For a clock updated by radio signals, see Radio clock. For the clock as a measure for risk of catastrophic destruction, see Doomsday Clock. For other topics, see Atomic Clock (disambiguation).
Atomic clock
NIST physicists Steve Jefferts (foreground) and Tom Heavner with the NIST-F2 caesium fountain atomic clock, a civilian time standard for the United States
Classification
Clock
Industry
Telecommunications, science
Application
TAI, satellite navigation
Fuel source
Electricity
Powered
Yes
The master atomic clock ensemble at the U.S. Naval Observatory in Washington, D.C., which provides the time standard for the U.S. Department of Defense.[1] The rack mounted units in the background are Microsemi (formerly HP) 5071A caesium beam clocks. The black units in the foreground are Microsemi (formerly Sigma-Tau) MHM-2010 hydrogen maser standards.
An atomic clock is a clock that measures time by monitoring the resonant frequency of atoms. It is based on atoms having different energy levels. Electron states in an atom are associated with different energy levels, and in transitions between such states they interact with a very specific frequency of electromagnetic radiation. This phenomenon serves as the basis for the International System of Units' (SI) definition of a second:
The second, symbol s, is the SI unit of time. It is defined by taking the fixed numerical value of the caesium frequency, , the unperturbed ground-state hyperfine transition frequency of the caesium-133 atom, to be 9192631770 when expressed in the unit Hz, which is equal to s−1.
This definition is the basis for the system of International Atomic Time (TAI), which is maintained by an ensemble of atomic clocks around the world. The system of Coordinated Universal Time (UTC) that is the basis of civil time implements leap seconds to allow clock time to track changes in Earth's rotation to within one second while being based on clocks that are based on the definition of the second, though leap seconds will be phased out in 2035.[2]
The accurate timekeeping capabilities of atomic clocks are also used for navigation by satellite networks such as the European Union's Galileo Programme and the United States' GPS. The timekeeping accuracy of the involved atomic clocks is important because the smaller the error in time measurement, the smaller the error in distance obtained by multiplying the time by the speed of light is (a timing error of a nanosecond or 1 billionth of a second (10−9 or 1⁄1,000,000,000 second) translates into an almost 30-centimetre (11.8 in) distance and hence positional error).
The main variety of atomic clock uses caesium atoms cooled to temperatures that approach absolute zero. The primary standard for the United States, the National Institute of Standards and Technology (NIST)'s caesium fountain clock named NIST-F2, measures time with an uncertainty of 1 second in 300 million years (relative uncertainty 10−16). NIST-F2 was brought online on 3 April 2014.[3][4]
^"USNO Master Clock". Archived from the original on 7 December 2010. Retrieved 23 November 2010.
^Brumfiel, Geoff (27 November 2022). "The world is doing away with the leap second". Weekend Edition Sunday. National Public Radio. Retrieved 30 April 2024.
^"NIST Launches a New U.S. Time Standard: NIST-F2 Atomic Clock". NIST. 3 April 2014 – via www.nist.gov.
^First Accuracy Evaluation of NIST-F2, T. P. Heavner, S. R. Jefferts, J. H. Shirley, T. E. Parker, E. A. Donley, N. Ashby, S. Barlow, F. Levi, and G. Costanzo, May 2014.
An atomicclock is a clock that measures time by monitoring the resonant frequency of atoms. It is based on atoms having different energy levels. Electron...
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mechanical clock. Hence most everyday quartz clocks do not have an adjustable drift correction. Atomicclocks are very precise and have nearly no clock drift...
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International Atomic Time (TAI) are also used alongside UTC. UTC is based on TAI, which is a weighted average of hundreds of atomicclocks worldwide. UTC...
frequency, in the same manner as an atomicclock uses the frequency of an electronic transition in an atom's shell. Such a clock is expected to be more accurate...
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settings atomicclocks had replaced quartz clocks as the basis for precision measurements of time and frequency, resulting in International Atomic Time....
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Gernot M. R. Winkler of the United States Naval Observatory. Caesium atomicclocks are one of the most accurate time and frequency standards, and serve...
133 Atomic Watch the first watch to keep time with an internal atomicclock. Unlike the radio watches described above, which achieve atomicclock accuracy...
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collaboration with Jack Parry, the first practical atomicclock by integrating the caesium atomic standard with conventional quartz crystal oscillators...
cesium-beam atomicclocks were flown around the world and the expected differences were found compared to a stationary clock. The clock hypothesis states...
field using accurate atomicclocks placed in orbit inside artificial satellites. Special and general relativity predicted that the clocks on GPS satellites...
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