Light Pollution Study: Stars dim in artificial light

WASHINGTON – Every year the night sky gets brighter and the stars look 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 estimated using satellite data. The research, which includes data from 2011 to 2022, is published in the journal on Thursday Science.

“We lose the ability to see the stars year after year,” 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 faintest stars, you are in a very dark place. But if you only see the brightest ones, you’re in a very light-polluted place,” he said.

As more cities expand and put up more lights, “skyglow,” or “artificial twilight,” as the study authors call it, becomes more intense.

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

Kyba and his colleagues gave this example: A child is born where 250 stars are visible on a clear night. When the child turns 18, only 100 stars will be visible.

“This is real pollution that is affecting people and wildlife,” said Kyba, who said he hoped policymakers would do more to curb light pollution. Some places have limits.

The study data of amateur stargazers in the non-profit organization globe at night Project was collected in a similar way. Volunteers look for the constellation of Orion – remember the three stars in its belt – and match what they see in the night sky against a series of charts showing an increasing number of surrounding stars.

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

But the satellites used are unable to detect light at wavelengths on the blue end of the spectrum – including the light emitted by energy-efficient LED lamps.

According to the researchers, more than half of the new outdoor lights installed in the United States over the past decade have been LED lights.

The satellites are also better at detecting light that’s scattered upward, like a spotlight, than light that’s scattered horizontally, like the glow of a lit billboard at night, Kyba said.

Skyglow disrupts the circadian rhythm of humans as well as other life forms, said Georgetown biologist Emily Williams, who was not involved in the study.

“Migratory songbirds typically use starlight to orientate themselves where they are in the sky at night,” she said. “And when baby sea turtles hatch, they use the light to orient themselves by the ocean – light pollution is a big deal for them.”

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

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