Abstract: Artificial skyglow, the fraction of artificial light at night that is emitted upwards from Earth and subsequently scattered back within the atmosphere, depends on atmospheric conditions but also on the ground albedo. One effect that has not gained much attention so far is the amplification of skyglow by snow, particularly in combination with clouds. Snow, however, has a very high albedo and can become important when the direct upward emission is reduced when using shielded luminaires. In this work, first results of skyglow amplification by fresh snow and clouds measured with all-sky photometry in a suburban area are presented. Amplification factors for the zenith luminance of 188 for snow and clouds in combination and 33 for snow alone were found at this site. The maximum zenith luminance of nearly 250 mcd/m2 measured with snow and clouds is a factor of 1000 higher than the commonly used clear sky reference of 0.25 mcd/m2. Compared with our darkest zenith luminance of 0.07 mcd/m2 measured for overcast conditions in a very remote area, this leads to an overall amplification factor of ca. 3500. Horizontal illuminance measurements show values of up to 0.79 lx, exceeding maximum possible full-moon illuminance levels by more than a factor of two. Additional measurements near the Arctic Circle for clear and overcast conditions are presented and strategies for further studies are discussed. We propose the term “snowglow” to describe the amplification of skyglow by snow with and without clouds.

Abstract: This work aims for choosing preliminary sites that can be candidates for a new astronomical observatory that will replace the Kottamia observatory. The candidate sites have been selected to be investigated after proposing a few criteria. Concerning light pollution and elevation of the sites as the main factors, we chose the candidate sites depending on the zenith sky brightness and the elevation. The night sky brightness has been measured using a Sky Quality Meter at different altitude degrees and the values of the zenith sky brightness were compared to those of different observatory sites. Our night sky brightness observations were found to be in agreement with the satellite’s data and comparable to those of dark sites, with average values of 22.07, 22.03, 21.57 and 21.58 magSQM/arcsec2. We also have obtained the Aerosol Optical Depth (AOD) and extinction coefficient due to the aerosol for the candidate sites using satellite data (Terra/MODIS).

Abstract: Freshwater ecosystems are hotspots of biodiversity. They are of major importance for humans because they provide vital ecosystem services. However, as humans tend to settle near freshwaters and coastal areas, these ecosystems are also over‐proportionally affected by anthropogenic stressors. Artificial light at night can occur as a form of environmental pollution, light pollution. Light pollution affects large areas on a worldwide scale, is growing exponentially in radiance and extent and can have diverse negative effects on flora, fauna and on human health. While the majority of ecological studies on artificial light at night covered terrestrial systems, the studies on aquatic light pollution have unraveled impact on aquatic organisms, ecosystem functions as well as land‐water‐interactions. Although monitoring of light pollution is routinely performed from space and supported by ground‐based measurements, the extent and the amount of artificial light at night affecting water bodies is still largely unknown. This information, however, is essential for the design of future laboratory and field experiments, to guide light planners and to give recommendations for light pollution regulations. We analyze this knowledge gap by reviewing night‐time light measurement techniques and discuss their current obstacles in the context of water bodies. We also provide an overview of light pollution studies in the aquatic context. Finally, we give recommendations on how comprehensive night‐time light measurements in aquatic systems, specifically in freshwater systems, should be designed in the future.