On the Adoption of Empirical Corrections to Woolard's Nutation Theory

Abstract

Commission 4 of the International Astronomical Union has deferred the question of revisions to the constants and theory of nutation in anticipation that there might be recommendations from Symposium No. 78 in Kiev. The present rigid-Earth theory of nutation does not adequately represent current precise astronomical observations for the major nutation terms. Discrepancies between the presently adopted theory and observations can accumulate to 0″1 in right ascension and significantly affect the determination of UT1 and materially influence the derivation of the new fundamental catalog of star positions and proper motions, FK5 There appears to be no obvious choice for a non-rigid-Earth model at present. The analysis of solid-Earth tides shows nutation coefficients in substantial agreement with astronomical observations and these values have been used in the reduction of radio interferometric and laser ranging observations. In the absence of a non-rigid-Earth model which can satisfy all requirements it is suggested that the coefficients found from the investigation of solid-Earth tides be adopted as a working standard until such a model can be adopted as a basis for nutation.