An Atomic Clock is one that uses the frequency of absorbtion and emittion of electromagnetic radiation of a compound as a mechanism by which to divide time. This absorbtion and emittion, or oscillation is highly accurate. The atomic clock also has the benefits that it is possible for the atoms to oscillate forever without any distortions. This makes the precision of the atomic clock far greater than the precision of the quartz clock, in fact the atomic clock is accurate to one second in 1.4 million years.

The original atomic clock was invented in 1955 by Dr L Esson and originally worked with the chemical Ammonia. Within a few years the atomic clock was based on the Cesium-133 atom and in 1967 the second was defined as 9,192,631,770 oscillations of the Cesium atoms resonant frequency. The atomic clock is the standard by which time is currently measured (and defined).

The atomic clock is an expensive piece of scientific equipment that only lives inside laboratories and standards organisations. The atomic clock should not be confussed with the radio controlled or R-Wave clocks, which resynchronize their time to the time of atomic clocks, but are not atomic clocks.