Dark Skies Over a Natural Bridge

Natural Bridges National Monument is the first national monument in Utah. In 2007, it also became the first recognized Dark Sky Park, earning a gold-star rating for extremely good visibility including air glow, the Milky Way, and faint meteors. Best of all, it's only $3 per week to visit.

Milky Way behind the Owachomo Bridge in Natural Bridges National Monument. Image credit: NPS/Jacob W. Frank

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Before the bridges, the Natural Bridges National Monument was a white-sand beach. In the Permian, 260 million years ago, the sand built up in dunes, creating cross-bedding still visible in the rocks today. Fast forward millions of years, with the ocean long-gone and the loose sand compacted and cemented into sandstone. Sometime in the last few thousand years — since the last glaciation scoured the land clear of delicate structures and loose sediments — the curving meanders of a stream cut down sandstone into canyons, and undercut canyons into bridges and arcs that give the park its name.

Long-exposure capturing star trails as the Earth rotates. Image credit: NPS/Jacob W. Frank

Natural Bridges National Monument is not just a park for the geology, animals, and artifacts — it's also an escape from city lights. While most people in the United States can see only a few hundred stars when gazing up at the night sky, in this little corner of Utah, you may see up to 15,000 stars. Back in 2007, the International Dark-Sky Association challenged the park to step their dedication to natural beauty up a notch by bringing their light pollution down, and they succeeded. More than 80% of light fixtures were replaced with full-cut-off shielding to direct light down instead of allowing it to spill up.

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Light pollution model for Natural Bridge and surrounding region (left). Image credit: NPS. Light pollution monitoring photograph. Image credit: Night Sky Team.

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How dark is dark? From the night sky models of the park and surrounding regions, Natural Bridge is far away from the light-glow of nearby urban centers. A handy mountain cluster protects the park from the major city lights to the north. When the Night Sky Team came to take light pollution monitoring photographs, almost the entire sky mapped onto the deepest purple of the darkest sky, and not a single glimmer of bright-light whites, reds, oranges, or yellows made it into the survey.

To soak in some of these truly dark skies, go camping in the park. It's open year-round, with 13 no-reservation camp sites. While entering the park is $3 per person per week (or $7 per carload), camp sites are a bit more pricy at $10 per night. The interpretive center has more information on preserving dark skies, and volunteers run astronomy programs throughout the summer.

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Pick up a stunning wallpaper of Owachomo Bridge at Night on National Geographic, or read the Natural Bridge's Dark Sky Park application. I love dark skies, and think Dark Sky Week is a fantastic excuse to turn off the lights.

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