Almucantar deformations in the method of equal altitudes

Abstract

Systematic deformations of apparent almucantar of order of 0.1 arcsec were derived from two five-year series of circumzenithal observations by the method of equal altitudes. Simple method is presented which makes it possible to check for almucantar deformation all data obtained by the method of equal altitudes, selected for rereducing earth rotation parameters in the HIPPARCOS reference frame.