28 January 2023
A new study has found that light pollution is making the night sky brighter and the stars dimmer.
The study examined data from more than 50,000 citizen star watchers across the world. It found that man-made, or artificial, lighting is making the night sky about 10 percent brighter each year.
Data for the study was collected from 2011 to 2022. The research findings recently appeared in the publication Science.
In this file photo, Dave Cooke observes the Milky Way over a frozen fish sanctuary in central Ontario, north of Highway 36 in Kawartha Lakes, Ontario, Canada, early Sunday, March 21, 2021. (Fred Thornhill/The Canadian Press via AP)
The result was a much faster rate of change than scientists had estimated in the past.
"We are losing, year by year, the possibility to see the stars," said Fabio Falchi. He is a physicist at the University of Santiago de Compostela in Spain. He was not involved in the study.
"If you can still see the dimmest stars, you are in a very dark place," Falchi said. "But if you see only the brightest ones, you are in a very light-polluted place."
As cities expand and put up more lights, a "skyglow" is created in the sky. Skyglow is a term scientists use to describe light that becomes more intense.
Christopher Kyba is a physicist at the German Research Centre for Geosciences in Potsdam. He was a co-writer of the study. He told The Associated Press that the 10 percent change was "a lot bigger" than he had expected.
The research team gave an example to explain the result. If a child is born where 250 stars can be seen on a clear night, by the time that child turns 18, only 100 stars will be seen.
"This is real pollution, affecting people and wildlife," Kyba said. He urged policymakers to do more to reduce light pollution. Some communities have set limits.
Past studies involving artificial lighting used satellite images of the Earth at night. They had estimated the yearly increase in sky brightness to be about 2 percent a year.
But the satellites used are not able to identify light with wavelengths toward the blue end of the spectrum – including light given off by energy-effective LED bulbs.
The researchers noted that more than half the new outdoor lights put in across the United States during the past 10 years have been LED lights.
The satellites are also better at finding light that gets spread upward – like a spotlight – than light that spreads out from side to side, Kyba said.
Skyglow affects human circadian rhythms as well as other forms of life, said Georgetown University biologist Emily Williams. She was not part of the study.
"Migratory songbirds normally use starlight to orient where they are in the sky at night," Williams said. "And when sea turtle babies hatch, they use light to orient toward the ocean – light pollution is a huge deal for them."
Falchi, the physicist at the University of Santiago de Compostela, said part of what is being lost is a universal human experience. "The night sky has been, for all the generations before ours, a source of inspiration for art, science, literature," he added.
I'm Bryan Lynn.
The Associated Press reported this story. Bryan Lynn adapted the report for Learning English.
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Words in This Story
dim – adj. not bright or clear
spectrum – n. all the different ideas, opinions and possibilities that exist
bulb – n. a glass object that contains a wire and produces light from electricity
circadian rhythms – n. a natural cycle of physical, mental and behavioral changes that the body goes through in 24 hours
orient – v. to direct something toward the interests of a particular group
hatch – v. to produce young by incubation: to sit on eggs to get them to open by the warmth of the body
inspiration – n. someone or something that gives you ideas for doing something