Definition of "nutation" []

• The act or an instance of nodding the head. (noun)
• A wobble in a spinning gyroscope or other rotating body. (noun)
• Astronomy A small periodic motion of the celestial pole of the earth with respect to the pole of the ecliptic. (noun)
• Botany A slight curving or circular movement in a stem, as of a twining plant, caused by irregular growth rates of different parts. (noun)

American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

• "If, however, the spheres were somewhat flattened at the poles, and the axes inclined to each other, then the pull of one mass on the other would cause the polar axes to keep up a constant movement which is called nutation, or nodding."
• "This phenomenon, known as "nutation," was discovered by the beautiful telescopic researches of Bradley, in 1747."
• "In addition to this steady decrease, there are also much smaller short term (18.6 years) variations, that is also affected by Sun's gravitation in its depleting angle relative to Earth's, known as nutation."