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In Southern Arizona, relatively dark night skies are taken for granted. Even in Tucson, we can see hundreds of stars in the sky. Rural residents can see even more. And astronomers at the area's many observatories also find that, even close to Tucson, conditions are excellent for sky gazing.

But not perfect.

Even at some of the darkest observatories in the state, light pollution creeps in from Tucson and Phoenix. In other parts of the world, light pollution has made all but the brightest objects in the sky impossible to see.

This troubled filmmaker Ian Cheney. He noticed it in particular when he moved from rural Maine to New York City and was shocked at how little he could see above him.

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Photo: Wicked Delicate Films LLC

Filmmaker Ian Cheney under a typical high-pressure sodium streetlight in New York City.

His documentary The City Dark looks at the increasing encroachment of light and what it means for humanity to slowly lose its connection to the night sky.

The film follows a group of boy scouts from the New York City area on a camping trip to a wilderness area. The boys, accustomed as they are to being able to see only a handful of stars in the city, are amazed to discover more than a hundred objects glowing above them.

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Photo: Wicked Delicate Films LLC

Stargazing in Times Square.

Scott Kardel with the Tucson-based International Dark Sky Association, says there are more than 2,500 objects in the night sky that should be visible with the naked eye. But most can only be seen in the darkest of places, like far from the city lights and at the state's many mountaintop observatories.

Grant Williams is the director of one of those observatories, the MMT on Mount Hopkins. It's home to a 6.5-meter telescope, one of the largest in North America. Williams says there are some faint objects in the sky that are troublesome to see with the MMT, because of the sky glow emanating from Tucson, 30 miles to the north. Despite that, Williams says the site is dark enough that most observations are not affected.

Watch "The City Dark" at 11 p.m., July 5, on PBS6.

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Photo: Wicked Delicate Films LLC

The Milky Way above an Arizona observatory.

More resources:
PBS' POV page on "The City Dark"
Globe At Night
Light Pollution Science and Technology Institute

Explore:
The International Dark Sky Association works with municipalities to enact what they call "Model Lighting Ordinances." Read more:

dark-skies-model-lighting-org.pdf: View at Google Docs | Download File