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For the last two years I have written about dark night skies and light pollution for the National Park Service. I use data collected by the Natural Sounds and Night Skies Division (NSNSD) to write reports detailing the night sky condition at parks across the southwestern U.S. Before I began writing these assessments, I had never heard of the NSNSD, but park scientists have been pioneering ways of measuring light pollution (and sound pollution) in America’s national parks since 2001. So far the NSNSD has collected night sky data in more than 100 national parks.

Below is series of panoramic images park scientists have collected in Yellowstone National Park. These images show that Yellowstone is a dark place with little light pollution from the surrounding area, although lights from West Yellowstone are obvious in the night sky at the Madison Campground (top image), which is about 14 miles away. And even the few lights at Old Faithful penetrate the dark night sky there (bottom left). The night sky in northern Yellowstone (lower right) is the darkest of the three images. For the most part, though, the mountains surrounding Yellowstone help shield the park from the lights of larger communities such as Livingston and Bozeman, Montana to the north and Jackson, Wyoming to the south.

Night sky at Madison Campground in Yellowstone NP. Figure Credit: NPS Natural Sounds and Night Skies Division

Night sky at Old Faithful in Yellowstone NP. Figure Credit: NPS Natural Sounds and Night Skies Division

Night sky at Frog Rock in northern Yellowstone NP. Figure Credit: NPS Natural Sounds and Night Skies Division

While the NSNSD uses specialized equipment to collect the images above, amateur astronomers use the Bortle Dark Sky Scale (shown below) to qualitatively assess the night sky for star gazing. The scale ranges from 1 (pristine) to 9 (highly degraded). In Yellowstone, the darkest of the three images above rates as a 2, whereas Old Faithful and Madison rated a 4 on the Bortle Scale. But lights aren’t the only factor that affect sky quality. Clouds, atmospheric dust, and air pollution can reduce the number of stars observed.

More and more people are visiting national parks to experience a dark night sky as they become rare elsewhere. A full two thirds of the world’s population cannot see the Milky Way from where they live. Although the night sky can be appreciated all on its own, many parks with dark night skies host star gazing parties, moonlit night hikes, and even astronomy festivals. Some parks have even been designated as International Dark Sky Parks by the International Dark Sky Association (IDA). Below are photos of of the night sky at three Dark Sky Parks.

Great Basin National Park. Photo Credit: NPS

Natural Bridges National Monument: Photo Credit: NPS/J.W. Frank

Grand Canyon National Park. Photo Credit: NPS/J. White

The IDA is a non-profit organization dedicated to improving dark night skies throughout the world. Parks, preserves, and even towns can apply for a dark sky designation. Flagstaff, Arizona was the first city in the world to be recognized as a Dark Sky Place, and it’s their foresight and love of dark night skies that helped the three national monuments located within 40 miles of city limits to achieve their own dark sky status last year.

The criteria for becoming a Dark Sky Park are stringent and requires a complete review of data collected by the park’s night skies division. Today there are 17 NPS units designated as International Dark Sky Parks, and several other parks are applying for dark sky status. Yellowstone is not yet a Dark Sky Park, but NPS staff are retrofitting lights that are  not in compliance with IDA standards – a first step toward improving the park’s nocturnal lightscape.

Unfortunately, national parks are not islands immune to the rest of the world. Lights from nearby towns bleed into parks and obscure stars at the horizon. Even cities hundreds of miles away can affect the night sky environment of a park. The National Park Service is working on maintaining and improving night sky quality at parks by collaborating with nearby communities to reduce light pollution.

Saguaro NP’s night sky has been heavily influenced by the city of Tuscon, Arizona. Tuscon is situated between the park’s two districts. There are more than 520,000 people living in Tucson and urban sprawl has pushed more homes up against the park’s border. Even the light dome from the city of Phoenix, which is 113 miles away, can be seen in this park.

This figure shows light pollution in and around Saguaro National Park. Figure Credit: NPS Natural Sounds and Night Skies Divistion

But not all hope is lost for parks like Saguaro. Night skies can be improved. It is often as simple as retrofitting current lights and eliminating unnecessary lights. Dark night skies are not purely for aesthetics, though.

Many birds migrate at night and bright city lights confuse them. Sea turtles use the light of the moon reflected off the ocean to guide them toward refuge once they emerge from their sandy nests, but lights from hotels and homes lining beaches disorients them. Bright city lights even influences predator hunting success and predator avoidance for  nocturnal animals.

Not only does light pollution affect ecosystem function, but it also has implications for human health. As Paul Bogard writes in The End of Night, humans evolved over millions of years with bright days and dark nights. It is only in the last century that we have “disrupted this ancient rhythm.” Electric lights keep us up well past dark, wreaking havoc with our circadian rhythms and the production of melatonin, the hormone that controls our sleep-wake cycles.

Humans have been lighting up the night since we discovered fire. And as lights have become brighter our eyes have adjusted to this new brightness, so we introduce more and brighter lights to compensate for this adjustment. But studies show that these lights may not be all that effective at helping us see better at night. In fact, they may even limit our ability to see well at night.

Think about driving down a road without overhead lights. Your headlights do just fine illuminating the road ahead and to the sides, but when overhead lights are present, they create bright bubbles of light interspersed by patches of darkness. These lights serve to illuminate only the road directly beneath them while making the shadows seem darker. Your eyes never have time to adjust to the ebb and flow of street lights so that a deer coming from the field off to the side of the road remains unseen until it meets your bumper.

The same thing happens in parking lots. We light them up to make us feel safer, but they only serve to make the thief in the shadows invisible while we step into the spotlight. By allowing our eyes to adjust to the night with well-placed, downward facing lights we are able to see more of our surroundings, which is safer overall. The added benefit is that more of the night sky becomes visible.

I am lucky to live in a park with dark night skies. My home is five miles up the hill from Gardiner, Montana – a town of less than 1,000 residents. But it’s growing. Homes are being squeezed into nooks and crannies that I would have never imagined possible ten years ago. Yet, when updates were made a year ago, planners took into account dark night skies. Our street lights point downward and are at a brightness level that doesn’t create pools of bright light and caves of darkness. Thanks to these efforts, the dark night sky in Gardiner and in Yellowstone was preserved.

Dark night skies are an attribute of wilderness, just as wild bison, old-growth forests, and clear running rivers are attributes of wilderness. They are parts that comprise the whole; each one is necessary. And we are a part of the wilderness in the most fundamental way. Humans are made of stardust. This isn’t some literary trick; it’s a fact of physics and chemistry. Carl Sagan says so.

“The nitrogen in our DNA, the calcium in our teeth, the iron in our blood, the carbon in our apple pies were made in the interiors of collapsing stars. We are made of starstuff.” Carl Sagan, Cosmos.

P.S. Check out our Facebook page this week for more night sky information, including tips on how to find your dark sky park, google maps for learning about the night sky in your neighborhood, and of course, excellent photography of dark night skies in national parks.