The quality of Las Campanas as a site.

Data on the quality of nights, seeing, and wind velocity as measured at the Las Campanas Observatory 2.5-meter Du Pont Telescope in the period 1978-1983 are presented. The incidence of nights with excellent seeing (image sharp, nearly motionless, less than 0.7 arcsec diameter) is 5 percent, and the incidence of nights with poor seeing (image soft, blurred, more than 2 arcsec diameter) is 15 percent during the time span covered by the data. On average, 13 percent of the nights were not usable either because of clouds, excessive wind, or high humidity.