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Science and Innovations

Earth Notes: Measuring the Night on the Colorado Plateau

National Park Service

Some 27 national parks and monuments protect the Colorado Plateau’s remarkable canyons, rivers, and wide-open spaces. But, people increasingly visit the plateau to experience another rare natural resource: its dark skies.

Last summer, Chaco Culture National Historical Park became the second site on the Colorado Plateau to be named an International Dark Sky Park. It joined Natural Bridges National Monument in a select group of just 13 parks worldwide with that status.

Limited light pollution is key to the plateau’s dazzling celestial vistas. How dark are these skies? Both Chaco and Natural Bridges receive a Class 2 ranking on the Bortle Dark Sky Scale, indicating exceptional views of celestial objects.

Developed by amateur astronomer John Bortle in 2001, the scale quantifies night sky quality from one to nine, or pristine dark to inner-city bright. Widely used by stargazers since then, the Bortle Scale has heightened public awareness of dark skies and light pollution, much the way that an air quality index quantifies and draws attention to air pollution.

That’s critical, says Flagstaff astronomer Chris Luginbuhl, since too often people have seen dark skies as a concern only for astronomers. But, just as protecting Grand Canyon serves far more than geologists, so conserving darkness benefits all who live in and visit this region.

That’s the intent of the newly formed Colorado Plateau Dark Sky Cooperative, a region-wide effort to limit light pollution. The goal is to ensure that our region’s night skies remain an unobscured, inspiring window on our universe.

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