Physical backgrounds of Earth's rotation, revision of the terminology

Abstract

Rotation of the Earth is a quite involved process. Deep knowledge of certain areas of physics is indispensable for its understanding and researching. It is necessary to clarify the physics of rigid bodies’ rotation because the usage of terms precession and nutation by experts in geosciences are generally not correct, sometimes confused. In physics nutation is the motion of a free gyroscope, and precession is the motion of a heavy one. The torque of an external force causes the precession of a heavy gyroscope, but nutation is a motion of a free gyroscope, if its rotation has not started around its symmetry axis. While the cause of precession of a rotating body always arises from the effect of external mass sources, nutation is exclusively a function of the intrinsic mass distribution of the rotating body. After discussing some important aspects of rotational mechanics (motion of a free and a heavy gyroscope), the Earth’s nutation and certain elements of Earth’s precession (normal precession, lunisolar precession, planetary precession, disturbing precession) are defined and discussed. A new terminology is proposed, e.g. disturbing precession instead of the widely spread deceptive expression of astronomical nutation.