Expressions for precession consistent with the IAU 2000A model Considerations about the ecliptic and the Earth Orientation Parameters

Since the adoption by the XXIVth General Assembly of an accurate model of nutation, the IAU encourages the development of new expressions for precession consistent with the new model. This paper presents new expressions for the precession quantities issued from the analytical solution of the rotation of the rigid Earth SMART97 (Bretagnon et al. 1998) which provides together the precession and the nutation. These expressions include the new value of the precession rate of the equator in longitude. As the SMART97 series are close to the Souchay et al. (1999) series used to build the new model, our expressions are consistent with the IAU 2000 Precession-Nutation Model. In the other parts of the paper, we discuss some concepts. In Sect. 3, we propose the definition of a conventional ecliptic plane close to the mean ecliptic J2000 and with a non-rotating origin. Section 4 deals with the Earth Orientation Parameters. We show that the celestial pole offsets, as well as the polar motion can be described with the Eulerʹs angles. At last, in Sect. 5, we give some recommendations about the precession-nutation variables and the arguments of the series of the nutation.