2005
DOI: 10.1088/0026-1394/42/3/s03
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The definition of the ‘atomic’ second

Abstract: When the reference of a unit is changed, the task remains of expressing the new definition in the terms of the previous one. In two centuries, for instance, the definition of the metre was changed six times. Around 1955, the definitions of the second as the SI unit of time were changed from astronomical ones, based on the rotation (or revolution) of the Earth, to a definition stemming from a quantum phenomenon. The expression of the new atomic second in terms of the previous definitions required a number of ac… Show more

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Cited by 22 publications
(16 citation statements)
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“…Atomic clocks keep time by first establishing the duration of the second based on counting the frequency of the transitions between two energy levels in an atom (a frequency of 9.192631770 GHz in the case of the cesium atom), and by then counting seconds to form longer time intervals such as minutes, hours, and days. The second had previously been defined by first establishing long astronomical intervals, such as the mean solar day and the tropical year, and then dividing to obtain shorter intervals [26][27][28].…”
Section: Reference Time Sourcesmentioning
confidence: 99%
“…Atomic clocks keep time by first establishing the duration of the second based on counting the frequency of the transitions between two energy levels in an atom (a frequency of 9.192631770 GHz in the case of the cesium atom), and by then counting seconds to form longer time intervals such as minutes, hours, and days. The second had previously been defined by first establishing long astronomical intervals, such as the mean solar day and the tropical year, and then dividing to obtain shorter intervals [26][27][28].…”
Section: Reference Time Sourcesmentioning
confidence: 99%
“…As expressed by Leschiutta, [9] this practice guarantees that by changing the unit no bias is introduced in series of measurements covering different unit definitions. As expressed by Leschiutta, [9] this practice guarantees that by changing the unit no bias is introduced in series of measurements covering different unit definitions.…”
Section: The Continuity Of the Successive Definitionsmentioning
confidence: 99%
“…That time scale, known as Ephemeris Time, promised a more stable definition but the advent of atomic standards rapidly overcame that definition. Atomic clocks offered a more accurate method of generating and maintaining time through the standardization of the "Second" from an astronomical variable to a fundamental constant based on atomic physics [4].…”
Section: Origins Of Utcmentioning
confidence: 99%
“…Atomic time maintained continuously in various laboratories since 1955 quickly become the basis of all time scales, although it was not formally adopted until 1971 as an international time scale [4]. Direct comparison of time keeping systems by means of radio transmissions became available in about 1961.…”
Section: Origins Of Utcmentioning
confidence: 99%
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