Phosphorescent describes something that glows in the dark after being exposed to light. Those glow-in-the-dark stars you stick on your bedroom ceiling are phosphorescent: you charge them up with light during the day, and they release that stored energy slowly as a gentle glow at night.

The process works differently from things that need constant electricity or batteries. A phosphorescent material absorbs light energy and then releases it gradually over time, sometimes for hours. Some minerals glow this way too, continuing to shine long after you turn off your flashlight.

Scientists distinguish phosphorescence from fluorescence, which stops glowing the instant you remove the light source. A phosphorescent watch dial keeps glowing after you leave a bright room, while a fluorescent poster only glows while a blacklight shines on it.

When people first saw foxfire (glowing fungi) illuminating rotting logs in dark forests, they called this mysterious glow phosphorescent.