Optical Sky Brightness at Cerro Tololo Inter‐American Observatory from 1992 to 200611Based in part on observations taken at the Cerro Tololo Inter‐American Observatory, National Optical Astronomy Observatory, which is operated by the Association of Universities for Research in Astronomy (AURA), Inc., under cooperative agreement with the National Science Foundation.

Abstract

ABSTRACTWe present optical (UBVRI) sky brightness measurements from 1992 through 2006. The data are based on CCD imagery obtained with the CTIO 0.9, 1.3, and 1.5 m telescopes. The B‐ and V‐band data are in reasonable agreement with measurements previously made at Mauna Kea, although on the basis of a small number of images per year, there are discrepancies for the years 1992 through 1994. Our CCD‐based data are not significantly different than values obtained at Cerro Paranal. We find that the yearly averages of V‐band sky brightness are best correlated with the 10.7 cm solar flux taken 5 days prior to the sky brightness measurements. This implies an average speed of 350 km s−1 for the solar wind. While we can measure an enhancement of the night‐sky levels over La Serena 10° above the horizon, at elevation angles above 45°, we find no evidence that the night‐sky brightness at Cerro Tololo is affected by artificial light of nearby towns and cities.