Sodium vapor light pollution in Theodore Roosevelt National Park, North Dakota. [Photo by Justin Kern]
According to the calendar, it's spring on the south rim of the Grand Canyon. But tell that to the biting 45-degree wind that sweeps across the Colorado Plateau and slams broadside into my parked car. It's cold and dark and an hour past my bedtime. I'm tempted to pull my down jacket up around my ears and sink deeper behind the steering wheel. But my companions, Teresa Jiles and Dan Duriscoe, waste little time getting started. They no sooner kill the headlights on their camper than they start rummaging through their gear, pulling on long johns and rustling camera and computer-monitoring equipment. Neither one complains. For Jiles and Duriscoe, pain goes with the gain of holding research positions on the elite Night Sky Team, a program of the National Park Service. The duo has endured freezing winds, lonely nights on remote mountaintops, tire-shredding roads and even the occasional stalking by curious mountain lions. For these astronomy buffs, who fell in love with the night sky at an early age and never lost their childhood fascination with globular clusters and galactic nebulas, this is a dream job come true.
As I step out of my car into the starry night, I understand why. Grand Canyon is among the few parks in the lower 48 whose nighttime skies are virtually untouched by artificial light pollution. Here, some 5,500 stars are visible to the naked eye; the profound darkness lends uncommon clarity and brilliance to the heavens. Against the boot-blackened field of outer space, solitary stars glint like polished diamonds on a jeweler’s velvet. Even tiny, faint stars cast a glow, some of them massing to form recognizable patterns such as the great highway of celestial light known as the Milky Way. Glimpsed on a cloudless night, it's easy to see why the northern tribe of Ojibwa Indians regarded the Milky Way as the road to the afterlife — its path appears thronged with shimmering souls.
Preserving the stars in all their glory is the goal of the Night Sky Team. The group was officially formed in 1999 by Duriscoe and NPS colleague Chad Moore; since then it has grown to include Jiles and two additional physical scientists. The sky team's goal aligns with the founding mission of the park service: "To conserve the scenery and the natural and historic objects and the wild life therein and to provide for the enjoyment of the same in such manner and by such means as will leave them unimpaired for the enjoyment of future generations."
Top: The Milky Way viewed at Death Valley National Park, California, photographed by the Night Sky Team. Click image to enlarge. Bottom left: Data from Joshua Tree National Park, California, showing Las Vegas light pollution in white and pink. Bottom right: Night sky camera and data collection system. [Courtesy of NPS Night Sky Program]
To date, the night sky researchers have established data-collection sites in 86 national parks, monuments and seashores, most located in the interior West. To gather information, the team uses an astronomical grade camera which has been custom-fitted by Duriscoe. Over the course of five hours, the camera methodically sweeps the sky from horizon to zenith, capturing data one shutter click at a time. The information is processed by a computer and translated into measurements of the sky's brightness. This work is helping to gauge the levels of light pollution in the national parks and neighboring communities.
Keeping the skies unimpaired in our national parks, however, has become increasingly challenging. Smog particles from Los Angeles, for example, drift 400 miles across the mountains and deserts of the American West to contaminate the air over the Grand Canyon. The haze can cut daytime visibility at the park from 200 miles down to 60 miles and reduce the clarity of the heavens at night.
In recent years, artificial light has joined the list of problem pollutants. Just three decades ago, Duriscoe says, light pollution in the national parks was pretty much a localized issue. Park managers, for example, worried about the illumination from developments such as open pit mines near their borders. Since then, however, artificial light pollution has become far more widespread, not just in the national parks but also around the world. In 2001 the Italian astronomer Pierantonio Cinzano and his colleagues published the first world atlas of artificial night-sky brightness. According to their data, more than one-half of the people living in the European Union and more than two-thirds of those in the continental U.S. can no longer see the Milky Way with the naked eye.
Preliminary map of the number of visible stars in Europe, 2005. [Copyright Pierantonio Cinzano, Light Pollution Science and Technology Institute]
Artificial lighting has so washed out the night sky in urbanized places that residents can count only a few hundred of the thousands of stars that shine overhead. In some places, all but a few of the brightest constellations have disappeared from view. Researchers caution that if the current pace of artificial illumination continues, by 2025 the pristine night sky will become extinct in the continental U.S. Because they are relatively undeveloped, national parks are some of the few public places where people can pull up a camp chair and take a front-row seat on the universe's most ancient legacy. But even remote areas increasingly are subject to light pollution. The Night Sky Team, for example, has given only a few parks a clean bill of lighting health.
Duriscoe points out that visitors don't need to be standing under a streetlamp or billboard floodlights to experience a diminished overhead view. Domes of diffused light that hover above major metropolitan areas, a phenomenon known as sky glow, can artificially illuminate the heavens from great distances. (Sky glow is created by light reflecting off moisture and dust in the air.) The explosion of bright light from Las Vegas, Nevada, alone has encroached on the night sky of no fewer than eight national parks in the interior West, including the Grand Canyon, which is 150 miles away.
Mounting evidence suggests that altering the natural patterns of light and darkness is doing more than spoiling the view for night-sky gazers. Artificial light increasingly is being implicated in disrupting the biology and behavior of people as well as the animals that share the nocturnal landscape. In spring 2008, for example, researchers at the University of Haifa in Israel published the results of a study showing an elevated incidence of breast cancer in women who live in light-saturated neighborhoods. Researchers suggest that artificial nighttime illumination may be interfering with the brain’s production of melatonin, a tumor-suppressing hormone.
Light pollution in Phoenix, Arizona. [Photo by AZAdam via Flickr]
And it turns out that critters need the natural modulation of light just as much as people. "Most species depend on light and dark for some portion of their daily or seasonal life cycle," write Travis Longcore and Catherine Rich, editors of the Ecological Consequences of Artificial Night Lighting.  Migrating birds use the stars as a navigational tool during spring and fall migrations. Confusing big city lights with the constellations, whole flocks of night-flying migrants can be lured into the maze of urban towers where they crash into windows and die or become disoriented by the bright lights and reflected glass. Eventually, many succumb to exhaustion, making them easy pickings for predators. After emerging from their beach-sand nests, sea turtle hatchlings scope out the brightest horizon. In natural darkness, the luminous glow of the ocean beckons. But the electric lights of human habitation can lure the tiny turtles landward. Instead of steering to safety, many end up instead in the jaws of hungry predators or die of exposure.
Other animals wait for the cover of darkness to begin their feeding rounds or to carry out reproduction. Many species of snakes, frogs and salamanders, for example, naturally take their cues from lunar cycles, restricting their activities during full moons and stepping up foraging activities in periods of darkness. Artificial lighting can curtail the ability of some of these animals to detect prey. To avoid being eaten, some species play possum in brightly lit areas, remaining motionless long after lights have gone out. Not only do they eat less under these artificial conditions, but they also reduce or halt their calling during mating season. Researchers caution that it doesn't take lights with the equivalent brightness of a Walmart parking lot to disrupt such essential functions. Even soft lighting can alter behavior.
Natural regimes of light and dark are important to many animals in the water as well as on land. In 2000 limnologist Marianne Moore and her colleagues published research on the effects of artificial lighting in a group of lakes in Massachusetts. Her team focused on the behavior of a common group of zooplankton known as Daphnia. Under natural conditions, Daphnia frequent deep waters during daylight hours, migrating up into the water column under the cover of darkness to graze on algae. Lights from roads, lakeside homes and boathouses, however, illuminate these upper waters, discouraging the extent to which these tiny animals are willing to venture into areas where they are more visible to predators. The researchers concluded that the reduced grazing could allow nuisance algae populations to explode, throwing off the whole aquatic food chain and fouling water for swimmers and anglers. 
Lava Beds National Monument, California. Click image to see panorama view. [Courtesy of NPS Night Sky Program]
The good news, Duriscoe says, is that unlike environmental issues such as global warming or urban smog, the problem of light pollution is easily solved, even in large metropolitan areas. The Audubon Society, for example, has teamed up with the City of Chicago to institute what’s known as the “Lights Out” program. During the annual spring and fall bird migration, the owners of a growing number of downtown skyscrapers have agreed to turn off unnecessary lights. According to researchers at Chicago's Field Museum, the simple act of flipping a switch during these critical times of the year has saved the lives of more than 10,000 migratory landbirds.
Many oceanfront settlements on the Eastern Seaboard — from small neighborhoods to entire municipalities — run similar lights-out campaigns during the nesting season of sea turtles. In addition, their highway departments are experimenting with placing filters on new or existing streetlamps or substituting lights embedded in roadways with those mounted on poles. These and other measures are credited with the gradual increase in the number of green turtle and leatherback nests in places like the beaches of Florida.
But for a shining example in the fight against light pollution, no one does it better than Flagstaff, Arizona. In 1958, for example, Flagstaff established the world's first lighting ordinance when it banned the use of advertising searchlights. Since then this growing mountain community of 60,000 people has beefed up its lighting codes by mandating strategies such as the installation of shielded light fixtures on all roadways and buildings. In 2001 Flagstaff was named the first International Dark-Sky City by the International Dark-Sky Association, a Tucson-based organization that promotes the preservation of the night sky.
Many of these measures have been taken to protect the area's investment in two famous astronomical facilities, the Lowell Observatory and the U.S. Naval Observatory Flagstaff Station. But the crusaders for dark skies haven't been professional astronomers alone. Flagstaff resident John Grahame, coordinator of Coconino County's Sustainable Economic Development Initiative, is one of the founders of the influential grassroots organization Flagstaff Dark Skies Coalition. He became a night-sky convert in the 1990s after spending many nights in his backyard hot tub watching the brilliantly lit comets Hale-Bopp and Hyakutake streak across the sky.
Over the years, the coalition has helped to craft ordinances and produced education and awareness campaigns that have included community festivals with live music, art exhibitions, dance and theater. The group also consults with area businesses on installing better lighting, even providing cost-share monies on replacement fixtures and lighting design. Their strategies have been extraordinarily effective. Look no further, Grahame says, than the town's Taco Bell, located on the Route 66 strip. "It's one of the most beautifully lit buildings in town," he says.
Globe lights (left column) and directional floodlights (center column) contribute to glare and light pollution, while full-cutoff fixtures (right column) direct light to where it is needed with less waste. [Slides from the International Dark Sky Association]
Most important, Grahame adds, they've dimmed the lights without sacrificing safety. According to estimates by the International Dark-Sky Association, 30 percent of artificial light in the U.S. is wasted. Pointed skyward, it washes out the stars while dangerously blinding or disorienting people with glare. These problems can be avoided by using lower-intensity bulbs fitted in light fixtures that direct light to the ground where it is most useful and effective. The strategy not only increases security but also delivers big energy savings. Just ask the operators of the county jail in Flagstaff whose facility exterior and parking lot are entirely outfitted with shielded, lower-wattage bulbs.
Flagstaff’s dark sky campaigns have been so successful that the night sky now is a much-touted point of civic pride. A group of local high school and college students, for example, formed a band known as Dark Sky Percussion. Their music, band members say, is inspired by the love of dark skies. Across town, the visitor center sells T-shirts that exclaim, “Flagstaff. World’s First International Dark-Sky City.” The city even takes out ads in astronomy magazines.
Flagstaff's wise but simple measures have kept waste lighting away from the Grand Canyon National Park, just 80 miles north. But perhaps the biggest beneficiaries of Flagstaff's lighting ordinances have been residents who are treated to a spectacular light show right outside their doors. "I have a friend who can sit in his back yard in downtown Flagstaff and see the whole Milky Way stretching across the sky," Duriscoe points out. "This is a city of 60,000 people. It's amazing. But that's possible in every city." Grahame concurs. "I get out of my car at the end of the day and can see the skunk stripe of the Milky Way against the sky. To have that experience near home is extraordinary," he says.
And safeguarding the night sky is ultimately an important part of preserving our own humanity. For millennia, people have looked to the night sky as a means of navigation, of keeping time and marking the seasons. They relied on the constellations as a kind of shorthand for recording mythic stories that would inspire future generations. As David Crawford of the International Dark-Sky Association puts it, "We human beings lose something of ourselves when we can no longer look up and see our place in the universe. It'd be like never again hearing the laughter of children; we'd be giving up part of what we are."
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