It takes a moment for the eyes to adjust. A faint spark appears in the darkness; then another, brighter one. Soon, stars, planets and entire constellations emerge. Before long, a whole galaxy stretches across the sky, visible to the naked eye. In Chile’s Atacama Desert, the night sky feels infinite. Considered the driest place on Earth , its darkness is also one of the clearest windows to the universe. A rare combination of dry climate, high altitude and, crucially, isolation from urban light pollution, makes the Atacama an unrivaled hub for world-class astronomy and home to the world’s largest ground-based astronomical projects. “The conditions in the Atacama Desert are unique in the world,” said Chiara Mazzucchelli, president of the Chilean Astronomical Society. “There are more than 300 clear nights per year, meaning no clouds and no rain.” But the world's darkest skies may be at risk.…