Transcript: There’s an important sense in which the analogy of an atom as a miniature solar system is wrong. In a solar system a planet can have any distance from the central star and any energy in its orbit. This is not true of an atom. In classical physics atoms can have any energy. However in the quantum theory atoms can only have particular discrete amounts of energy, and they can only change their energy by fixed or discrete amounts. These fixed amounts of change of energy for atoms correspond to the photons that atoms can emit and receive.