nutation (redirected from Nutation (astronomy and mechanics))

nutation, in astronomy, a slight wobbling motion of the earth's axis. The causes of nutation are similar to those of the precession of the equinoxes, involving the varying attraction of the moon on the earth's equatorial bulge. However, the period of the motion is only 18.6 years, the same as that of the precession of the moon's nodes, as opposed to the nearly 26,000-year period of the precession of the equinoxes. Nutation was discovered by the English astronomer James Bradley in 1728 but was not explained until 20 years later.

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nutation [nü′tā·shən]

(astronomy)

A slight, slow, nodding motion of the earth's axis of rotation which is superimposed on the precession of the equinoxes; it is the combination of a number of perturbations (lunar, solar, and fortnightly nutation).

(botany)

The rhythmic change in the position of growing plant organs caused by variation in the growth rates on different sides of the growing apex.

(mechanics)

A bobbing or nodding up-and-down motion of a spinning rigid body, such as a top, as it precesses about its vertical axis.

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Nutation (astronomy and mechanics)

In mechanics, a bobbing motion that accompanies the precession of a spinning rigid body, such as a top. In simple precession, the axis of a top with a fixed point of contact sweeps out a cone, whose axis is the vertical direction. In the general motion, the angle between the axis of the top and the vertical varies with time. This motion of the top's axis, bobbing up and down as it precesses, is known as nutation. See Rigid-body dynamics

Astronomical nutation refers to irregularities in the precessional motion of the equinoxes caused by the varying torque applied to the Earth by the Sun and Moon. Astronomical nutation should not be confused with nutation as defined in mechanics; the latter is present even if the source of the torques is unvarying.