A term used to describe the gradual movement caused by the wobble of the earth on its axis. The gradual turning of the earth's poles, much like that of a spinning top as it winds down, causes the seasons of the year to begin slightly earlier each year. Thus the exact moments of Spring and Autmnal equinoxes each year occurs a few minutes earlier than the year before. This gradual movement which takes 25,800 years to complete its cycle, causes the ages. (We are now in the Age of Aquarius.)
The intersection between the ecliptic and the celestial equator does not remain fixed with respect to the background constellations, but slowly move through them. Since this intersection is the position of the sun at the time of the equinoxes, this slow shift of position is called precession of the equinoxes.
The westward movement of the Vernal and Autumnal Equinoxes, relative to the orbit of the Earth, or the stars. The period of this movement is variously given as 21,000 or 26,000 years, leading to great confusion for students. The reason for this confusion is that the Vernal Equinox takes 26,000 years to move once around the sky, relative to the stars; but during that time, the orbit of the Earth is regressing (changing in the opposite direction), so it takes less time (only 21,000 years) for the Vernal Equinox to move once around the sky, relative to our orbit.
The axis of the earth's rotation slowly changes its direction, maintaining a constant tilt with respect to the ecliptic and making a complete rotation once every 26000 years. In consequence, the equinoxes on the intersections of the celestial equator and the ecliptic slowly drift westward.
a slow westward shift of the equinoxes along the plane of the ecliptic caused by precession of the Earth's axis of rotation
The slow wobbling of Earth's axis in a 25,800-year cycle, caused by the gravitational attraction of the Moon on Earth's equatorial bulge. Precession causes the vernal equinox (and all other points on the ecliptic) to move westward along the ecliptic, slowly changing the equatorial co-ordinate grid.
A slow motion of the axis of the Earth around a cone, one cycle in about 26000 years. As a result, the celestial pole moves around a circle in the sky, and in ancient times, for instance, was quite far from Polaris. Discovered by Hipparchus around 130 BC as a slow shift of the vernal equinox around the ecliptic (i.e. around the zodiac).
Slow westward motion of the equinoxes along the ecliptic that results from precession.
The gradual westward shift (about 50" each year) of the equinoctial points along the ecliptic due to the ecliptic due to the rotational movement of the poles of Earth's axis. This phenomena creates an increasing difference in the tropical (based upon the ecliptic and the Sun's ingress into the sing Aries) and the sidereal zodiacs (based upon constellations) or about 50" each year.
The precession of the equinoxes refers to the precession of Earth's axis of rotation with respect to inertial space.