I don’t know why you get out on the Appalachian Trail, but for me it’s always been an escape. Going for a hike powered by my own two feet and sleeping under the stars, I can escape the modern world. For huge stretches of Trail, I lose sight of the 21st Century and walk through a world of trees, streams, waterfalls, and mountains. As light pollution increases though, that sense of escape becomes more difficult at night.

Just the phrase, “sleeping under the stars” evokes an image of childhood for me. I was a Boy Scout in Oregon and then Alaska as my father moved from one job to another. As a kid, I first saw the Milky Way from the Pacific Crest Trail near Mount Hood in Oregon and still remember what it was like seeing a sky splashed full of stars reflected in the lake beside which we camped. It was our universe: an infinite expanse even greater than the distant ridgeline of trees or the more distant mountains of the Cascades to north and south. I felt I could get lost in that starry sky and who knows what wonders there might be out there among those stars? In Alaska, I fell in love with the aurora borealis during the long dark winter months and still remember what it was like to have them light up the snow around me on the frozen lake where our troop had set up our tents. No wonder I eventually became an astronomer.

But even as I gained access to some of the world’s largest telescopes and wrote papers on dark matter and pulsating stars, I never forgot where my love of the sky started. I once spent a year traveling the country working with National Park Service rangers and writing a book on all the ways visitors could experience astronomy in the parks. I led tours to see the aurora in Alaska and have trained river rafting guides in the Grand Canyon how to answer the question, “what star is that?” and “why are there so many more stars here than at home?” Because those visions of stars, the Milky Way, and even the northern lights, are becoming harder to see every year.

Eighty percent of Americans and Europeans can no longer see the Milky Way from their homes. When I first started paying attention to this issue back in 2005, that number was 66 percent, so getting to experience a dark sky is becoming more elusive and requires greater travel every year. Yet, even when I am able to finally reach a place where I can see the Milky Way overhead, often it is just a pale imitation of what it could be. Artificial light knows no regional boundary and distant cities and towns (or coal mines and oil wells) create “light domes” that illuminate the clouds, cast shadows on the ground, and reduce the light of our galaxy — the light of over 400 billion stars — into a faint smear across the sky. The world around me that I have come to see in all of its beauty is being rendered pale and muted at night. We have allowed a fog of light to blow in on our natural landscape and render the universe beyond our own atmosphere a little more invisible every year, and it has happened so slowly that few have even noticed.

I’m an astronomer, but I’ve also traveled all over the world to observe the sky both professionally and as a tourist (and now tour leader). I’ve seen the heart of our galaxy from the Outback in Australia and high in the Chilean Andes after a solar eclipse. I once stargazed my way across the Atlantic on a four-masted sailing ship and I’ve seen a star-filled sky while hiking the Continental Divide. I care about the darkness because I know what I am missing due to light pollution. But why should anyone else?

Fireflies in the Wild East near Dover, New York – By Julian Diamond.

The Wild East initiative acknowledges that what makes the Trail special is more than just the dirt of the path. It’s the landscape around it, an interconnected tapestry of plants, animals, waterways, geography, and sky. Sacrifice any one of these threads and the cloth unravels. The sky is an integral part of that whole. Think about the nocturnal animals that hunt, feed, mate, and survive under the darkness of night. Under most skies in the eastern United States, true darkness no longer falls. In more urban areas along the Trail, the sky can be almost as bright as moonlight, every night, especially on nights where clouds reflect our urban lighting back down to us. Yet hikers can still find pockets of darkness in some of those areas, shielded by the mountains in the Wild East landscape (near Pawling New York for instance).

Astronomers are not the only species that depend on darkness to thrive. Take fireflies for instance. I’d never seen a firefly before moving to the East Coast. Even today after 25 years I think they are still an utterly magical sight blinking and flashing in a wooded darkness. Recent research shows female fireflies exposed to increasing ambient light do not flash back to males as much as those under natural darkness and thus decrease their chances of finding a mate. How much would we lose to live in a world without fireflies?

Birds navigate by the stars. Their seasonal migrations spanning multiple continents put even the most avid A.T. thru-hiker to shame. Yet the constellation of city lights that grows ever brighter — and increasingly blue-white like the stars overhead thanks to the advent of LED streetlights — appears to throw that navigation into disarray. Who among us could imagine any place claiming to be “wild” that didn’t have birds?

This change to our nocturnal landscape has been slow, but is picking up speed, especially as communities all across the country change their street lighting to the less yellow and more white LED lighting. Unless you have actively looked for it at night, you probably haven’t noticed the change. But the number of people who tell me they remember there being so many more stars when they were kids grows every year.

One way to gauge how much light has affected your view of the sky and how non-pristine your sky may be, is by consulting the Bortle Scale. A Bortle class of 9 is an inner-city sky so bright that only a handful of the brightest stars are visible, none making up even a full constellation beyond maybe the Big Dipper. Under a Bortle class 9 night, the Milky Way is completely invisible and city lights illuminate the clouds overhead and your eyes never fully adapt to the darkness. At the other end is a Bortle class 1 sky that is utterly pristine, with no light domes even faintly visible on the horizon and a sky so dark that clouds (and even your hand in front of your face) are just a dark hole on the sky. The Milky Way from these locations is visible all the way to the horizon and looks so bright that the dark clouds of interstellar gas and dust that span the light years throughout our galaxy, render the Milky Way overhead richly veined as if it was carved from celestial marble.

Believe it or not, while the sky above nearly every major population center is classified on a Bortle Class 8 or 9, there are literally fewer than a dozen regions in the continental U.S. that are still Bortle class 1. While most of these pristine skies are in the Western U.S. along the Continental Divide and Pacific Crest Trails, one is in the East and it is in the area around Katahdin at the northern end of the Appalachian Trail in Maine. There are many maps you can find online that will show you light pollution and Bortle scale maps for the country, and I’ve even published a small field guide that shows you the Milky Way at different times of year and how to estimate the Bortle brightness for wherever you happen to be. Think about that the next time you go out for a hike or just outside your front door at night. Think how much the lights of our civilization have already altered our wild places, even areas hundreds of miles away from major cities.

The nice thing about light pollution is that, unlike nearly all other forms of pollution, the minute you stop producing it, you’ve restored the darkness of the sky at the speed of light. The way to be more night-sky friendly at home and in your community is to behave like you would on the Trail. A hiker whose headlamp shines right in my eyes produces glare that ruins my night vision and makes it harder to see what’s around me. Same thing at home: street lights and house lights that shine directly in your eyes don’t make you safer at night, in fact, they make it harder to see what’s around. Similarly, don’t put a flood light in your camp that shines on all your neighbors; this is called light trespass. If you have to have a light outside at night, put a shade on top that restricts light to only shining downward. In camp, use only as much light as is needed and don’t leave it on all night, same thing at home. Red head lamps on the Trail don’t ruin your night vision, and yellowish lamps (not the blue-white ones that seem to be everywhere now) don’t attract as many insects. Now, if only communities would do the same and swap out those new blue-white street lights or at least cover them with yellower filters, we’d all be a lot more night sky friendly and see more stars without sacrificing safety.

I once had a lighting engineer take issue with my desire to see the stars. He asked me, “isn’t that what the Hubble Space Telescope is for?” A year later, I was in Bryce Canyon National Park talking to one of the NASA astronauts who worked on Hubble about what he thought of that question. He looked out over the hoodoos and buttes to the distant horizon and wryly said, “Why do we need national parks? Isn’t that what pictures on the internet are for?” Our parks, our forests, and our trails are the single best ways we can touch, breathe, hear and see the natural world on which we live. As our ideas of conservation have expanded to include not just the rock at our feet, but the water that flows through it, the plants and wildlife that make it their home, and the clear air that allows us to breathe and enjoy it, the night sky above is the latest addition. We wouldn’t settle for a world made invisible by smog, so why should we accept the same situation at night?