atomic clock

noun
an extremely accurate electronic clock regulated by the resonance frequency of atoms or molecules of certain substances, as cesium.

Origin:
1935–40

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Collins
World English Dictionary
atomic clock
 
n
an extremely accurate clock in which an electrical oscillator is controlled by the natural vibrations of an atomic or molecular system such as caesium or ammonia

Collins English Dictionary - Complete & Unabridged 10th Edition
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American Heritage
Science Dictionary
atomic clock  
An extremely precise clock whose rate is controlled by a periodic process (such as vibration, or the absorption or emission of electromagnetic radiation) that occurs at a steady rate in atoms or molecules. The standard atomic clock is based on the vibrations of cesium atoms and is so accurate that it would gain or lose less than one second in three million years. Atomic clocks are used to help track satellites, run navigation systems, and study movements of the Earth's crust.
The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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American Heritage
Cultural Dictionary

atomic clock definition


The most accurate clock available. Time is measured by the movement of electrons in cesium atoms. The standard second is now defined by measurements on an atomic clock.

The American Heritage® New Dictionary of Cultural Literacy, Third Edition
Copyright © 2005 by Houghton Mifflin Company.
Published by Houghton Mifflin Company. All rights reserved.
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Encyclopedia Britannica
Encyclopedia

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. Only when this radiation is maintained at a highly specific frequency will it induce the quantum transition (energy change) of the cesium or rubidium atoms. In an atomic clock these quantum transitions are observed and maintained in a feedback loop that trims the frequency of the electromagnetic radiation; like the recurrent events in other types of clocks, these waves are then counted.

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Encyclopedia Britannica, 2008. Encyclopedia Britannica Online.
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Example sentences
The atomic clock may have slowed a bit, but it is still ticking.
He was a self-educated mathematician and amateur scientist who bought an atomic
  clock and an electron microscope.
It would go everywhere you go, and it would always be correct since it would be
  an atomic clock.
His work would end up making the atomic clock even more precise.
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