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Sky & Telescope magazine in 2001. It classifies the darkness of skies from point of view of an astronomer, ranging from 1 ("an observer's Nirvana!") to 9, in which "the only celestial objects that really provide pleasing telescopic views are the Moon, the planets, and a few of the brightest star clusters." This illustration of the scale comes via The Bortle scale was originally published inmagazine in 2001. It classifies the darkness of skies from point of view of an astronomer, ranging from 1 ("an observer's Nirvana!") to 9, in which "the only celestial objects that really provide pleasing telescopic views are the Moon, the planets, and a few of the brightest star clusters." This illustration of the scale comes via Stellarium

Exploring the Night Sky by Terence Dickinson, Sky & Telescope, February 2001. Left: Winter constellations in a Bortle Class 4 or 5 sky. Right: The same constellation panorama in an urban, Class 8 or 9 sky. Illustrations by John Bianchi fromby Terence Dickinson,, February 2001.

A member of the Night Skies team setting up the wide-field CCD camera that the National Parks Service uses to measure light pollution, at Homestead National Monument , Nebraska.

New York 40º 44' 39" N 2010-10-13 LST 0:04, photo illustration by Thierry Cohen as part of the Villes Eteintes series, via The New York Times. Cohen photographs major cities at night, digitally manipulates them to remove all lights, and then inserts a starry night sky from somewhere with much less light pollution on the same latitude, to create an image that shows us what New York City or Sao Paulo would look like under the Milky Way. , photo illustration by Thierry Cohen as part of theseries, via. Cohen photographs major cities at night, digitally manipulates them to remove all lights, and then inserts a starry night sky from somewhere with much less light pollution on the same latitude, to create an image that shows us what New York City or Sao Paulo would look like under the Milky Way.

Los Angeles 34º 06' 58" N 2012-06-15 LST 14:52, photo illustration by Thierry Cohen as part of the Villes Eteintes series, via The New York Times. , photo illustration by Thierry Cohen as part of theseries, via

Landmarks in our short history of artificial street lighting include gas lamps (these arrived in New York City in 1827, with each one having to be lit by hand), and arc-light moontowers (several cities experimented with these in the late 1800s, but Austin, Texas, is the only place to still use them today).

Centurion Security Lighting Kit, via

Metropolis' Next Generation 2007 contest for their Civil Twilight Design Collective won' Next Generation 2007 contest for their lunar-resonant streetlight system , which would brighten and dim in response to ambient lighting levels.

Notre-Dame de Paris illuminated at night, by Atoma

The increase in artificial night sky brightness in North America, including an extrapolated prediction for light pollution levels in 2025. Maps created by P. Cinzano, F. Falchi, and C. D. Elvidge.

Paris 48º 50' 55" N 2012-08-13 LST 22:15, photo illustration by Thierry Cohen as part of the Villes Eteintes series, via The New York Times. , photo illustration by Thierry Cohen as part of theseries, via

Paris 48º 51' 46" N 2012-09-13 LST 2:16, photo illustration by Thierry Cohen as part of the Villes Eteintes series, via The New York Times. , photo illustration by Thierry Cohen as part of theseries, via

The Luxor beam in Las Vegas is equal to the light of more than forty billion candles.

Light domes from cities at various distances from Mt. Dellenbaugh, Grand Canyon Parashant National Monument, in 2007. NPS photo

Poster designed by Tyler Nordgren

A satellite view of Earth at night shows the prevalence of artificial lighting. NASA.

Gas station in the middle of Nevada, photograph by James Reeves . "Gas stations," Bogard told us, "are the worst offenders by far. They are just egregiously bright."

The National Radio Quiet Zone boundaries, via the National Radio Astronomy Observatory.

Hallway lighting in a supermax prison is never switched off. Photograph via

Across the United States, natural darkness is an endangered resource. East of the Mississippi, it is already extinct; even in the West, night sky connoisseurs admit that it's quicker to find true darkness by flying to Alice Springs, Australia, than traveling to anywhere in the Lower Forty-eight.Ever since the nation's first electric streetlight made its debut in Cleveland, on April 29, 1879, the American night has become steadily brighter. In his new book,, Paul Bogard aims to draw attention to the naturally dark night as a landscape in its own right—a separate, incredibly valuable environmental condition that we overlook and destroy at our own peril.took the opportunity to visit Bogard in his office on the campus of James Madison University, in Harrisonburg, Virginia, to learn more about nocturnal America and its dark skies—and what we have lost by dissociating the two.Our conversation touches on the difficulty of measuring and preserving such an ephemeral quality, as well as the ecological and health consequences of endless artificial light, with speculative detours into evolutionary shifts in human vision and the possibility of preserving Las Vegas (the brightest pixel in the world in NASA photographs) as a "light pollution park.": Darkness is easy to overlook, if you’ll excuse the pun. How did you go about structuring the story of such a familiar, yet intangible quality?: People think they know darkness, and that they experience darkness everyday, but they don’t, really. That’s one of the reasons I borrowed the Bortle scale for the table of contents. I think John Bortle’s point, when he created this tool for measuring the darkness of skies, was that we have no idea what darkness really is. We think night is dark—full stop, end of story. But, on the Bortle scale, cities would be a Class 9—the brightest. Most of us spend our nights in what he would call a 5 at best, or more likely a 6 or 7. We rarely, if ever, get any darker than that.Until the coming of electric light, people experienced a darkness that Bortle would classify as 2 or 3, every night. What I tried to do in the book is to show that difference, by working my way down from places that are bright to those that are less bright, but also by talking to people who are living and working in those places.: It’s interesting that, in order to see the nuances in darkness, we need to measure and name it. It was certainly a revelation to me to read in your book that twilight has three stages—civil, nautical, and astronomical, with civil being when cars should use headlights, nautical meaning that enough stars are visible for navigational purposes, and astronomical referring to the point at which the sky is dark enough for the faintest stars to emerge. Previously, I had thought of twilight as a single condition on the light-to-dark spectrum, rather than a multiplicity.: For sure. For me, one of the reasons why identifying different depths of darkness is so important is that we don’t recognize that we’re losing it, unless we have a name to recognize it by. It’s also a way to talk about what we might regain.That’s also what the National Parks Service Night Sky team , who I describe in the book, is trying to do with their sky quality index. If you’re charged with preserving darkness as natural resource, unimpaired for future generations, then you need to be able to put a number on the level of darkness. You need to be able to see and measure any losses before you even know what you’re trying to protect.: It’s astonishing to read the description of a Bortle Class 1, where the Milky Way is actually capable of casting shadows!: It is. There’s a statistic that I quote, which is that eight of every ten kids born in the United States today will never experience a sky dark enough to see the Milky Way. The Milky Way becomes visible at 3 or 4 on the Bortle scale. That’s not even down to a 1. One is pretty stringent. I’ve been in some really dark places that might not have qualified as a 1, just because there was a glow of a city way off in the distance, on the horizon. You can’t have any signs of artificial light to qualify as a Bortle Class 1.A Bortle Class 1 is so dark that it’s bright. That’s the great thing—the darker it gets, if it’s clear, the brighter the night is. That’s something we never see either, because it’s so artificially bright in all the places we live. We never see the natural light of the night sky.: There are a few popular urban legends about the extent to which people no longer experience true, natural darkness. One is that, even though telescopes sell really well in New York, no one has seen a star over Manhattan since 1976 or something like that. The other one, which I have to assume is also at least partially an exaggeration, is that, after the Northridge earthquake in 1994, the L.A.P.D. was flooded with worried phone calls because people were seeing all these mysterious lights in the sky—lights that turned out to be stars.: I’ve heard that one, too—that people were seeing the Milky Way for the first time, and they didn’t know what it was.Those stories make me think of a couple of things. While I was writing the book, I went to Florence, on the trail of Galileo, and they still have two of his four telescopes . An astronomer there had this amazing line that he told me, which was that 400 years ago, in Florence, everyone could see the stars, but only Galileo had a telescope. Now, everybody has a telescope, but nobody can see the stars.That really speaks to that New York legend. Telescope sales continue to be good, astronomy books continue to be published, and there are sky-watching apps on your phone. People are interested in the night sky. But we can’t really see any of it.The other thing it reminds me of is a guy I met in Paris, who told me that he thinks that, for the amateur astronomer, the most important instrument is not the telescope, but the automobile, because you have to have a car to drive somewhere dark enough to see anything.: At the start of the book, you differentiate between darkness and night. Is it just that the two are no longer synonymous, or were they ever?: It’s a good question. They’re so obviously intertwined, but it seemed to make sense to differentiate them or to specify one or the other. Night, obviously, in many places, is no longer really dark, or at least not naturally dark. In that sense, you can’t say that night means darkness. They’re not synonymous anymore. Sometimes I think that what makes night night, what makes night special, and what I love about it, is more than darkness. It is light, whether it’s natural light, like candles, or beautiful artificial light. A lot of electric lighting is really quite beautiful now.Artificial lighting has meant a lot of really good things, arguably. We are able to extend the day into the night, which means that we can keep working, we can pursue our hobbies, we can go out to dinner, we can entertain—we can party all night long! We can do all these things that we like to do, that night has become known for. But there are other things that we have lost through this process of nocturnalization.It’s not really my thrust in the book, but I guess what I’m saying is that, if that’s all that night is, and we have lost so many of these other qualities of night, whether it’s quiet or darkness or solitude, then I think the night that we are experiencing now is really a lessened version of what it could be.Night has a lot of qualities beyond darkness or lack of darkness—things like nocturnal sounds and smells. Those sensory things have more to do with night, for me. I’ve always had that sense that, at night, the world reduces in size and fury and sound and we start to feel not so overrun by everything. At night, that’s how I feel—free, to pursue my writing and reading or whatever. We let go of those burdens that the day holds. Those sorts of things mean that night is much more than just darkness. Yet darkness itself has so much importance alone, too, for human health and ecological health.: People also assume that darkness is inherently dangerous, yet you show how the connection between light and security is often a false promise.: Exactly. Historically, that connection is really interesting. The state really encouraged light, because officials felt as though they could control a well-lit city better. Illumination was conflated with the power of the state, going back to Louis XIV, the Sun King, who decreed that candles should be hung in the streets, to demonstrate his might by banishing dark. In the years before the French Revolution, for many Parisians, public street lighting stood for tyranny. Oil-lamp smashing was a regular thing.Ironically, what has happened now is that we have so much light that we can no longer see. We’re blinded—sometimes literally, by the brightness and glare of our security lighting—but also metaphorically, which is to say that when we light everything up, there is really no reason to look over and notice something, and say, “Wow, that’s a weird thing.”When everything is so brightly lit, why should we look? It’s light, so it’s safe, so we switch off. And, while no one is looking, we’ve actually made life easier for the bad guys. Some studies even show that criminals actually prefer well-lit areas. I had several policemen and security consultants tell me that criminals are as afraid of the dark as we are. They don’t want to go in the dark. The light makes them feel safe, just as it does us.The other thing is that, physically, so much light makes it hard for our eyes to see. We don’t adapt from bright to dark quickly, so if we look toward the light, we can’t see anything else, and then most street lighting is incredibly badly designed and actually reduces contrast.Sure, some lighting is helpful, in terms of safety and security. But we are not safe or secure simply because of lights. We are safe and secure when we are conscious of our surroundings. Most of our security lights are a huge waste of money and energy.It’s a difficult issue. The entire third chapter is all about safety and security. I spent a lot of time on it, because the minute you start talking about light pollution, or the importance of darkness, people’s first response is, “Yeah, but we need light for safety and security.” It touches a nerve. I would just say that we don’t need all this light for safety and security. We use way more than we need, and it isn’t making anybody any safer.One thing I’d say is that our eyes are amazing organs. Given the chance to adjust to darkness, we can see quite a bit and see fairly well. I would imagine that if you got rid of wall-packs and security lights and so on, you could rely on more subtle lighting design in crosswalks, stairwells, and doorways. A couple of the lighting designers I spoke to were very excited about responsive lighting.For example, I spoke with a woman in Boulder, Colorado, whose thing was that putting lights on poles is ridiculous, and that, instead, we should have step-lights at foot level that get triggered with a motion detector. Another guy I talked with was mapping the night geography of Paris, with the idea that you could match the lux level of street lighting to the level of activity.: There seem to be significant disparities in the quality of different cities’ nightscapes. In the book, you engage in some comparative darkness tourism in London and Paris, and London comes across as a completely wasted opportunity, in terms of lighting.: I thought so. I’ve noticed again and again that cities will spend all this money on making themselves pretty to draw visitors, and then they having glaring light all over the place. At night, they are as ugly as every place else.In Paris, the lighting is designed to make the buildings beautiful at night. In London, and really all over the United States with very few exceptions, much of the lighting is just a big light shining on a building. You can see it, sure, but it’s not really very beautiful.: Speaking of darkness tourism, I just noticed a book calledon the bookshelf behind you, and it reminded me of something I read about the poet Samuel Taylor Coleridge. Apparently, Coleridge would take massive walks in the middle of the night. He would show up at Wordsworth’s house at 3 a.m., and they would head out into the Lake District together, talking and walking beneath the stars. It made me wonder if there are—such as night walking—lost practices of darkness, so to speak, through which people once pursued certain experiences defined by the absence of light.: I have always loved the experience—wherever I’ve been living—of going out walking at night, usually at around eleven-ish. Nobody is out, for the most part. You can look through windows into people’s houses, if you want to, which is sort of like an Advent calendar thing. Everything looks a little different, somehow. It’s just quieter. My dog and I go walking at night, before we go to bed.What’s interesting is that I love being out at night, but I’m also still somebody who’s afraid of the dark. That’s why the experience that I have in the book, being in Death Valley and just walking around in this incredible darkness over a several hour period, was a really great one, because after two or three hours, your eyes seem to shift again and you can see even more. You begin to feel much more comfortable. I’d love to do that again.: The most astonishing statistic in the book, for me, was the fact that 40 percent of Americans live in such bright environments that their eyes never transition to night vision—from the cones to rods. I can’t help but wonder if, thanks to our saturation in artificial light, we might end up losing one of our ways of seeing the world.: I actually asked Alan Lewis, a former head of the Illuminating Engineering Society of North America , exactly that question. He said he didn’t have any proof that our physiology was changing in response to the disappearance of darkness. Of course, it hasn’t been very long. My guess is that, if we keep going down the path of more and more artificial lighting, we would eventually lose scotopic vision —that’s the technical term for low-light vision using the eye’s rod cells.That’s one of the things about all this light—it’s been so recent. Our grandparents and our great-grandparents grew up in a time when it was just so much darker. In the book, I’ve included the map that Fabio Falchi, the Italian I meet towards the end of the book, has made of the increase of artificial night sky brightness in North America. It shows the late 1950s, the mid-1970s, 1997, and then a prediction for 2025.I remember the 1970s. It wasn’t that long ago. And it’s significantly darker on those maps then than it is now.: That raises the question of historic preservation and what it means to bring darkness back. I’m reminded of architect Jorge Otero-Pailos and his experimental olfactory reconstruction of Philip Johnson’s Glass House in New Canaan, Connecticut. He realized that, to recreate the original smell of the house, you not only had to recreate all the VOCs off-gassing from new paint and furniture, etc., but you also bring back the smell of tobacco and the smell of certain colognes that were ubiquitous at the time—an entire olfactory aesthetic, as it were, that has been lost in the subsequent years. I mention that because you can imagine that a true historic reconstruction of a 1950s suburb would require not only a totally different light level at night but, by today’s standards, a blinding sky full of stars.Along those lines, I’d love to hear how the National Park Service’s Night Sky Team plans to go about actually protecting such an intangible resource as darkness, and maybe even reconstructing it to “original” levels. I’m also curious whether, in the other direction, you could maybe imagine a time where, thirty years from now, we might actually have a nostalgic “light pollution park.” People would pay admission to see how crazily well-lit our cities used to be.: We could just wall off Las Vegas and declare it a light pollution sacrifice zone right now.: That is such a neat idea. I hope that, in thirty years, or perhaps even less, that would make some sense.As you probably know, for Earth Hour every March, people turn off the lights on certain buildings. When I met with Fabio Falchi, he was trying to get his town, Mantua, to turn off the lights after midnight. He said that he went to the Leaning Tower of Pisa for Earth Hour, and he suddenly realized how magical it was to see these famous monuments with the lights off. He thought that if more people could see these places surrounded by darkness, it would be like a discovery, because no one has seen them like that in fifty years.Of course, he said, even with the lights off, it’s not how it was, because there’s so much sky glow. There is so much cumulative light from the surroundings reflecting that you could probably never get back to what it was originally like.: In the book you mention that, even in Death Valley, one of the darkest places in North America, you can see the light dome of Las Vegas on the horizon, and the lights of flights heading into San Francisco above.: Exactly. That’s the challenge of preserving darkness: you can’t do it on your own. The National Parks Service team, in addition to figuring out how to measure darkness in order to put a number to what we have to lose, figures that their best bet is education. Of course, the parks themselves have overhauled their own lighting, but they’re also starting to offer all kinds of night programs, whether it be focused on the sensory experience of the land at night or astronomical observation or whatever. If they can’t get the rest of us to care about darkness, they don’t stand a chance of preserving their own.There are some positive signs. For example, Acadia National Park in Maine had its first Night Sky Festival in 2009, and now the local community of Bar Harbor has enacted a light ordinance to reduce their sky glow.That’s the National Park Service idea, essentially. Americans will come and learn about light pollution and darkness and all of the ecological and health reasons why darkness is important and endangered. Then we will go home and, hopefully, apply some of those lessons there.I would imagine that lots of people west of the Mississippi might say, “It’s dark where I live.” But we have changed things so much that anywhere you go east of the Mississippi, there is no true darkness. It has all been tainted.One guy on the Night Sky team told me that sometimes people will ask, “What are you going to do with the cities? You’ll never get the cities dark again—that’s just impossible. There are too many people and too many lights.” He said that, to a certain extent, that’s true. You’re probably not going to bring the Milky Way back over Manhattan or Chicago.His reply, though, is that if you were able to just reduce the lighting in these major cities you would see great benefits. You could address a lot of the health issues that people in the cities, who are exposed to huge amounts of light at night, are suffering from.The other thing is that, when you draw the lighting down in the cities, the darkness ripples out into the suburbs and the country. The reason the suburbs and the countryside are so bright is because of the cities. Plenty of suburbs and towns have awful lighting as well, of course, but they could fix that lighting or even turn it all off and their skies would still be bright, because of the nearest city.: To follow up on that, I’m curious about the question of legislation. Some cities, like Flagstaff, have lighting ordinances , of course. But one of the really interesting implications in your book is that, if you think about darkness as a common resource like water or clean air, we have environmental legislation and acceptable levels for pollution for them. Or, if you think about the health side, you could make the analogy with secondhand smoke and the ways in which we regulate that. At one point you mention the phrase “light trespass,” which implies we could treat darkness like property. Would any of these be effective models for preserving darkness?: Realistically, I think we have to start with the places that are still dark, and preserve them, because, as with so many things, they are not making it anymore. The pressures are all headed in one direction. Any kind of forward-looking lighting plan that I’ve seen starts with a solid core of darkness and then works its way out from there.In terms of legislation, in the UK, British astronomers are taking the approach of putting lighting standards into building code. That way, any new building has to have dark-sky-friendly lighting. Then lower lighting levels become more and more normal, and you don’t get that escalation effect I describe, where older buildings look dim next to new ones, and upgrade their lighting to match, and so on. People just get used to it.: Of course, there is potential for a huge backlash against that, at least in the United States. If you use even something as universally beneficial as vehicle emission limits in cars as an example, you see people railing against government intrusion all the time. I can easily see someone on cable news complaining, “They want to tell me when I can?”: My hope is that part of that just takes time, and those voices will eventually fade away. I see this with my students. They’ve never really been asked to think about lighting and darkness, and they assume that this super-bright world in which we live today is just the way the world is. If you could shift that and, for example, make a college campus a place where you became sensitive to good lighting, then everybody would leave with at least a sense of what’s possible. Roger Narboni , who designed the world’s first urban “lighting master plan” for the French city of Montpellier way back in the 1980s, told me that his dream is to have education about light and darkness beginning in kindergarten, as a core part of the curriculum.: There’s a certain poetry to having a conversation about dark sky reserves in the National Radio Quiet Zone . This is a landscape, after all, where, by federal decree, electromagnetic “pollution” has to be kept to a bare minimum.: Wow, I didn’t know that. I had never heard of that.: The regulations were put in place to protect the work of the National Radio Astronomy Observatory in Green Bank. The result is a 13,000-square-mile radio quarantine zone. It’s one of the few places in the United States where the air is not completely saturated by electromagnetic emissions from cell phones and power lines and radio stations and everything else.: What’s also interesting is that people move here for that reason —people who feel that they are sensitive to electromagnetic emissions will move here for their health.: So, while we were driving here, we were thinking about the idea of a luxury darkness retreat, as a well-being thing.: I can definitely imagine that. The thing I write about in the book is the question of who will have access to darkness. It’s like so many of these other things—green space, trees, quiet, and so on. It could end up being unevenly distributed; where the only way to get real darkness is to be able afford to live in a community like Aspen or Vail or somewhere like that.This makes me think of when I was in Phoenix. I can’t remember the name of the wealthiest suburb, but what I noticed is that when you drive up towards it, all of a sudden, it’s dark. These people are rich enough to have anything they want, and they choose to have darkness at night.Meanwhile, kids who are growing up in cities whose families don’t have the resources to travel are never going to experience that. I wonder if it will get to the point where none of us can get there, unless you’re the one percent. Then you can afford to go someplace really dark.: It already seems as though there are huge inequalities in our exposure to light at night. I was shocked by the statistic you quote about nearly 20 percent of African-Americans in the United States working the night shift.: And then there’s the fact that public housing is almost always over-lit in an effort to deter crime. There’s another darkness-deprived population I hadn’t considered either, before I wrote this book, which is prisoners. There’s this former convict, Ken Lamberton , who wrote about his time in prison and the way he was forced to be in the light—he wasn’t even allowed to cover his face with a blanket at night. It’s as if being constantly illuminated was actually part of his punishment.One thing that appeals to me about light a lot is how symbolic it is. Our usage of light right now is hugely symbolic of our lack of awareness of how we use things and the way we use so much more of everything than we need. It seems to me that if we could control our light use and use light more intelligently, then it could also be symbolic of us finally getting our act together in a lot of different ways.