ATOMIC CLOCK

An atomic clock uses as its oscillator the very high and regular frequency of the electromagnetic radiation emitted by an electron when moving from one energy level to another. There are atomic clocks based on caesium-133, hydrogen, and rubidium. Atomic clocks often operate in networks, thereby mutually correcting one another. The precision of modern atomic clocks enables them to have a drift of about one second every 13 billion years. They are used to define Coordinated Universal Time (UTC) as well as for numerous scientific applications (space observation, etc.).