Monitoring Long-Term Trends in the Anthropogenic Night Sky Brightness

Abstract

Monitoring long-term trends in the evolution of the anthropogenic night sky brightness is a demanding task due to the high dynamic range of the artificial and natural light emissions and the high variability of the atmospheric conditions that determine the amount of light scattered in the direction of the observer. In this paper, we analyze the use of a statistical indicator, the mFWHM, to assess the night sky brightness changes over periods of time larger than one year. The mFWHM is formally defined as the average value of the recorded magnitudes contained within the full width at half-maximum region of the histogram peak corresponding to the scattering of artificial light under clear skies in the conditions of a moonless astronomical night (sun below −18°, and moon below −5°). We apply this indicator to the measurements acquired by the 14 SQM detectors of the Galician Night Sky Brightness Monitoring Network during the period 2015–2018. Overall, the available data suggest that the zenithal readings in the Sky Quality Meter (SQM) device-specific photometric band tended to increase during this period of time at an average rate of +0.09 magSQM/arcsec2 per year.

Monitoring transition: Expected night sky brightness trends in different photometric bands

“…Two main and complementary approaches are commonly used: (a) tracking the changes of the emitted artificial radiance by means of ground-based measurements [21][22][23], airborne surveys [24][25], or remote sensing from Earth orbiting platforms [26][27][28][29][30][31], and (b) monitoring the evolution of the night sky brightness using specific detectors [32][33][34][35][36][37][38][39], CCD and general purpose DSLR cameras [40][41][42][43], and even by means of comprehensive citizen science observations [44]. Different trends have been reported, sometimes apparently at odds with each other, including a sustained increase of the radiance and overall lit surface around the world, at an estimated 2% yearly rate [45], and a tendency to darker readings in the long-term series recorded by ground-based night sky brightness detectors [46][47], whose progressive aging has not been discarded as a potential cause.…”

Classification of Continuous Sky Brightness Data Using Random Forest

“…In short, these statistical selections are the other ways of selecting clear and moonless data that represent the true value of night sky brightness. e stability of sky brightness during the whole night becomes the main key to the selections both in the studies by Bará et al [35,36] or in the study reported here. e difference is that Bará et al [35,36] used statistical approaches to the density distribution constructed using long term data while the current study evaluates nightly characteristics to determine the class.…”

“…e stability of sky brightness during the whole night becomes the main key to the selections both in the studies by Bará et al [35,36] or in the study reported here. e difference is that Bará et al [35,36] used statistical approaches to the density distribution constructed using long term data while the current study evaluates nightly characteristics to determine the class. For the case of data obtained in tropical region where the clear sky fraction is somewhat lower [37], there is a caution that the sharp distribution of the ideal data is likely to be overwhelmed (or smoothed) by data obtained during cloudy or overcast conditions.…”

“…e ideal night in this regard is defined as the condition of astronomical darkness, when the sun is below -18°and the moon is below −5°. Recently, it is [36]. In short, these statistical selections are the other ways of selecting clear and moonless data that represent the true value of night sky brightness.…”

Identifying, Examining, and Planning Areas Protected from Light Pollution. The Case Study of Planning the First National Dark Sky Park in Greece

“…Light pollution poses a significant threat to our health, the dark skies, and the natural environment. This fact is backed by extensive research in the fields of medicine, astronomy, and the environmental sciences [59][60][61][62][63][64][65][66][67]. It is imperative to push for measures against light pollution because research regarding its impact on human health has helped make headlines worldwide.…”