Years ago, Christopher Kyba was skeptical of astronomical data collected by citizen scientists. After all, that’s because humans rely on evaluating the night sky with the naked eye. But when a student asked about measuring the brightness of the sky, he thought of his Globe at Night citizen science project. This project he started in 2006 to help students track the stars they see. He downloaded the data and pored over it. “I have completely changed my mind,” said Kiva, a scientist at the German Geoscience Research Center in Berlin. analyzes to quantify the surprising increase in recent years.
The project is run by NOIRLab, the National Science Foundation’s Astronomy Research Center in Tucson, Arizona. A volunteer (mostly in North America and Europe) is given his eight possible maps of the local night sky, showing the stars visible at various levels of brightness in the sky. Volunteers look out and choose the map that best matches what they actually see, based on the brightness of the faintest star they find at that moment. Then use your phone, tablet, or computer to do a quick report on his website for Globe at Night. (A few citizen scientists, mostly amateur astronomers, also own a light intensity meter called the Sky Quality Meter, and there’s even a place on their website to mark their measurements.)
In January, Kyba and his team published an analysis in the journal chemistry Data collected between 2011 and 2022 revealed a dramatic increase in light pollution, with the night sky brightening nearly 10% annually during that decade. This striking trend means that, at least in some regions, the sky is doubling in brightness every eight years. “It was a big shock. I want to be an optimist, but data knocks me down so many times,” he says.
For thousands of years, humans have gazed into the heavens, and people around the world have seen night skies that are nearly identical to those seen by their ancestors. In recent years, however, that has clearly changed. Artificial light from bright urban areas continues to invade surrounding areas, while dark airspace such as sparsely populated US national and state parks recedes. (This is a different phenomenon than the problems caused by orbiting reflecting satellites, which add artificial light to the night sky.) Amateur and professional astronomers have been working for decades, if not centuries. I’ve been aware of light pollution for a long time. Nevertheless, the problem continues to get worse.
Kyba and his team fitted the model to the NOIRLab data and found that sky brightness increased by about 6.5% in Europe, 10.4% in North America and 7.7% in the rest of the world each year, for a global average of 9.6%. Globe at Night volunteers also report that fainter stars are disappearing and some are disappearing from the sky. said he could no longer discern the iconic streaks of the Pleiades star cluster or the stars of the Milky Way.
Connie Walker, NOIRLab scientist, Globe at Night director, and study co-author, said: These findings dwarf the meager 2% rise previously estimated by weather satellites. But these spacecraft are completely blind to blue light, so they missed much of the trend, says Walker. Over the past decade or so, many cities have switched from yellow, high-pressure sodium streetlights to more energy-efficient, bluer LEDs. Also, human eyes (and some wildlife eyes) are particularly sensitive to blue light at night. Satellites also miss sideways lights like billboards. Overall, brightness is accumulated from light sources such as the sides of a house or business, roads, stairs, and signs.
Air pollution may explain some of the trends in certain regions, but it hasn’t increased to such an extent, says Kiba. There may be errors and inaccuracies, he says, but they’re offset by averaging reports from hundreds of thousands of volunteers. He concludes that light pollution is the main cause of star disappearance.
So what can be done about it? “Light pollution activists often say, ‘It’s the easiest problem to solve just by turning off the lights.’ It’s true and it doesn’t help,” says Kiva. Decisions are made by many people, businesses and city officials. But unlike climate change, it’s not that hard to turn around, and the benefits are immediate. For example, it is not difficult or expensive to use only the minimum amount of light necessary, to have lights on timers when they are not needed at night, or to protect or point them down. It’s just a matter of convincing the thousands of people involved in lighting decisions at scale to make better choices.
Astronomers like Walker worry that an entire generation will lose access to the starry sky. “As astronomers, it’s scary to lose the inspiration that brings people into our field. There are millions of people in big cities who are lucky enough to see Venus and Saturn. University of Texas at Austin.” Tesney Pugh, president of the McDonald Observatory and co-chair of the American Astronomical Society Commission on Light Pollution, Radio Interference, and Space Debris, said: Such regulation may be difficult to achieve in the near future, so she and her colleagues are focusing on getting more attention to support local campaigns.
There are good reasons for night lighting, including ensuring public safety. But it doesn’t have to be in tension with protecting the night sky, says Dirk, a Tucson-based astronomer and executive director of his Sky Consulting, which advises businesses and city officials on outdoor lighting designs. Mr. John Valentine claims. He cites Tucson as a success story. Although the city and surrounding areas have a population of about one million, many residents are aware of the impact lighting has on the night sky, and having a major observatory nearby helps. About five years ago, the city converted 20,000 of her streetlights to LEDs, but opted for a lower lumen output than many other cities. For years, the city was “too bright,” Valentin said. After reducing street-level lighting by about 60%, city officials received few complaints about being too bright. “I don’t understand why the policy here can’t be exported elsewhere,” he says. “We know they work.”
