There's a Reason Stars Appear Dimmer

Night sky is becoming 10% brighter per year, research shows
By Newser Editors and Wire Services
Posted Jan 19, 2023 6:50 PM CST
There's a Reason Stars Appear Dimmer
Dave Cooke observes the Milky Way over a frozen fish sanctuary in central Ontario in March 2021.   (Fred Thornhill/The Canadian Press via AP)

Every year, the night sky grows brighter, and the stars look dimmer. A new study that analyzes data from more than 50,000 amateur stargazers finds that artificial lighting is making the night sky about 10% brighter each year. That's a much faster rate of change than scientists had previously estimated from satellite data. The research was published Thursday in the journal Science, the AP reports. "We are losing, year by year, the possibility to see the stars," said Fabio Falchi, a physicist at the 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."

As cities put up more lights, skyglow or artificial twilight, as the study authors, who used data from 2011 to 2022, call it, becomes more intense. The 10% annual change "is a lot bigger than I expected—something you'll notice clearly within a lifetime," said Christopher Kyba, a study co-author. Kyba and his colleagues 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. "This is real pollution, affecting people and wildlife," said Kyba, who said he hoped that policymakers would do more to curb light pollution. Some localities have set limits.

Prior studies, which used satellite images of the Earth at night, had estimated the increase in sky brightness at about 2% a year. But the satellites used can't detect light with wavelengths toward the blue end of the spectrum—including light emitted by energy-efficient LED bulbs. Skyglow disrupts human circadian rhythms, as well as other forms of life, said a biologist who was not part of the study. Part of what's being lost is a universal human experience, said Falchi. "The night sky has been, for all the generations before ours, a source of inspiration for art, science, literature," he said.

(More night sky stories.)

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