ruddy duck: reddish-brown stiff-tailed duck of North America and northern South America
duck: small wild or domesticated web-footed broad-billed swimming bird usually having a depressed body and short legs
bohr theory: (physics) a theory of atomic structure that combined Rutherford's model with the quantum theory; electrons orbiting a nucleus can only be in certain stationary energy states and light is emitted when electrons jump from one energy state to another