A universal human experience is fading: Sky gets 10% brighter each year, survey shows; previous estimate was 2%

Screenshot of interactive Light Pollution Map, which shows where skies are dark and bright all over the planet.

Seeing stars keeps getting more difficult because "artificial lighting is making the night sky about 10% brighter each year," according to a study that analyzed reports "from more than 50,000 amateur stargazers," reports Christina Larson of The Associated Press. "That’s a much faster rate of change than scientists had previously estimated looking at satellite data.

The research, which includes reports from the nonprofit Globe at Night project in 2011-22, was published Thursday in the journal Science. To illustrate the magnitude of the change, researchers "gave this example: A child is born where 250 stars are visible on a clear night. By the time that child turns 18, only 100 stars are still visible," Larson reports.

“We are losing, year by year, the possibility to see the stars,” which has been a universal human experience, said Fabio Falchi, a physicist at Chile's University of Santiago de Compostela, who was not involved in the study. “If you can still see the dimmest stars, you are in a very dark place. But if you see only the brightest ones, you are in a very light-polluted place.”

“This is real pollution, affecting people and wildlife,” Christopher Kyba, a study co-author and physicist at the German Research Centre for Geosciences in Potsdam, told Larson. "Kyba said he hoped that policymakers would do more to curb light pollution," Larson reports. "Some localities have set limits. . . . Prior studies of artificial lighting, which used satellite images of the Earth at night, had estimated the annual increase in sky brightness to be about 2% a year. But the satellites used aren’t able to detect light with wavelengths toward the blue end of the spectrum — including the light emitted by energy-efficient LED bulbs. More than half of the new outdoor lights installed in the United States in the past decade have been LED lights, according to the researchers. The satellites are also better at detecting light that scatters upward, like a spotlight, than light that scatters horizontally, like the glow of an illuminated billboard at night, said Kyba."

Georgetown University biologist Emily Williams, who was not part of the study, said skyglow disrupts circadian rhythms in humans and other forms of life: “Migratory songbirds normally use starlight to orient where they are in the sky at night. And when sea turtle babies hatch, they use light to orient toward the ocean – light pollution is a huge deal for them.”