پیشایان ِ آسهای
Fr.: précession axiale
1) A change in the orientation of the → rotation axis
of a non-spherical, spinning body caused by → gravity.
A rotating top will precess in a direction determined by the
→ torque exerted by its → weight.
→ angular velocity is
inversely proportional to the spin angular velocity, so that the
precession is faster and more pronounced as the top slows down.
2) In particular, the gradual shift in the orientation of Earth's rotation axis
which traces out a conical path once every ~ 26,000 years.
The cause of the Earth's precession is the → equatorial bulge
of the Earth, brought about by the → centrifugal force
of the → rotation, which has
changed the Earth from a perfect sphere to a slightly flattened
one, thicker across the equator. The attraction of the Moon and Sun
on the bulge is the reason which makes the Earth precess.
→ axial; → precession.