Meteors, also called shooting stars, normally begin as bits of dust from the tails of comets or even small pieces chipped off asteroids. Falling toward Earth, these particles enter the atmosphere at extremely high speeds. Friction with the air heats them up and makes them glow brightly. Their rapid motion across the sky causes them to show up as bright streaks in photographs. In this picture, however, the bright streaks which appear to be meteor trails are believed to be two large pieces of the Apollo 13 spacecraft, the service and lunar modules, reentering the atmosphere.