What is light pollution?

Light pollution comes from streetlights, buildings, signs and other outdoor lighting that spills upward or outward instead of where it is needed. A 2016 world atlas estimated that more than 80 percent of people live under light-polluted skies, and about a third of humanity cannot see the Milky Way. Artificial light confuses migrating birds and hatching sea turtles, which use natural light cues to navigate. It can also disturb human sleep by suppressing the hormone melatonin. Dark-sky reserves, certified by DarkSky International, protect areas where the night sky remains naturally dark.