Light pollution covers the night sky. RIP Stargazing
A citizen science initiative called Globe at Night offers sobering news to humanity. Our artificial light is drowning out the night sky for more and more people. And it’s happening faster than you think.
Earth at night is an international citizen science project of the National Science Foundation’s NOIRLab. It raises awareness of light pollution and how it affects our view of the night sky. A new research paper based on Globe at Night observational data shows that the average night sky has brightened by 10% each year under artificial light over the past 11 years. And as our artificial light brightens, more and more stars are obscured.
The paper is “Citizen scientists report a global rapid decline in star visibility from 2011 to 2022,” and it was published in the journal Science. The lead author is Christopher Kyba, a researcher at the German Center for Geosciences.
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We should be able to see several thousand stars on a clear night. We should also be able to see the great arc of the Milky Way. But it’s getting harder and harder for more and more people. Our growing artificial lighting is responsible, but difficult to measure with satellites. Much of our artificial light is spread horizontally, which satellites cannot measure effectively.
The authors of this article obtained their data from citizen scientists who participated in Globe at Night. The participants evaluated their view of the night sky by comparing it to ordinary pictures. The images were calibrated to show the night sky as seen by each participant at their location on Earth. The images are in a gradient so that each shows progressively fewer stars to mimic increasing light pollution. Participants then selected the image that best matched their actual view. The data gives an estimate of the limiting magnitude with the naked eye. It tells you how bright a sky object must be to see.
Research shows that our increasing light pollution is having a profound effect. About 30% of people around the world and about 80% of people in the United States can no longer see the Milky Way. This is changing faster than scientists thought. But they’ve based their conclusions on satellite data, which has trouble measuring the glow of surface light. Globe at Night collects data about the country, and this study is a wake-up call.
At a time when war is raging in Europe and humanity is facing climate change, the changes in the night sky may not seem very impressive. But there is something poignant and sad about it. The night sky is part of humanity’s natural and cultural heritage. And it is fading before our eyes.
However, this is about more than humanity’s contemplative relationship with the night sky, something that goes back far into prehistory. Increasing artificial lighting conflicts with our natural day/night cycles and can be detrimental to human sleep cycles. It is also harmful to wildlife because their natural cycles have also evolved alongside the natural day/night cycle. Not only can our artificial lighting disrupt the habitat in the same way as a bulldozer, it also disrupts predator-prey relationships, as predators use light to hunt and prey use darkness to hide. It also drives nocturnal animals away from our lighted areas.
In an interview at Darksky.org, study leader Christopher Kyba said, “The introduction of artificial light represents probably the most drastic change humans have made to their environment. Predators use light to hunt, and prey species use darkness for protection,” Kyba explained. “The cloudy sky near the cities is now hundreds or even thousands of times brighter than 200 years ago. We’re only just beginning to learn how drastic an impact this has had on the nocturnal ecology.”
We know intuitively that we light up the night sky as more and more of us live in ever larger cities. However, collecting data has been difficult. This is where Globe at Night comes in. Since 2006, they have been collecting data on the visibility of stars. In their article, the authors analyzed more than 50,000 observations Earth at nightt in 2011-2022.
The data illustrates the growing price we pay for our light pollution. It shows that for the average Globe at Night user, the sky brightens by 9.6% every year. During the average person’s childhood, which lasts 18 years, the brightness of the night sky increases fourfold. This is not true for all places on Earth, so it wouldn’t be so bad for people in rural or remote areas. But for people living in cities or urban suburbs, it’s probably even more obvious.
“At this rate of change, a child born in a place where 250 stars were visible would only see about 100 by the time they turn 18. said lead author Kyba.
Kyba was also the lead author of a 2017 research paper looking at artificial light. Its title is “The artificially lit surface of the earth at night increases the radiance and extent”, and was published in the journal Science Advances.
Some of our lighting problems are related to technology. The development of LED street lights created more energy-efficient lighting, which has reduced the lighting costs of outdoor areas. However, lower energy lighting technology has not reduced the light because it is cheaper to run. People can use it more without paying more. “Regardless of historical or geographic context, people tend to use as much artificial light as they can buy for ~0.7% of GDP,” note the authors of the 2017 study.
Humanity grew up under the night sky, and evidence from ancient cultures makes that clear. Numerous ancient structures still standing today were oriented towards the celestial bodies in the night sky and the changing seasons. These are called archaeoastronomical structures and archaeoastronomical observatories. From Machu Picchu In Peru Gaocheng In China, these structures show how strong the relationship was between people and the sky. (There is even evidence that the Incas used the observatory at Machu Picchu for observation The Pleiades and schedule corn sowing.)
For the majority of people, our connection to nature through the night sky is broken. But all is not lost. Part of that depends on how much we value the night sky and what policies we’re willing to put in place. The Globe at Night project is important because it illustrates what it’s all about.
From the paper: “We draw two conclusions from these results. First, star visibility is rapidly declining despite (or perhaps because of) the introduction of LEDs in outdoor lighting applications. Current lighting practices are not preventing the increase in skylight, at least continentally and globally. Second, naked-eye observations by citizen scientists provide complementary information to satellite datasets.
“The increase in skyglow over the past decade underscores the importance of redoubling our efforts and developing new strategies to protect dark skies,” said study co-author Constance Walker of the National Optical Astronomy Observatory. “The Globe at Night dataset is essential to our ongoing assessment of skyglow changes, and we encourage everyone who can to contribute to protecting the starry sky.”
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