equinoxes (Astron.), the slow, backward motion of the equinoctial points along the ecliptic, at the rate of 50″.1 annually, caused by the action of the sun, moon, and planets upon the protuberant matter about the earth's equator, in connection with its diurnal rotation;—so called because either equinox, owing to its westerly motion, comes to the meridian sooner each day than the point it would have occupied without the motion of precession, and thus precedes that point continually with reference to the time of transit and motion.