nutation

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nutation A periodic oscillation of the Earth's pole about its mean position on the celestial sphere, due to the attractions of the Sun and Moon on the Earth's equatorial bulge. It causes a small periodic variation in the positions of stars, and is superimposed on the much larger effect of precession. The main oscillation has an amplitude of about ±9ʺ and a period of 18.6 years, equal to the revolution period of the Moon's nodes around the ecliptic. In addition there are many smaller oscillations, some with periods as small as a few days. Nutation is conventionally resolved into nutation in longitude and nutation in obliquity, which are respectively parallel and perpendicular to the ecliptic.

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.

nutation Oscillating movement (period 18.6 years) superimposed on the steady precessional movement of the Earth's axis so that the precessional path of each celestial pole on the celestial sphere follows an irregular rather than a true circle. It results from the varying gravitational attraction of the Sun and Moon on the Earth. See also precession

nutation The spiral movement of a plant organ during growth, also known as circumnutation. It is seen in climbing plants and helps the plant find a suitable support to twine around. Examples are the coiling movements of the shoot tips of runner beans and of the tendrils of sweet peas.

nutation nodding XVII; oscillation of the earth's axis XVIII. — L. nūtātiō, -ōn-, f. nūtāre, nūtāt- nod, f. base of -nuere nod; see -ATION.

nutation Irregularities in the orbital motion of the Earth (or other planets) superimposed on the precession of its axis. The dominant nutation of the Earth's axis has an 18.6-year periodicity.

nutation (new-tay-shŏn) n. the act of nodding the head.

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