1996A&AS..119..153M

We have measured the sky brightness at the European Southern Observatory (ESO), La Silla, during 40 moonless nights in the years 1978-1988. Most of the measurements were performed in five intermediate band filters between 3500 and 5470A, including the Stroemgren u, b, and y bands. In addition we made measurements in the uvgr and BVRI photometric systems. Typically 20 to 40 readings were obtained each night at a fixed (α, δ) position, selected to be free of stars down to a limiting magnitude of B≃20. The sky brightnesses were calibrated using standard stars. We discuss the sky brightness variations both during individual nights and from year to year. We have found that the long-term variations are well correlated with the solar activity, for which the 10.7cm radio flux is used as a measure. We compare the sky brightnesses as observed at La Silla with the published values for several other sites. Finally, based on the tight correlation of the airglow variations in two pass bands near 4000A we propose a new method for the separation of airglow and zodiacal light contributions.