An atomic clock is based on a system of atoms which may be in one of two possible energy states. A group of atoms in one state is prepared, then subjected to microwave radiation. If the radiation is of the correct frequency, a number of atoms will transition to the other energy state.

Time.is displays exact, official atomic clock time for any time zone (more than 7 million locations) in 57 languages.

Learn how atomic clocks measure the precise length of a second using the natural oscillations of caesium-133 atoms. Find out how accurate they are and why they are important for time standards and navigation systems.

Atomic clocks combine a quartz crystal oscillator with an ensemble of atoms to achieve greater stability. NASA’s Deep Space Atomic Clock will be off by less than a nanosecond after four days and less than a microsecond (one millionth of a second) after 10 years.

They use atomic clocks. These remarkable devices tap into frequencies hidden in the hearts of atoms to produce astoundingly stable, accurate ticks of time — far better than any other kind of clock. This animation explains why we use atoms to keep time and how they keep us all on the beat.

atomic clock, type of clock that uses certain resonance frequencies of atoms (usually cesium or rubidium) to keep time with extreme accuracy. The electronic components of atomic clocks are regulated by the frequency of the microwave electromagnetic radiation.

Atomic clocks have revolutionized how we tell time. These astoundingly accurate devices touch the lives of every person on Earth and keep us in sync no matter where we are. They make possible world-changing technologies such as GPS and help scientists explore some of the universe’s deepest mysteries.

Learn how NIST developed and improved atomic clocks based on cesium and ammonia molecules, and how they defined the second and measured time. See the milestones, photos and references of the NIST atomic clock history.

NASA's Deep Space Atomic Clock could be the most stable atomic clock ever flown in space. But what does that mean, and what do clocks have to do with space navigation?