DYNAMICS AND EPHEMERIDES OF EARTH ROTATION

Nicole CAPITAINE (Observatoire de Paris, FRANCE)


ABSTRACT: The theory of Earth rotation provides solutions for
 precession, nutation and the Earth's angle of rotation in space
through the integration with respect to time of the dynamical
 equations of motion. The classical solutions generally separate
 precession from nutation and refer to the equinox and ecliptic
 of date.
        On the other hand, observations by modern astrometric
 techniques as Very Long Baseline Interferometry (VLBI) or
 Lunar Laser Ranging (LLR) provide Earth orientation
 parameters (EOP) referred to the Celestial Reference System
 (CRS); these observations are sensitive to the motion of the
 equator in the CRS which include both precession and
 nutation and to the variations of UT1. The EOP estimated from
 observations depend on the form of the coordinate
 transformation between the terrestrial and celestial frames
 which is used in the reduction of the observations.

        This paper gives a comparison between the parameters
 provided by the theory and used for the ephemerides of
Earth rotation and the parameters which are estimated from
 the observations of Earth rotation according to the form of the
 coordinate transformation which is used and to the frequency
 of the observations. This emphasizes the necessity of the best
consistency as possible between the parameters as derived
 from the theory and those to which the observations are
really sensitive.