atomic clock

An atomic clock is a clock that uses the resonance frequencies of atoms to keep time with extreme accuracy. The electronic components of an atomic clock are regulated by the frequency of microwave radiation that is emitted or absorbed by the quantum transition (energy change) of an atom or a molecule. In atomic clocks, quantum transitions produce extremely regular waves of electromagnetic radiation. Clocks that run on the radiation from hydrogen atoms, for example, lose only one second in about 1,700,000 years.