Luminosity and Astrometry of Comets: A Review

Abstract

By far the greatest number of observations of the brightness of comets, and the only ones that cover a long enough time span for investigation of secular effects, have been made by visual methods, mostly with small instruments. Such observations record the contribution of a large part of the coma, and possibly some light from the tail, at wavelengths to which the eye is sensitive. Three distinct observational techniques have been defined:1)Comparison of similar-appearing extrafocal images of comet and comparison stars for equal apparent brightness. (Most observations have been made by this method.) The technique has been described by Bobrovnikoff (1941a, 1941b).2)Comparison of the in-focus image of the comet with extrafocal images of comparison stars for equal apparent brightness. This method has been described by Sidgwick (1955).3)A method used extensively by Max Beyer (1950), in which grossly out-of-focus images of the comet and comparison stars are examined for similarity of extinction against the sky.