Cesium Atomic Clock is 50 Years Old
-- Test & Measurement World, 7/28/2005 12:36:00 PM
2005 marks the 50th anniversary of the cesium atomic clock. In 1955, Dr. Louis Essen and Jack Perry developed the first accurate cesium atomic clock at the National Physical Laboratory (www.npl.co.uk/essen). A cesium clock uses the natural frequency of the cesium-133 atom, which produces an oscillation at 9,192,631,770 Hz.
The cesium clock led to the redefinition of the second as a unit of time, which is now 9,192,631,770 cycles produced by the cesium-133 atom. Prior to 1967, the second was based on the movements of celestial bodies (www.imakenews.com/symmttm/e_article000432361.cfm).
Today, some 40 countries coordinate the outputs of cesium clocks to produce the world standard for time. Universal coordinated time (UTC) keeps everyone in sync. The global positioning system (GPS) uses atomic clocks and serves as a timekeeper for millions of GPS receivers. These, in turn, are often used to keep time for many computer networks. The accuracy of cesium clocks has led to the discovery of small changes in the Earth's rotational speed.
To learn more about cesium atomic clocks, see:
"NIST-F1 Cesium Fountain Atomic Clock: The Primary Time and Frequency Standard for the United States"
National Institute of Science and Technology, Boulder, CO.
tf.nist.gov/cesium/fountain.htm
"The USNO Cesium Fountain Project"
United States Naval Observatory, Washington, DC.
tycho.usno.navy.mil/clockdev/cesium.html
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