World map of light pollution. (Photo via Wikimedia Commons.)

Until 140 years ago, the night sky was dark. When the sun set, the moon shone and stars twinkled. The Milky Way splashed across the dark sky. The Northern Lights flickered and rippled.

Then came the invention of electricity.

Who turned on the lights?

Today, our cities are so brightly lit they can be seen from space. Businesses, signs, and homes blaze with lights. Streetlights and headlights pierce the night. Light pollution leaks out of cities and spreads through the night sky. The glow even reaches wilderness areas.