Spatial and temporal analysis of artificial light pollution of the city night sky. A case study from Toruń

Abstract Artificial light pollution of the night sky over urban areas and in their immediate vicinity has become a common anthropogenic phenomenon and a major problem of the modern urban landscape. It is no longer only scientists or environmentalists, but increasingly ordinary citizens too, who perceive a decline in the quality of the night sky and suffer the health consequences of this systematically aggravating process. In order to observe the naturally starry sky, it is now necessary to travel to places far away, not only from large conurbations, but also from smaller human settlements. In order for there to be an improvement in the level of night sky pollution, it is necessary to monitor the phenomenon, provide targeted education and take systemic countermeasures to reduce its negative effects in time and space. Several interdisciplinary research groups and non-governmental organisations around the world conduct research on light pollution. In Toruń, the first measurements of this phenomenon were carried out in 2017 using handheld SQM devices, and a wireless automatic network monitoring the state of the city’s night sky has been developed since 2020. This paper presents the results of the analysis of measurement data recorded during the two-year operational operation of the monitoring network. The conducted measurements provided data to analyse the seasonal variability of the phenomenon, as well as to perform selected spatial analyses within the city limits. The results obtained were related to the results of measurements made outside human settlements, which made it possible to determine the variation of sky brightness in a gradient of decreasing human impact.