Hiding in our brighter sky

WASHINGTON (AP) – Every year the night sky gets brighter and the stars appear dimmer.

A new study analyzing data from more than 50,000 amateur stargazers finds that artificial lighting makes the night sky about 10% brighter each year.

That’s a much faster rate of change than scientists had previously predicted by looking at satellite data. The research, which includes data from 2011 to 2022, was published Thursday in the journal Science.

“We are losing the possibility of seeing stars from year to year,” said physicist Fabio Falchi of the University of Santiago de Compostela, who was not involved in the study.

“If you can still see the faintest stars, you are in a very dark place. “But if you’re only seeing the brightest ones, you’re in a place with a lot of light pollution,” he said.

As cities expand and receive more light, the “sky glow” or “artificial twilight,” as the study authors call it, becomes more intense.

The 10% annual change is “much bigger than I expected – something you’ll clearly notice in a lifetime,” said Christopher Kyba, a physicist at the German Research Center for Geosciences in Potsdam and co-author of the study.

Kyba and his colleagues gave the following example: On a clear night, a child is born in a place where 250 stars are visible. By the time that child turns 18, only 100 stars are still visible.

Saying he hopes policymakers will do more to reduce light pollution, Kyba said, “This is real pollution affecting people and wildlife.” Limits are set in some areas.

Study data from amateur stargazers in the nonprofit Globe at Night project were similarly collected. Volunteers search for the constellation of Orion – remembering the three stars in its belt – and match what they see in the night sky to a series of charts showing an increasing number of surrounding stars.

Previous studies of artificial lighting using satellite images of the Earth at night had estimated the annual increase in sky brightness to be about 2% per year.

However, the satellites used cannot detect light with wavelengths towards the blue end of the spectrum, including the light emitted by energy-efficient LED bulbs.

According to researchers, more than half of the new outdoor lights installed in the United States in the last decade are LED lights.

Kyba said satellites are better at detecting light that scatter upwards, like a spotlight, than horizontally scattering light, such as the glow of a lit billboard at night.

Georgetown biologist Emily Williams, who was not part of the study, said Skyglow disrupts human circadian rhythms and other forms of life.

“Migratory songbirds normally use starlight to guide where they are in the night sky,” he said. “And when sea turtle babies hatch, they use it to direct light toward the ocean — light pollution is very important to them.”

Part of what is lost is a universal human experience, said Falchi, a physicist at the University of Santiago de Compostela.

“The night sky has been an inspiration for art, science and literature for all generations before us,” he said.


Follow Christina Larson on Twitter: larsonchristina


The Associated Press Department of Health and Science has support from the Howard Hughes Medical Institute’s Science and Education Media Group. The AP is solely responsible for all content.

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