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Language:enStatus: Standard
Term: universal time
Synonym1: UT (abbreviation)
Synonym2: GMT, (abbreviation strongly deprecated in this sense)
Definition: one of the time scales based on the rotation of the Earth

NOTE 1 – In applications in which an imprecision of a few hundredths of a second cannot be tolerated, it is necessary to specify the forms of universal time which should be used:

– UT0 is the mean solar time of the prime meridian obtained from direct astronomical observation;

– UT1 is UT0 corrected for the effects of small movements of the Earth relative to the axis of rotation in a stellar reference frame (polar variation);

– UT2 is UT1 corrected for the effects of small seasonal fluctuation in the rate of rotation of the Earth in a stellar reference frame.

NOTE 2 – The Mean Solar Time of Greenwich called Greenwich Mean Time (GMT) may be regarded as the equivalent of Universal Time, but with a difference of 12 hours.

Publication date:1998-04
Source:ITU-R Rec. 686 MOD
Internal notes:2016-02-01: Synonym2Status updated in accordance with mail from Jean Schwob. JGO
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