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Nutation is a nodding or swaying motion in an axis of rotation, seen in planets and symmetrical objects. Earth’s nutation is caused by tidal forces affecting precession, resulting in a wobbling effect. Gyroscopes demonstrate precession and nutation, while the moon has the greatest pull on Earth’s nutation cycles. Astronomers use established formulas to calculate nutations of other planets.
Nutation is a word derived from the Latin nutare which means to nod. It means a nodding, swaying or swinging motion in an axis of rotation. The rotation can be of a symmetrical object, such as a flying projectile or a gyroscope. Planets also have nutation in their axis of rotation; terrestrial nutation was first discovered by a British astronomer in 1728. Years later, this nutation was described in greater detail and is said to be due to tidal forces affecting the precession of the winter and summer equinoxes which vary from time to time time. Precession is a term for the elliptical orbit of the Earth’s axis point as it rotates; sometimes it points to Polaris as the North Star, and sometimes to Vega, in the constellation Lyra.
Earth’s equatorial mass follows this precessional orbit in seasons and orientation, and as a result, Earth appears to wobble on its axis. Other planets also have such nutation. Astronomers calculate the nutations of other planets using a pre-established calculation formula in order to pinpoint the exact coordinates and get a fix on an object in the sky. None of the objects in the sky are in a fixed position from day to day. Known nutation patterns are calculated when determining your exact location on any given day.
A gyroscope is similar to a child’s top; as long as it rotates quickly, it can stay well balanced on its tiny point in contact with the ground. As the top begins to lose speed due to air friction and loss of momentum, it will begin to wobble and eventually fall over. When the top is spinning fast and standing upright, this is a representation of precession spinning around a vertical axis. Gravity is in suspension with its horizontal pull, due to the torque of the speed of the precessing momentum. When the top begins a slow vibration with small nods out of a perfect vertical position, this is a representation of nutation nod.
The tidal forces of the sun and moon on Earth are the major sources of its ever-changing position, causing a nutation of the Earth’s axis. The moon has the greatest pull, as the Earth’s nutation cycles coincide with the precession of the moon’s orbital nodes. The simple rigid-body mechanics of the gyro-top illustration, however, does not take into account the deformations of the Earth, which is not perfectly smooth, nor the attraction of other planets, which also cause nutation variations.
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