[ntp:questions] Re: Newbie questions, UTC vs. Greenwich

Markus Kuhn n06W04+mgk25 at cl.cam.ac.uk
Tue Jan 24 13:41:56 UTC 2006

alkruse at gmail.com (Alan Kruse) writes:
|> What is the difference between Universal Coordinated Time (UTC) and
|> Greenwich Mean Time?

Greenwich Mean Time is a historic term that is no longer used among
time-keeping experts or in many languages (other than English). There
is no modern official definition of what GMT is exactly, but astronomers
generally will tell you that GMT is pretty much the same as the modern
astronomical definition of time they call UT1 today. UTC is a time
produced by precision clocks (mostly cesium resonantors) that is
guaranteed to be within 0.9 seconds of UT1.

So the difference between UTC and GMT is: < 0.9 s

For non-astronomical purposes, e.g. computer timekeeping,
UTC is the modern-day replacement for GMT. UTC is today widely
announced with far greater accuracy over radio signals than
any time called GMT ever was.



Markus Kuhn, Computer Laboratory, University of Cambridge
http://www.cl.cam.ac.uk/~mgk25/ || CB3 0FD, Great Britain

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