Night sky brightness above Zagreb 2012.-2017

TL;DR

This study monitored night sky brightness in Zagreb from 2012 to 2017, revealing stable average brightness with seasonal and meteorological variations, and comparing light pollution levels with other cities.

Contribution

It provides a long-term dataset of night sky brightness in Zagreb, analyzing seasonal patterns, meteorological effects, and comparing light pollution levels with Vienna and Hong Kong.

Findings

Average brightness remained stable over years.

Brightness varies significantly with weather and season.

Zagreb's light pollution is several times higher than Vienna and Hong Kong.

Abstract

The night sky brightness at the RGN site (near the centre of Zagreb, Croatia) was monitored form January 2012. to December 2017. The gathered data show that the average night sky brightness in this period did not change significantly, apart from differences 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. Two peaks correspond to cloudy and clear nights respectively, the difference in brightness between them being about 3 magnitudes. A crude clear/cloudy criterion can be defined too: the minimum between two peaks is around 16.7 mag/arcsec2. The brightness values smaller than this are attributed to clear nights and vice-versa. Comparison with Vienna and Hong-Kong indicates that the light pollution of Zagreb is a few times larger.