Fig. 19 Comparisons between sky brightness NPS CCD observations and atlas predictions. Comparisons between sky brightness NPS CCD observations and atlas predictions. (Left) Plots comparing CCD observations to the predictions of the atlas (upper graph, aerosol clarity K = 1; lower graph, K = 0.5). (Right) Fit residuals (observed minus predicted values) for the SQM-based calibration versus CCD NPS observations (upper histogram, K = 1; lower histogram, K = 0.5). Fabio Falchi et al. Sci Adv 2016;2:e1600377 Copyright © 2016, The Authors