The arkness was falling at the national observatory. The associate director would usually be inside preparing for a night on the telescope at this hour. She stood next to me in the dark, watching two worlds collide. As the stars came out, electric lights illuminated the landscape below, leaving a diminished Milky Way in the sky. He was taken aback by the huge city glow.

There was a bright bubble in the sky. A snake of lesser lights, called Interstate 10, traveled 100 miles north towards the glare of Phoenix. There was a half-circle from the lights of Nogales to the south.

The light on Kitt Peak is threatening to high-quality astronomy. Astronomers have taken steps to slow or reverse its spread over the years. It was a testament to local policy and millions of collective actions that the imperfect darkness overhead was a testament to the boundary of each dome.

The glow continues to spread. One Kitt Peak astronomer told me that it takes twice as long to resolve an astronomer's target as it usually would. Even though there are more obvious risks to the telescopes there, the subtle effects of ever brighter nights could eventually become a bigger threat to astronomy.

Many of our era's ecological disasters are difficult to see with the naked eye. Astronomers may have been the first to notice light pollution. It's impact is not limited to astronomy. Over the past ten years biologists have discovered that wasteful nighttime lighting affects animals, plants and the ecology of the world. The effects are far outside of cities. Kevin Gaston, a prominent U.K.-based biology professor, says that you need to think about it more like plastic pollution or climate change.

Light pollution can be reduced without sacrificing much. New research shows the scope of the problem, which makes it easier to fix it. Like smokestack emissions or factory wastewater, light pollution can be understood and managed. It's better to act sooner. Satellites show that more than three in five Europeans and four in five North Americans can't see the sky because it's too light. Earth's artificially lit surface area increases by 2 percent a year, making the map of true night into Swiss cheese. Consumers don't seem to be pocketing the savings from the new lighting technology that is more energy efficient. Humans seem to be turning on more lights.

This doesn't have to be the case. The rule of dark, star-filled skies can once again become the norm, easing the burden on already struggling ecosystems while restoring some heavenly wonder into ordinary human lives. Legislation aimed at achieving as much is already being drafted. Can we afford the necessary research to properly define and address light pollution? We don't know how much nighttime lighting we need. Does anyone pay attention?

It has always been difficult to assess the ecological consequences of bathing the world in a false twilight. Some creatures think a lamp is a call, while others think it's a repulsive field. Light's timing, wavelength, direction and intensity, as well as the eyes of the beholder, all matter, and unlike mercury in tuna or DDT in bald eagles, photons don't leave behind a long lasting chemical trace. Studies on at least 160 species show that artificial lights can cause a lot of trouble. It's a good idea to hide! The hunt is on. This is how to fly. It's time to change your metabolism.

One morning in May of last year, I drove out to a cattle farm in rural North Carolina to meet Murry Burgess, a graduate student at North Carolina State University who was decorating a barn with Christmas lights. She went up on a ladder and pulled out what looked like dinosaurs, one by one, and put them through a series of tests. She said that the light took a toll on the babies' bodies because the parents didn't know to move their nest away from it. When these birds were growing up under no lights, they were not as thin or as fat as they are today. Light goes all the way into their cells.

The harms of individual baby barn swallows operate on the scale of entire species. Artificial light can cause reef-building corals to stop spawning all at once, turning what should be a synchronized explosion of fresh life into useless puffs of eggs and sperm. Between one billion and hundreds of million birds die in the U.S. every year after being thwacked into windows.

The insects are facing a lot of problems. Scientists don't quite understand why the molts keep flapping into the light bulbs. Cricket calls are taking a back seat to the rhythms of the day and night. There are caterpillar populations in the British countryside. Although little research has focused on this grim end point, light pollution is almost certainly making the insect apocalypse worse.

Light pollution is felt through many different areas of life. Scientists used night-vision goggles to observe cabbage thistle plants and found that ambient light deterred insects from going to sleep. Plants bore less fruit because daytime pollinators couldn't make up the deficit. The mosquito Aedes aegypti, which causes a staggering 400 million infections a year, seems to be encouraged to bite more in the presence of light.

It used to be possible to document such observations in a single journal. In the late 1990s, a pair of graduate students and self-proclaimed environmental troublemakers in Los Angeles began building up a collection of stories. Catherine Rich tried to find an adviser who would allow her to study the effects of light pollution on wildlife, but she couldn't find one. She says she heard things like "you might not get any results." A seminal academic conference on the topic was organized by Rich and her husband.

In their 2002 conference, Longcore and Rich steered clear of another field of research, the ongoing exploration of what living in a brighter outdoors and brighter indoors does to human health. We know light exposure at night is associated with many problems, ranging from the obvious, like sleep disruption, to the more surprising, like higher breast cancer risk, but we don't know how much of this is from outdoor light pollution. Journalists and the public started to think that light pollution was real pollution. European ecology laboratories began cranking out their own results and meta reviews after picking up on the topic. Longcore and Rich's review paper has been cited over 1500 times.

The easiest type of light pollution to see is a single intense light source shining at you with the harsh glare of a new-model SUV. The light bubble effect I saw from Kitt Peak has been the focus of others. Ambient light pollution has biological consequences even with no specific light sources in sight.

A series of recent experiments, conducted in tanks and under domes bobbing in a German lake, showed that bright skies alone can cause sagging levels of melatonin. A paper published last year showed that dung beetles in South Africa look toward the stars to find their way to the savanna. A study led by Longcore showed that low thresholds of light on stretches of California beach can prevent birds from roosting.

Domes of light from skyglow are visible for hundreds of miles across state and international borders and studies show they lure birds and insects. In the rare corners of the planet where these domes haven't yet reached, organisms are already aware of the changes in lighting. plankton rise and fall in the winter in the Arctic Ocean despite the sun not setting. There could be artificial light from fishing or mining.

There is no organized opposition on the other side of the issue. Scientists say that current lighting trends are driven by millions of oblivious human decisions. Few communities have been able to slow down light's advance due to poverty and neglect.

Two weeks before my trip to Kitt Peak, I stood in the dark under the pines around the observatory looking up at the moon. As Earth's shadow slid across the face of the moon, the stars popped brighter, as if a photo editor were fiddling with the vista's contrast levels.

The downward view overlooking Flagstaff was one of the highlights of the experience. Individual stoplights shone back up. You could think that you were overlooking a sleepy coastal hamlet, not a mountain town that was hoping to lure tourists to the Grand Canyon. It looked like a small part of modernity had taught itself to sleep.

The most successful defenses of dark skies have been mounted in places where astronomy could thrive. Astronomers at the Lowell Observatory began to worry about the effects of spinning searchlights on their view of the sky around the same time as Silent Spring and modern environmentalism came about. The world's first light-pollution law was put on the books. The heartland of the dark sky movement has always been Arizona.

Astronomers and tribal guides from the Tohono O'odham nation rode on horseback to the top of Kitt Peak two years ago, to exchange stories about the stars. Bigger and better telescopes could be seen on the mountaintop after the federal government leased the land from the tribe.

As light pollution in nearby Tucson ballooned, Kitt Peak astronomy found allies such as Tim Hunter, a doctor who had grown up seeing the stars through elms in the Chicago suburbs. The International Dark Sky Association was formed in 1988 by Kitt Peak astronomer David Crawford and his friend Hunter.

Tools and techniques required to track darkness have been used by advocates over the years. Light-pollution modeling began with pen and paper equations. Satellite images started showing spidery webs of light spreading across the globe, and it was easy to measure skyglow from the ground. The general trend is dismal, the better researchers can study the problem, the worse it is.

Light pollution must not intensify as cities grow according to the IDA. The reason for banishing the night is usually crimeprevention. How do this works? The most conclusive evidence that light suppresses crime comes from an experiment begun in 2016 in which criminologists lugged nearly 400 basketball hoop–sized lighting towers into public outdoor spaces. The blue-white fixture were powered by their own portable fuel generators, which allowed them to stay on from sunset to sunrise.

The towers were much brighter than streetlights. The ethically dubious nature of any anticrime policy that relies on subjecting majority-minority communities to prison yard-esque floodlights all night long is something they note. According to a 2020 study from the University of Utah, Black, Hispanic and Asian American neighborhoods tend to be more illuminated at night than whites.

Aerial view of Miami streets and freeway lights at night.
Miami’s infrastructure forms a dazzling landscape of light. Credit: Vincent Laforet

There are many reasons for the proliferation of lights at night. Scientists say that brightness standards are driven by convention. Researchers from England and the U.S. scanned regulations in Europe. They concluded that there appears to be little, if any, credible empirical support for light levels recommended.

Many of the people who remain unreached or unmoved by the issue are industries. If you spend a lot of time in dark sky circles, you will hear about a curse: a moment of revelation, of veil lifting, when you suddenly see bad, wasteful lighting. On a walk in my Raleigh, N.C., neighborhood, I realized a richer, whiter section of blocks had dimmer amber streetlights, while the Black neighborhood had harsher white lights.

Activists took that curse as a call to action. Chris and I sat down at the Dark Sky Brewery in the city to watch the eclipse. He ordered a song called a "circadian rhythm." He settled for a brown beer after the on-the-nose brew ran out.

The former astronomer at the U.S. Naval Observatory knows more about dark sky science than most people. One colleague told me that he and his coalition are similar to John Muir. The dim orange streetlights here are due to the fact that blue-tinged light is more disruptive to most animals at night. A fog of light is created when bluer, shorter- wavelength photons scatter more readily.

He praised his town as a proof of concept that other communities could follow. The U.S. National Park Service deployed an ultrasensitive panoramic camera outside of both Flagstaff and the similarly sized city of Cheyenne, Wyo., which does not have similar dark sky ordinances. The bubble of trapped light around it was eight times larger. He has been trying to convince people that there is no conflict between growth and wilderness and that seeing the stars is a choice. Is it possible that stars will win out over light? "It's almost every time." Everybody needs to have their minds focused on something.

In the spring of 1942, Nazi Germany sent U-boats across the Atlantic to attack American ships. Cargo sank by the ton, drowned bodies washed up on the shore, and it soon became clear that the submarine gunners were picking off ships at night by watching for their dark silhouettes against the sky.

In cities such as Miami, elected officials and chambers of commerce were told to dim lights. This light pollution had dire consequences. Community leaders dragged their heels because of economic concerns. The U-boat attacks waned as defensive patrols were stepped up and communities for many miles inland restricted their use of nighttime lights. My late grandmother told stories about how serious it was to keep the lights off in Wrightsville Beach, N.C., when she was a teenager.

Christopher Kyba is a physicist and advocate for dark skies at the German Research Center for Geosciences. The U.S. government was able to control skyglow. We're not going to wait for a breakthrough technology. Collective will to act on smarter, more data driven guidance on unnecessary lighting can exist.

It's easy to imagine the planet's wealthier regions cranking out ever more wasted light powered by wasted carbon, evaporating the remnants of true night like water from a drying lake bed and subjecting life on Earth to an additional stressor. As a neighbor's garden sprinkler accidentally set to water the street, we could come to notice the stray light. The Milky Way can shine once more if it's restrained.

The pressure to dim the lights is growing. Proposed legislation is being reviewed by multiple U.S. states. In Texas cities such as Dallas and Houston, more than 100 downtown buildings dimmed their lights during the bird migration season. Since 2001, when the IDA began to recognize places where dark skies are being preserved, nearly 200 such sites have been certified around the globe.

bolder policies are happening in Europe Businesses in France are not allowed to illuminate their signs all night. Control of light pollution is one of the goals of the legal action plan developed by Germany. Dark sky–friendly, downward-pointing, long-wavelength lights are being added to the market by the manufacturers. The Holker Lab in Berlin has developed prototype lights that are not disruptive to most insects. The crazy thing about this problem is that it's so fixable.

It's difficult to care for what you haven't seen. The Milky Way is the greatest reward for limiting light pollution. Unlike residents of the American West who can summon its appearance with modest reductions in light, people in the more densely populated, brighter eastern U.S. can't get a good view of our universe. There are other points of view that can be considered.

A species of ghost firefly has been found near my home in the Piedmont of central North Carolina. The males of this species keep their lights on for up to 30 seconds at a time, scrawling faint, floating messages, and the females sit still below.

The population of this firefly was spotted in some of the state's most urbanized counties. They could have been wiped out before anyone knew about it. The entomologist searching for the species found a population in his own backyard. I asked him how long he had been living there.

I pulled up in his driveway in the middle of the night in order to get some reenchantment. A bullFrog bellowed in the background as we set out into the adjoining wood lot. We did not know the exact time of year to expect it or the weather. We were aware that darkness was needed.

The medium in which they communicate is light. Some firefly species don't bother to try because of the effects of light pollution. When we walked that night, the rays from our phones, streetlights, and neighbor's security lamp kept coming back in.

City lights of Las Vegas seen from an elevated distance at night.
A typical starless sky over Las Vegas, one of the brightest nighttime cities on Earth. Credit: Vincent Laforet

Three women were glowing from a shadowy spot of leaf litter. Their bodies were very large. Each firefly's star divided into two emerald dots, two side-by-side light organs cranking out their own feeble wattage into the scattered remnants of the dark, until that evening's shift ended.

*Editor’s Note (9/29/22): This sentence was edited after posting to correct the description of when the blue-white fixtures were left on.