Less and less visible stars, light pollution increases up to 10% every year

The night sky he is losing his stars because the speed with which the stars are becoming invisible to the human eye is higher than previously thought. An international research has estimated an increase in brightness of the sky
night between 7 and 10% annually, an intensification of thelight pollution due to terrestrial artificial lights and faster and faster. The increase in light pollution is much faster than satellite surveys of the phenomenon have so far led to believe, according to the result of the international study reported by globalscience.it, the Agency’s ‘science storytelling’ website Italian Space. The research, published in Science, was based on more than 50,000 naked-eye observations made between 2011 and 2022 by citizen scientists of the Globe at Night project. The work was conducted by the Gfz German Research Center for Geosciences and Ruhr-Universität Bochum with the collaboration of the US National Science Foundation’s NoirLab, which initiated the Globe at Night project in 2006. The change in the sky over time has never been measured globally. Furthermore, satellite data lack accuracy in this monitoring or have insufficient sensitivity. “Satellites are most sensitive to light directed towards the sky. But it is horizontally emitted light, such as illuminated advertisements and facades, that accounts for the most skyglow,” says Christopher Kyba, lead author of the study.

Skyglow, Global Science also reports, is the form of light pollution that consists of artificial twilight that persists long after sunset. To measure this phenomenon, from the negative effects on animal physiological processes as well as on stargazing and astronomy, the Globe at Night project called on people from all over the world to observe their skies on cloudless and moonless nights. The nearly 52,000 citizen scientists engaged then selected the star chart online that best matched what they were seeing, choosing from 8 possible scenarios of skies with different levels of light pollution. With just under 20,000 different locations from which observations were made with the naked eye, in order to compare all the data, the researchers had to use a global model of sky brightness, based on satellite observations in 2014. The more than 100,000 human eyes thus they functioned as a single network of global sensors. The work showed that the number of stars visible in different regions of the globe can be explained by the increase in the brightness of the night sky. In Europe this phenomenon sees an increase rate of 6.5% per year; in North America, on the other hand, it reaches peaks of over 10%.

Global Science points out that the researchers have estimated a global average of 9.6% per year of increase in light pollution, calculated from the average of the 20 thousand places in the world engaged to observe the sky. “If development continues at this rate, a child born today in a place where 250 stars are visible will only be able to see 100 by his 18th birthday,” says Kyba. Despite the drama of the scenario suggested by the research, the approach used by the Globe at Night project also reveals its investigation limits: with a greater participation of people from North America and Europe, the inevitable consequence of the experiment it was an underestimation of the increase in light pollution especially in developing countries, where on the contrary rapid changes in the artificial sky are suspected. A gap that does not diminish the value of the integration of traditional scientific research with the active participation of citizen scientists, continues Global Science.