Precession of Axis
						q There are two kinds of precession: (1) the precession of the spin axis and (2) the precession of the ellipse. q Earth’s wobbling motion is called the axial precession.  It is caused by the gravitational pull of the Sun and Moon. q Axial precession is a slow turning of Earth’s axis of rotation through a circular path, with a full turn every 25,700 years.