This web page describes the precession of the Earth’s axis of rotation relative to the stars. It describes the discovery by the Greek astronomer Hipparchus that the position of the Sun at any season, measured against the background stars, migrates in a slow cycle of about 26000 years. This “”precession of the equinoxes”” is caused by the rotation axis of the Earth slowly moving around a cone. Precession may be one of several astronomical processes contributing to the ice ages, as proposed by the Serbian astronomer Milutin Milankovich. This page is part of a large web site, “”From Stargazers to Starships”” that presents physics concepts through applications to space science and an historical perspective. A related lesson plan and other resources are linked to this page.