Each year as Earth journeys around the sun, it slams into streams of particles that comets have spewed into space. When these particles, known as meteoroids, smash into the atmosphere, they generate streaks of light called meteors. The most reliable meteor showers--the Perseids in August and the Geminids in December--sport about 60 meteors an hour and require nothing more than a dark, moonless sky in order to appreciate them.