The Rotation of the Earth and Other Planets

Abstract

This and the following chapter are devoted to a complex subject which ties together three different fields: astrometry, geophysics and celestial mechanics. The earth provides the basic frame of reference with respect to which most of our celestial observations are made: the determination of its (variable!) rotation with respect to the stars and the planets is a prerequisite of astrometry, the discipline that determines the position and the motion of celestial objects. This is of course connected with the fundamental problem of absolute rotation in mechanics. This chapter is also an appropriate place to introduce the problem of measurement of time and distance in space physics. Rotation produces an oblateness and at the same time is affected by the internal motion of the planet, an important chapter of geophysics. The presence of other bodies in the solar system also deeply influences the structure and the rotation of the earth through tidal phenomena.