Light pollution threatens our dark night skies

September 3, 2009, 9:51 am

Our national parks—from Death Valley to the Grand Canyon to Acadia—are home to some of the best dark night skies in the country. These treasured dark skies are diminishing at an alarming rate–light pollution is the culprit. At the rate we’re going, there will be no dark skies left in the continental United States by 2025.

With two-thirds of Americans unable to see the Milky Way from their backyards, national parks used to be a place where people could get away from the artificial light and into the dark night skies and landscapes. As light can travel a long way, this is no longer the case. Increasing population density and consequent increases in traffic, development, overflights (airplanes flying overhead) and other human-related activities are now pushing their way into the proximity of the parks and bringing light pollution into remote wilderness areas.

Light pollution doesn’t just affect us humans and our quest for union with nature—it is a serious problem for nocturnal animals as well. According to the National Park Service, many animals depend on darkness to hunt, conceal their location, navigate and reproduce. Stray light disrupts not only their habitat, but their life cycles too. Even plants can be affected—for example, a tree beneath a bright street lamp may lose its leaves in the fall later than neighboring trees.

In response to this alarming threat, the National Park Service created the Night Sky Team to preserve the country’s last remaining dark skies. The team documented light from distant cities affecting night skies from more than 200 miles away and came back with some astonishing results—they found out that the lights from Las Vegas, for example, were visible from eight different parks! A more frightening revelation, perhaps, is that every park surveyed was found to have noticeable light pollution.

It is more important than ever for park lovers to understand the severity of light pollution and its imminent threat on our national parks. Luckily the negative effects of light pollution are reversible, and there are even a few simple things you can do to help.

You can start off by doing something fun—head to a night sky or stargazing event at a park near you this fall, gain some knowledge and spread awareness. Next, you can make your home dark-sky friendly. First, replace your outdoor lighting fixtures with shielded lights. Shielded lights direct light downward and prevent it from needlessly shining out into the night sky. You can also reduce the wattage on your light bulbs at home and put a motion sensor on your outdoor lights, which will both save you money, too. At night, remember to close your blinds/drapes to keep indoor light where it belongs—indoors!

If you want to go one step further, then get active and approach local schools, businesses and cities. Ask them to replace their conventional lighting fixture with dark sky-friendly shielded lights. You can mention this will improve safety, visibility and energy cost savings.

Last but not least, if you have an e-mail list or website, you can pass the message on with these animated videos courtesy of

Image: A map of artificial night sky brightness. Dark regions indicate nearly pristine, naturally dark skies, where thousands of stars can be seen. Yellow designates urban skies with fewer than 1,000 visible stars. White indicates city skies where as few as 20 stars are visible--fewer than can be seen on the American flag. Source: