What do we lose when we lose the night? This central question begins the film The City Dark (thecitydark.com), filmmaker Ian Cheney's quest to find the night sky and understand the complex relationship between light and dark. The film is Cheney's personal journey, a three-year-long project prompted by his memory of the starry Maine nights of his childhood.

“Why couldn't I experience the same thing in New York City?” he asks when I meet him in Washington, D.C., for the film's August screening at the Environmental Film Festival. “I was acutely missing something, but I couldn't exactly say what it was. How do you give value to something like that?”

Cheney is no stranger to documentary filmmaking or tackling subjects that have to do with the environment. With several films already to his credit—including the Peabody Award–winning King Corn (2007), which is a look at food production in the United States, and The Greening of Southie (2008), which is the story about a Boston housing developer who is integrating green-building strategies—The City Dark continues the theme of environmental queries. “I didn't really know anything about the [dark sky] issue or anything about lighting when I began the project,” he says. “Each interview led me to the next person or angle to examine.”

One thing he did know was where he wanted to start—with astronomers. He first spoke with some astronomers at the Mont-Mégantic observatory in Notre Dame des Bois, Quebec, Canada, which is the first observatory to have its dark-sky reserve be recognized by the International Dark-Sky Association in 2007. (A dark-sky reserve is an international preserve of darkness around a facility to maintain ability to view the night sky.)

From Quebec, Cheney's journey took him back to New York, then Maine, Arizona, New Mexico, Florida, and Hawaii. Along the way he met people as diverse as the subject matter itself—astrophysicists, astronauts, astronomers (professional and amateur), writers and historians, night-sky enthusiasts, Boy Scouts, biologists, neurologists, criminologists, and lighting designers (Howard Brandston and Hervé Descottes make appearances). More than two dozen interviews are incorporated into the film, which unfolds in a series of six “chapters,” each of which looks at the issue—the loss of the night sky—from a different vantage point.

The first chapter, The City Bright, sets the stage and begins to suggest that the loss of the night sky is about more than merely not being able to see the stars. As amateur astronomer Sam Storch says in a scene filmed at Jones Beach on Long Island—where stargazing was prevalent and popular in the 1970s—“It just doesn't get dark anymore.”

The next section, Islands of Dark, sees Cheney travel to “Sky Village” in Arizona, a community of amateur night-sky enthusiasts founded by astrophotographer Jack Newton more than 30 years ago. In this chapter, Cheney also travels to Hawaii to interview the astronomers and scientists at the University of Hawaii, considered to be the best location on the planet from which to observe the Milky Way and the night sky in all its glory.

Nature and the Night explores how manmade light impacts animals and their natural habitats. From the disruption of bird migration caused by the reflections from building glass to the plight of hatching baby sea turtles along the Florida coast that walk inland instead of toward the ocean, more wildlife is impacted by artificial light than we realize.

Night Shifts, the fourth chapter, examines the relationship between light and human health, in particular long-term exposure to artificial light late at night. Cheney interviews a breast cancer patient and several noted physicians, including neurologist Dr. George Brainard at the University of Pennsylvania, one of the leading researchers on the subject of melatonin production.

The fifth chapter, Why We Light, examines the social context of light and touches on some of the traditional arguments about why there is the need for light at night—mainly, safety and prevention of crime.

By the time we arrive at the final chapter, Astrophilia, we have made the complete journey with Cheney and have witnessed his realization: The illuminated city plays an important role in our cultural imagery, and is just as important as the stars and the night sky.

Overall the film's narrative is balanced and the discussion is thought provoking. You come away with the conclusion that something is indeed lost in our human condition when we lose our connection to nature and the ability to see the stars. But that loss must also be put into perspective by countering it with the benefits of living in a modern society. Unfortunately, sorting out the pros and cons of these two competing interests will only continue to get more difficult as we live faster and faster lives in a 24/7 world. The real challenge is how we find a way to balance these two competing interests.

The City Dark is an honest and very reasonable portrayal of the issue without being preachy. Cheney hopes that it will help people to have a greater awareness about the physical environment and how we light it. “I don't want to give up on the idea that you can see stars in the city,” he says. “Its a way of thinking about the future and grappling with modernity.”