COMPARISON BETWEEN THE VARIABLES AND PARAMETERS …

COMPARISON BETWEEN THE VARIABLES AND PARAMETERSUSED FOR HIGH ACCURACY precession AND NUTATIONN. CAPITAINESYRTE, Observatoire de Paris, CNRS, UPMC61, avenue de l Observatoire, 75014 Paris, Francee-mail: forms of VARIABLES and PARAMETERS , which refer to various celestial referencesystems, have been used in the development of high accuracy equations and models for the Earth sprecession and nutation, as well as for the estimation of thetime-dependent celestial pole offsets fromthe most accurate astrometric observations. The purpose ofthis presentation is to compare and relaterigorously those various forms of VARIABLES and parametersand recommend the most appropriate ones tobe used for providing the best accuracy for the celestial motion of the Celestial intermediate THE precession -NUTATION PARAMETERSThe CIO based precession -nutation PARAMETERS reflect the motion of the Celestial intermediate pole,CIP, in the Geocentric celestial reference system (GCRS); they consist in the coordinates of the CIP unitvector, either in their polar form (Eandd), or their rectangular form (X= sindcosE, Y= sindsinE).

The equinox based precession-nutation parameters refer either to the ecliptic of date, or the ecliptic of epoch (e.g. J2000.0). Figure 2 shows a number of those parameters, e.g. ψA, ωA, which refer to the ecliptic and equinox of epoch, ǫA, zA and the usual nutation angles, ∆ψ, ∆ǫ, which refer to the ecliptic and (mean or true) equinox of date, and χA +∆χA that measures the ...

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  Precession, Equinox

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