Nutation Nutation is the short-period oscillations in the motion of the pole of rotation of a freely rotating body that is undergoing torque from external gravitational forces. Nutation of the Earth's pole is discussed in terms of components in obliquity and longitude.
Obliquity The angle between the equatorial and orbital planes (or the rotational and orbital poles) of a body. The obliquity of the ecliptic for the Earth is the angle between the equatorial and ecliptic planes. content://media/external/file/7689S

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