WASHINGTON –
Every year the night sky gets brighter and the stars seem dimmer.
A new study that analyzed data from more than 50,000 amateurs found that artificial lighting makes the night sky about 10 percent brighter each year.
That’s a much faster rate of change than scientists had previously estimated by looking at satellite data. The study, which includes data from 2011 to 2022, was published Thursday in the journal Science.
“Year by year we lose the opportunity to see the stars,” said Fabio Falci, a physicist at the University of Santiago de Compostela who was not involved in the study.
“If you can still see the darkest stars, you are in a very dark place. But if you’re only seeing the brightest, you’re in a very light-polluted place,” he said.
As cities expand and put in more lights, the “sky glow,” or “artificial twilight,” as the study authors call it, becomes more intense.
The 10 percent annual change “is much larger than I expected — something you will notice clearly within your lifetime,” said Christopher Kiba, study co-author and a physicist at the German Research Center for Geosciences in Potsdam.
Kiba and his colleagues gave the following example: A child is born where 250 stars are visible on a clear night. By the time this child turns 18, only 100 stars are still visible.
“This is real pollution that affects people and wildlife,” said Kiba, who said he hopes politicians will do more to curb light pollution. Some settlements have certain restrictions.
Survey data from amateur stargazers at the non-profit Globe at Night Project was collected in a similar manner. Volunteers look for the constellation Orion – remember the three stars on its belt – and match what they see in the night sky with a series of charts showing an increasing number of surrounding stars.
Previous studies of artificial lighting, which used satellite images of Earth at night, had estimated the annual increase in sky brightness at about 2 percent per year.
But the satellites in use are unable 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 over the past decade were LED lights, according to the researchers.
Satellites are also better at detecting light that scatters upward, like a floodlight, than light that scatters horizontally, like the glow of an illuminated billboard at night, Kiba said.
Skyglow disrupts the human circadian rhythm, as well as other life forms, said Georgetown biologist Emily Williams, who was not part of the study.
“Migrating songbirds typically use starlight to navigate where they are in the night sky,” she said. “And when baby sea turtles hatch, they use light to navigate the ocean — light pollution is a huge deal for them.”
Part of what is being lost is a universal human experience, said Falci, a physicist at the University of Santiago de Compostela.
“The night sky has been, for all generations before ours, a source of inspiration for art, science, literature,” he said.
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The Associated Press Health and Science Division is supported by the Science and Education Media Group of the Howard Hughes Medical Institute. AP is solely responsible for all content.
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