Earth rotation as an interdisciplinary topic shared by astronomers, geodesists and geophysicists

Earth rotation is characterized by its angular speed and by the position of the rotation axis both in space and in a frame tied to the Earth. The changes of the angular velocity induce changes in the length-of-day, and the variation of the position of the rotation axis is associated with polar motion (in the reference frame tied to the Earth) and with precession-nutation (in the space-fixed reference frame). These effects can be decomposed into components varying at different time scales. The study of their causes involves in different fields of physics, from astronomy for the rigid Earth nutation, through internal geophysics for the length-of-day variation at the decadal time scale, to external geophysics for seasonal polar motion. In this paper, we show how each discipline brings its own light into the observation, understanding and modeling of the Earth's rotation. (C) 2002 COSPAR. Published by Elsevier Science Ltd. All rights reserved.