The impact of lunar illumination on narrow-band wide-field surveys

Wide field photometric surveys aim at observing large areas of sky in various filters. Yet, almost all surveys use constant exposure times, regardless of the quality of the images or the level of background, mostly due to the moon, which may result in a lack of homogeneity in the data sets. In the J-PLUS survey,1 modulating the exposure time with the sky background has resulted not only in an improved homogeneity of the data but also in a significant improvement of the efficiency of the survey execution. In this paper, we show the effect on J-PAS and J-PLUS of using fixed exposure times, regardless of the Moon background, and we describe the system to estimate this background reliably and provide a significant improvement, not only in the quality of the observations, but also in the survey speed.