CARL SAGAN ONCE said anything shining in the night sky does so because of distant nuclear fusion. The physics involved are awesome, and so too are the billions and billions of stars seen from here on Earth. But with every passing day, increasing light and air pollution from growing cities diminishes our ability to observe the cosmos.French artist Thierry Cohen draws attention to this creeping loss in his series Villes éteintes (Darkened Cities), which imagines the world’s largest cities under clear night skies. His photographs are as impossible as they are beautiful. The dark urban landscapes and vibrant constellations are composites of two images—one of the city and one of the sky.