- i Astronomy, nutation is a periodic variation
in precession: in other words, a
wobble on top of the main wobble of Earth's axis. The chief cause of
nutation is the Moon moving in an orbit that is inclined (by 5°)
to the ecliptic. This lunar
nutation amounts to a +/- 9" back-and-forth jiggling of Earth's
poles every 18.6 years (the time it takes for the Moon's orbit to walk
around to the same relative position again). The net result is that,
instead of describing a perfectly circular path in the sky, every 25,800
years or so, due to precession, the precessional path of Earth's axis
is more like the crinkly shape of a cooky-cutter.
- In mechanics, nutation is a bobbing superimposed
on the precession of a spinning body such as a gyroscope.
With increasing spin rate there is an increase in the frequency and
decrease in the magnitude of the nutation.