WASHINGTON — Every year the night sky gets brighter and the stars dimmer.
A new study analyzing data from more than 50,000 amateur stargazers finds that artificial lighting makes the night sky 10% brighter each year.
That’s a much faster rate of change than scientists had previously estimated by looking at satellite data. The research, which includes data from 2011 to 2022, is published Thursday in the journal Science.
“We are losing, year after year, the possibility of seeing 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 faintest stars, you are in a very dark place. But if you only see the brightest ones, you are in a very light polluted place,” she said.
As cities expand and put up more lights, the «sky glow» or «artificial twilight,» as the study authors call it, becomes more intense.
The 10% annual change «is much larger than I expected, something you will clearly notice within your lifetime,» said Christopher Kyba, study co-author and a 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 seen on a clear night. When that kid turns 18, you only see 100 stars.
“This is real pollution that affects people and wildlife,” said Kyba, who said he hoped lawmakers would do more to curb light pollution. Some localities have established limits.
Data from the study of amateur stargazers at the non-profit organization balloon at night The project was compiled in a similar way. Volunteers search for the constellation Orion (remember the three stars on your belt) and compare what they see in the night sky to a series of graphs showing an increasing number of surrounding stars.
Previous studies of artificial lighting, which used satellite images of the Earth at night, had estimated the annual increase in the brightness of the sky is about 2% per year.
But the satellites used cannot detect light with wavelengths toward the blue end of the spectrum, including light emitted by energy-saving LED bulbs.
According to the researchers, more than half of the new exterior lights installed in the United States in the last decade have been LED lights.
Satellites are also better at detecting light that is scattered upward, like a spotlight, than light that is scattered horizontally, like the glow from an illuminated billboard at night, Kyba said.
Skyglow disrupts human circadian rhythms as well as other life forms, said Georgetown biologist Emily Williams, who was not part of the study.
«Migratory songbirds normally use starlight to orient themselves in the sky at night,» he said. “And when sea turtle hatchlings hatch, they use light to orient themselves toward the ocean; light pollution is a big problem for them.”
Part of what is being lost is a universal human experience, said Falchi, 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.