Coordinated Universal Time
<time, standard> (UTC, World Time) The standard time common to every
place in the world. UTC is derived from International Atomic Time (TAI) by the
addition of a whole number of "leap seconds" to synchronise it with Universal
Time 1 (UT1), thus allowing for the eccentricity of the Earth's orbit, the
rotational axis tilt (23.5 degrees), but still showing the Earth's irregular
rotation, on which UT1 is based.
Coordinated Universal Time is expressed using a 24-hour clock and uses the
Gregorian calendar. It is used in aeroplane and ship navigation, where it also
sometimes known by the military name, "Zulu time". "Zulu" in the phonetic
alphabet stands for "Z" which stands for longitude zero.
UTC was defined by the International Radio Consultative Committee (CCIR), a
predecessor of the ITU-T. CCIR Recommendation 460-4, or ITU-T Recommendation
X.680 (7/94), contains the full definition.
The language-independent international abbreviation, UTC, is neither English nor
French. It means both "Coordinated Universal Time" and "Temps Universel
The Royal Observatory Greenwich.
History of UTC and GMT.
U.S. National Institute of Standards & Technology.
UK National Physical Laboratory.
US Naval Observatory.
International Telecommunications Union.
Earth's irregular rotation.
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