Meteor showers occur when Earth passes through debris trails left by comets.

Comets are dirty snowballs. As they orbit the Sun, they shed dust and rock along their path. These debris trails persist for centuries. Each year, Earth's orbit crosses several of these trails. When we plow through one, the rate of meteors jumps dramatically — dozens or hundreds per hour. The shower gets its name from the constellation where the meteors appear to radiate. The Perseids come from comet Swift-Tuttle. The Geminids are unusual — they come from an asteroid, 3200 Phaethon, that behaves like a comet.