Daytime Sky Quality at El Leoncito, Argentina

Abstract

We characterize the daytime sky quality in terms of its brightness, cloud coverage and main weather variables at the Carlos Ulrico Cesco station of the Felix Aguilar Astronomical Observatory (OAFA), located in El Leoncito national park, San Juan, Argentina. We have collected more than 15 years of daily observations from the auxiliary sky brightness detectors of the Mirror Coronagraph for Argentina (MICA, in operations from 1997 to 2012), including daily observing reports. We additionally present data from two meteorological stations that operated at the site from 2000 to 2020. We determine the main statistical properties and seasonal variability of daytime sky brightness, clear sky time fraction (CSTF), precipitable water vapor (WV), temperature, humidity and wind speed, which are relevant for solar and particularly coronal observations. Our results confirm that El Leoncito is an excellent place to perform daytime astronomical observations. We measure a median sky brightness of 15.8 ppm, estimated at 526.0 ± 1 nm and 6 solar radii from the solar disk center; a median CSTF of 0.7; and a median WV below 6 mm. These values, and those of other relevant weather variables, are comparable to the levels found among the best F. A. Iglesias