A Photometer for Measurement of Sky Brightness Near the Sun

Abstract

Measurement of the brightness of the sky near the sun is difficult because instrumental scattered light originating in the solar disk is usually many times brighter than light from the sky. An optical system for eliminating this scattered light and providing means for a visual photometric comparison between the sky and the sun has been constructed and tested. The principles of the instrument are explained in sufficient detail to permit the design of similar instruments for a wide range of applications.