Imagine a space traveler arriving on our planet after a voyage of some years. She lands during the daytime, near the United Nations in New York City, and when she steps from her ship she has to shield her eyes. She has been away from her sun, from any sun, for so long that she’s unaccustomed to daylight; space is dark, though dotted with a billion points of light. Soon she’s ushered indoors to meet a long succession of diplomats and functionaries. Sometime that evening, she steps outside again, knowing that the planet has turned. Looking up, she expects to see the familiar blanket of bright dots, though in new arrangements, for the sky looks different depending on where you are, and she hasn’t been here before; maybe she hopes to glimpse, in particular, a few of those 12 constellations that some humans believe rule their lives. She is shocked. “My god—where are all the stars?” she asks, for only a handful are visible overhead.
Our visitor had taken the precaution of learning English before she arrived, but she knows nothing of sky glow. Also called light pollution, this is what happens when you pour so much artificial light into the night that it begins to suffuse the very air, brightening the sky, blotting out all but the most brilliant of stars and planets. A couple of things have reminded me of it lately.
In a story posted online Friday, The New York Times reported on the release of a new world atlas, one that graphs the brightness of the sky at night, based on recently collected data. The Times article includes an embedded version of the interactive atlas as well as a link to the atlas’s main page and a link to the Science Advances article that includes it. Whether or not sky glow is new to you, a few quotations are likely to give you pause. “One third of humanity cannot see the Milky Way,” says an Italian researcher quoted in the Times article. The Science Advances study adds, “More than 80% of the world and more than 99% of the U.S. and European populations live under light-polluted skies.”
As often in science, this new project follows on previous work. In 2003, NASA published a poster showing the Earth at night as a composite of many satellite images captured during the previous decade; the National Geographic Society published a similar poster in 2004 based on images from the previous year, which intriguingly includes gas flares, wildfires, and even nighttime fishing for squid. NASA published a new composite in 2012, and it released another one this year. Comparing the two most recent images* pretty clearly shows a greater spread of light across North America, Europe, India, and eastern Asia.
There’s a slight difference between what the composite images show and what the new atlas shows. The photographs depict the brightness of a particular area as seen from space; they show darkness where there are no lights. Thus, if you have any sense of geography, you can locate particular cities (at least on larger versions of these photos, such as you can find here for the 2012 image), and all the landmasses of Earth retain their borders. The atlas, on the other hand, depicts actual sky glow—it plots how bright the zenith point of the sky looks from the ground—and this spreads far beyond the cities where most of it originates. In the atlas, the English Channel is bridged by Anglo-French illumination, and the Strait of Gibraltar disappears into a wide blob of light. The less developed and undeveloped regions of the world are clear. By chance, I noticed that, apart from Pyongyang, North Korea is a veritable pit of gloom, while the lights of South Korea and Japan spread far into the seas around them.
To me, what’s most striking in the Times article has nothing to do with the new atlas. It’s the photo at the top of the story, showing a nighttime view from the north rim of the Grand Canyon. Above the geological carvings of the canyon, you can see a myriad of stars, including a grand swath of the Milky Way. You can also see something for which a science-fiction comparison may be the most apt: ominous glows on the horizon, as if invading Martians with their heat-ray weapons were blasting their way across the desert. Those aren’t Martians—the glow is us. It’s the light of our cities.
Given that many urban dwellers can no longer see the Milky Way, one wonders how children learn about it these days. Instead of a thing that your own parents can show you right outside your door, as it was when I was growing up, the Milky Way must have become one of those many lessons you’re expected to take on faith: like atoms or radio waves, you can’t see it, but you must believe it’s there. Marcin Wichary, who works for and writes for Medium, grew up that way and recently saw the Milky Way for the first time. “I felt,” he writes here, “a kinship with the world above.” Wichary’s pictures are stirring reminders of what the sky looks like when we can really see it. One of them is so big that you can’t view the whole image at one time. You’ll have to scroll it in your web browser, just as you’d have to move your head to take in the whole of the sky.
In our cities, can we hope to see again something like what Wichary saw in Joshua Tree National Park—the Milky Way itself, if not everything else? Can we arrange to show a future space visitor something better than a nearly blank prospect overhead? If we wait past sunset at the Grand Canyon, will we ever be able to confront the immemorial vistas before us and above us without being forcibly reminded of streetlights and neon from Las Vegas? Maybe not. The temptation is strong among us to believe, as Melisandre and others sometimes say on Game of Thrones, that the night is dark and full of terrors. Like moths, we flutter toward the light, or draw it around us. But a recognition has been dawning for some time that darkness has its place; a movement is afoot to change the balance. You’ll find some of its proponents mentioned in the Times article.
*I’m not absolutely sure about the provenance of the second image, but for various reasons I believe it to date from 2016.