The Diffuse Ultraviolet Foreground

Abstract

Ultraviolet observations from low Earth orbit (LEO) have to deal with a foreground comprised of airglow and zodiacal light which depend on the look direction and on the date and time of the observation. We have used all-sky observations from the GALEX spacecraft to find that the airglow may be divided into a baseline dependent on the sun angle and a component dependent only on the time from local midnight. The zodiacal light is observable only in the near ultraviolet band (2321 \AA) of GALEX and is proportional to the zodiacal light in the visible but with a color of 0.65 indicating that the dust grains are less reflective in the UV.