Planetary Rotation

Abstract

The present and the following chapter are devoted to a complex subject which brings together three different fields: astrometry, geophysics and celestial mechanics. The Earth provides the basic frame of reference in which most of our celestial observations are expressed: the determination of its (variable) rotation with respect to very distant matter (e.g., quasars) is a fundamental task of astrometry, the discipline that determines the position, the distance and the motion of celestial objects. In this way an inertial reference system is provided. This chapter is also an appropriate place to introduce the problem of time and distance measurement in space physics. The Earth’s rotation produces an oblateness and, at the same time, is affected by its internal motion, an important topic in geophysics. The presence of other bodies in the solar system also deeply influences the structure and rotation of a planet through tidal phenomena.