values in  and other statistical parameters for the NSB are calculated for time intervals between the astronomical twilights of the given date. As described in Section \[sec:methods\] the device “FOA2” mounted at our remote site was calibrated against our older SQM “IFA” located at our institute in Vienna.

Detection of the natural circalunar rhythm
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Our measurements meanwhile cover a period of one year. We were therefore interested in the behavior of the mean night sky brightness at IfA and at LFOA during this period (March 2012 – March 2013). At a rural site, a strong influence of the lunar phase on the NSB is expected: full moon nights should be recognizable by much brighter night skies, especially for clear sky conditions. In contrast, nights around new moon should be much darker. Since LFOA is a rural site, this pattern is indeed detected and a nice circalunar periodicity of the mean NSB becomes evident (see Fig. \[fig:lightcurve\]). The NSB data from Vienna show a completely different picture. Instead of the moon, the degree of cloudiness has the strongest influence on the NSB in Vienna. The more clouds over a big city, the stronger the backscattering of urban light. Of course, 