A "shooting star" is not actually a star but a meteor. It occurs when a small piece of space debris, often no larger than a grain of sand, enters the Earth's atmosphere at high speed. As it travels through the atmosphere, the friction causes it to heat up and produce a bright streak of light, which we see as a shooting star. Most shooting stars burn up completely before reaching the ground. However, if a larger piece survives the journey and lands on Earth, it is called a meteorite. Shooting stars are most commonly seen during meteor showers, which happen when Earth passes through trails of debris left by comets.