The night sky brightness at Potsdam-Babelsberg including overcast and moonlit conditions

•We performed night sky brightness (NSB) photometry in Potsdam-Babelsberg.•The level of light pollution in the city ranges from 16.5 to 20.3 mag arcsec−2.•Despite its proximity to Berlin, a circalunar periodicity of the NSB is still present.•The Light-pollution-enhancing effect of clouds dominates the NSB.•Overcast nights with light pollution are brighter than clear full moon nights.

We analyze the results of 2 years (2011-2012) of night sky photometry performed at the Leibniz Institute for Astrophysics in Potsdam-Babelsberg. This institute is located 23 km to the southwest of the center of Berlin. Our measurements have been performed with a Sky Quality Meter. We find night sky brightness values ranging from 16.5 to 20.3 magSQM arcsec−2; the latter value corresponds to 4.8 times the natural zenithal night sky brightness. We focus on the influence of clouds and of the moon on the night sky brightness. It turns out that Potsdam-Babelsberg, despite its proximity to Berlin, still shows a significant correlation of the night sky brightness with the lunar phases. However, the light-pollution-enhancing effect of clouds dominates the night sky brightness by far: overcast nights (up to 16.5 magSQM arcsec−2) are much brighter than clear full moon nights (18-18.5 magSQM arcsec−2).