The equations of the Earth's rotation in the framework of the IAU 2000 Resolutions

This paper describes the objectives of the European DESCARTES sub-project entitled “Advances in the integration of the equations of the Earth’s rotation in the framework of the new parameters adopted by the IAU 2000 Resolutions” and reports on preliminary results. 1. THE EUROPEAN DESCARTES SUB-PROJECT For many applications in Celestial Mechanics and Astrometry, the x, y-coordinates (denoted X, Y ) of the Celestial Intermediate Pole (CIP) unit vector in the Geocentric Celestial Reference System (GCRS), are extremely useful. They are for example the parameters to which the VLBI observations are directly sensitive. It is therefore important to obtain the equations of the Earth’s rotation as function of these parameters. This would allow us to provide a precession-nutation model directly in the form recommended by the IAU 2000 Resolutions. With these considerations in mind, the European DESCARTES sub-project entitled: “Advances in the integration of the equations of the Earth’s rotation in the framework of the new parameters adopted by the IAU 2000 Resolutions” has been undertaken. The main objectives of the project can be summarized as follows: 1. discussing the most suitable sets of variables to be used for integrating the equations of the Earth rotation, 2. obtening the equations of the Earth rotation explicitly expressed with the Earth Orientation Parameters (EOP) that are recommended by the IAU 2000 Resolutions, 3. integrating these equations in order to provide the results with an accuracy compliant with that required by the IAU 2000 Resolutions, 4. comparing the new solutions for X and Y with those derived indirectly from the IAU 2000 solutions for the classical ∆ψ and ∆ε variables, 5. transforming the solution for a rigid Earth to the non-rigid Earth, 6. comparing the solution obtained analytically with the observed parameters.