The Sun and the objects that travel around it form the solar system. Nine planets travel in a path called a(n) orbit. These planets don’t give off light; instead they reflect sunlight. Each planet spins, or rotates, making a complete turn during its day. For Earth, this day-night cycle takes 24 hours. Earth is the third planet from the Sun. An invisible force called gravity keeps Earth from flying off into space. This force of attraction depends on distance and mass.