Light pollution is increasing, veiling the celestial vault: in just 10 years, the difference is noticeable.
It is paradoxical: as the sky becomes brighter, the celestial vault darkens. Light pollution, especially in urban areas, generates a kind of “haze”. You see more stars in the countryside than through the window of a Parisian apartment. This phenomenon is known, 85% of France is exposed to this pollution, but it seems to be seriously increasing.
A published report in Science January 19, 2023 mobilizes 51,351 observations provided by citizen science. The data comes from all over the world, but is mostly located in Europe and North America. The objective of the study: to take stock of the stellar cover visible to the naked eye. The conclusion is not good.
The night sky has become twice as clear
The report shows that each year, between 2011 and 2022, the sky absorbed about 9.6% more brightness. The night sky has therefore become at least twice as clear in the meantime. What the report links to an equally exponential increase light pollution — light emitted by humans (public lighting, household lighting, car headlights, etc.).
To illustrate the concrete impact on the observation of the sky, the authors write that in a place where one would have seen 250 stars with the naked eye in 2011, this figure now drops to 100 in 2022.
” This increase is faster than changes in emissions [de lumière] satellite observations “, write the authors. Why such a discrepancy? The answer is to be found in the nature of the light emitted: the detectors installed on the satellites are blind to the light emitted by the LEDs (light-emitting diodes) which were developed in the 21st century.
In question, more powerful technologies which make it possible to illuminate more for the same economic cost. “ This results in the blooming of new lights to illuminate roads, buildings and natural landscapes, for digital billboards and for the ‘beautification’ of gardens, among other applications. “, note the authors.
Pollution caused by artificial light is a problem for astronomers, who are moving their observatories ever further from urban areas. But it is, more seriously still, an ecological threat. Biodiversity is disrupted by these changes in light cover — like fireflies, for example, whose reproductive cycle is hampered.
The authors invite a deeper awareness of the danger of light pollution. ” Looking at images and videos of Earth’s nocturnal hemisphere taken by the International Space Station, people are usually only struck by the ‘beauty’ of city lights, as if they were the lights of ‘a Christmas tree “, they worry. ” They do not perceive that these are images of pollution. It’s like admiring the beauty of the rainbow colors that gasoline produces in water and not recognizing that it’s chemical pollution. They also note that artificial light is associated with an advantage for road safety (which is not not really proven) and individual (this is not not proven either).
They therefore call for real, strong measures to be taken against this form of pollution, in order to restore the nocturnal environment. We need new approaches treating light as a real pollutant. »
