Within national parks we preserve the continuation of natural processes. This includes allowing bears to roam, letting rivers run free of dams and diversions, and understanding the beneficial roles that fire can play. A dark night is a resource integral to many natural processes. Many of the darkest night skies in the country are found within national park boundaries. With the loss of night sky quality over the last five decades to light pollution, this resource has become nationally significant.
We generally think of dark night skies as a scenic resource, valued by amateur astronomers as well as casual stargazers. Sometimes forgotten is the importance of natural darkness for wildlife. Nearly half the species on Earth are nocturnal—active at night instead of during the day. The absence of light, natural or otherwise, is a key element of their habitat. Many species rely on natural patterns of light and dark to navigate, nest, mate, hide from predators, and cue behaviors.
Adding artificial light to natural habitat may result in substantial impact to certain species (Rich &Longcore, 2006). For example, migrating passerine birds reference stars to fly at night and can be disoriented by city lights and towers. Sea turtle hatchlings orient toward the brightest light on the beach, but instead of being drawn to the safety of sparkling waves on the ocean, they are often drawn toward roads and parking lots, where they quickly perish. And amphibians, with vision far more sensitive than that of humans, are prone to be disoriented by light. Changes to cave environments can have a similarly disruptive effect. Research into the ecological consequences of artificial night lighting is revealing numerous connections between light pollution and species disruption.
Dark night skies are also considered an air quality related value under the 1977 Clean Air Act Amendments, and air quality in turn affects the quality of the night sky. Just as air pollution decreases the visibility during the day, hazy air at night dims the stars and scatters more light from cities, resulting in a gray appearance to the night sky instead of sparkling stars on a black canvas.
Rich, C. and Longcore, T. 2006. Ecological Consequences of Artificial Lighting, Island Press.