|1.||astronomy a periodic variation in the precession of the earth's axis causing the earth's poles to oscillate about their mean position|
|2.||physics a periodic variation in the uniform precession of the axis of any spinning body, such as a gyroscope, about the horizontal|
|3.||Also called: circumnutation the spiral growth of a shoot, tendril, or similar plant organ, caused by variation in the growth rate in different parts|
|4.||the act or an instance of nodding the head|
|[C17: from Latin nutātiō, from nūtāre to nod]|
nutation nu·ta·tion (nōō-tā'shən, nyōō-)
The act of nodding the head, especially involuntarily.
|nutation (n-tā'shən) Pronunciation Key
in astronomy, a small irregularity in the precession of the equinoxes. Precession is the slow, toplike wobbling of the spinning Earth, with a period of about 26,000 years. Nutation (Latin nutare, "to nod") superimposes a small oscillation, with a period of 18.6 years and an amplitude of 9.2 seconds of arc, upon this great slow movement. The cause of nutation lies chiefly in the fact that the plane of the Moon's orbit around the Earth is tilted by about 5 from the plane of the Earth's orbit around the Sun. The Moon's orbital plane precesses around the Earth's in 18.6 years, and the effect of the Moon on the precession of the equinoxes varies with this same period. The British astronomer James Bradley announced his discovery of nutation in 1748.
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