Sky light pollution is growing faster than expected

If in the light of streetlights our streets take shape, the stars fade away. All the artificial lighting that illuminates our nights is the source of many consequences, including environmental ones. We are talking about light pollution. A study published Friday, January 20 in the journal Science highlights the magnitude of its increase, underestimated until now.

The team of scientists led by Christopher Kyba, an astrophysicist at the German Earth Science Research Center, analyzed just over 50,000 naked-eye observations of the night sky, collected from 2011 to 2022 by citizens around the world. as part of the citizen science program The Globe at Night. One of their conclusions is the evidence of a marked increase in light pollution over the past twelve years.

This was known, but until now researchers monitored it using satellites measuring from space the light emitted by our facilities. However, it turns out that the technical limitations of this method led to underestimating the magnitude of the phenomenon and the speed of its evolution. Based on these observations made with the naked eye, Christopher Kyba calculated an invisibilization of stars increasing by about 10% per year, while satellite measurements estimated this rate at 2%. According to Christopher Kyba, this figure means that, if in a given place, 250 stars are visible, eighteen years later, only a hundred will still be.

Transition to blue light

These results do not make it possible to explain this extent of the growth of light pollution, which is too rapid to come exclusively from the installation of new sources. Christopher Kyba hypothesizes that another factor contributes to this phenomenon: the evolution of the nature of lighting over the last decade. Indeed, LEDs have made their appearance and have begun to replace incandescent bulbs and other types of lighting. However, they emit light with lower wavelengths, also called “blue light”. Our eye is very sensitive to these wavelengths, increasing the impact of this light on our vision of the night sky. In addition, this blue light diffuses more widely in the sky.

Sébastien Vauclair, an astrophysicist specializing in the field of light pollution, however, has reservations about this study, particularly in terms of statistical reliability. Indeed, the data used come from a participatory science program, and the quantity of observations would be potentially insufficient to erase the approximations of measurements and the weaknesses of the observation protocol.

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