Twinkle, twinkle fading stars: Hiding in our brighter skies

Every year, the night sky grows brighter, and the stars look dimmer.

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

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

“We are losing, year by year, the possibility to see 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 dimmest stars, you are in a very dark place. But if you see only the brightest ones, you are in a very light-polluted place," he said.

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

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

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

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

The study data from amateur stargazers in the nonprofit Globe at Night project was collected in a similar fashion. Volunteers look for the constellation Orion – remember the three stars of his belt – and match what they see in the night sky to a series of charts showing an increasing number of surrounding stars.

“The night sky has been, for all the generations before ours, a source of inspiration for art, science, literature," he said.

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