precession of the equinoxes definition of precession of the equinoxes in the Free Online Encyclopedia.

precession of the equinoxes, westward motion of the equinoxes equinox , either of two points on the celestial sphere where the ecliptic and the celestial equator intersect. The vernal equinox, also known as "the first point of Aries," is the point at which the sun appears to cross the celestial equator from south to north.
..... Click the link for more information. along the ecliptic ecliptic , the great circle on the celestial sphere that lies in the plane of the earth's orbit (called the plane of the ecliptic). Because of the earth's yearly revolution around the sun, the sun appears to move in an annual journey through the heavens with the
..... Click the link for more information. . This motion was first noted by Hipparchus c.120 B.C. The precession is due to the gravitational attraction of the moon and sun on the equatorial bulge of the earth, which causes the earth's axis to describe a cone in somewhat the same fashion as a spinning top. As a result, the celestial equator (see equatorial coordinate system equatorial coordinate system, the most commonly used astronomical coordinate system for indicating the positions of stars or other celestial objects on the celestial sphere. The celestial sphere is an imaginary sphere with the observer at its center.
..... Click the link for more information. ), which lies in the plane of the earth's equator, moves on the celestial sphere celestial sphere, imaginary sphere of infinite radius with the earth at its center. It is used for describing the positions and motions of stars and other objects.
..... Click the link for more information. , while the ecliptic, which lies in the plane of the earth's orbit around the sun, is not affected by this motion. The equinoxes, which lie at the intersections of the celestial equator and the ecliptic, thus move on the celestial sphere. Similarly, the celestial poles move in circles on the celestial sphere, so that there is a continual change in the star at or near one of these poles (see Polaris Polaris or North Star, star nearest the north celestial pole (see equatorial coordinate system). It is in the constellation Ursa Minor (see Ursa Major and Ursa Minor; Bayer designation Alpha Ursae Minoris) and marks the end of the handle of the
..... Click the link for more information. ). After a period of about 26,000 years the equinoxes and poles lie once again at nearly the same points on the celestial sphere. Because the gravitational effects of the sun and moon are not always the same, there is some wobble in the motion of the earth's axis; this wobble, called nutation nutation, in astronomy, a slight wobbling motion of the earth's axis. The causes of nutation are similar to those of the precession of the equinoxes, involving the varying attraction of the moon on the earth's equatorial bulge.
..... Click the link for more information. , causes the celestial poles to move, not in perfect circles, but in a series of S-shaped curves with a period of 18.6 years. There is some further precession caused by the gravitational influences of the other planets; this precession affects the earth's orbit around the sun and thus causes a shift of the ecliptic on the celestial sphere. The precession of the earth's orbital plane is sometimes called planetary precession, and that of the earth's equatorial plane (caused by the sun and moon) is called luni-solar precession; the combined effect of the moon, the sun, and the planets is called general precession. Planetary precession is much less than luni-solar precession. The precession of the equinoxes was first explained by Isaac Newton in 1687.

precession of the equinoxes [prē′sesh·ən əvthə ′ē·kwə‚näk·səz]

(astronomy)

A slow conical motion of the earth's axis about the vertical to the plane of the ecliptic, having a period of 26,000 years, caused by the attractive force of the sun, moon, and other planets on the equatorial protuberance of the earth; it results in a gradual westward motion of the equinoxes.

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No references found	These cycles are attributed to perturbations of the sun's orbit by the moon that cause the precession of the equinoxes and by other small effects due to the planets and are confirmed by world-wide measurements of glaciers, coral reefs, peat bogs, and polar ice caps. On climate change by Hodgson, P.E. / Modern Age Evidently hoping to prove astrologers are know-nothings, Dawkins' interview started with a lengthy grilling about astronomy - the precession of the equinoxes, sidereal and tropical zodiacs, Kuiper Belt objects. The Dawkins delusion: science good, the rest bad by guardian.co.uk / guardian.co.uk Astrology begins to recede from the center of intellectual life by the late seventeenth century, perhaps not only because of the accumulation of scientific evidence, which had already begun (as Hubner reminds us) with the ancient astronomers' observation of the precession of the equinoxes, but more particularly because of the emergence of a scientific method whereby astrological hypotheses could no longer appear to constitute true knowledge. Zukunftsvoraussagen in der Renaissance by Dooley, Brendan / Renaissance Quarterly	precancerous Precarium precast precast concrete precast concrete pile precast concrete wall panel precast pile precast stone PRECCX precedence precedence diagram method precedence effect precedence lossage precedence relation Precedent preceding limb precentor precentral gyrus precept preceptor Precession precession camera precession in declination precession in right ascension precession of nodes precession of the equinoxes precessional torque precharge Prechistoe prechlorination Precieuse precinct precinctio Preciosity precious metal precious stone precipice precipitable water precipitable water vapor precipitant precipitate Precipitation precipitation area precipitation attenuation precipitation ceiling precipitation cell precipitation clutter suppression precipitation current precipitation echo precipitation effectiveness precipitation electricity	Preces Preces and responses precess precess precess precess precessed precessed precessed precessed precesses precesses precesses precesses precessing precessing precessing precessing Precessing Jet precession precession precession precession Precession (astronomy) Precession (astronomy) Precession (astronomy) precession camera precession in declination precession in right ascension precession of nodes precession of the equinoxes precessional precessional precessional precessional precessional torque Precessor Precettato Prechambered Explosive precharge Precharged Pneumatic prechiasmal anisocoria prechiasmal anisocoria Prechistoe prechlorination prechlorination prechordal PRECHUR Precieuse Precieuse precinct precinct precinct precinct Precinct Committee Person Precinct Count Optical Scan Precinct-Based Optical Scanner precinctio precincts precincts precincts

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These cycles are attributed to perturbations of the sun's orbit by the moon that cause the precession of the equinoxes and by other small effects due to the planets and are confirmed by world-wide measurements of glaciers, coral reefs, peat bogs, and polar ice caps.

On climate change by Hodgson, P.E. / Modern Age

Evidently hoping to prove astrologers are know-nothings, Dawkins' interview started with a lengthy grilling about astronomy - the precession of the equinoxes, sidereal and tropical zodiacs, Kuiper Belt objects.

The Dawkins delusion: science good, the rest bad by guardian.co.uk / guardian.co.uk

Astrology begins to recede from the center of intellectual life by the late seventeenth century, perhaps not only because of the accumulation of scientific evidence, which had already begun (as Hubner reminds us) with the ancient astronomers' observation of the precession of the equinoxes, but more particularly because of the emergence of a scientific method whereby astrological hypotheses could no longer appear to constitute true knowledge.

Zukunftsvoraussagen in der Renaissance by Dooley, Brendan / Renaissance Quarterly