What is typically measured by an atomic clock?

An atomic clock measures time based on atomic transitions, which is the process of electrons moving between different energy levels in an atom. These transitions occur at remarkably stable and predictable frequencies, which means that atomic clocks are able to maintain extremely accurate timekeeping. By using specific types of atoms, such as cesium or rubidium, atomic clocks can define the second in terms of the vibrations of these atoms.

The consistency and precision of atomic transitions make them the standard for high-precision timekeeping, allowing atomic clocks to keep time to within a few billionths of a second. This remarkable accuracy is utilized in various applications, including GPS satellites, telecommunications, and scientific research, where precise time measurement is crucial.