engleski

Night sky brightness above Zagreb 2012.-2017.

Night sky brightness at the RGN site (near the centre of Zagreb, Croatia) was monitored from January 2012 to December 2017. The gathered data shows that the average night sky brightness in this period did not change signifi cantly, apart from diff erences caused by yearly variations in meteorological parameters. The nightly minima, maxima and mean values of the sky brightness do change considerably due to changes in meteorological conditions, often being between 2 and 3 magnitudes. The seasonal probability curves and histograms are constructed and are used to obtain additional information on the light pollution at the RGN site. They reveal that the night sky brightness clutters around two peaks, at about 15.0 mag/arcsec2 and at about 18.2 mag/arcsec2. The tendency to slightly lower brightness values in spring and summer can also be seen in the data. The two peaks correspond to cloudy and clear nights respectively, the diff erence in brightness between them being about 3 magnitudes. A crude clear/cloudy criterion can be defi ned too: the minimum between two peaks is around 16.7 mag/arcsec2. The brightness values smaller than this are attributed to clear nights and viceversa. Comparison with Vienna and Hong-Kong indicates that the light pollution of Zagreb is a few times larger.

light pollution ; night sky brightness ; site testing ; atmospheric effects ; Zagreb

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