Spin-orbit coupling

In atomic physics, spin-orbit coupling describes the interaction of the particle spin and the orbital motion of this particle, e.g. the electron spin and its motion around an atomic nucleus. One of its effects is to degenerate the energy level for the parallel and anti parallel cases, of the spin and the Angular momentum.

In astronomy, spin-orbit coupling is the ratio between the frequency with which a planet or other celestial body spins about its own axis to that with which it orbits another body. This is more commonly known as orbital resonance.