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Encyclopedia > Coordinated Universal Time

Coordinated Universal Time (UTC,--Fr. Temps Universel Coordonné) is International Atomic Time (TAI [Temps Atomique International]) with leap seconds added at irregular intervals to compensate for the Earth's slowing rotation. Leap seconds are used to allow UTC to closely track UT1, which is mean solar time at the Royal Observatory, Greenwich. UTC may mean Coordinated Universal Time University of Tennessee at Chattanooga Union Treiziste Catalane Universal Terran Church United Technologies Corporation United Trading Company This is a disambiguation page — a list of articles associated with the same title. ... French (français, langue française) is one of the most important Romance languages, outnumbered in speakers only by Spanish and Portuguese. ... International Atomic Time (TAI, from the French name Temps Atomique International) is a high-precision atomic time standard that tracks proper time on Earths geoid. ... A leap second is a one-second adjustment to civil time in order to keep it close to the mean solar time. ... This article is about Earth as a planet. ... Royal Observatory, Greenwich. ...


The difference between UTC and UT1 cannot exceed 0.9 s, so if high precision is not required the general term Universal Time (UT) (without a suffix) may be used. Universal Time (UT) is a timescale based on the rotation of the Earth. ...


In casual use, Greenwich Mean Time (GMT) is the same as UTC and UT1. Owing to the ambiguity of whether UTC or UT1 is meant, and because timekeeping laws usually refer to UTC, GMT is avoided in careful writing. GMT redirects here. ...


Time zones around the world are expressed as positive or negative offsets from UTC. Local time is UTC plus the time zone offset for that location, plus an offset (typically +1) for daylight saving time, if in effect. UTC replaced Greenwich Mean Time on 1 January 1972 as the basis for the main reference time scale or civil time in various regions.[1] Although DST is common in Europe and North America, most of the worlds people do not use it. ... GMT redirects here. ... is the 1st day of the year in the Gregorian calendar. ... Year 1972 (MCMLXXII) was a leap year starting on Saturday (link will display full calendar) of the Gregorian calendar. ... Civil time is another name for mean solar time reckoned from midnight. ...

Example: Wednesday, 2008-05-14 11:15 UTC
This was the time in UTC when this page was last generated.

Contents

Abbreviation

Compromise abbreviation
source abbreviation
English CUT (coordinated universal time)
French TUC (temps universel coordonné)
compromise UTC (universal time, coordinated)

The International Telecommunication Union wanted Coordinated Universal Time to have a single abbreviation for all languages. English speakers and French speakers each wanted the initials of their respective languages' terms to be used internationally: "CUT" for "coordinated universal time" and "TUC" for "temps universel coordonné". This resulted in the final compromise of using "UTC".[2] The International Telecommunication Union (ITU; French: Union internationale des télécommunications, Spanish: Unión Internacional de Telecomunicaciones) is an international organization established to standardize and regulate international radio and telecommunications. ... The English language is a West Germanic language that originates in England. ...


"UTC" also has the benefit that it fits in with the pattern for the abbreviations of variants of Universal Time. UT0, UT1, UT1R, and others exist, so appending "C" for "coordinated" to the base "UT" is very satisfactory for those who are familiar with the other types of UT. Universal Time (UT) is a timescale based on the rotation of the Earth. ...


"UTC" has been erroneously expanded into "Universal Time Code" or "Universal Time Convention".[3]


Mechanism

As a time scale, UTC divides up time into days, hours, minutes, and seconds. Days are conventionally identified using the Gregorian calendar, but Julian day numbers can also be used. Each day contains 24 hours and each hour contains 60 minutes, but the number of seconds in a minute can be 60 or sometimes 61. A time scale specifies divisions of time. ... For the calendar of religious holidays and periods, see liturgical year. ... “JDN” redirects here. ...


Most UTC days contain exactly 86,400 SI seconds, with exactly 60 seconds in each minute. However, since the mean solar day is slightly longer than 86,400 SI seconds, occasionally the last minute of a UTC day will have 61 seconds. The extra second is called a leap second. It accounts for the grand total of the extra length (about 2 milliseconds each) of all the mean solar days since the previous leap second. The last minute of a UTC day is allowed to contain 59 seconds to cover the remote possibility of the Earth rotating faster, but that has never happened. The irregular day lengths mean that fractional Julian days do not work properly with UTC. Look up si, Si, SI in Wiktionary, the free dictionary. ... This article is about the unit of time. ... Solar time is based on the idea that, when the sun reaches its highest point in the sky, it is noon. ... A leap second is a one-second adjustment to civil time in order to keep it close to the mean solar time. ... “JDN” redirects here. ...


UTC is derived from International Atomic Time (TAI), which is a time scale tracking proper time on the rotating surface of the Earth (the geoid). At any particular time, UTC proceeds as a linear function of TAI. From 1972 onwards UTC ticks at the same rate as TAI, but earlier (back to the 1961 start of UTC) UTC ticked at a different rate from TAI. In order to remain a close approximation of UT1 (equivalent to GMT before 1960), UTC occasionally has discontinuities where it changes from one linear function of TAI to another. These discontinuities take the form of leaps implemented by a UTC day of irregular length, and (prior to 1972) changes to the rate at which UTC ticks relative to TAI. Discontinuities in UTC have only ever occurred at the end of a Gregorian month.[4] In relativity, proper time is time measured by a single clock between events that occur at the same place as the clock. ... This article is about Earth as a planet. ... The GOCE project will measure high-accuracy gravity gradients and provide an accurate geoid model based on the Earths gravity field. ... A linear function is a mathematical function term of the form: f(x) = m x + c where c is a constant. ... Universal Time (UT) is a timescale based on the rotation of the Earth. ... For alternate meanings of GMT, see GMT (disambiguation). ... In mathematics, a continuous function is one in which arbitrarily small changes in the input produce arbitrarily small changes in the output. ... For the calendar of religious holidays and periods, see liturgical year. ...


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 range −0.9 s < DUT1 < +0.9 s. Since 1972 the discontinuities have consisted only of a leap of one second at the end of June 30 or December 31. The IERS publishes its decision on whether to have a leap second on each of these dates a few months in advance, in Bulletin C.[5] In principle, leap seconds can also occur on March 31 or September 30, but the IERS has never found this necessary. The International Earth Rotation and Reference Systems Service is the body responsible for maintaining global time and reference frame standards, notably through its Earth Orientation Parameter (EOP) and International Celestial Reference System (ICRS) groups. ... The time correction DUT1 is the difference between the Universal Time scale UT1 (which corresponds to the Earths rotation) and the Coordinated Universal Time (UTC) (which corresponds, except for a constant offset, to International Atomic Time (TAI)). DUT1 = UT1 - UTC DUT1 is maintained in the range -0. ... is the 181st day of the year (182nd in leap years) in the Gregorian calendar. ... is the 365th day of the year (366th in leap years) in the Gregorian calendar. ... A leap second is a one-second adjustment to civil time in order to keep it close to the mean solar time. ... is the 90th day of the year (91st in leap years) in the Gregorian calendar. ... is the 273rd day of the year (274th in leap years) in the Gregorian calendar. ...


As with TAI, UTC is only known with the highest precision in retrospect. The International Bureau of Weights and Measures (BIPM) publishes monthly tables of differences between canonical TAI/UTC and TAI/UTC as estimated in real time by participating laboratories. (See the article on International Atomic Time for details.) The International Bureau of Weights and Measures is the English name of the Bureau international des poids et mesures (BIPM, often written in English Bureau International des Poids et Mesures), a standards organisation, one of the three organizations established to maintain the International System of Units (SI) under the terms... International Atomic Time (TAI, from the French name Temps Atomique International) is a high-precision atomic time standard that tracks proper time on Earths geoid. ...


History

Originally, the local time at the Royal Observatory, Greenwich, England, was chosen as standard at the 1884 International Meridian Conference, leading to the widespread use of Greenwich Mean Time (GMT) in order to set local clocks. This location was chosen because by 1884 two-thirds of all charts and maps already used it as their Prime Meridian. In 1929, the term Universal Time (UT) was introduced to refer to GMT with the day starting at midnight. Until the 1950s, broadcast time signals were based on UT, and hence on the rotation of the Earth. Royal Observatory, Greenwich. ... The Prime Meridian, Greenwich The Prime Meridian is the meridian (line of longitude) passing through the Royal Greenwich Observatory, Greenwich, England; it is the meridian at which longitude is 0 degrees. ... GMT redirects here. ... Location of the Prime Meridian Image:Prime Meridian. ... A time signal is a visible, audible, mechanical, or electronic signal used as a reference to determine the time of day. ...


In 1955, the caesium atomic clock was invented. This provided a form of timekeeping that was both more stable and more convenient than astronomical observations. In 1956 the US National Bureau of Standards started to use atomic frequency standards in generating the WWV time signals. In a controversial decision, the frequency of the signals was initially set to match the rate of UT, but then kept at the same frequency by the use of atomic clocks and deliberately allowed to drift away from UT. When the divergence grew significantly, the signal was phase shifted (stepped) by 20 ms to bring it back into agreement with UT. Many such steps were used. The signal frequency was changed less often. General Name, Symbol, Number caesium, Cs, 55 Chemical series alkali metals Group, Period, Block 1, 6, s Appearance silvery gold Standard atomic weight 132. ... “Nuclear Clock” redirects here. ... As a non-regulatory agency of the United States Department of Commerce’s Technology Administration, the National Institute of Standards (NIST) develops and promotes measurement, standards, and technology to enhance productivity, facilitate trade, and improve the quality of life. ... WWV Transmitter Building WWV is the callsign of NISTs shortwave radio station located in Fort Collins, Colorado. ... One millisecond is one-thousandth of a second. ...


In 1958, the International Atomic Time (TAI) service started. It was based on the frequency for the caesium transition, newly established,[6] that was later used to redefine the second in 1967. The WWV time signal's frequency was set to a simple offset from the TAI frequency: initially an offset of 1.0 × 10-8, so that WWV ticked exactly one second for every 1.00000001 s of TAI. Many 20 ms time steps were used.


Despite the initial controversy, it became clear that basing time signals on atomic clocks was an improvement over the prior system. However, it was widely desired to keep civil time synchronised with the Earth's rotation, and many uses of time signals (such as for navigation) relied on their closely matching Universal Time. WWV's compromise approach was copied by other agencies worldwide, such as the Royal Greenwich Observatory. It now became a concern that time signals should be synchronised with each other, rather than independently determining their own frequency offsets and phase shifts. Civil time is another name for mean solar time reckoned from midnight. ... This article is about determination of position and direction on or above the surface of the earth. ...


In 1960 an international agreement was made on atomic-based time signals. A frequency offset of 1.5 × 10-8 was adopted by all the participating institutions, matching the then-current rate of UT2. Ad hoc phase shifts were used to synchronise the time signals as far as possible. It was determined that the Bureau International de l'Heure should henceforth choose the frequency offsets and coordinate the time steps. It was also decided to use larger jumps, of 50 ms instead of 20 ms. The first two pages of the Treaty of Brest-Litovsk, in (left to right) German, Hungarian, Bulgarian, Ottoman Turkish and Russian A treaty is an agreement under international law entered into by actors in international law, namely states and international organizations. ... The Bureau International de lHeure (BIH) or the International Time Bureau, seated at the Paris Observatory, was the international bureau responsible for combining different measurements of Universal Time. ...


UTC was officially initiated at the start of 1961. The TAI instant 1961-01-01T00:00:01.422818 exactly was identified as UTC instant 1961-01-01T00:00:00.000000 exactly, and UTC ticked exactly one second for every 1.000000015 s of TAI. Time steps occurred every few months thereafter, and frequency changes at the end of each year. The jumps increased in size to 100 ms, with only one 50 ms jump having ever occurred. This UTC was intended to permit a very close approximation of UT2, within around 0.1 s.


In 1967, the SI second was redefined in terms of the frequency supplied by a caesium atomic clock. This was the frequency that had been provisionally used in TAI since 1958. It was soon recognised that having two types of second with different lengths, namely the UTC second and the SI second used in TAI, was a bad idea. It was thought that it would be better for time signals to maintain a consistent frequency, and that that frequency should match the SI second. Thus it would be necessary to rely on time steps alone to maintain the approximation of UT. This was tried experimentally in a service known as "Stepped Atomic Time" (SAT), which ticked at the same rate as TAI and used jumps of 200 ms to stay synchronised with UT2. Look up si, Si, SI in Wiktionary, the free dictionary. ...


There was also dissatisfaction with the frequent jumps in UTC (and SAT). In 1968, Louis Essen, the inventor of the caesium atomic clock, and G. M. R. Winkler both independently proposed that steps should be of 1 s only.[7] This system was eventually approved, along with the idea of maintaining the UTC second equal to the TAI second. At the end of 1971 there was a final irregular jump of 0.107758 TAI seconds exactly, so that 1972-01-01T00:00:00 UTC was 1972-01-01T00:00:10 TAI exactly, making the difference between UTC and TAI an integer number of seconds. At the same time the tick rate of UTC was changed to exactly match TAI. UTC also started to track UT1 rather than UT2. Some time signals started to broadcast the DUT1 correction (UT1 − UTC), for applications which required a closer approximation of UT1 than UTC now provided. Louis Essen (September 6, 1908 – August 24, 1997) was an English physicist whose most notable achievements were in the precise measurement of time and the determination of the speed of light. ... Not to be confused with Natural number. ...


The first leap second occurred on 1972-06-30. Since then leap seconds have occurred on average once every 18 months, always on June 30 or December 31. As of 2007 there have been 23 leap seconds in total, all positive, putting UTC 33 seconds behind TAI. It seems unlikely that a negative leap second will ever occur, but there is a small chance of one due to the acceleration of the Earth's crust in the 2000s. This acceleration has already led to the longest-ever period without a leap second, from 1999-01-01 to 2005-12-31. A leap second is a one-second adjustment to civil time in order to keep it close to the mean solar time. ... Year 1972 (MCMLXXII) was a leap year starting on Saturday (link will display full calendar) of the Gregorian calendar. ... is the 181st day of the year (182nd in leap years) in the Gregorian calendar. ... is the 181st day of the year (182nd in leap years) in the Gregorian calendar. ... is the 365th day of the year (366th in leap years) in the Gregorian calendar. ... Events of 2008: (EMILY) Me Lesley and MIley are going to China! This article is about the year. ... is the 1st day of the year in the Gregorian calendar. ... Year 2005 (MMV) was a common year starting on Saturday (link displays full calendar) of the Gregorian calendar. ... is the 365th day of the year (366th in leap years) in the Gregorian calendar. ...


Rationale

Graph showing the difference DUT1 between UT1 and UTC. Vertical segments correspond to leap seconds.
Graph showing the difference DUT1 between UT1 and UTC. Vertical segments correspond to leap seconds.

The Earth's rotational speed is very slowly decreasing due to tidal deceleration, causing the mean solar day to increase in length. The length of the SI second was based on the mean solar day observed between 1750 and 1892, analysed by Simon Newcomb. As a result, the SI second was exactly 1/86400 of a mean solar day in around 1820. In earlier centuries the mean solar day was shorter than 86400 SI seconds, and in later centuries it is longer than 86400 seconds. At the end of the 20th century the length of the mean solar day (also known simply as "length of day" or "LOD") was approximately 86,400.002 s. For this reason, UT is now "slower" than TAI. Image File history File links Leapsecond. ... Image File history File links Leapsecond. ... The time correction DUT1 is the difference between the Universal Time scale UT1 (which corresponds to the Earths rotation) and the Coordinated Universal Time (UTC) (which corresponds, except for a constant offset, to International Atomic Time (TAI)). DUT1 = UT1 - UTC DUT1 is maintained in the range -0. ... Rotational speed (sometimes called speed of revolution) indicates for example how fast the motor is running. ... It has been suggested that Tidal friction be merged into this article or section. ... Solar time is based on the idea that when the sun reaches its highest point in the sky, it is noon. ... Simon Newcomb. ...


The excess of the LOD over the nominal 86,400 s accumulates over time, causing the UTC day, initially synchronised with the mean sun, to become desynchronised and run ahead of it. At the end of the 20th century, with the LOD at 2 ms above the nominal value, UTC ran faster than UT by 2 ms per day, getting a second ahead roughly every 500 days. Thus leap seconds were inserted at approximately this interval, retarding UTC to keep it synchronised in the long term. Note that the actual rotational period varies on unpredictable factors such as tectonic motion and has to be observed rather than computed. In astronomy, a rotation period is the time an astronomical object takes to complete one revolution around its rotation axis relative to the background stars. ... The tectonic plates of the world were mapped in the second half of the 20th century. ...


The insertion of a leap second every 500 days does not mean that the mean solar day is getting longer by a second every 500 days: it will take approximately 50,000 years for a mean solar day to lengthen by one second (at a rate of 2 ms/cy). This is a mean rate within the range of 1.7–2.3 ms/cy. The rate due to tidal friction alone is about 2.3 ms/cy, but the uplift of Canada and Scandinavia by several metres since the last ice age has temporarily reduced this to 1.7 ms/cy over the last 2700 years.[8] The correct reason for leap seconds is not the current difference between actual and nominal LOD, but rather the accumulation of this difference over a period of time: in the late twentieth century, this difference was about 1/500 of a second, so it accumulated to 1 second after about 500 days. Tidal friction is a process that transferes energy between the planets. ... For other uses, see Scandinavia (disambiguation). ... Variations in CO2, temperature and dust from the Vostok ice core over the last 400 000 years For the animated movie, see Ice Age (movie). ...


For example, assume you start counting the seconds from the Unix epoch of 1970-01-01T00:00:00 UTC with an atomic clock. At midnight on that day (as measured on UTC), your counter registers 0 s. After Earth has made one full rotation with respect to the mean Sun, your counter will register approximately 86400.002 s (the precise value will vary depending on plate tectonic conditions). Based on your counter, you can calculate that the date is 1970-01-02T00:00:00 UT1. After 500 rotations, your counter will register 43,200,001 s. Since 86,400 s × 500 is 43,200,000 s, you will calculate that the date is 1971-05-16T00:00:01 UTC, while it is only 1971-05-16T00:00:00 UT1. If you had added a leap second on December 31, 1970, retarding your counter by 1 s, then the counter would have a value of 43,200,000 s at 1971-05-16T00:00:00 UT1, and allow you to calculate the correct date. Unix time passed 1,000,000,000 seconds in 2001-09-09T03:46:40. ... The tectonic plates of the world were mapped in the second half of the 20th century. ... is the 365th day of the year (366th in leap years) in the Gregorian calendar. ... Year 1970 (MCMLXX) was a common year starting on Thursday (link shows full calendar) of the Gregorian calendar. ...


In the graph of DUT1 above, the excess of LOD above the nominal 86,400 s corresponds to the downward slope of the graph between vertical segments. (Note that the slope became shallower in the 2000s, due to a slight acceleration of the Earth's crust temporarily shortening the day.) Vertical position on the graph corresponds to the accumulation of this difference over time, and the vertical segments correspond to leap seconds introduced to match this accumulated difference. Leap seconds are timed to keep DUT1 within the vertical range depicted by this graph. The frequency of leap seconds therefore corresponds to the slope of the diagonal graph segments, and thus to the excess LOD. The time correction DUT1 is the difference between the Universal Time scale UT1 (which corresponds to the Earths rotation) and the Coordinated Universal Time (UTC) (which corresponds, except for a constant offset, to International Atomic Time (TAI)). DUT1 = UT1 - UTC DUT1 is maintained in the range -0. ...


Future

See also: leap second

As the Earth's rotation continues to slow, positive leap seconds will be required more frequently. The long-term rate of change of LOD is approximately +1.7 ms per century. At the end of the 21st century LOD will be roughly 86,400.004 s, requiring leap seconds every 250 days. Over several centuries, the frequency of leap seconds will become problematic. A leap second is a one-second adjustment to civil time in order to keep it close to the mean solar time. ... For other uses, see Derivative (disambiguation). ...


Sometime in the 22nd century, two leap seconds will be required every year. The current use of only the leap second opportunities in June and December will be insufficient, and the March and September options will have to be used. In the 25th century, four leap seconds will be required every year, so the current quarterly options will be insufficient. Thereafter there will need to be the possibility of leap seconds at the end of any month. In about two thousand years even that will become insufficient, and there will have to be leap seconds that are not at the end of a month.[9]


In a few tens of thousands of years (the timing is very uncertain) LOD will exceed 86,401 s, causing the current form of UTC to break down due to requiring more than one leap second per day. It would be possible to then continue with double leaps, but this becomes increasingly untenable.


Both the one-leap-second-per-month and one-leap-second-per-day milestones are considered (by different theorists) to mark the theoretical limit of the applicability of UTC. The actual number of leap seconds to keep track of time would become unwieldy by current standards well before these, but presumably if UTC were to continue then horological systems would be redesigned to cope with regular leap seconds much better than current systems do.


There is a proposal to redefine UTC and abolish leap seconds, such that sundials would slowly get further out of sync with civil time.[10] The resulting gradual shift of the sun's movements relative to civil time is analogous to the shift of seasons relative to the yearly calendar that results from the calendar year not precisely matching the tropical year length. This would be a major practical change in civil timekeeping, but would take effect slowly over several centuries. An ITU study group is to vote on this possibility during 2008, possibly leading to official approval by the World Radio Conference in 2011 and the cessation of leap seconds in 2013. For other uses, see Sundial (disambiguation). ... Civil time is another name for mean solar time reckoned from midnight. ... This article or section is in need of attention from an expert on the subject. ... A tropical year is the length of time that the Sun, as viewed from the Earth, takes to return to the same position along the ecliptic (its path among the stars on the celestial sphere). ...


There is also a proposal that the present form of UTC could be improved to track UT1 more closely, by allowing greater freedom in scheduling leap seconds.[11]


Uses

UTC is the time system used for many Internet and World Wide Web standards. In particular, the Network Time Protocol, which is designed to synchronize the clocks of many computers over the Internet (usually to that of a known accurate atomic clock), uses UTC. The World Wide Web and WWW redirect here. ... The Network Time Protocol (NTP) is a protocol for synchronizing the clocks of computer systems over packet-switched, variable-latency data networks. ...


Those who transmit on the amateur radio bands often log the time of their radio contacts in UTC, as transmissions can go worldwide on some frequencies. In the past, the FCC required all amateur radio operators in the United States to log their radio conversations. Amateur radio station with modern solid-state transceiver featuring LCD and DSP capabilities Amateur radio, often called ham radio, is both a hobby and a service that uses various types of radio communications equipment to communicate with other radio amateurs for public service, recreation and self-training. ... FCC redirects here. ... An amateur radio operator is an individual who, typically, uses equipment at an amateur radio station to engage in two-way personal communications with other similar individuals on radio frequencies assigned to the Amateur Radio Service. ... logbook aboard the frigate Grand Turk A Logbook is a book for recording readings from the log (see also maritime log). ...


UTC is also the time system used in aviation, referred to as Zulu.[12] Weather reports, flight plans, air traffic control clearances, and maps all use UTC to avoid confusion about time zones and daylight saving time. Aviation encompasses all the activities relating to airborne devices created by human ingenuity, generally known as aircraft. ... For the song Weather Report by The American Analog Set, see The Golden Band. ... For the movie, see Flightplan. ... For the Canadian musical group, see Air Traffic Control (band). ... Although DST is common in Europe and North America, most of the worlds people do not use it. ...


Because of time dilation, a standard clock not on the geoid, or in rapid motion, will not maintain synchronicity with UTC. Therefore, telemetry from clocks with a known relation to the geoid is used to provide UTC, when required, on locations such as that of spacecraft. Time dilation is the phenomenon whereby an observer finds that anothers clock which is physically identical to their own is ticking at a slower rate as measured by their own clock. ... The GOCE project will measure high-accuracy gravity gradients and provide an accurate geoid model based on the Earths gravity field. ... Telemetry is a technology that allows the remote measurement and reporting of information of interest to the system designer or operator. ...


UTC is a discontinuous timescale, so it is not possible to compute the exact time interval elapsed between two UTC timestamps without consulting a table that describes how many leap seconds occurred during that interval. Therefore, many scientific applications that require precise measurement of long (multi-year) intervals use TAI instead. TAI is also commonly used by systems that can not handle leap seconds. A fixed 19-second offset from TAI also gives GPS time. This article is about the concept of time. ... International Atomic Time (TAI, from the French name Temps Atomique International) is a high-precision atomic time standard that tracks proper time on Earths geoid. ... GPS redirects here. ...


For most common and legal-trade purposes, the fractional second difference between UTC and UT (GMT) is inconsequentially small, so UTC is often called GMT, for example by the BBC, although that usage is not technically correct.[13] For alternate meanings of GMT, see GMT (disambiguation). ... For other uses, see BBC (disambiguation). ...


Time zones

Main articles: Time zone and List of time zones

Time zones usually differ from UTC by an integral number of hours[14], although the laws of each jurisdiction would have to be consulted if sub-second accuracy was required. Several jurisdictions established time zones that differ by an integer number of half-hours from UT1 or UTC.[15] Timezone and TimeZone redirect here. ... // This is a list of time zones, sorted by time offsets from Coordinated Universal Time (UTC). ...


The UTC time zone is sometimes denoted by the letter Z – a reference to the equivalent nautical time zone (GMT), which has been denoted by a Z since about 1950. The letter also refers to the "zone description" of zero hours, which has been used since 1920 (see time zone history). Since the NATO phonetic alphabet and amateur radio word for Z is "Zulu", UTC is sometimes known as Zulu time. This is especially true in aviation, where Zulu is the universal standard.[16] This ensures all pilots regardless of location are using the same 24-hour clock, thus avoiding confusion when flying between time zones.[17][18] Timezone and TimeZone redirect here. ... For alternate meanings of GMT, see GMT (disambiguation). ... Timezone and TimeZone redirect here. ... FAA radiotelephony phonetic alphabet and Morse code chart. ... Amateur radio station with modern solid-state transceiver featuring LCD and DSP capabilities Amateur radio, often called ham radio, is both a hobby and a service that uses various types of radio communications equipment to communicate with other radio amateurs for public service, recreation and self-training. ... The 24-hour clock is a convention of time keeping in which the day runs from midnight to midnight and is divided into 24 hours, numbered from 0 to 23. ...


See also

Ephemeris Time (ET) is a now obsolete time scale used in ephemerides of celestial bodies, in particular the Sun (as observed from the Earth), Moon, planets, and other members of the solar system. ... Terrestrial Time (TT) is the modern time standard for time on the surface of the Earth. ... ISO 8601 is an international standard for date and time representations issued by the International Organization for Standardization (ISO). ...

Bibliography

  • Allan, David W., Neil Ashby, Clifford C. Hodge: The Science of Timekeeping. Hewlett Packard Application Note 1289, 1997.
  • ITU-R Recommendation TF.460-4: Standard-frequency and time-signal emissions. International Telecommunication Union. (Annex I of this document contains the official definition of UTC.)
  • McCarthy, Dennis D.: "Astronomical Time". Proc. IEEE, Vol. 79, No. 7, July 1991, pp. 915-920.
  • Nelson, McCarthy, et al.: "The leap second: its history and possible future"PDF (381 KiB), Metrologia, Vol. 38, pp. 509–529, 2001.
  • Seidelman, P.K. (ed). Explanatory Supplement to the Astronomical Almanac. Sausalito, CA: University Science Books. 1992.

The Hewlett-Packard Company (NYSE: HPQ), commonly known as HP, is a very large, global company headquartered in Palo Alto, California, United States. ... There are very few or no other articles that link to this one. ... The ITU Radiocommunication Sector (ITU-R) is a standards body subcommittee of the International Telecommunication Union (ITU) relating to radio communication. ... The International Telecommunication Union (ITU; French: Union internationale des télécommunications, Spanish: Unión Internacional de Telecomunicaciones) is an international organization established to standardize and regulate international radio and telecommunications. ... Year 1991 (MCMXCI) was a common year starting on Tuesday (link will display full calendar) of the Gregorian Calendar. ... “PDF” redirects here. ... A kibibyte (a contraction of kilo binary byte) is a unit of information or computer storage, commonly abbreviated KiB (never kiB). 1 kibibyte = 210 bytes = 1,024 bytes The kibibyte is closely related to the kilobyte, which can be used either as a synonym for kibibyte or to refer to...

References

  1. ^ Leap Second
  2. ^ Why is UTC used as the acronym for Coordinated Universal Time instead of CUT?. Retrieved on 2007-06-02.
  3. ^ POES Acronyms and Abbreviations. Retrieved on 2006-07-26.
  4. ^ History of TAI−UTC
  5. ^ Bulletin C. Retrieved on 2007-06-02.
  6. ^ Frequency of cesium in terms of Ephemeris TimePDF (560 KiB)
  7. ^ Time Scales by L. EssenPDF (851 KiB)
  8. ^ F.R. Stephenson, L.V. Morrison, "Long-term fluctuations in the Earth's rotation: 700 BC to AD 1990", Philosophical Transactions of the Royal Society of London, Series A (1995) 165–202.
  9. ^ UTC is doomed. Retrieved on 2007-06-02.
  10. ^ UTC might be redefined without Leap Seconds. Retrieved on 2007-06-02.
  11. ^ A Proposal to Upgrade UTC. Retrieved on 2007-06-02.
  12. ^ AOPA Aviation Time. AOPA's PATH to Aviation. Accessed 2007-02-25.
  13. ^ A Few Facts Concerning GMT, UT, and the RGO. Retrieved on 2007-08-19.
  14. ^ Seidelmann, (1992), 7
  15. ^ Seidelman, (1992), 57
  16. ^ Military & Civilian Time Designations
  17. ^ Williams, Jack. Understanding and using Zulu time USA Today. Accessed 2007-02-25.
  18. ^ Smith, Sandi. Zulu Time. Sandismith Keynotes and Workshops. Accessed 2007-02-07.

Year 2007 (MMVII) was a common year starting on Monday of the Gregorian calendar in the 21st century. ... is the 153rd day of the year (154th in leap years) in the Gregorian calendar. ... Year 2006 (MMVI) was a common year starting on Sunday of the Gregorian calendar. ... is the 207th day of the year (208th in leap years) in the Gregorian calendar. ... Year 2007 (MMVII) was a common year starting on Monday of the Gregorian calendar in the 21st century. ... is the 153rd day of the year (154th in leap years) in the Gregorian calendar. ... “PDF” redirects here. ... A kibibyte (a contraction of kilo binary byte) is a unit of information or computer storage, commonly abbreviated KiB (never kiB). 1 kibibyte = 210 bytes = 1,024 bytes The kibibyte is closely related to the kilobyte, which can be used either as a synonym for kibibyte or to refer to... “PDF” redirects here. ... A kibibyte (a contraction of kilo binary byte) is a unit of information or computer storage, commonly abbreviated KiB (never kiB). 1 kibibyte = 210 bytes = 1,024 bytes The kibibyte is closely related to the kilobyte, which can be used either as a synonym for kibibyte or to refer to... Year 2007 (MMVII) was a common year starting on Monday of the Gregorian calendar in the 21st century. ... is the 153rd day of the year (154th in leap years) in the Gregorian calendar. ... Year 2007 (MMVII) was a common year starting on Monday of the Gregorian calendar in the 21st century. ... is the 153rd day of the year (154th in leap years) in the Gregorian calendar. ... Year 2007 (MMVII) was a common year starting on Monday of the Gregorian calendar in the 21st century. ... is the 153rd day of the year (154th in leap years) in the Gregorian calendar. ... The Aircraft Owners and Pilots Association (AOPA) is a not-for-profit organization whose membership consists mainly of general aviation pilots in the United States. ... Year 2007 (MMVII) was a common year starting on Monday of the Gregorian calendar in the 21st century. ... is the 56th day of the year in the Gregorian calendar. ... Year 2007 (MMVII) was a common year starting on Monday of the Gregorian calendar in the 21st century. ... is the 231st day of the year (232nd in leap years) in the Gregorian calendar. ... Year 2007 (MMVII) was a common year starting on Monday of the Gregorian calendar in the 21st century. ... is the 56th day of the year in the Gregorian calendar. ... Year 2007 (MMVII) was a common year starting on Monday of the Gregorian calendar in the 21st century. ... is the 38th day of the year in the Gregorian calendar. ...

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A tropical year is the length of time that the Sun, as viewed from the Earth, takes to return to the same position along the ecliptic (its path among the stars on the celestial sphere). ... For other uses, see Equinox (disambiguation). ... “Summer solstice” redirects here. ... This article is about days of the week. ... This article details various mathematical algorithms to calculate the day of the week for any particular date in the past or future. ... The days of the year are sometimes designated letters A, B, C, D, E, F and G in a cycle of 7 as an aid for finding the day of week of a given calendar date and in calculating Easter. ... The International Commission on Stratigraphy concerns itself with stratigraphy on a global scale. ... Diagram of geological time scale. ... Dating material drawn from the archaeological record can made by a direct study of a artifact or may be deduced by association with materials found in the context the item is drawn from or inferred by its point of discovery in the sequence relative to datable contexts. ... The precession of Earths axis of rotation with respect to inertial space is also called the precession of the equinoxes. ... Sidereal time is time measured by the apparent diurnal motion of the vernal equinox, which is very close to, but not identical with, the motion of stars. ... // Galactic time NGC 4414, a typical spiral galaxy alike our Milky Way Galactic time, not to confuse with siderial time, is the time that is described by our spin relative to the center of the galaxy. ... Look up fortnight in Wiktionary, the free dictionary. ... The term jiffy (or jiffie) is used in different applications for various different short periods of time, usually 1/60 of a second. ... Lustrum was a sacrifice for expiation and purification offered by one of the censors of Rome in name of the Roman people at the close of the taking of the census, and which took place after a period of five years, so that the name came to denote a period... A saeculum is a length of time roughly equal to the lifetime of a person, or about 90 years. ... A shake is an informal unit of time equal to 10 nanoseconds, or 10-8 seconds. ... A tide is an obsolete or archaic term for time, period or season, such as eventide, shrovetide, Eastertide, etc. ... For the novel by Michael Crichton, see Timeline (novel). ... A duration is an amount of time or a particular time interval. ... In computer science and computer programming, system time represents a computer systems notion of the passing of time. ... // Definition and history Psychologists have investigated mental chronometry for over 100 years. ... The time value of money is the premise that an investor prefers to receive a payment of a fixed amount of money today, rather than an equal amount in the future, all else being equal. ... Look up timekeeper in Wiktionary, the free dictionary. ... A time offset is defined by international convention as a number of hours and minutes from Coordinated Universal Time in Greenwich, England. ... −12 | −11 | −10 | −9:30 | −9 | −8 | −7 | −6 | −5 | −4 | −3:30 | −3 | −2:30 | −2 | −1 | −0:25 | UTC (0) | +0:20 | +0:30 | +1 | +2 | +3 | +3:30 | +4 | +4:30 | +4:51 | +5 | +5:30 | +5:40 | +5:45 | +6 | +6:30 | +7 | +7:20 | +7... −12 | −11 | −10 | −9:30 | −9 | −8 | −7 | −6 | −5 | −4 | −3:30 | −3 | −2:30 | −2 | −1 | −0:25 | UTC (0) | +0:20 | +0:30 | +1 | +2 | +3 | +3:30 | +4 | +4:30 | +4:51 | +5 | +5:30 | +5:40 | +5:45 | +6 | +6:30 | +7 | +7:20 | +7... −12 | −11 | −10 | −9:30 | −9 | −8 | −7 | −6 | −5 | −4 | −3:30 | −3 | −2:30 | −2 | −1 | −0:25 | UTC (0) | +0:20 | +0:30 | +1 | +2 | +3 | +3:30 | +4 | +4:30 | +4:51 | +5 | +5:30 | +5:40 | +5:45 | +6 | +6:30 | +7 | +7:20 | +7... −12 | −11 | −10 | −9:30 | −9 | −8 | −7 | −6 | −5 | −4 | −3:30 | −3 | −2:30 | −2 | −1 | −0:25 | UTC (0) | +0:20 | +0:30 | +1 | +2 | +3 | +3:30 | +4 | +4:30 | +4:51 | +5 | +5:30 | +5:40 | +5:45 | +6 | +6:30 | +7 | +7:20 | +7... −12 | −11 | −10 | −9:30 | −9 | −8 | −7 | −6 | −5 | −4 | −3:30 | −3 | −2:30 | −2 | −1 | −0:25 | UTC (0) | +0:20 | +0:30 | +1 | +2 | +3 | +3:30 | +4 | +4:30 | +4:51 | +5 | +5:30 | +5:40 | +5:45 | +6 | +6:30 | +7 | +7:20 | +7... −12 | −11 | −10 | −9:30 | −9 | −8 | −7 | −6 | −5 | −4 | −3:30 | −3 | −2:30 | −2 | −1 | −0:25 | UTC (0) | +0:20 | +0:30 | +1 | +2 | +3 | +3:30 | +4 | +4:30 | +4:51 | +5 | +5:30 | +5:40 | +5:45 | +6 | +6:30 | +7 | +7:20 | +7... −12 | −11 | −10 | −9:30 | −9 | −8 | −7 | −6 | −5 | −4 | −3:30 | −3 | −2:30 | −2 | −1 | −0:25 | UTC (0) | +0:20 | +0:30 | +1 | +2 | +3 | +3:30 | +4 | +4:30 | +4:51 | +5 | +5:30 | +5:40 | +5:45 | +6 | +6:30 | +7 | +7:20 | +7... -12 | -11 | -10 | -9:30 | -9 | -8 | -7 | -6 | -5 | -4 | -3:30 | -3 | -2:30 | -2 | -1 | -0:25 | UTC (0) | +0:20 | +0:30 | +1 | +2 | +3 | +3:30 | +4 | +4:30 | +4:51 | +5 | +5:30 | +5:40 | +5:45 | +6 | +6:30 | +7 | +7:20 | +7... −12 | −11 | −10 | −9:30 | −9 | −8 | −7 | −6 | −5 | −4 | −3:30 | −3 | −2:30 | −2 | −1 | −0:25 | UTC (0) | +0:20 | +0:30 | +1 | +2 | +3 | +3:30 | +4 | +4:30 | +4:51 | +5 | +5:30 | +5:40 | +5:45 | +6 | +6:30 | +7 | +7:20 | +7... −12 | −11 | −10 | −9:30 | −9 | −8 | −7 | −6 | −5 | −4 | −3:30 | −3 | −2:30 | −2 | −1 | −0:25 | UTC (0) | +0:20 | +0:30 | +1 | +2 | +3 | +3:30 | +4 | +4:30 | +4:51 | +5 | +5:30 | +5:40 | +5:45 | +6 | +6:30 | +7 | +7:20 | +7... −12 | −11 | −10 | −9:30 | −9 | −8 | −7 | −6 | −5 | −4 | −3:30 | −3 | −2:30 | −2 | −1 | −0:25 | UTC (0) | +0:20 | +0:30 | +1 | +2 | +3 | +3:30 | +4 | +4:30 | +4:51 | +5 | +5:30 | +5:40 | +5:45 | +6 | +6:30 | +7 | +7:20 | +7... −12 | −11 | −10 | −9:30 | −9 | −8 | −7 | −6 | −5 | −4 | −3:30 | −3 | −2:30 | −2 | −1 | −0:25 | UTC (0) | +0:20 | +0:30 | +1 | +2 | +3 | +3:30 | +4 | +4:30 | +4:51 | +5 | +5:30 | +5:40 | +5:45 | +6 | +6:30 | +7 | +7:20 | +7... -12 | -11 | -10 | -9:30 | -9 | -8 | -7 | -6 | -5 | -4 | -3:30 | -3 | -2:30 | -2 | -1 | -0:25 | UTC (0) | +0:20 | +0:30 | +1 | +2 | +3 | +3:30 | +4 | +4:30 | +4:51 | +5 | +5:30 | +5:40 | +5:45 | +6 | +6:30 | +7 | +7:20 | +7... Central European Time West Africa Time British Summer Time* Irish Summer Time* Western European Summer Time* Category: ... Eastern European Time Central Africa Time Israel Standard Time South Africa Standard Time Central European Summer Time West Africa Summer Time Category: ... -12 | -11 | -10 | -9:30 | -9 | -8 | -7 | -6 | -5 | -4 | -3:30 | -3 | -2:30 | -2 | -1 | -0:25 | UTC (0) | +0:20 | +0:30 | +1 | +2 | +3 | +3:30 | +4 | +4:30 | +4:51 | +5 | +5:30 | +5:40 | +5:45 | +6 | +6:30 | +7 | +7:20 | +7... Moscow Summer Time Category: ... UTC +5 is the timezone for : Pakistan Standard Time in Pakistan. ... UTC +6 is the timezone for : Bhutan Time Generic UTC+6 in other countries. ... UTC+7 is used in: Laos Thailand Cambodia Vietnam External links Find cities currently in UTC+7 Category: ... -12 | -11 | -10 | -9:30 | -9 | -8 | -7 | -6 | -5 | -4 | -3:30 | -3 | -2:30 | -2 | -1 | -0:25 | UTC (0) | +0:20 | +0:30 | +1 | +2 | +3 | +3:30 | +4 | +4:30 | +4:51 | +5 | +5:30 | +5:40 | +5:45 | +6 | +6:30 | +7 | +7:20 | +7... Japan Standard Time Korea Standard Time External links Find cities currently in UTC+9 Category: ... UTC+10 time zone Australia (AEST—Australian Eastern Standard Time) Australian Capital Territory**, New South Wales** (except Broken Hill, which observes South Australia time), Queensland, Tasmania** (which observes DST starting on the first weekend of October instead of the last), Victoria** Guam (Chamorro Standard Time via US Law) Federated States... as non DST time Federated States of Micronesia Kosrae, Pohnpei, and surrounding area New Caledonia Russia Kuril Islands* Magadan Oblast* Sakha Republic* (eastern portion) Solomon Islands Vanuatu as DST Australia (Australian Eastern Daylight Time) Australian Capital Territory** New South Wales** Tasmania** (where daylight saving time starts on the first weekend... Fiji Gilbert Islands, Kiribati Marshall Islands New Zealand (except Chatham Islands) Korsae, Micronesia Nauru Parts of Russia: Kamchatka Oblast Koryakia Autonomous District Chukotka Autonomous District Tuvalu Wake Island Wallis and Futuna External links Find cities currently in UTC+12 Category: ... Enderbury, Kiribati (Phoenix Islands Time) Tonga External links Find cities currently in UTC+13 Category: ... UTC+14 is the easternmost time zone currently in use anywhere in the world, and thus the first part of the planet to start each new calendar day. ... Although DST is common in Europe and North America, most of the worlds people do not use it. ... Northern hemisphere highlighted in yellow. ... southern hemisphere highlighted in yellow (Antarctica not depicted). ...

  Results from FactBites:
 
The Time (3957 words)
More precisely, it is the time coordinate of a space-time coordinate system that is centered in space on the barycenter of the solar system, that is nonrotating with respect to distant galaxies, and that tends asymptotically to the proper time of an observer at rest with respect to the coordinate system.
Geocentric Coordinate Time, or TCG, is the same as Barycentric Coordinate Time, except that it uses the Earth's center, rather than the barycenter of the solar system (and an “asymptotic” observer is one free from the gravitational field of the Earth rather than that of all the solar system).
Coordinated Universal Time, or UTC is the official standard of time throughout the world, being the basis for legal time.
Coordinated Universal Time - Wikipedia, the free encyclopedia (2832 words)
Coordinated Universal Time (UTC) is a high-precision atomic time standard which approximately tracks Universal Time (UT).
UTC is derived from International Atomic Time (TAI), which is a time scale tracking proper time on the surface of the Earth with no reference to the rotation of the Earth.
However, it was widely desired to keep civil time synchronised with the Earth's rotation, and many uses of time signals (such as for navigation) relied on their closely matching Universal Time.
  More results at FactBites »

 
 

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