An atomic clock is a timepiece that keeps time based on the very regular vibrations certain molecules make when they are subjected to an electric charge. These clocks are so accurate that they need to be occasionally adjusted to compensate for the constant, gradual slowing of the Earth's rotation. A high-precision pendulum clock, by contrast, keeps precise time within about three seconds per year.
Atomic clocks can maintain accuracy because they're based on the atomic properties of substances.
This substance is introduced into metal chambers charged to a high voltage. The charge separates the higher energy NH 3 molecules from the lower energy ones. The high-energy molecules are collected and focused into a resonator where they begin to vibrate at a constant rate. The unvarying vibrations provide a basis for the precise measurement of time. Some atomic clocks are available on the Internet so you can synchronize your personal computer's daytime clock.