The number of stars that humans can see with the naked eye has decreased significantly over the past decade.
The reason is “Skyglow” from artificial lighting – the brightness of this glow has increased every year since 2011.
Dr Christopher Kyba, a scientist at the German Geosciences Research Center in Potsdam, told the BBC: “Our view of the stars is being lost”.
He and his colleagues have published this discovery in the journal Science.
This is the result of 12 years of amateur astronomers and citizen scientists going out at night to count stars.
The change in the visibility of stars that people reported—by submitting their star counts to an online project called the Globe at Night—was equivalent to an annual increase in sky brightness of about 10% each year.
According to the scientists, this means that a child born in an area where 250 stars can be seen will likely see fewer than 100 stars in the same location 18 years later.
As light pollution researchers Fabio Falchi and Salvador Bará point out in an expert commentary published with the research: “When looking at images and videos of the Earth at night from the International Space Station, people are often fascinated by the ‘beauty’ of the city lights. If they were the lights on the Christmas tree.
“They don’t perceive that these are images of pollution. It’s like admiring the beauty of rainbow colors that gasoline creates in water and not realizing it’s chemical pollution.”
Dr Kyba said he hopes to see some signs of improvement in light pollution in recent years, as many city centers have recently changed their lighting to be more energy efficient. Towns and cities, especially in developed countries, are swapping old streetlights for modern LEDs, which are more carefully directed downwards where light is beneficial.
“The hope was that the situation would be better if the light was better directed,” he said.
“But there are so many types of lighting – streetlights, decorative, advertising. So, when it all comes together – and probably more lighting in general – [we’re] makes the sky shine worse.”
The relatively low cost of LED lighting also adds to the problem, according to a 2022 study by the European Space Agency.
The agency described this as a “lighting paradox” and explained: “While the LED lighting revolution promises to reduce energy consumption and improve human vision at night, overall [light pollution has] increased. Paradoxically, the cheaper and better the lighting, the higher society’s dependence on light.”
Light pollution doesn’t just reduce our view of the stars. It has been shown to affect human health and disrupt sleep patterns. It also affects the behavior of some nocturnal animals, and a recent study links it to local insect decline.
“It doesn’t have to be like that,” insists Dr Kyba. “There is a lot of room for improvement – if you light more carefully, you can reduce sky glare while continuing to illuminate the ground.
“And remember that light pollution is wasted energy. We keep releasing that light energy into the atmosphere, and maybe that’s not what we should be doing.”
Additional reporting by Kate Stephens
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