[HECnet] How long has your 20 been up?

[Peter Lothberg]

Time.... 


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>Not quite. The acronym actually says that it is not solar time, it's Greenwich MEAN Time. UTC is merely the new name for GMT, obviously adopted to keep the French from fulminating. 
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GMT was established by the Greenwich observatory observing the sun. 

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When the atomic second was created the target was the year 1900 GMT second. 

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GMT is based on earth position, and it's modern equivalent is UT1, when UTC and UT1 differs more than 0.92 sec 

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we do leap seconds. 

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[ https://www.iers.org/IERS/EN/Science/EarthRotation/UT1LOD.html | https://www.iers.org/IERS/EN/Science/EarthRotation/UT1LOD.html ] 

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UTC is based on a constant running timescale based on the frequency of CS133 oscillating between two 
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hyper fine states. 

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So the difference between GMT and UTC can be almost a second, and there is no system that 

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distributes GMT, BTP, GPS etc are all UTC based. 

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-P 

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