Of the 10,000 or so nights I've spent on this planet, I've never seen a completely dark night sky.
This doesn't make me unusual. In virtually every city across the United States — and increasingly, around the developing world — street lamps, outdoor signs, and car headlights are shining 24 hours a day, drowning out the stars above in a dull orange glow. For years, I've written about astronomical phenomena like meteor showers. But the sad truth is that, like most of the people reading and sharing these articles, I can barely see what's described in them.
Light pollution isn't exactly breaking news. But by nature, it's a problem that obscures its own severity. "We're losing the night sky so gradually that people don't quite realize what we're giving up," says Tyler Nordgren, an astronomer and dark-sky advocate. He worries that the older generation of people who grew up being able to see the Milky Way is disappearing — and today's children literally have no idea what our ancestors looked at every evening as they went to sleep.
I'm one of those kids. I grew up in the suburbs and live in a city: The night sky I know is flat and nearly featureless. But recently, I've been traveling to some of the few relatively dark spots east of the Mississippi. In Dolly Sods Wilderness, West Virginia, and Cherry Springs State Park, Pennsylvania, I've laid under overwhelming domes of stars, the ground lit by the shockingly bright river of the Milky Way. I've see meteors fly by on nights when there aren't showers — evidence of the fact that burning fragments of space rock are crashing into our atmosphere all the time, they're just mostly hidden by the glare of city lights.
This sky is an astonishing sight. It was once regular and banal, as inescapable as the weather. But despite the efforts of a small community of passionate astronomers, it's now disappearing faster than ever.
How we drowned out the night sky
Light pollution is a quintessentially modern environmental problem. For most of human history, nighttime illumination — in the form of fires, candles, and oil lamps — was precious and rare. In wealthy countries like the US, that began to change in the early 20th century with the spread of electricity and the incandescent light bulb.
The problem is that an ordinary street light is thousands of times brighter than the stars on a moonless night — and unless it's shielded, its light travels way beyond the area we intend to illuminate. An average outdoor light fixture emits a glow that affects the darkness of the night sky for about 15 miles or so in every direction, estimates John Barentine of the International Dark-Sky Association. One street light might not make a huge difference, but pack enough of these in one place — along with hundreds of excessively lit billboards, building exteriors, and parking lots — and you blot out the stars for miles and miles.
Still, it took until the 1970s and '80s for anyone to fully grasp the depth of the problem. "One big revelation was when we started sending back images of the Earth at night from space," says Carolyn Collins Petersen, a science writer and producer of the film Losing the Dark. "It was thought to be just an urban problem, but if you look at the pictures, there were very few places in the country that weren't affected." Even photos like this, though, undersell the severity of light pollution, because they don't capture how far glow can travel from cities into the countryside.
This led to the birth of what's now called the dark-sky movement, with astronomers initially organizing to fight light pollution in the areas surrounding their observatories. In 1989, Flagstaff, Arizona, enacted the first dark-sky code, restricting the brightness and color of outdoor lights. Still, the movement's successes have been limited: When I asked Barentine which major US city was doing the best job on light pollution, he said that it's basically getting worse in all of them.
Of course, it'd be one thing if this were an inescapable cost of doing business. It'd be hard to argue that we should give up safe nighttime travel and convenient indoor lighting just to see the stars.
But by and large, that's not the case. Barentine explains that it's outdoor lights that mainly contribute to light pollution, not indoor, and it turns out that blasting streets with light doesn't actually make them any safer. A number of different studies have looked at levels of street lighting and crime in various cities and found no clear correlation. This may be because excessive light makes it harder for us to see possible dangers lurking in the shadows — and because, as Nordgren bluntly puts it, "bad guys need to be able to see what they're doing too."
What's more, a surprising proportion of light pollution — the International Dark-Sky Association estimates 30 percent — comes from wasted light that shines in places where it doesn't benefit anyone in the first place. The majority results from poorly designed fixtures that emit light up into the sky, rather than focusing it on the ground. Lights that are left on at times and in places where no one needs them (think of the fully illuminated office buildings you sometimes drive by at midnight) also contribute. Just cutting out this waste could save a ton of energy and money — and could let us see the stars again.
What we lose when we lose the stars
As Vox's Brad Plumer has written, there are very tangible costs to light pollution. Most notably, it interferes with a huge range of organisms that have evolved to live under a dark night sky — including humans. Research shows that light pollution alters the migratory patterns of everything from birds to sea creatures, and it may disrupt our ability to get a good night's sleep.
But what prompted me to seek out dark skies was something a little different. Earlier this year, thousands of Facebook users shared an image promising that on August 27, Earth would pass uncommonly close to Mars, causing the red planet to appear as big in the sky as the full moon. The meme wasn't new: It appears to have originated in a 2003 viral email, and it seems to pop up every year in August.
Of course, Mars never looks as big as the moon. But the part of the meme that really depressed me was that we actually can see Mars if we know where to look — and if our skies aren't too polluted with excess light. For much of the year, it appears as a dot, an unusually bright and large star touched with a tinge of red. That this rumor surfaces over and over again shows just how divorced we are from our night sky.
There are other factors contributing to this disconnect besides light pollution. Appreciating the night sky is a slow, meditative process. Even if you're somewhere dark, you have to wait for 20 minutes or so, without looking at your phone, to let your eyes adjust. And even something as dramatic as a meteor shower reveals its wonders slowly — you have to patiently take in the whole sky for minutes or hours to get a brief glimpse of a shooting star. It's the opposite of a news feed: a barely changing field hiding just a few bits of remarkable information.
Still, when I drove and hiked into the forests of Pennsylvania and West Virginia, I became convinced that if city dwellers had a chance to see this sky, they'd happily put down their phones for it. It was peppered with stars in every direction, but the truly astounding thing was that the longer I looked at any given spot, the more and more points of light emerged from the darkness. I understood why, when Bronx native Neil deGrasse Tyson first went to a planetarium at age 9, he was convinced the projection was a hoax. This sky had depth: It wasn't a 2D surface, like a planetarium's, but a 3D field. I was enclosed in a cup of stars, looking straight out the windshield of the hurtling spaceship that is Earth.
Each tiny point of light was really a gigantic, burning orb of hydrogen, billions of miles away. The rich, cloudy ribbon of white cutting diagonally across the sky was a cross-section of the disc that is our galaxy, made up of hundreds of billions of stars, many of which are orbited by planets of their own. Over the course of hours, the stars seemed to migrate across the sky, but in reality, the Earth was moving underneath me. Like Carl Sagan's famous "Pale Blue Dot" photo, the sight briefly allowed me to grasp our true, unlikely position in the universe. Every single one of us, everywhere we go, is pinned to the surface of a tiny, spinning sphere, surrounded by an unimaginably vast cluster of stars.
The moment passed. I eventually returned to a world filled with smartphones and computers, a universe where I and many other people spend an inordinate amount of time looking down. You can come up with practical reasons why this is a problem — some experts worry that a lack of dark skies could make kids less likely to get into space or other STEM fields — but I've become convinced there's something deeper at stake: a sense of where we are.
"Increasingly, our concept of the universe simply stops at the atmosphere," says Nordgren, the astronomer. "We're raising a generation that believes there's just nothing to see past that. So why even bother looking up?"
We could still restore the stars — or drown them out entirely
As bright as the skies already are in many places, we're at a particularly pivotal moment for light pollution for a few different reasons.
In the US, many of the street lights first built in the 1950s and '60s are due for replacement. These lights broadcast light up and out, contributing hugely to light pollution, whereas newer "full-cutoff" models focus illumination downward. The International Dark-Sky Association and other advocates have been trying to convince cities to require these sorts of fixtures, but they're far from universal.
And there's another new technology that could present problems: white LEDs. Cities like New York and Los Angeles have been using them to replace the older yellow sodium lights many of us are familiar with, and LA has even billed them as a way to reduce light pollution.
But some experts say they can have just the opposite effect. For one, they're more efficient, allowing cities to produce more light while using less electricity, which could lead to brighter streets overall, as some residents have complained about in New York. An even bigger problem is that they produce more light in the shorter, blue wavelengths, which scatters more widely in the atmosphere. "Right now a city that's 100 miles away is not a big contributor to light pollution where you live," says Barentine. "But if cities convert to LED street lights, that can influence spread for thousands of square miles." As a result, he worries that within a generation, there might just be a few patches of true darkness left in the continental US, mostly in remote areas of the West.
There are solutions, such as yellow LEDs, as well as timers and sensors that ensure lights are only on when we actually need them — say, cutting them off at 3 am, unless people are actually on the street. Municipal codes that limit the amount of light individuals and businesses can emit could also make a huge difference.
But right now, just a few cities in the US have been proactive in adopting these measures. Worldwide, 49 municipalities and parks (including Cherry Springs) have officially designated themselves "International Dark-Sky Places," strictly limiting light pollution. In Flagstaff, for instance, property owners are only allowed to emit specific amounts of light, based on the size of their property, and the majority of it must be produced by shielded fixtures that solely broadcast light downward.
Across the vast majority of the country, though, light pollution seems to be getting worse — and doing so at a rate faster than population growth. One reason is that increasingly efficient fixtures allow us to produce more light at a lower cost, a phenomenon economists call the Jevons paradox. (One example of the phenomenon in action: the rows of giant animated LED screens that have replaced static billboards along many urban highways.) And the transition to bright skies at night seems to be happening even more rapidly in the developing world, with many cities getting more reliable access to electricity and quickly putting into place Western-style, overlit streets.
Today, it's hard for many people to believe the skies our grandparents and great-grandparents saw on a regular basis growing up; I had to venture far away from small towns just to get a rough idea of them. If nothing changes, it's very possible that our current urban night skies — with a handful of stars here and there peeking through a blanket of orange glow — will eventually also seem like a quaint relic of premodern times, an era before we drowned out the night sky entirely.