Coordinated Universal Time

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coordinated universal time

(UTC) See universal time.

Coordinated Universal Time (UTC)

A time based on the fundamental properties of an atom, the isotope of cesium 133, and not on the movement of heavenly bodies. Atomic time increases at a constant rate, unlike the GMT (Greenwich mean time). This time is corrected for the seasonal variation in the earth's rotation about the sun to bring it within +/−0.1 s of GMT. When the correction reaches +/−0.7 s, a positive or negative leap second is applied to the UTC.

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 Coordonn?".


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.