Abstract
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.
Highlights
Light pollution (LP) is most de¿ned as any arti¿cial light that spills into the environment
The gathered data shows that the average night sky brightness in this period did not change signiƤcantly, apart from diơerences caused by yearly variations in meteorological parameters
Apart from a few measurements that amateur astronomers did for their needs (LPO1, 2018) and a few measuring campaigns in the past, the only systematic long-time observations of light pollution are those carried on at the RGN site and at the site of the Merenje observatory, located about 30 km NW from Zagreb
Summary
At that time, no dedicated instruments for measuring light pollution existed, an astronomical CCD camera was used in these attempts. In 2006, all-sky photography and SQM instruments were introduced and the ¿rst usable data on LP was obtained, limited to several places in the Istria peninsula. The ¿rst model of light pollution in Croatia was ¿nished in 2007. Apart from a few measurements that amateur astronomers did for their needs (LPO1, 2018) and a few measuring campaigns in the past (see for instance Andreiü, 2012; Sharma 2015), the only systematic long-time observations of light pollution are those carried on at the RGN site (started in 2012.) and at the site of the Merenje observatory, located about 30 km NW from Zagreb (started in 2014)
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