While city dwellers sleep bathed in the warm glow of artificial light that surrounds their city centre, stargazers feel the chill of the night sky and see all the constellations blurred by the same city lights. This is an alarming trend that goes back decades. In 1973, astronomer Kurt Riegel warned that artificial lighting was rapidly changing our view of the night sky. Since then, we’ve learned that light pollution from expanding urban areas is also damaging ecosystems and insect populations.

A new study shows that the night sky is getting brighter around the world at an astonishing rate and much faster than the previously mentioned satellites. In other words, the faintest stars in the night sky quickly disappear as artificial light illuminates the night sky. Based on observations of more than 50,000 citizen scientists from around the world comparing their views of the stars with maps of the starry sky showing different levels of light pollution, physicist Christopher Kiba of the German Geosciences Research Center (GFZ) and colleagues analyzed the night sky from 2011 to 2022. It got brighter by about 7 to 10 percent each year.

This is equivalent to doubling the brightness of the night sky in less than eight years, or more than quadrupling in 18 years. Researchers estimate that a child born under a night sky with 250 visible stars will see fewer than 100 stars in the same darkness by the time he graduates from school. They suspect this recent trend towards brighter night skies is partly due to the installation of modern light-emitting diodes (LEDs), which emit more light at a given wattage than incandescent bulbs.

Satellites measuring global sky glare are often “blind” to the blue light produced by LEDs and cannot detect wavelengths below 500 nm. These shorter wavelengths also diffuse more easily in the atmosphere than longer wavelengths, creating a large haze that prevents the night sky from completely darkening.

“Despite (or perhaps because of) the use of LEDs in outdoor lighting, the visibility of stars is rapidly deteriorating,” the researchers wrote in their published paper.

“Having a lighting policy does not prevent sky lighting from increasing, at least on a continental and global scale.”

Public scientists from North America reported the largest increase in sky brightness, averaging 10.4 percent per year; The night sky over Europe lit up about 6.5 percent slower per year. While this is a rough average, the rest of the world sees light pollution illuminating the starry sky by 7.7 percent each year.

This surpasses estimates from satellite measurements of global sky brightness, which recorded a 2.2 percent increase in night sky brightness each year between 2012 and 2016, compared to an annual brightness of 1.6 percent 25 years ago. When scientists, most of them from North America and Europe, look at stars visible to the naked eye, they take into account changes in both the brightness and spectral profile of the night sky, regardless of whether the light is faint or not. more blue or redder, shorter or longer waves. In addition to what we know about the intense glow of artificial light, the study shows how quickly people are changing our view of the starry sky.