Upper limit on the extragalactic background light

An experiment to determine the brightness of the extragalactic background light at 5115 A is described. The separate contributions to the night sky brightness from several sources are eliminated or measured independently. Light from discrete sources (stars and resolved galaxies) is blocked from the photometer by a telescope focal-plane mask; the zodiacal light is measured using its Fraunhofer spectrum; airglow and atmospheric scattered light are determined by their zenith-angle dependence. The remaining sky brightness of 1.0 + or - 1.2 S(10) is attributed to the extragalactic background light plus a possible diffuse galactic component. An attempt to detect the latter by analysis of the galactic-latitude dependence of the sky brightness was inconclusive, so the result may be interpreted only as an upper limit on the extragalactic light of 3.4 S(10) at the 90% confidence level.