Interferometers, Aberration and the Sagnac Effect

Abstract

In this note we show that the usual expression for diurnal aberration (see e.g. Woolard and Clemence 1966) is not valid for some types of radio interferometers. The difference (usual minus correct) is a constant of the instrument, and is absorbed in the calibration procedure. The analysis of multibaseline VLBI may also be affected.