What Is The Atomic Clock?

An atomic clock is a clock that keeps time using the various periodic processes that occur in atoms and molecules, such as atomic vibration or the frequency at which atoms and molecules absorb or emit radiation. These events occur at a constant rate that are unaffected by outside factors such as temperature, pressure, or others, so the time measured is incredibly accurate.

The first atomic clock was the ammonia clock that was invented at the US National Bureau of Standards in 1948. It measured the speed at which a nitrogen atom in an ammonia molecule vibrated backwards and forwards.

A more accurate atomic clock is the caesium clock. This is based on the production and absorption of radiation by the caesium atom which occurs at the very precise frequency of 9 192 631 770 Hz. The variation occurs at a rate less than one part in 10 billion. Hydrogen maser clocks, based on the radiation from hydrogen atoms are the most accurate and lose less than one second in one and a half million years.