The night sky brightness at Potsdam-Babelsberg

TL;DR

This study measures and analyzes the night sky brightness at Potsdam-Babelsberg over two years, revealing the effects of clouds, moonlight, and light pollution, with brightness levels up to 4.7 times natural darkness.

Contribution

It provides the first detailed long-term photometric data of night sky brightness at this specific location, including the influence of various environmental factors.

Findings

Night sky brightness varies from 16.5 to 20.3 mag_SQM/arcsec^2.

Cloud cover significantly increases sky brightness, overshadowing lunar effects.

Despite proximity to Berlin, a weak circalunar periodicity is observed.

Abstract

We analyze the results of a 2 years (2011--2012) time series of night sky photometry performed at the Leibniz Institute for Astrophysics in Potsdam (AIP). This observatory is located on top of a hill ("Babelsberg"), 22\,km to the southwest of the center of Berlin. The measurements have been performed with a Unihedron Sky Quality Meter. We find night sky brightness values ranging from 16.5 to 20.3 mag$_{\rm SQM}$ arcsec$^{-2}$; the latter (best) value corresponds to 4.7 times the natural zenithal night sky brightness. We discuss the influence of clouds, of the Moon and other factors on the night sky brightness. With respect to the influence of the Moon, it turns out that Potsdam-Babelsberg, despite its proximity to Berlin, still shows a circalunar periodicity of the night sky brightness, although it is much weaker than naturally. The light-pollution-enhancing effect of clouds dominates the night sky brightness by far. Overcast nights with light pollution (up to 16.5 mag$_{\rm SQM}$ arcsec$^{-2}$) are brighter than clear full moon nights ($\approx$ 18.5 mag$_{\rm SQM}$ arcsec$^{-2}$) in roughly the same proportion as the latter compared to clear nights with light pollution (20.3 mag$_{\rm SQM}$ arcsec$^{-2}$).