There are undeniable bright sides to electric lighting. It is hard to work, travel or read in the dark, but with the flip of a switch the problem disappears. The economic boons are so profound that you can see their effects from deep space, in the shining networks of nighttime lights that outline our flourishing global civilization. But our modern love of light-filled nights casts a long shadow—wasting energy, disrupting ecosystems, and in some cases harming human health. And the same lights that lace our planet and reveal our presence to the outside universe are also smothering our views of the stars.
According to the atlas, roughly one in three humans on Earth cannot see the Milky Way when they look up into the night sky. For Americans, the percentage is higher: Light pollution prevents four out of five from seeing our home galaxy as a gauzy river of light arcing overhead. Residents of particularly light-polluted countries such as Singapore, South Korea and Qatar can scarcely see any stars at all, and instead spend their nights in perpetual “artificial twilight.” Outside of the relatively barren open ocean and polar wastelands, the fraction of the populated planet with naturally dark skies is limited to off-the-beaten-path places like Chad, Papua New Guinea and Madagascar—and is steadily shrinking.