Why do meteor showers happen on schedule?

The answer

Meteor showers occur when Earth passes through trails of debris left behind by comets (or occasionally asteroids) as they orbit the Sun. Each time a comet passes near the Sun, it sheds particles that spread along its orbit like a dusty highway. When Earth intersects this debris stream, the particles (usually no bigger than grains of sand) enter our atmosphere at speeds of 11 to 72 km/s and burn up as shooting stars. Because Earth's orbit is consistent, we encounter the same debris streams at the same dates each year - the Perseids every August, the Geminids every December.