Optical sky brightness at Cerro Tololo Inter-American observatory from 1992 to 2006
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We 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. 2007. The Astronomical Society of the Pacific. All rights reserved.