Progress Report of the IAU Working Group on Precession and the Ecliptic

Résumé du livre

The IAU Working group on Precession and the Ecliptic looked at several solutions for replacing the precession part of the IAU 2000A precession-nutation model, which is not dynamically consistent. These comparisons show that the Capitaine et al. (2003) precession theory, P03, is both dynamically consistent and the solution most compatible with the IAU 2000A nutation model. The two greatest sources of uncertainty in the precession theory are the rate of change of the Earth's dynamical flattening, DELTA J2, and the precession rates (i.e., the constants of integration used in deriving the precession). The combined uncertainties limit the accuracy in the precession theory to approximately 2 mas cent(exp -2). Given that there are difficulties with the traditional angles used to parameterize the precession, the working group has decided that the choice of parameters should be left to the user. They shall provide a consistent set of parameters that may be used with either the traditional rotation matrix, or those rotation matrices described in Capitaine et al. (2003) and Fukushima (2003). They recommend that the ecliptic pole be explicitly defined by the mean orbital angular momentum vector of the Earth-Moon barycenter in an inertial reference frame, and explicitly state that this definition is being used to avoid confusion with previous definitions of the ecliptic. Finally, they recommend that the terms "precession of the equator" and "precession of the ecliptic" replace the terms "lunisolar precession" and "planetary precession," respectively.