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Plenty of earthly things can glow, or make their own light. Puerto Mosquito bay, Puerto Rico, is a sparkling example.
Run your hand through water in the bay, and millions of very tiny plankton (microscopic plants and animals) twinkle, like stars. Glow-in-the-dark creatures such as plankton create light with little heat. But other things glow because they’re hot—coal, charcoal, lava from a volcano. When they’re cold, these things are black and lightless. When they’re hot, they glow a bright reddish orange.
