The term ‘Precession‘ means a change in the orientation of the rotational axis of a rotating body.

The Earth rotates on it’s own axis (the red line) once every 24 hours (shown by the white arrows) and this is called Axial Rotation.

Axial Rotation of the Earth

The earth’s axis itself rotates slowly (white circle), completing a rotation in approximately 25,772 years, which is known as Axial Precession.

Precession of the Equinoxes

As axial precession occurs, the constellation that the sun rises into on the spring equinox changes over a very slow period of time. It takes about 2160 years for the constellation to change. This is called the ‘Precession of the Equinoxes‘.

If this rate remains constant, it will take between 25,700 and 25,800 years to complete one full precession of the equinoxes. (Full cycle of the sun rising in each sign of the zodiac.)

How has the precession of the equinoxes played a fundamental role in outlining the major time periods in the earth's history?

Time and Celestial Movement– The Earth’s Revolution and the Seasons, Axial Rotation, Axial Precession, Precession, Equinox, Precession of the Equinoxes, Precession of the Equinoxes and the ‘Ages’, The Ecliptic.