A meteor shower in the night sky. Mezzotint, August 18, 1783. As astronomers began to explore the physical nature of comets, they found that meteors came from dust left by comets. A meteor shower is a celestial event in which a number of meteors are observed to radiate, or originate, from one point in the night sky. These meteors are caused by streams of cosmic debris called meteoroids entering Earth's atmosphere at extremely high speeds on parallel trajectories. Most meteors are smaller than a grain of sand, so almost all of them disintegrate and never hit the Earth's surface.