From the moment I first encountered Bortle’s scale, I wondered about the places I had visited and lived and loved, like the lake in northern Minnesota where as a child I first experienced real darkness and began to learn about night. I wondered as well if there were any Bortle Class 1 places left in my country. Another way to phrase that question is this: In the Lower 48 states, are there any places left with natural darkness? Or, yet another way, Is every place in my country now tarnished by light?
I decided to find out. I would travel from our brightest nights to our darkest, from the intensely lit cities where public lighting as we know it began to the sites where darkness ranking a 1 might still remain. Along the way, I would chronicle how night has changed, what that means, what we might do about it, and whether we should do anything at all. I wanted to understand especially how artificial light can be both undeniably wonderful, beautiful even, and still pose a long list of costs and concerns. I would start in cities such as Las Vegas—in NASA photographs the brightest pixel in the world—and in Paris, the City of Light. I would travel to Spain to explore “the dark night of the soul” and to Walden Pond to check in with Thoreau. I would meet with scientists, physicians, activists, and writers working to raise awareness of the value of darkness and the threats from light pollution: the epidemiologist who first connected artificial light at night with increased rates of cancer, and the retired astronomer who founded the world’s first “dark sky” organization; the minister who preaches the necessity of the unknown, and the man whose work has saved countless nocturnal migrating songbirds in several major cities—it’s through people like these that I would tell this story.
My first move was to contact Chad Moore, a founder of the National Park Service’s Night Sky Team. For over a decade, Moore has been chronicling levels of darkness in the U.S. national parks, and I wanted to know what he thought I would find.
“Well,” he explained, “as you slide down this ramp from nine to one into darkness it’s not a smooth slide. It’s … bumpy.” Moore explained that with the Bortle scale, while the difference between 9 and 5, or between 5 and 2 would be obvious to anyone, the difference between 9 and 8 or between 2 and 1 can be difficult to discern. “There’s so much fuzziness that it’s prone to misinterpretation, and so if you’re grumpy you’ll give yourself a five, and if you’re optimistic you’ll give yourself a three … and it’s really a four,” he laughed.
That made sense, but are there still any Class 1 places left in the United States?
“There are rare places and rare moments where places in the U.S. compare with the rest of the world,” he said. “I would like to think that I’ve seen that, that I’ve glimpsed Class One. But it takes some diligence. It’s easier to get a plane ticket to Australia and drive out past Alice Springs … It could take a while before you find that combination here in the United States.”
Satellite photographs of the earth at night tell of two worlds—the illuminated civilization of developed (and developing) countries and the darkness of poor or uninhabited areas—and in some ways Moore is right; it would be easier to fly somewhere exotic and remote. But I wanted to know night closer to home. I wanted to know the darkness we experience in our daily life.
I decided to focus my journey on North America and western Europe. First, this is where the artificial lighting now sprawling over the world began and where it continues to evolve: It is Western thinking about darkness and light—and Western technology—that shapes the developed world’s night. Second, few of us will ever fly to Australia and drive out past Alice Springs, but we all experience night where we live and work and love.
And most of us, if we wanted, could get ourselves out to real darkness closer to home, like the darkness of a rural highway in eastern Nevada.
“Our sun is one star in a disk-shaped swarm of several hundred billion stars,” writes astronomer Chet Raymo. That disk-shaped swarm is our Milky Way Galaxy, and what arcs in three dimensions above this dark Nevada desert is the outer arm of that spiral, toward which we look from our inner-galaxy location. Raymo continues:
I have often constructed a model of the Milky Way Galaxy on a classroom floor by pouring a box of salt into a pinwheel pattern. The demonstration is impressive, but the scale is wrong. If a grain of salt were to accurately represent a typical star, then the separate grains should be thousands of feet apart; a numerically and dimensionally precise model of the Galaxy would require 10,000 boxes of salt scattered in a flat circle larger than the cross-section of the Earth.
This means that every star in our night sky, every individual star any human has ever seen with his or her naked eye, is part of our galaxy and its “several hundred billion stars.” Outside our galaxy exist innumerable other galaxies—one recent estimate put the number at 500 billion. At some quick point the size of the universe becomes overwhelming, its distances and numbers bending our brains as we try to comprehend the incomprehensible—that our night sky is but one tiny plot in a glowing garden too big to imagine.
But of course, for all of human history we have indeed imagined. Ancient civilizations from North America to Australia and Peru created constellations not only from groups of individual stars but even from the black shapes made by the gas and dust that lie between Earth and our view of the Milky Way’s smokelike stream. And for ages we imagined it might well be smoke, or steam, or even milk—not until 1609 did Galileo’s telescope confirm what he suspected, that the Milky Way’s glow was the gathered light of countless stars.
In these countless stars, in their clusters and colors and constellations, in the “shooting” showers of blazing dust and ice, we have always found beauty. And in this beauty, the overwhelming size of the universe has seemed less ominous, Earth’s own beauty more incredible. If indeed the numbers and distances of the night sky are so large that they become nearly meaningless, then let us find the meaning under our feet. There is no other place to go, the night sky makes this clear.
So let us go dark.
From a Starry Night to a Streetlight
It often seems to me that the night is much more alive and richly colored than the day.
—VINCENT VAN GOGH (1888)
The growth of light pollution in the United States from the 1950s to the 1990s, and what light pollution might look like in 2025. (P. Cinzano, F. Falchi [University of Padova], C. D. Elvidge [NOAA National Geophysical Data Center, Boulder]. Copyright Royal Astronomical Society. Reproduced from the Monthly Notices of the Royal Astromical Society by permission of Blackwell Science.)
The brightest beam of light on Earth shoots from the apex of the Luxor casino’s black pyramid in Las Vegas, thirty-nine brilliant blended xenon lamps, each six feet tall and three feet wide (the greatest number of lamps they could fit in the space), reflecting off mirrors and marking, like a push-pin on the night map of the known world, the brightest city on earth. New York, London, and Paris, Tokyo, Madrid, and a slew of cities in China—with their larger geographies and populations—may send more light into space overall than this single desert city in the American Southwest. But the “overall” qualifier is important, for it would be foolish to think there is any brighter real estate in the world than the Las Vegas Strip.
Standing on the corner of Las Vegas Boulevard and Bellagio Drive, I am immersed in artificial light, subsumed in the accumulated glow from the city’s thousands of businesses and tens of thousands