The paper presents results of research on light pollution in the night sky of Toruń. A permanent network of measuring stations has been established in the city, consisting of 24 sites representing various types of land development and land cover: single-family housing, city centre, multi-family housing, areas overgrown with vegetation and open areas. Within this network, a repeatable direct measurement of the sky brightness using an SQM photometer was carried out over a period of three consecutive months in the summer season, i.e. from June to September 2017. The measurement sessions were conducted in similar weather and astronomical conditions. Based on the obtained data, a spatial distribution of light pollution was determined, ranges of values obtained during the measurements were provided, and the results were additionally referred to the distinguished land cover categories and land development types.

Light pollution is one of the types of environmental pollution. The sky illuminated by the excessive light emission is an inherent element of the modern world. This phenomenon has been known for over a century, but research has been carried out only for several decades. Analysis of the brightness of the sky was made for Toruń (Poland) and neighboring areas. The main aim of the study was to study the distribution of brightness of the sky over a medium-sized city. The basic research method was a direct measurement of brightness made with the SQM photometer. The conducted research was carried out throughout the calendar year on 24 measurement stations located in Toruń. Measurement stations represented various types of buildings occurring in every city. On the basis of the obtained data, a map was made showing the extent of light pollution and its intensity, as well as the spatial distribution of this phenomenon. The brightness of the sky was also examined in terms of astronomical and weather conditions. Each aspect is documented in tabular and visual form.

Morphometry changes of Lake Ostrowskie (the Gniezno Lakeland) on the basis of cartographic, remote sensing and geodetic surveying: The authors studied changes in the morphometry of Lake Ostrowskie over the period of 123 years on the grounds of cartographic materials, remote sensing data, land surveying, and data referring to the water stages. The changes that occurred in the lake up to the 1960s were related to the regulation and melioration works conducted in the entire area of the Gniezno Lakeland. On the other hand, drainage of the open pits of brown coal resulted in the considerable decline of the water table by another 2.5 m in the years 2002-2009. As a result of the decline of water down to 96.4 m a.s.l. the present lake was divided into two water bodies (the eastern one and the western one) joint with a channel. This led to the decline in the lake area from 346.7 ha in 1887 to 242.0 ha, and its volume by 28.9%, out of which by 18.3% only in recent twenty-eight years.

Excessive amounts of artificial light emitted into the lower atmosphere at night have already become an everyday feature of modern urban landscapes, and gradually also a phenomenon associated with areas located out- side large human settlements. Urban islands of light have been the subject of targeted research conducted for several decades by scientists representing miscellaneous fields of science. In Toruń, regular research on the phenomenon of light smog has been carried out for several years at a number of sites located throughout the city. Recently, research has been started on the variability of the night sky brightness in a vertical gradient. To this end, repeatable measurements were made at specific altitudes at two locations in the city using a drone with an automatic light metre on board. The values of the night sky brightness thus obtained allowed us to determine its variability in the vertical gradient up to an altitude of 120 m, as well as to test the possibility of using drones in targeted studies of the light pollution phenomenon.