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The slow westward shift of the equinoxes along the plane of the ecliptic, resulting from precession of the earth's axis of rotation, and causing the equinoxes to occur earlier each year.

Precessional movement of Earth. Earth rotates (white arrows) once a day around its rotational axis (red); this axis itself rotates slowly (white circle), completing a rotation in approximately 26,000 years

The slow westward shift of the equinoxes along the plane of the ecliptic, resulting from precession of the earth's axis of rotation, and causing the equinoxes to occur earlier each year.

Precession of a gyroscope. In a similar way to how the force from the table generates this phenomenon of precession in the spinning gyro, the gravitational pull of the Sun and Moon on the Earth's equatorial bulge generates a very slow precession of the Earth's axis (see §Cause). This off-center push or pull causes a torque, and a torque on a spinning body results in precession. The gyro can be analyzed in its parts, and each part within the disk is trying to fall, but the rotation brings it from down to up, and the net result of all particles going through this is precession.

The slow westward shift of the equinoxes along the plane of the ecliptic, resulting from precession of the earth's axis of rotation, and causing the equinoxes to occur earlier each year.

The coincidence of the annual cycles of the apses (closest and further approach to the Sun) and calendar dates (with seasons noted) at four equally spaced stages of a fictitious precessionary cycle of 20,000 years (rather than the Earth's true precessionary cycle of 26,000 years). The season dates are those in the north. The tilt of fictitious Earth's axis and the eccentricity of its orbit are exaggerated. Approximate estimates. Effects of weak planetary precession on the stages shown are ignored.