Conserving America’s dark skies
Humans have always looked up. Generation after generation of our species have stared up into the night and wondered about our place in the cosmos. The planets’ dances set against a backdrop of stars and constellations provided ancient peoples with a way of organizing their lives, of understanding themselves and their origins. Artists and writers once looked up to find inspiration and meaning in the inky black and smudgy white of the Milky Way splashed across the sky. Even today, our culture revolves around the rhythms of the sun and moon.
Nowadays, though, we’re lucky to get a glimpse of the Big Dipper or Orion’s belt.
Rapid development and urbanization (and lots of light bulbs) have deprived many of us from seeing much of anything beyond the moon and the brightest of stars. By some estimates, 99% of the terrestrial world’s skies were light polluted by the year 2000, and at least two thirds of Americans can’t see the Milky Way from their yards. Light from urban areas can degrade the quality of the night sky as far as 200 miles away. To put that into context, if the entire country shut off all its lights except for Los Angeles, stargazers in San Diego and even in parts northern Baja California could miss out on seeing some of their stars, while those in Las Vegas would be just far enough to not notice, most nights.
In many parts of the country, national parks are some of the last refuges of dark skies, and the National Park Service (NPS) is increasingly recognizing the need to act as a steward over that rapidly diminishing natural resource. A relatively new unit within NPS, the Natural Sounds and Night Skies Division, was created recently to protect and manage those valuable assets. Some parks have even instituted events organized around night skies, such as star parties (Yosemite, Acadia, and Death Valley), while another has built an observatory (Chaco), and a fifth has hired a “night sky ranger” (Bryce Canyon).
Formal recognition of the importance of curbing light pollution in and around national parks is clearly a good sign, but more concrete standards are needed. Park managers rely upon indicators (“standards of quality” or “reference points”) to describe the minimum acceptable condition for the objectives they’re tasked with managing. For example, one indicator for a wilderness experience is the number of other groups encountered per day along hiking trails before visitors experience a decline in their subjective enjoyment of that experience. Once those indicators have been established, park managers monitor them and implement actions to maintain them. If trails become too congested, for example, park managers might decide they need to expand their trail system.
To identify such indicators for night sky viewing, University of Vermont researcher Robert Manning distributed a series of surveys to visitors at Acadia National Park in Maine. Because it is located so far away from a major city, Acadia is thought of as one of the best spots for viewing the night sky in the eastern US.
Together with his team, Manning first distributed a questionnaire to groups camping overnight at the park’s two campgrounds. It was designed to assess the importance of night sky viewing to park visitors, and to account for all sources of light (both celestial and terrestrial) that overnight visitors might see, such as the moon, planets, stars, campfires, car headlights, flashlights, street lights, and so on. In addition, they rated the extent to which those light sources added to or detracted from their experience in the park.
While most visitors said that they visited Acadia in part because of its reputation for good stargazing, 40% said that increased light pollution would not necessarily prevent them from returning in the future. While most visitors didn’t report seeing celestial objects, it greatly enhanced their experience when they did. Likewise, most visitors didn’t report seeing many anthropogenic sources of light, and that too added to their experience. The one exception was campfires; despite the light, visitors enjoyed seeing them. Overall, the survey showed that the brightness of celestial objects, and therefore light pollution, is an important indicator at Acadia National Park.
A second survey was designed to determine the maximum amount of light pollution that visitors would find acceptable. To do that, the researchers presented visitors with an array of night sky photos. On one end of the spectrum was a photo of the night sky taken at the park in 2008. Each subsequent photo was modified to appear as if light pollution was increased by a factor of three. As might have been expected, increasing amounts of light pollution are increasingly unacceptable, but the point at which acceptability rating fell below the acceptable level was somewhere between the fifth and sixth image (between 15 and 18 times more light pollution than existed in 2008), though when combined with information from the first survey and from interviews with park rangers, Manning recommends a maximum acceptable light pollution level of not more than 12 times more than 2008 levels (photo 4).
Monitoring the condition of night skies in national parks is the easy part. The more challenging task is to control light pollution. While NPS can adopt best practices for lighting within parks, controlling light pollution outside of park boundaries will require working proactively with the so-called “gateway communities.”
Manning and his team recommend promoting the value of dark skies for astronomical tourism. “As the opportunity for high-quality stargazing has diminished, its value may be increasing,” they say. The economic benefits of drawing tourism centered on stargazing might encourage those communities to do their part in reducing light pollution.
While global light pollution may have already caused significant damage to contemporary ecosystems, dark skies are themselves a renewable resource. All it takes is thoughtful urban planning, and the night sky can once again become darker. What better place to advance that cause than America’s national parks? – Jason G. Goldman | 09 September 2015
Source: Robert Manning, Ellen Rovelstad, Chadwick Moore, Jeffrey Hallo, & Brandi Smith. (2015). Indicators and standards of quality for viewing the night sky in the national parks. Park Science 32(2). Link.
Header image: shutterstock.com
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