Idling on a beach, I sometimes wonder why the rings on a shell are so much like the rings of Saturn. The connectedness of earth to space and especially to mystery is at the heart of Patricio Guzman’s beautiful, poetic film “Nostalgia for the Light.”

The film, making its U.S. broadcast debut tonight on “POV” (PBS, 10 p.m., check local listings), is ostensibly about the Atacama Desert, 10,000 above sea level and the driest spot on the planet, allowing it clear looks at the stars, attracting astronomers from all over the world.

But the telescopes were closed during the dark days of the Pinochet years. Instead, concentration camps were made out of old mines in the desolate area, and thousands of the disappeared were disposed there.

Archeologists have found many of the bodies, or parts of them, alarmingly intact, thanks also to the dry conditions. But they’ve also found pre-Columbian mummies and 19th century explorers beneath the sand as well. For years, mothers of the disappeared have walked the sands as well, looking for loved ones and closure.

Guzman has thoughtful conversations with each of these truth-seekers – the astronomers, the archeologists and the determined but worn loved ones and find they’re all looking for answers that might be connected. It’s an extraordinary film, quite different from anything you’ll see on TV tonight or any other night.