Coordinated Universal Time

UTCUTC-3UTC-4UTC+05:30ZCoordinated Universal Time (UTC)UTC−3UTC-5UTC±0Universal Coordinated Time
Coordinated Universal Time (abbreviated to UTC) is the primary time standard by which the world regulates clocks and time.wikipedia
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Greenwich Mean Time

GMTGMT+4UTC±00:00
In some countries where English is spoken, the term Greenwich Mean Time (GMT) is often used as a synonym for UTC.
English speakers often use GMT as a synonym for Coordinated Universal Time (UTC).

Leap second

leap secondsabolish the leap secondAnother second
This change also adopted leap seconds to simplify future adjustments.
A leap second is a one-second adjustment that is occasionally applied to civil time Coordinated Universal Time (UTC) to keep it close to the mean solar time at Greenwich, in spite of the Earth's rotation slowdown and irregularities.

List of UTC time offsets

list of time zones by UTC offset
Time zones around the world are expressed using positive or negative offsets from UTC, as in the list of time zones by UTC offset. Current civil time in a particular time zone can be determined by adding or subtracting the number of hours and minutes specified by the UTC offset, which ranges from UTC−12:00 in the west to UTC+14:00 in the east (see List of UTC time offsets).
This is a list of the UTC time offsets, showing the difference in hours and minutes from Coordinated Universal Time (UTC), from the westernmost (−12:00) to the easternmost (+14:00).

Earth's rotation

rotationrotation of the EarthEarth rotates
The current version of UTC is defined by International Telecommunications Union Recommendation (ITU-R TF.460-6), Standard-frequency and time-signal emissions, and is based on International Atomic Time (TAI) with leap seconds added at irregular intervals to compensate for the slowing of the Earth's rotation.
Atomic clocks show that a modern day is longer by about 1.7 milliseconds than a century ago, slowly increasing the rate at which UTC is adjusted by leap seconds.

Universal Time

UTUTCUT1
This CCIR Recommendation 460 "stated that (a) carrier frequencies and time intervals should be maintained constant and should correspond to the definition of the SI second; (b) step adjustments, when necessary, should be exactly 1 s to maintain approximate agreement with Universal Time (UT); and (c) standard signals should contain information on the difference between UTC and UT."
In fact, the expression "Universal Time" is ambiguous (when accuracy of better than a few seconds is required), as there are several versions of it, the most commonly used being Coordinated Universal Time (UTC) and UT1 (see ).

UTC offset

time offset from UTCtime offsetoffsets from UTC
Time zones around the world are expressed using positive or negative offsets from UTC, as in the list of time zones by UTC offset. Current civil time in a particular time zone can be determined by adding or subtracting the number of hours and minutes specified by the UTC offset, which ranges from UTC−12:00 in the west to UTC+14:00 in the east (see List of UTC time offsets).
The UTC offset is the difference in hours and minutes from Coordinated Universal Time (UTC) for a particular place and date.

International Atomic Time

TAIatomic timeTemps Atomique International
The current version of UTC is defined by International Telecommunications Union Recommendation (ITU-R TF.460-6), Standard-frequency and time-signal emissions, and is based on International Atomic Time (TAI) with leap seconds added at irregular intervals to compensate for the slowing of the Earth's rotation.
It is also the basis for Coordinated Universal Time (UTC), which is used for civil timekeeping all over the Earth's surface.

Daylight saving time

DSTPSTdaylight saving
It is within about 1 second of mean solar time at 0° longitude, and is not adjusted for daylight saving time.
The European Union has a coordinated shift, shifting all zones at the same instant, at 01:00 Coordinated Universal Time (UTC), which means that it changes at 02:00 Central European Time (CET) or 03:00 Eastern European Time (EET), the result is that the time differences across European time zone remain constant.

UTC−10:00

UTC−10−10:00-10 h
In 1995, the island nation of Kiribati moved those of its atolls in the Line Islands from UTC−10 to UTC+14 so that Kiribati would all be on the same day.
UTC−10:00 is a time offset that subtracts 10 hours from Coordinated Universal Time (UTC).

UTC−12:00

Howland and Baker IslandsIDLWEtc/GMT+12
The westernmost time zone uses UTC−12, being twelve hours behind UTC; the easternmost time zone, uses UTC+14, being fourteen hours ahead of UTC. Current civil time in a particular time zone can be determined by adding or subtracting the number of hours and minutes specified by the UTC offset, which ranges from UTC−12:00 in the west to UTC+14:00 in the east (see List of UTC time offsets).
UTC−12:00 is a time offset that subtracts 12 hours from Coordinated Universal Time (UTC).

Network Time Protocol

NTPNetwork TimeNTP server
The Network Time Protocol (NTP), designed to synchronise the clocks of computers over the Internet, transmits time information from the UTC system.
NTP is intended to synchronize all participating computers to within a few milliseconds of Coordinated Universal Time (UTC).

Time standard

time standardstimeflying clock
Coordinated Universal Time (abbreviated to UTC) is the primary time standard by which the world regulates clocks and time.
But Coordinated Universal Time (UTC) (an atomic-based time scale which is always kept within 0.9 second of UT1) is in common actual use in the UK, and the name GMT is often inaccurately used to refer to it. (See articles Greenwich Mean Time, Universal Time, Coordinated Universal Time and the sources they cite.)

Julian day

JDJulian dateday
Days are conventionally identified using the Gregorian calendar, but Julian day numbers can also be used.
Time intervals calculated from differences of Julian Dates specified in non-uniform time scales, such as Coordinated Universal Time (UTC), may need to be corrected for changes in time scales (e.g. leap seconds).

UTC±00:00

UTCUTC+0UTC±0
The time zone using UTC is sometimes denoted UTC±00:00 or by the letter Z—a reference to the equivalent nautical time zone (GMT), which has been denoted by a Z since about 1950.
Coordinated Universal Time (UTC), the basis for the world's civil time.

International Bureau of Weights and Measures

BIPMInternational Conference on Weights and MeasuresBIPM spelling
The time of events may be provisionally recorded against one of these approximations; later corrections may be applied using the International Bureau of Weights and Measures (BIPM) monthly publication of tables of differences between canonical TAI/UTC and TAI(k)/UTC(k) as estimated in real time by participating laboratories.
It combines, analyses, and averages the official atomic time standards of member nations around the world to create a single, official Coordinated Universal Time (UTC).

DUT1

DUT
The International Earth Rotation and Reference Systems Service (IERS) tracks and publishes the difference between UTC and Universal Time, DUT1 = UT1 − UTC, and introduces discontinuities into UTC to keep DUT1 in the interval (−0.9 s, +0.9 s).
The time correction DUT1 (sometimes also written DUT) is the difference between Universal Time (UT1), which is defined by Earth's rotation, and Coordinated Universal Time (UTC), which is defined by a network of precision atomic clocks.

Time zone

Sri Lanka Standard Time Zonetime zoneslocal time
Time zones around the world are expressed using positive or negative offsets from UTC, as in the list of time zones by UTC offset. The time zone using UTC is sometimes denoted UTC±00:00 or by the letter Z—a reference to the equivalent nautical time zone (GMT), which has been denoted by a Z since about 1950. Current civil time in a particular time zone can be determined by adding or subtracting the number of hours and minutes specified by the UTC offset, which ranges from UTC−12:00 in the west to UTC+14:00 in the east (see List of UTC time offsets).
Most of the time zones on land are offset from Coordinated Universal Time (UTC) by a whole number of hours (UTC−12 to UTC+14), but a few zones are offset by 30 or 45 minutes (e.g. Newfoundland Standard Time is UTC−03:30, Nepal Standard Time is UTC+05:45, and Indian Standard Time is UTC+05:30).

Second

ssecmegasecond
Nearly all UTC days contain exactly 86,400 SI seconds with exactly 60 seconds in each minute.
The international standard for timekeeping is Coordinated Universal Time (UTC).

Civil time

civil dayclock time
Current civil time in a particular time zone can be determined by adding or subtracting the number of hours and minutes specified by the UTC offset, which ranges from UTC−12:00 in the west to UTC+14:00 in the east (see List of UTC time offsets).
Modern civil time is generally standard time in a time zone at a fixed offset from Coordinated Universal Time (UTC) or from Greenwich Mean Time (GMT), possibly adjusted by daylight saving time during part of the year.

Time

temporaldurationintervals
It is not possible to compute the exact time interval elapsed between two UTC timestamps without consulting a table that shows how many leap seconds occurred during that interval.
A few countries have replaced it with Coordinated Universal Time, UTC.

UTC+14:00

UTC+14+14:00Etc/GMT-14
In 1995, the island nation of Kiribati moved those of its atolls in the Line Islands from UTC−10 to UTC+14 so that Kiribati would all be on the same day. The westernmost time zone uses UTC−12, being twelve hours behind UTC; the easternmost time zone, uses UTC+14, being fourteen hours ahead of UTC. Current civil time in a particular time zone can be determined by adding or subtracting the number of hours and minutes specified by the UTC offset, which ranges from UTC−12:00 in the west to UTC+14:00 in the east (see List of UTC time offsets).
Alaska (Russian America) had local times from UTC+11:30 to UTC+15:10 until 1867 (UTC was introduced in 1960).

NATO phonetic alphabet

phonetic alphabetmilitary alphabetphonetic
Since the NATO phonetic alphabet word for Z is "Zulu", UTC is sometimes known as "Zulu time".
Several letter codes and abbreviations using the spelling alphabet have become well-known, such as Bravo Zulu (letter code BZ) for "well done", Checkpoint Charlie (Checkpoint C) in Berlin, and Zulu Time for Greenwich Mean Time or Coordinated Universal Time.

International Space Station

ISSInternational Space Station (ISS)Space Station
The International Space Station also uses UTC as a time standard.
All dates are UTC. Dates are the earliest possible dates and may change.

List of military time zones

militarymilitary and aviation timemilitary Golf time zone (G)
See the list of military time zones for letters used in addition to Z in qualifying time zones other than Greenwich.
The letter "Z" ("Zulu") indicates Coordinated Universal Time (UTC).

Atomic clock

atomic clocksatomiccaesium clock
In 1955, the caesium atomic clock was invented.
For civil time, another time scale is disseminated, Coordinated Universal Time (UTC).