axial precession پیشایان ِ آسهای pišâyân-e âse-yi Fr.: précession axiale 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.
The precession
→ angular velocity is
inversely proportional to the spin angular velocity, so that the
precession is faster and more pronounced as the top slows down.
- 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.
See also: → axial; → precession. |
