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