Brighter and Brighter: How Light Pollution Is Erasing the Stars

Data collected by citizen scientists reveals a dramatic increase.

Skyscrapers in the evening.Frank Rumpenhorst/Getty

This story was originally published by WIRED and is reproduced here as part of the Climate Desk collaboration.

Years ago, Christopher Kyba was skeptical about astronomy data collected by citizen scientists—after all, it relies on people making naked-eye assessments of the night sky. But when a student wrote to him with a question about measuring the sky’s brightness, he thought of the Globe at Night citizen science project, which launched in 2006 to let students track the stars they could see. He downloaded and pored over the data. “I became a complete convert,” says Kyba, a scientist at the German Research Center for Geoscience in Berlin. He has since devoted his career to studying light pollution and has now analyzed Globe at Night data from around the world to quantify its astonishing rise in recent years.

The project is run by the National Science Foundation’s NOIRLab, an astronomy research center in Tucson, Arizona. Volunteers—most of them in North America and Europe—are given eight possible maps of their local night sky, showing the stars visible at varying levels of sky brightness. The volunteers look outside and pick the map that best matches what they can actually see, based on the brightness of the faintest star they can spot at that moment. Then they make a brief report on the Globe at Night’s website using their phone, tablet, or computer. (A few citizen scientists, mostly amateur astronomers, also possess a light-intensity-measuring instrument called a Sky Quality Meter, and there’s a place on the website to mark its reading too.) 

In January, Kyba and his team published an analysis in the journal Science of the data collected between 2011 and 2022, revealing a dramatic increase in light pollution, with the night sky brightening nearly 10 percent annually over that decade. The striking trend means that, at least in some areas, the sky’s brightness is doubling every eight years. “It was a big shock. I like to be an optimist, but I keep getting kicked down by the data,” says Kyba.

For millennia, humans have peered into the heavens, and people around the world have seen a night sky that’s virtually identical to what their ancestors saw—save for the occasional star that dies by supernova. But in recent years, that has clearly changed. Artificial light from glowing urban areas continues to encroach into surrounding regions, while dark-sky areas, such as in minimally populated national and state parks in the United States, recede. (This is a different phenomenon from the problem posed by reflective satellites in orbit, which add artificial lights to the night sky.) Amateur and professional astronomers have been aware of light pollution for decades, if not centuries. Nevertheless, the problem keeps worsening.

Kyba and his team fit a model to the NOIRLab data, finding that every year the sky’s brightness has been rising by about 6.5 percent in Europe, 10.4 percent in North America, and 7.7 percent in the rest of the world, with a global average of 9.6 percent. The Globe at Night volunteers also reported that fainter stars are becoming less visible, and some are even disappearing from the dwindling sky. As Kyba conducted his research, people contacted him to say that they couldn’t discern the Pleiades anymore, or the iconic streak of Milky Way stars.

“I was kind of astounded at first,” says Connie Walker, who is a scientist at NOIRLab, director at Globe at Night, and a study coauthor. These findings dwarf the mere 2 percent rise previously estimated by weather satellites. But those spacecraft are completely blind to blue light, so they missed a big part of the trend, Walker says. Over the past decade or so, many cities have switched from yellow high-pressure sodium streetlights to energy-efficient but bluer LEDs—and people’s eyes (and those of some wildlife) are particularly sensitive to blue light at night. Satellites also miss lights that point sideways, like those from billboards. Overall, the brightness accumulates from sources like lights on the side of homes or businesses and on streets, stairways, and signs.

It’s possible that air pollution explains some of the trend in certain areas, but there’s no way it is increasing to such a degree, Kyba says. And while an individual citizen scientist’s assessments might vary or have some inaccuracies, those are cancelled out when reports from hundreds of thousands of volunteers are averaged, he says. Light pollution, he concludes, is the main culprit behind the vanishing stars.

Walker and other astronomers worry about a whole generation losing access to the starry night sky. “As an astronomer, it’s terrifying that we’re going to lose the inspiration that brings people into our field. There are millions of people in major cities who are lucky if they see Venus and Saturn. The moon is all they’ve got anymore,” says Teznie Pugh, superintendent of the University of Texas at Austin’s McDonald Observatory and cochair of the American Astronomical Society’s committee on light pollution, radio interference, and space debris. National policies or international regulations on light pollution may be tough to realize in the near future, so she and her colleagues are focused on drawing more attention to supporting local campaigns.

There are good reasons for nighttime lighting, including ensuring public safety. But that doesn’t have to be in tension with protecting the night sky, argues John Barentine, a Tucson-based astronomer and executive officer of Dark Sky Consulting, which advises companies and city officials on outdoor lighting use. He points to Tucson as a success story. The city and its outer regions have a population of about 1 million, but many residents understand how lighting affects the night sky—and it helps that there are major observatories in the vicinity. About five years ago, the city converted 20,000 streetlights to LEDs but chose a lower lumen output than many other cities. The city had been “overlighting” for years, Barentine says, and after reducing the street-level lighting by about 60 percent, city officials received almost no complaints about it being too dim. “I don’t see why the policies here can’t be exported to other places,” he says. “We know they work.”

More Mother Jones reporting on Climate Desk

WE'LL BE BLUNT

It is astonishingly hard keeping a newsroom afloat these days, and we need to raise $253,000 in online donations quickly, by October 7.

The short of it: Last year, we had to cut $1 million from our budget so we could have any chance of breaking even by the time our fiscal year ended in June. And despite a huge rally from so many of you leading up to the deadline, we still came up a bit short on the whole. We can’t let that happen again. We have no wiggle room to begin with, and now we have a hole to dig out of.

Readers also told us to just give it to you straight when we need to ask for your support, and seeing how matter-of-factly explaining our inner workings, our challenges and finances, can bring more of you in has been a real silver lining. So our online membership lead, Brian, lays it all out for you in his personal, insider account (that literally puts his skin in the game!) of how urgent things are right now.

The upshot: Being able to rally $253,000 in donations over these next few weeks is vitally important simply because it is the number that keeps us right on track, helping make sure we don't end up with a bigger gap than can be filled again, helping us avoid any significant (and knowable) cash-flow crunches for now. We used to be more nonchalant about coming up short this time of year, thinking we can make it by the time June rolls around. Not anymore.

Because the in-depth journalism on underreported beats and unique perspectives on the daily news you turn to Mother Jones for is only possible because readers fund us. Corporations and powerful people with deep pockets will never sustain the type of journalism we exist to do. The only investors who won’t let independent, investigative journalism down are the people who actually care about its future—you.

And we need readers to show up for us big time—again.

Getting just 10 percent of the people who care enough about our work to be reading this blurb to part with a few bucks would be utterly transformative for us, and that's very much what we need to keep charging hard in this financially uncertain, high-stakes year.

If you can right now, please support the journalism you get from Mother Jones with a donation at whatever amount works for you. And please do it now, before you move on to whatever you're about to do next and think maybe you'll get to it later, because every gift matters and we really need to see a strong response if we're going to raise the $253,000 we need in less than three weeks.

payment methods

WE'LL BE BLUNT

It is astonishingly hard keeping a newsroom afloat these days, and we need to raise $253,000 in online donations quickly, by October 7.

The short of it: Last year, we had to cut $1 million from our budget so we could have any chance of breaking even by the time our fiscal year ended in June. And despite a huge rally from so many of you leading up to the deadline, we still came up a bit short on the whole. We can’t let that happen again. We have no wiggle room to begin with, and now we have a hole to dig out of.

Readers also told us to just give it to you straight when we need to ask for your support, and seeing how matter-of-factly explaining our inner workings, our challenges and finances, can bring more of you in has been a real silver lining. So our online membership lead, Brian, lays it all out for you in his personal, insider account (that literally puts his skin in the game!) of how urgent things are right now.

The upshot: Being able to rally $253,000 in donations over these next few weeks is vitally important simply because it is the number that keeps us right on track, helping make sure we don't end up with a bigger gap than can be filled again, helping us avoid any significant (and knowable) cash-flow crunches for now. We used to be more nonchalant about coming up short this time of year, thinking we can make it by the time June rolls around. Not anymore.

Because the in-depth journalism on underreported beats and unique perspectives on the daily news you turn to Mother Jones for is only possible because readers fund us. Corporations and powerful people with deep pockets will never sustain the type of journalism we exist to do. The only investors who won’t let independent, investigative journalism down are the people who actually care about its future—you.

And we need readers to show up for us big time—again.

Getting just 10 percent of the people who care enough about our work to be reading this blurb to part with a few bucks would be utterly transformative for us, and that's very much what we need to keep charging hard in this financially uncertain, high-stakes year.

If you can right now, please support the journalism you get from Mother Jones with a donation at whatever amount works for you. And please do it now, before you move on to whatever you're about to do next and think maybe you'll get to it later, because every gift matters and we really need to see a strong response if we're going to raise the $253,000 we need in less than three weeks.

payment methods

We Recommend

Latest

Sign up for our free newsletter

Subscribe to the Mother Jones Daily to have our top stories delivered directly to your inbox.

Get our award-winning magazine

Save big on a full year of investigations, ideas, and insights.

Subscribe

Support our journalism

Help Mother Jones' reporters dig deep with a tax-deductible donation.

Donate