Айналу осінің дірілдеуі

Wobble of the axis of rotation
the concept in physics

Nutation is a rocking, swaying, or nodding motion in the axis of rotation of a largely axially symmetric object, such as a gyroscope, planet, or bullet in flight, or as an intended behaviour of a mechanism. In an appropriate reference frame it can be defined as a change in the second Euler angle. If it is not caused by forces external to the body, it is called free nutation or Euler nutation.

The nutation of a planet occurs because the gravitational effects of other bodies cause the speed of its axial precession to vary over time, so that the speed is not constant. English astronomer James Bradley discovered the nutation of Earth's axis in 1728.

Nutation subtly changes the axial tilt of Earth with respect to the ecliptic plane, shifting the major circles of latitude that are defined by the Earth's tilt (the tropical circles and the polar circles). In the case of Earth, the principal sources of tidal force are the Sun and Moon, which continuously change location relative to each other and thus cause nutation in Earth's axis. The largest component of Earth's nutation has a period of 18.6 years, the same as that of the precession of the Moon's orbital nodes. However, there are other significant periodic terms that must be accounted for depending upon the desired accuracy of the result. A mathematical description (set of equations) that represents nutation is called a "theory of nutation". In the theory, parameters are adjusted in a more or less ad hoc method to obtain the best fit to data. Simple rigid body dynamics do not give the best theory; one has to account for deformations of the Earth, including mantle inelasticity and changes in the core–mantle boundary. The principal term of nutation is due to the regression of the Moon's nodal line and has the same period of 6798 days (18.61 years). It reaches plus or minus 17″ in longitude and 9.2″ in obliquity. All other terms are much smaller; the next largest, with a period of 183 days (0.5 year), has amplitudes 1.3″ and 0.6″ respectively. The periods of all terms larger than 0.0001″ (about as accurately as available technology can measure) lie between 5.5 and 6798 days; for some reason (as with ocean tidal periods) they seem to avoid the range from 34.8 to 91 days, so it is customary to split the nutation into long period and short period terms. The long period terms are calculated and mentioned in the almanacs, while the additional correction due to the short period terms is usually taken from a table. They can also be calculated from the Julian day according to IAU 2000B methodology.

In the 1961 disaster film The Day the Earth Caught Fire, the near simultaneous detonation of two super hydrogen bombs near the poles causes a change in Earth's nutation, as well as an 11° shift in the axial tilt and a change in Earth's orbit around the Sun. In Star Trek: The Next Generation, rapidly 'cycling' or 'changing' the 'shield nutation' is frequently mentioned as a means by which to delay the antagonist in their efforts to break through the defences and pillage the Enterprise or other spacecraft.