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.Coordinated Universal Time (UTC)[1] (French: Temps Universel Coordonné) is a time standard based on International Atomic Time (TAI) with leap seconds added at irregular intervals to compensate for the Earth's slowing rotation.^ All times in Coordinated Universal Time (UTC).
  • Remailer Reliability Stats [citrus] 10 February 2010 14:44 UTC privacy.outel.org [Source type: FILTERED WITH BAYES]
  • Remailer Reliability Stats [Mixmin Pinger] 10 February 2010 14:44 UTC pinger.mixmin.net [Source type: FILTERED WITH BAYES]

^ In 1972, GMT was replaced by Coordinated Universal Time (UTC) as the international time reference.

^ In 1958, the International Atomic Time (TAI) service started.
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

[2] .Leap seconds are used to allow UTC to closely track UT1, which is mean solar time at the Royal Observatory, Greenwich.^ This is the modern equivalent of Greenwich Mean Time.

^ Greenwich Mean Time updated with leap seconds.
  • coordinated universal time 10 February 2010 14:44 UTC www.mahalo.com [Source type: FILTERED WITH BAYES]

^ It's also approximately equal to mean solar time from Greenwich.
  • NASA - Time Zones and Universal Time 10 February 2010 14:44 UTC eclipse.gsfc.nasa.gov [Source type: FILTERED WITH BAYES]

.The difference between UTC and UT1 is not allowed to exceed 0.9 seconds, so if high precision is not required the general term Universal Time (UT) may be used.^ All times in Coordinated Universal Time (UTC).
  • Remailer Reliability Stats [citrus] 10 February 2010 14:44 UTC privacy.outel.org [Source type: FILTERED WITH BAYES]
  • Remailer Reliability Stats [Mixmin Pinger] 10 February 2010 14:44 UTC pinger.mixmin.net [Source type: FILTERED WITH BAYES]

^ Coordinated Universal Time (UTC) is used as the official world reference for time.

^ Returns the difference in minutes between the local time in this time zone and the Coordinated Universal Time (UTC).
  • RDOTimezone object 10 February 2010 14:44 UTC www.dimastr.com [Source type: FILTERED WITH BAYES]

[3]
.In casual use, when fractions of a second are not important, Greenwich Mean Time (GMT) can be considered equivalent to UTC or UT1. Owing to the ambiguity as to whether UTC or UT1 is meant, GMT is generally avoided in technical contexts.^ This is the modern equivalent of Greenwich Mean Time.

^ Greenwich Time (GMT) is also known as Zulu Time .
  • Greenwich Time. GMT Greenwich Mean Time and Greenwich Time. 10 February 2010 14:44 UTC 247clocks.com [Source type: News]

^ Greenwich Mean Time updated with leap seconds.
  • coordinated universal time 10 February 2010 14:44 UTC www.mahalo.com [Source type: FILTERED WITH BAYES]

[3]
Time zones around the world can be expressed as positive or negative offsets from UTC; UTC replaced GMT as the basis for the main reference time scale or civil time in various regions on 1 January 1972.[4]

Contents

Abbreviation

Compromise abbreviation
Source Abbreviation Unabbreviated
English CUT Coordinated Universal Time
French TUC Temps Universel Coordonné
compromise UTC unofficial English backronym: "Universal Time, Coordinated"
.Coordinated Universal Time is abbreviated UTC. The International Telecommunication Union wanted Coordinated Universal Time to have a single abbreviation for all languages.^ In 1972, GMT was replaced by Coordinated Universal Time (UTC) as the international time reference.

^ Instead, a common time called Coordinated Universal Time (UTC) is used.
  • New Page 1 10 February 2010 14:44 UTC www.kf4l.org [Source type: FILTERED WITH BAYES]

^ A. UTC is the international abbreviation for Coordinated Universal Time.
  • Environment Canada: Atlantic Region Air Quality Services - Time Zones and Coordinated Universal Time (UTC) 10 February 2010 14:44 UTC atlantic-web1.ns.ec.gc.ca [Source type: News]

.English speakers and French speakers each wanted the initials of their respective language's terms to be used internationally: "CUT" for "coordinated universal time" and "TUC" for "temps universel coordonné".^ Instead, a common time called Coordinated Universal Time (UTC) is used.
  • New Page 1 10 February 2010 14:44 UTC www.kf4l.org [Source type: FILTERED WITH BAYES]

^ Coordinated Universal Time (UTC) is used as the official world reference for time.

^ The time on the Coordinated Universal Time (UTC) scale.
  • Amazon.com: "Coordinated Universal Time": Key Phrase page 10 February 2010 14:44 UTC www.amazon.com [Source type: FILTERED WITH BAYES]

This resulted in the final compromise of using "UTC".[5]
."UTC" also has the benefit that it fits in with the pattern for the abbreviations of variants of Universal Time.^ A. UTC is the international abbreviation for Coordinated Universal Time.
  • Environment Canada: Atlantic Region Air Quality Services - Time Zones and Coordinated Universal Time (UTC) 10 February 2010 14:44 UTC atlantic-web1.ns.ec.gc.ca [Source type: News]

^ The time on the Coordinated Universal Time (UTC) scale.
  • Amazon.com: "Coordinated Universal Time": Key Phrase page 10 February 2010 14:44 UTC www.amazon.com [Source type: FILTERED WITH BAYES]

^ UTC is an acronym for Coordinated Universal Time .
  • UTC - Wikiversity 26 January 2010 1:27 UTC en.wikiversity.org [Source type: FILTERED WITH BAYES]

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.
The U.S. Federal Aviation Administration refers to the abbreviation as "Universal Coordinated Time".[6]

Mechanism

.As a time scale, UTC divides up time into days, hours, minutes and seconds.^ The time on the Coordinated Universal Time (UTC) scale.
  • Amazon.com: "Coordinated Universal Time": Key Phrase page 10 February 2010 14:44 UTC www.amazon.com [Source type: FILTERED WITH BAYES]

^ The UTC minutes and seconds are exactly the same as your local time, but the hours are different.
  • NIST Time and Frequency FAQ 10 February 2010 14:44 UTC tf.nist.gov [Source type: FILTERED WITH BAYES]

^ For example, a wall clock can display UTC in hours, minutes, and seconds.
  • NIST Time and Frequency FAQ 10 February 2010 14:44 UTC tf.nist.gov [Source type: FILTERED WITH BAYES]

.Days are conventionally identified using the Gregorian calendar, but Julian day numbers can also be used.^ Days are conventionally identified using the Gregorian calendar , but Julian day numbers can also be used.
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

^ Coordinated Universal Time is expressed using a 24-hour clock and uses the Gregorian calendar.
  • Coordinated Universal Time - Computing Reference - eLook.org 10 February 2010 14:44 UTC www.elook.org [Source type: Academic]

^ Coordinated Universal Time is expressed using a 24-hour clock and uses the Gregorian calendar .
  • Coordinated Universal Time Definition | Definition of Coordinated Universal Time at Dictionary.com 10 February 2010 14:44 UTC dictionary.reference.com [Source type: FILTERED WITH BAYES]

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 or 59.
.Thus, in the UTC time scale, the second and all smaller time units (millisecond, microsecond...^ The time on the Coordinated Universal Time (UTC) scale.
  • Amazon.com: "Coordinated Universal Time": Key Phrase page 10 February 2010 14:44 UTC www.amazon.com [Source type: FILTERED WITH BAYES]

^ UTC and all time scales based on UTC will be affected by this adjustment.
  • UTC Time Step December 2005 10 February 2010 14:44 UTC www.navcen.uscg.gov [Source type: FILTERED WITH BAYES]

^ Thus, in the UTC time scale, the second and all smaller time units (millisecond, microsecond...
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

) are of constant duration, but the minute and all larger time units .(hour, day, week...^ Second · Minute · Hour · Day · Week · Fortnight · Month · Year · Decade · Century · Millennium · Jiffy · Lustrum · Saeculum · Shake · Tide .
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

) are of variable duration.
.Most UTC days contain exactly 86,400 SI seconds, with exactly 60 seconds in each minute.^ For GPS, the leap second correction contained within the UTC data of subframe 4, page 18 of the navigation message transmitted by satellites will change.
  • UTC Time Step December 2005 10 February 2010 14:44 UTC www.navcen.uscg.gov [Source type: FILTERED WITH BAYES]

^ For most of the last two hundred years the mean solar day has been slightly longer than the 86,400 s currently defined by the International System.
  • Time - The Physics Hypertextbook 10 February 2010 14:44 UTC physics.info [Source type: FILTERED WITH BAYES]

^ Leap seconds are the difference between the mean solar time in 1820 (determined by "Newcomb's Table of the Sun" which in 1954 was agreed to be 86,400 secs/days) and the caesium atomic clock which is 86,400.002 secs/day.
  • Keeping time › Science Features (ABC Science) 10 February 2010 14:44 UTC www.abc.net.au [Source type: FILTERED WITH BAYES]

.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.^ As a result, the SI second is close to 1/86400 of a mean solar day in around 1820.
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

^ For most of the last two hundred years the mean solar day has been slightly longer than the 86,400 s currently defined by the International System.
  • Time - The Physics Hypertextbook 10 February 2010 14:44 UTC physics.info [Source type: FILTERED WITH BAYES]

^ 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.
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

.The extra second is called a leap second.^ The extra second is called a leap second .
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

^ In UTC, however, about once every year or two there is an extra second, called a "leap second."
  • Date (Java 2 Platform SE 5.0) 10 February 2010 14:44 UTC java.sun.com [Source type: Reference]

^ Note: A UTC clock has the same rate as a Temps Atomique International (TAI) clock or international atomic time clock, but differs by an integral number of seconds called leap seconds.
  • Time Standards 10 February 2010 14:44 UTC www.beaglesoft.com [Source type: FILTERED WITH BAYES]

.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 extra second is called a leap second .
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

^ 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.
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

^ For most of the last two hundred years the mean solar day has been slightly longer than the 86,400 s currently defined by the International System.
  • Time - The Physics Hypertextbook 10 February 2010 14:44 UTC physics.info [Source type: FILTERED WITH BAYES]

.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 not yet been necessary since UTC was introduced.^ 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 not yet been necessary since UTC was introduced.
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

^ This minute will therefore be 59 seconds long.
  • Time Standards 10 February 2010 14:44 UTC www.beaglesoft.com [Source type: FILTERED WITH BAYES]

^ What better way to end out UTC TELECOM 2007 than ending the last full day with a presentation honoring colleagues and friends.

The irregular day lengths mean that fractional Julian days do not work properly with UTC.
.UTC is derived from International Atomic Time (TAI), which is a coordinate time scale tracking notional proper time on the rotating surface of the Earth (the geoid).^ In 1958, the International Atomic Time (TAI) service started.
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

^ The time on the Coordinated Universal Time (UTC) scale.
  • Amazon.com: "Coordinated Universal Time": Key Phrase page 10 February 2010 14:44 UTC www.amazon.com [Source type: FILTERED WITH BAYES]

^ UTC is derived from International Atomic Time (TAI), which is a coordinate time scale tracking notional proper time on the rotating surface of the Earth (the geoid ).
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

.At any particular time, UTC proceeds as a linear function of TAI. From 1972 onward, UTC ticks at the same rate as TAI, but earlier (back to the 1961 start of UTC) UTC ticked at a different rate.^ At the same time the tick rate of UTC was changed to exactly match TAI. UTC also started to track UT1 rather than UT2.
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

^ Zulu time : This is the same as UTC. .
  • NSDL AVC HOME 26 January 2010 1:27 UTC www.nsdl.arm.gov [Source type: Academic]

^ At any particular time, UTC proceeds as a linear function of TAI. From 1972 onward, UTC ticks at the same rate as TAI, but earlier (back to the 1961 start of UTC) UTC ticked at a different rate.
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

.In order to maintain a close approximation to UT1 (equivalent to GMT before 1960), UTC occasionally has discontinuities where it changes from one linear function of TAI to another.^ GMT and UTC are considered equivalent.
  • Date (Java 2 Platform SE 5.0) 10 February 2010 14:44 UTC java.sun.com [Source type: Reference]

^ In order to maintain a close approximation to UT1 (equivalent to GMT before 1960), UTC occasionally has discontinuities where it changes from one linear function of TAI to another.
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

^ Based on both TAI and GMT, UTC allows for the slowing of the Earth's rotation by adding leap seconds every year or two (and sometimes twice a year).
  • coordinated universal time 10 February 2010 14:44 UTC www.mahalo.com [Source type: FILTERED WITH BAYES]

.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 occurred only at the end of a Gregorian month.^ 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 occurred only at the end of a Gregorian month.
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

^ When it appears that the difference between the two kinds of time may approach this limit, a one-second change called a "leap second" is introduced into UTC. This occurs on average about once every year to a year and a half.
  • New Page 1 10 February 2010 14:44 UTC www.kf4l.org [Source type: FILTERED WITH BAYES]

^ What better way to end out UTC TELECOM 2007 than ending the last full day with a presentation honoring colleagues and friends.

[7]
.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.^ In 1972, GMT was replaced by Coordinated Universal Time (UTC) as the international time reference.

^ Coordinated Universal Time (UTC) is used as the official world reference for time.

^ Returns the difference in minutes between the local time in this time zone and the Coordinated Universal Time (UTC).
  • RDOTimezone object 10 February 2010 14:44 UTC www.dimastr.com [Source type: FILTERED WITH BAYES]

.Since 1972 the discontinuities have consisted only of a leap of one second at the end of 30 June or 31 December.^ Leap seconds are usually added at the end of either June or December.
  • Time Standards 10 February 2010 14:44 UTC www.beaglesoft.com [Source type: FILTERED WITH BAYES]

^ Since 1972 the discontinuities have consisted only of a leap of one second at the end of 30 June or 31 December.
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

^ Since then, leap seconds have occurred on average about once every 19 months, always on 30 June or 31 December.
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

.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.[8] In principle, leap seconds can also occur on 31 March or 30 September, but the IERS has never found this necessary.^ 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. [ 8 ] In principle, leap seconds can also occur on 31 March or 30 September, but the IERS has never found this necessary.
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

^ Are leap seconds even necessary?
  • Time - The Physics Hypertextbook 10 February 2010 14:44 UTC physics.info [Source type: FILTERED WITH BAYES]

^ The first leap second occurred on 30 June 1972.
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

.As with TAI, UTC is only known with the highest precision in retrospect.^ As with TAI, UTC is only known with the highest precision in retrospect.
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

.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.^ The International Bureau of Weights and Measures (BIPM) acts as the official time keeper of atomic time for the world.
  • Galleon UTC, Co-ordinated Universal Time 26 January 2010 1:27 UTC www.galleon.eu.com [Source type: FILTERED WITH BAYES]

^ Both agencies contribute to the Coordinated Universal Time (UTC) scale maintained by the International Bureau of Weights and Measures (BIPM).
  • NIST Time and Frequency FAQ 26 January 2010 1:27 UTC www.boulder.nist.gov [Source type: FILTERED WITH BAYES]

^ 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.
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

.(See the article on International Atomic Time for details.^ (See the article on International Atomic Time for details.
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

^ It takes into account relativistic effects and is based on International Atomic Time (TAI), which is a high-precision standard using several hundred atomic clocks worldwide.

^ In the Quick Reference Card at the end of this course, we've included a link to a detailed technical article about Outlook meetings and time zones.
  • More on time zones - Training - Microsoft Office Online 10 February 2010 14:44 UTC office.microsoft.com [Source type: General]
  • More on time zones - Training - Microsoft Office Online 10 February 2010 14:44 UTC office.microsoft.com [Source type: General]

)

History

.The local mean solar time at the Royal Observatory, Greenwich, England, United Kingdom, was chosen at the 1884 International Meridian Conference to define the Universal day, counted from zero hours at mean midnight, in recognition of the widespread use of Greenwich Mean Time (GMT).^ GMT was the standard time reference based on the mean solar time on the 0° longitude meridian in Greenwich, England.

^ At the International Meridian Conference of 1884, GMT[ 1 ] was adopted as the reference time for all clocks around the world.

^ Greenwich Mean Time (GMT) is a 24 hour astronomical time system based on the local time at Greenwich, England.
  • NIST Time and Frequency FAQ 26 January 2010 1:27 UTC www.boulder.nist.gov [Source type: FILTERED WITH BAYES]

.In 1884, the Greenwich Meridian was used for two-thirds of all charts and maps as their Prime Meridian.^ In 1884, the Greenwich Meridian was used for two-thirds of all charts and maps as their Prime Meridian .
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

^ UTC uses 24-hour (military) time notation and is based on the local standard time on the 0° longitude meridian which runs through Greenwich, England.
  • Coordinated Universal Time (UTC) 10 February 2010 14:44 UTC www.spacearchive.info [Source type: FILTERED WITH BAYES]

^ At the International Meridian Conference of 1884, GMT[ 1 ] was adopted as the reference time for all clocks around the world.

.In 1928, the term Universal Time (UT) was introduced by the International Astronomical Union to refer to GMT with the day starting at midnight.^ The time 2400 refers to the day ending while the time 0000 refers to the day starting.
  • Space Today Online -- Solar System Planet Earth -- Angkor 10 February 2010 14:44 UTC www.spacetoday.org [Source type: FILTERED WITH BAYES]

^ In 1972, GMT was replaced by Coordinated Universal Time (UTC) as the international time reference.

^ Coordinated Universal Time is a reference time for events.
  • WonderQuest: Does anybody know the time? Catch a wave 10 February 2010 14:44 UTC www.wonderquest.com [Source type: FILTERED WITH BAYES]
  • USATODAY.com - Time and time again; catching a wave 10 February 2010 14:44 UTC www.usatoday.com [Source type: News]

.Until the 1950s, broadcast time signals were based on UT, and hence on the rotation of the Earth.^ Until the 1950s, broadcast time signals were based on UT, and hence on the rotation of the Earth.
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

^ Universal Time (UT) The Universal Time Family is the general designation of time scales based on the rotation of the Earth.
  • Time Standards 10 February 2010 14:44 UTC www.beaglesoft.com [Source type: FILTERED WITH BAYES]

^ Because the earth's rotation is not uniform (it slows down and speeds up in complicated ways), UT does not always flow uniformly.
  • Date (Java 2 Platform SE 5.0) 10 February 2010 14:44 UTC java.sun.com [Source type: Reference]

.In 1955, the caesium atomic clock was invented.^ In 1955, the caesium atomic clock was invented.
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

^ 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.
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

^ Atomic clocks measure time by tracking the magnetic spin of caesium atoms.
  • Keeping time › Science Features (ABC Science) 10 February 2010 14:44 UTC www.abc.net.au [Source type: FILTERED WITH BAYES]

.This provided a form of timekeeping that was both more stable and more convenient than astronomical observations.^ This provided a form of timekeeping that was both more stable and more convenient than astronomical observations.
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

^ In these early days, timekeeping probably had more to do with religious rituals than secular needs.
  • Galleon UTC, Co-ordinated Universal Time 26 January 2010 1:27 UTC www.galleon.eu.com [Source type: FILTERED WITH BAYES]

^ These upgrades will provide a more stable service as well as some minor performance increases.
  • lj_maintenance: Site maintenance scheduled for January 23 @ 3 AM UTC 26 January 2010 1:27 UTC community.livejournal.com [Source type: FILTERED WITH BAYES]

.In 1956, the U.S. National Bureau of Standards started to use atomic frequency standards in generating the WWV time signals, named for the shortwave radio station which broadcasts them.^ Several radio stations worldwide transmit precise time signals 2 .
  • Coordinated Universal Time (UTC) 10 February 2010 14:44 UTC www.spacearchive.info [Source type: FILTERED WITH BAYES]

^ In 1956, the U.S. National Bureau of Standards started to use atomic frequency standards in generating the WWV time signals, named for the shortwave radio station which broadcasts them.
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

^ Returns the standard name of the time zone.
  • RDOTimezone object 10 February 2010 14:44 UTC www.dimastr.com [Source type: FILTERED WITH BAYES]

.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. Twenty-nine such steps were used before 1960.[9] The signal frequency was changed less often.^ Why are Cesium atomic clocks used?
  • NIST Time and Frequency FAQ 10 February 2010 14:44 UTC tf.nist.gov [Source type: FILTERED WITH BAYES]

^ The signal frequency was changed less often.
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

^ 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. Twenty-nine such steps were used before 1960.
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

.In 1958, the International Atomic Time (TAI) service started.^ In 1958, the International Atomic Time (TAI) service started.
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

^ The hyperfine transition is the basis of International Atomic Time (TAI).
  • Time - The Physics Hypertextbook 10 February 2010 14:44 UTC physics.info [Source type: FILTERED WITH BAYES]

^ TAI is maintained by the Bureau International des Poids et Mesures (BIPM) in Paris, which periodically averages the time kept by various atomic clocks around the world.
  • Time - The Physics Hypertextbook 10 February 2010 14:44 UTC physics.info [Source type: FILTERED WITH BAYES]

.It was based on the frequency for the caesium transition, newly established,[10] that was later used to redefine the second in 1967, at a length practically equal to the second of ephemeris time.^ The length of second so defined was practically equal to the second of ephemeris time .
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

^ In 1967 the SI second was redefined in terms of the frequency supplied by a caesium atomic clock.
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

^ It was based on the frequency for the caesium transition, newly established, [ 10 ] that was later used to redefine the second in 1967, at a length practically equal to the second of ephemeris time .
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

[11] 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.
.Despite the initial controversy, it became clear that basing time signals on atomic clocks was an improvement over the prior system.^ Despite the initial controversy, it became clear that basing time signals on atomic clocks was an improvement over the prior system.
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

^ International time, UTC, is based on the average of the world's atomic clocks.
  • Keeping time › Science Features (ABC Science) 10 February 2010 14:44 UTC www.abc.net.au [Source type: FILTERED WITH BAYES]

^ In 1960, an international agreement was made on atomic-based time signals.
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

.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.^ Who uses universal time?
  • Space Today Online -- Solar System Planet Earth -- Angkor 10 February 2010 14:44 UTC www.spacetoday.org [Source type: FILTERED WITH BAYES]

^ Use coordinated universal time (UTC).
  • Space Today Online -- Solar System Planet Earth -- Angkor 10 February 2010 14:44 UTC www.spacetoday.org [Source type: FILTERED WITH BAYES]

^ 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.
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

.WWV's compromise approach was copied by other agencies worldwide, such as the Royal Greenwich Observatory.^ WWV's compromise approach was copied by other agencies worldwide, such as the Royal Greenwich Observatory.
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

^ Leap seconds are used to allow UTC to closely track UT1 , which is mean solar time at the Royal Observatory, Greenwich .
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

^ As a result, when the concept of time zones was introduced, the "starting" point for calculating the different time zones was/is at the Royal Greenwich Observatory.
  • Space Today Online -- Solar System Planet Earth -- Angkor 10 February 2010 14:44 UTC www.spacetoday.org [Source type: FILTERED WITH BAYES]

.It then became a concern that time signals should be synchronised with each other, rather than independently determining their own frequency offsets and phase shifts.^ It then became a concern that time signals should be synchronised with each other, rather than independently determining their own frequency offsets and phase shifts.
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

^ The time maintained by both agencies should never differ by more than 0.000 0001 seconds from UTC. .
  • King County Library System - - Answers 10 February 2010 14:44 UTC www.kcls.org [Source type: General]

^ Caesium fountains are more accurate than conventional caesium beam clocks especially because the atoms in fountain clocks are slower so that there is more time available to determine the decisive property of the caesium atoms which is necessary for 'time generation': their resonance frequency.
  • Science Centric | News | From now on, 4 PTB primary atomic clocks will contribute to UTC 10 February 2010 14:44 UTC www.sciencecentric.com [Source type: Academic]

.In 1960, an international agreement was made on atomic-based time signals.^ International time, UTC, is based on the average of the world's atomic clocks.
  • Keeping time › Science Features (ABC Science) 10 February 2010 14:44 UTC www.abc.net.au [Source type: FILTERED WITH BAYES]

^ In 1960, an international agreement was made on atomic-based time signals.
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

^ It takes into account relativistic effects and is based on International Atomic Time (TAI), which is a high-precision standard using several hundred atomic clocks worldwide.

.A frequency offset of 1.5 × 10−8 was adopted by all the participating institutions, matching the then-current rate of UT2, a version of UT1 smoothed from seasonal variations.^ A frequency offset of 1.5 × 10 −8 was adopted by all the participating institutions, matching the then-current rate of UT2 , a version of UT1 smoothed from seasonal variations.
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

^ At the same time the tick rate of UTC was changed to exactly match TAI. UTC also started to track UT1 rather than UT2.
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

^ As the nation's national metrology institute, NIST is responsible for providing the ultimate measurement reference for all physical quantities in the United States (not just time and frequency).
  • NIST Time and Frequency FAQ 26 January 2010 1:27 UTC www.boulder.nist.gov [Source type: FILTERED WITH BAYES]

.Ad hoc phase shifts were used to synchronise the time signals as far as possible.^ Ad hoc phase shifts were used to synchronise the time signals as far as possible.
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

^ In 1956, the U.S. National Bureau of Standards started to use atomic frequency standards in generating the WWV time signals, named for the shortwave radio station which broadcasts them.
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

^ Cycle slips introduce phase shifts equal (in time units) to the period of the carrier frequency, or to a multiple of its period.
  • Time and Frequency from A to Z 26 January 2010 1:27 UTC tf.nist.gov [Source type: Academic]

.It was determined that the Bureau International de l'Heure should henceforth choose the frequency offsets and coordinate the time steps.^ It was determined that the Bureau International de l'Heure should henceforth choose the frequency offsets and coordinate the time steps.
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

^ What is the role of NIST in determining international time?
  • NIST Time and Frequency FAQ 26 January 2010 1:27 UTC www.boulder.nist.gov [Source type: FILTERED WITH BAYES]

^ Time offsets from Coordinated Universal Time (UTC) .
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

.It was also decided to use larger jumps, of 50 ms instead of 20 ms.^ It was also decided to use larger jumps, of 50 ms instead of 20 ms. .
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

^ The jumps increased in size to 100 ms, with only one 50 ms jump having ever occurred.
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

^ MS SQL (use instead of GETDATE()) DECLARE @currentTime datetime SET @currentTime = GETUTCDATE() .
  • ASP.NET.4GuysFromRolla.com: Using Coordinated Universal Time (UTC) to Store Date/Time Values 10 February 2010 14:44 UTC aspnet.4guysfromrolla.com [Source type: FILTERED WITH BAYES]
  • 4GuysFromRolla.com: Using Coordinated Universal Time (UTC) to Store Date/Time Values 10 February 2010 14:44 UTC aspnet.4guysfromrolla.com [Source type: FILTERED WITH BAYES]

.UTC was officially initiated at the start of 1961 (but the name Coordinated Universal Time was not adopted by the International Astronomical Union until 1967).^ In 1972, GMT was replaced by Coordinated Universal Time (UTC) as the international time reference.

^ Time and time again; catching a wave Q: Is International Standard Time the same as Coordinated Universal Time (UTC)?
  • USATODAY.com - Time and time again; catching a wave 10 February 2010 14:44 UTC www.usatoday.com [Source type: News]

^ Results found for: Coordinated Universal Time .
  • EETimes Encyclopedia 10 February 2010 14:44 UTC www.eetimes.com [Source type: News]

[12][13] .The TAI instant 1 January 1961 00:00:01.422818 exactly was identified as UTC instant 1 January 1961 00:00:00.000000 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 exact times of the solstices change from year to year.
  • Solar Calculator Glossary 26 January 2010 1:27 UTC www.srrb.noaa.gov [Source type: FILTERED WITH BAYES]

^ Thereafter there will need to be the possibility of leap seconds at the end of any month.
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

^ The speed of time is one second per second.
  • Time - The Physics Hypertextbook 10 February 2010 14:44 UTC physics.info [Source type: FILTERED WITH BAYES]

.The jumps increased in size to 100 ms, with only one 50 ms jump having ever occurred.^ The jumps increased in size to 100 ms, with only one 50 ms jump having ever occurred.
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

^ It was also decided to use larger jumps, of 50 ms instead of 20 ms. .
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

.This UTC was intended to permit a very close approximation of UT2, within around 0.1 s.^ This UTC was intended to permit a very close approximation of UT2, within around 0.1 s.
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

^ UTC(NIST) and UTC(USNO) are kept in very close agreement , and can be considered equivalent for nearly all purposes.
  • NIST Time and Frequency FAQ 10 February 2010 14:44 UTC tf.nist.gov [Source type: FILTERED WITH BAYES]

^ UTC has employees around the world, operates in approximately 180 countries and trades in every major market.
  • UTC - High technology for building & aerospace industries 26 January 2010 1:27 UTC careers.utc.com [Source type: News]

.In 1967 the SI second was redefined in terms of the frequency supplied by a caesium atomic clock.^ In 1955, the caesium atomic clock was invented.
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

^ In 1967 the SI second was redefined in terms of the frequency supplied by a caesium atomic clock.
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

^ Leap seconds are the difference between the mean solar time in 1820 (determined by "Newcomb's Table of the Sun" which in 1954 was agreed to be 86,400 secs/days) and the caesium atomic clock which is 86,400.002 secs/day.
  • Keeping time › Science Features (ABC Science) 10 February 2010 14:44 UTC www.abc.net.au [Source type: FILTERED WITH BAYES]

.The length of second so defined was practically equal to the second of ephemeris time.^ It is the ideal time scale for scientific use, but it is not practical for everyday use since it is not linked to the rotation of the Earth and the actual length of the day.
  • A debate about time - The Planetary Society Blog | The Planetary Society 10 February 2010 14:44 UTC planetary.org [Source type: FILTERED WITH BAYES]

^ For a primary reference time less than the leap seconds update event time, the old leap seconds value applies; for a primary reference time equal to or greater than the leap seconds update event time, the new leap seconds value applies.
  • DIRECTLY OBTAINING BY APPLICATION PROGRAMS INFORMATION USABLE IN DETERMINING CLOCK ACCURACY - Patent application 10 February 2010 14:44 UTC www.faqs.org [Source type: Reference]

^ One thing to note is the steep slope resulting from initializing UT to the old Ephemeris Time definition of so many seconds in 1900.
  • A Proposal to Upgrade UTC 26 January 2010 1:27 UTC iraf.noao.edu [Source type: FILTERED WITH BAYES]

[11] .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 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.
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

^ As of mid-July 2004, UTC differs from TAI by 32 seconds.
  • SBF Glossary: UR to .uy 26 January 2010 1:27 UTC www.plexoft.com [Source type: FILTERED WITH BAYES]

^ This was the frequency that had been provisionally used in TAI since 1958.
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

.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.^ 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.
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

^ The SI unit of time is the second [s].
  • Time - The Physics Hypertextbook 10 February 2010 14:44 UTC physics.info [Source type: FILTERED WITH BAYES]

^ Coordinated Universal Time (UTC) is a coordinated time scale maintained by the Bureau International des Poids et Mesures (BIPM), which forms the basis of a coordinated dissemination of standard frequencies and time signals.
  • Time Standards 10 February 2010 14:44 UTC www.beaglesoft.com [Source type: FILTERED WITH BAYES]

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.
.There was also dissatisfaction with the frequent jumps in UTC (and SAT).^ There was also dissatisfaction with the frequent jumps in UTC (and SAT).
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

.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.^ 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.
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

^ In 1955, the caesium atomic clock was invented.
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

^ Atomic clocks measure time by tracking the magnetic spin of caesium atoms.
  • Keeping time › Science Features (ABC Science) 10 February 2010 14:44 UTC www.abc.net.au [Source type: FILTERED WITH BAYES]

[14] .This system was eventually approved, along with the idea of maintaining the UTC second equal to the TAI second.^ This system was eventually approved, along with the idea of maintaining the UTC second equal to the TAI second.
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

^ 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.
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

^ As of mid-July 2004, UTC differs from TAI by 32 seconds.
  • SBF Glossary: UR to .uy 26 January 2010 1:27 UTC www.plexoft.com [Source type: FILTERED WITH BAYES]

.At the end of 1971 there was a final irregular jump of 0.107758 TAI seconds exactly, so that 1 January 1972 00:00:00 UTC was 1 January 1972 00:00:10 TAI exactly, making the difference between UTC and TAI an integer number of seconds.^ As of mid-July 2004, UTC differs from TAI by 32 seconds.
  • SBF Glossary: UR to .uy 26 January 2010 1:27 UTC www.plexoft.com [Source type: FILTERED WITH BAYES]

^ At the end of 1971 there was a final irregular jump of 0.107758 TAI seconds exactly, so that 1 January 1972 00:00:00 UTC was 1 January 1972 00:00:10 TAI exactly, making the difference between UTC and TAI an integer number of seconds.
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

^ UTC runs at the same frequency as TAI. However, it differs from TAI by an integral number of seconds.
  • Time and Frequency from A to Z 26 January 2010 1:27 UTC tf.nist.gov [Source type: Academic]

.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.^ Some time signals started to broadcast the DUT1 correction (UT1 − UTC), for applications which required a closer approximation of UT1 than UTC now provided.
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

^ At the same time the tick rate of UTC was changed to exactly match TAI. UTC also started to track UT1 rather than UT2.
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

^ At other times, UTC tracks TAI , a consensus of atomic clocks.
  • SBF Glossary: UR to .uy 26 January 2010 1:27 UTC www.plexoft.com [Source type: FILTERED WITH BAYES]

[15][16]
.The first leap second occurred on 30 June 1972. Since then, leap seconds have occurred on average about once every 19 months, always on 30 June or 31 December.^ Leap seconds are usually added at the end of either June or December.
  • Time Standards 10 February 2010 14:44 UTC www.beaglesoft.com [Source type: FILTERED WITH BAYES]

^ Leap seconds have been added to UTC at a rate averaging about 8 every 10 years, beginning in 1972.
  • Time and Frequency from A to Z 26 January 2010 1:27 UTC tf.nist.gov [Source type: Academic]

^ When necessary, leap seconds are added to UTC on either June 30 or December 31.
  • Time and Frequency from A to Z 26 January 2010 1:27 UTC tf.nist.gov [Source type: Academic]

.As of 2009, there have been 24 leap seconds in total, all positive, putting UTC 34 seconds behind TAI.[17] It seems unlikely that a negative leap second will ever occur, but there is a small chance of one due to changes in the moment of inertia of the Earth's crust in the 2000s.^ As of 2009, there have been 24 leap seconds in total, all positive, putting UTC 34 seconds behind TAI. [ 17 ] It seems unlikely that a negative leap second will ever occur, but there is a small chance of one due to changes in the moment of inertia of the Earth's crust in the 2000s.
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

^ This difference increases when leap seconds occur.
  • Time and Frequency from A to Z 26 January 2010 1:27 UTC tf.nist.gov [Source type: Academic]

^ Since it has not been changed since 1958, there is now a 32-second time difference between UTC and TAI." It's nice to have a timekeeping standard that doesn't have fits and starts like UTC does, especially if you care about millisecond-level precision timing.
  • A debate about time - The Planetary Society Blog | The Planetary Society 10 February 2010 14:44 UTC planetary.org [Source type: FILTERED WITH BAYES]

[citation needed] This acceleration has already led to the longest-ever period without a leap second, from 1 January 1999 to 31 December 2005.

Rationale

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 Earth's rotational speed is very slowly decreasing due to tidal deceleration , causing the mean solar day to increase in length.
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

^ For most of the last two hundred years the mean solar day has been slightly longer than the 86,400 s currently defined by the International System.
  • Time - The Physics Hypertextbook 10 February 2010 14:44 UTC physics.info [Source type: FILTERED WITH BAYES]

^ It is the ideal time scale for scientific use, but it is not practical for everyday use since it is not linked to the rotation of the Earth and the actual length of the day.
  • A debate about time - The Planetary Society Blog | The Planetary Society 10 February 2010 14:44 UTC planetary.org [Source type: FILTERED WITH BAYES]

.The length of the SI second was calibrated on the basis of the second of ephemeris time,[10][11] and can now be seen to have a relationship with the mean solar day observed between 1750 and 1892, analysed by Simon Newcomb.^ As a result, the SI second is close to 1/86400 of a mean solar day in around 1820.
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

^ The length of second so defined was practically equal to the second of ephemeris time .
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

^ The length of the SI second was calibrated on the basis of the second of ephemeris time , [ 10 ] [ 11 ] and can now be seen to have a relationship with the mean solar day observed between 1750 and 1892, analysed by Simon Newcomb .
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

.As a result, the SI second is close to 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.^ As a result, the SI second is close to 1/86400 of a mean solar day in around 1820.
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

^ In earlier centuries the mean solar day was shorter than 86400 SI seconds, and in later centuries it is longer than 86400 seconds.
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

^ For most of the last two hundred years the mean solar day has been slightly longer than the 86,400 s currently defined by the International System.
  • Time - The Physics Hypertextbook 10 February 2010 14:44 UTC physics.info [Source type: FILTERED WITH BAYES]

.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.^ 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.
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

^ For most of the last two hundred years the mean solar day has been slightly longer than the 86,400 s currently defined by the International System.
  • Time - The Physics Hypertextbook 10 February 2010 14:44 UTC physics.info [Source type: FILTERED WITH BAYES]

^ Leap seconds are the difference between the mean solar time in 1820 (determined by "Newcomb's Table of the Sun" which in 1954 was agreed to be 86,400 secs/days) and the caesium atomic clock which is 86,400.002 secs/day.
  • Keeping time › Science Features (ABC Science) 10 February 2010 14:44 UTC www.abc.net.au [Source type: FILTERED WITH BAYES]

For this reason, UT is now "slower" than TAI.
.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.^ 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.
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

^ For most of the last two hundred years the mean solar day has been slightly longer than the 86,400 s currently defined by the International System.
  • Time - The Physics Hypertextbook 10 February 2010 14:44 UTC physics.info [Source type: FILTERED WITH BAYES]

^ Leap seconds are the difference between the mean solar time in 1820 (determined by "Newcomb's Table of the Sun" which in 1954 was agreed to be 86,400 secs/days) and the caesium atomic clock which is 86,400.002 secs/day.
  • Keeping time › Science Features (ABC Science) 10 February 2010 14:44 UTC www.abc.net.au [Source type: FILTERED WITH BAYES]

.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.^ At the end of the 21st century LOD will be roughly 86,400.004 s, requiring leap seconds every 250 days.
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

^ 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.
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

^ What better way to end out UTC TELECOM 2007 than ending the last full day with a presentation honoring colleagues and friends.

.Thus leap seconds were inserted at approximately this interval, retarding UTC to keep it synchronised in the long term.^ Thus leap seconds were inserted at approximately this interval, retarding UTC to keep it synchronised in the long term.
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

^ When necessary, leap seconds are added to UTC on either June 30 or December 31.
  • Time and Frequency from A to Z 26 January 2010 1:27 UTC tf.nist.gov [Source type: Academic]

^ Impending leap seconds for UTC are announced at least eight weeks in advance by the International Earth Rotation and Reference Systems Service at the Paris Observatory , however.
  • Coordinated Universal Time (UTC) -- Britannica Online Encyclopedia 10 February 2010 14:44 UTC www.britannica.com [Source type: FILTERED WITH BAYES]

.Note that the actual rotational period varies on unpredictable factors such as tectonic motion and has to be observed rather than computed.^ Note that the actual rotational period varies on unpredictable factors such as tectonic motion and has to be observed rather than computed.
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

.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 (just as a leap year every four years doesn't mean the year is getting longer by one day every four years): 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.
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

^ Intercalation · Leap second · Leap year .
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

^ Astronomical · Julian · Gregorian · Islamic · Lunisolar · Solar · Lunar · Epact · Intercalation · Leap year · Tropical year · Equinox · Solstice · Seven-day week · Week-day names · Calculating the day of the week · Dominical letter .
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

.This is a mean rate within the range of 1.7–2.3 ms/cy.^ This is a mean rate within the range of 1.7–2.3 ms/cy.
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

^ 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).
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

.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.^ 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.
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

^ The first 32 bits divide NTP into eras lasting 136 years, since … .
  • Time - The Physics Hypertextbook 10 February 2010 14:44 UTC physics.info [Source type: FILTERED WITH BAYES]

^ This is a mean rate within the range of 1.7–2.3 ms/cy.
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

[18] .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 per day, so it accumulated to 1 second after about 500 days.^ 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 per day, so it accumulated to 1 second after about 500 days.
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

^ The speed of time is one second per second.
  • Time - The Physics Hypertextbook 10 February 2010 14:44 UTC physics.info [Source type: FILTERED WITH BAYES]

^ Since it has not been changed since 1958, there is now a 32-second time difference between UTC and TAI." It's nice to have a timekeeping standard that doesn't have fits and starts like UTC does, especially if you care about millisecond-level precision timing.
  • A debate about time - The Planetary Society Blog | The Planetary Society 10 February 2010 14:44 UTC planetary.org [Source type: FILTERED WITH BAYES]

.For example, assume you start counting the seconds from the Unix epoch of 1970-01-01T00:00:00 UTC with an atomic clock.^ For example, a wall clock can display UTC in hours, minutes, and seconds.
  • NIST Time and Frequency FAQ 10 February 2010 14:44 UTC tf.nist.gov [Source type: FILTERED WITH BAYES]

^ Today, UTC uses precise atomic clocks, shortwave time signals, and satellites to ensure that UTC remains a reliable, accurate standard for scientific and navigational purposes.
  • UTC GMT Conversion 10 February 2010 14:44 UTC www.dxing.com [Source type: FILTERED WITH BAYES]

^ If the attempt is successful, the time indicated is returned represented as the distance, measured in milliseconds, of that time from the epoch (00:00:00 GMT on January 1, 1970).
  • Date (Java 2 Platform SE 5.0) 10 February 2010 14:44 UTC java.sun.com [Source type: Reference]

.At midnight on that day (as measured on UTC), your counter registers 0 s.^ At midnight on that day (as measured on UTC), your counter registers 0 s.
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

^ After 500 rotations, your counter will register 43,200,001 s.
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

.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).^ This system is based on the rotation of the Earth with respect to the stars, instead of the sun.
  • Solar Calculator Glossary 26 January 2010 1:27 UTC www.srrb.noaa.gov [Source type: FILTERED WITH BAYES]

^ After 500 rotations, your counter will register 43,200,001 s.
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

^ 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).
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

.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.^ After 500 rotations, your counter will register 43,200,001 s.
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

^ 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.
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

^ Based on your counter, you can calculate that the date is 1970-01-02T00:00:00 UT1.
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

.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.^ Leap seconds are usually added at the end of either June or December.
  • Time Standards 10 February 2010 14:44 UTC www.beaglesoft.com [Source type: FILTERED WITH BAYES]

^ After 500 rotations, your counter will register 43,200,001 s.
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

^ Since the date is also UTC, you need to listen at 10:00 p.m.
  • UTC GMT Conversion 10 February 2010 14:44 UTC www.dxing.com [Source type: FILTERED WITH BAYES]

.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.^ The frequency of leap seconds therefore corresponds to the slope of the diagonal graph segments, and thus to the excess LOD. .
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

^ 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.
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

^ Graph showing the difference DUT1 between UT1 and UTC. Vertical segments correspond to leap seconds.
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

.(Note that the slope became shallower in the 2000s, due to a slight acceleration of the Earth's crust temporarily shortening the day.^ (Note that the slope became shallower in the 2000s, due to a slight acceleration of the Earth's crust temporarily shortening the day.
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

^ The Earth's rotational speed is very slowly decreasing due to tidal deceleration , causing the mean solar day to increase in length.
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

) .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.
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

^ 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.
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

^ Graph showing the difference DUT1 between UT1 and UTC. Vertical segments correspond to leap seconds.
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

.Leap seconds are timed to keep DUT1 within the vertical range depicted by this graph.^ Leap seconds are timed to keep DUT1 within the vertical range depicted by this graph.
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

^ To remedy this discrepancy, UTC is kept within 0.9 second of UT1 by adding a leap second to UTC as needed; the last minute of December or June is made to contain 61 seconds.
  • Coordinated Universal Time (UTC) -- Britannica Online Encyclopedia 10 February 2010 14:44 UTC www.britannica.com [Source type: FILTERED WITH BAYES]

^ Leap seconds are used to allow UTC to closely track UT1 , which is mean solar time at the Royal Observatory, Greenwich .
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

The frequency of leap seconds therefore corresponds to the slope of the diagonal graph segments, and thus to the excess LOD.

Future

.As the Earth's rotation continues to slow, positive leap seconds will be required more frequently.^ See also: Leap second As the Earth's rotation continues to slow, positive leap seconds will be required more frequently.
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

^ Because the earth's rotation is not uniform (it slows down and speeds up in complicated ways), UT does not always flow uniformly.
  • Date (Java 2 Platform SE 5.0) 10 February 2010 14:44 UTC java.sun.com [Source type: Reference]

^ In a few tens of thousands of years (the timing is 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.
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

.The long-term rate of change of LOD is approximately +1.7 ms per century.^ The long-term rate of change of LOD is approximately +1.7 ms per century.
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

^ Thus leap seconds were inserted at approximately this interval, retarding UTC to keep it synchronised in the long term.
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

^ 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.
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

.At the end of the 21st century LOD will be roughly 86,400.004 s, requiring leap seconds every 250 days.^ At the end of the 21st century LOD will be roughly 86,400.004 s, requiring leap seconds every 250 days.
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

^ Sometime in the 22nd century, two leap seconds will be required every year.
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

^ For most of the last two hundred years the mean solar day has been slightly longer than the 86,400 s currently defined by the International System.
  • Time - The Physics Hypertextbook 10 February 2010 14:44 UTC physics.info [Source type: FILTERED WITH BAYES]

.Over several centuries, the frequency of leap seconds will become problematic.^ Over several centuries, the frequency of leap seconds will become problematic.
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

^ See also: Leap second As the Earth's rotation continues to slow, positive leap seconds will be required more frequently.
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

^ In the 25th century, four leap seconds will be required every year, so the current quarterly options will be insufficient.
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

.Some time in the 22nd century, two leap seconds will be required every year.^ In the 25th century, four leap seconds will be required every year, so the current quarterly options will be insufficient.
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

^ Intercalation · Leap second · Leap year .
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

^ Sometime in the 22nd century, two leap seconds will be required every year.
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

.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.^ Leap seconds are usually added at the end of either June or December.
  • Time Standards 10 February 2010 14:44 UTC www.beaglesoft.com [Source type: FILTERED WITH BAYES]

^ 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.
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

^ 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. [ 8 ] In principle, leap seconds can also occur on 31 March or 30 September, but the IERS has never found this necessary.
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

.In the 25th century, four leap seconds will be required every year, so the current quarterly options will be insufficient.^ In the 25th century, four leap seconds will be required every year, so the current quarterly options will be insufficient.
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

^ Intercalation · Leap second · Leap year .
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

^ Sometime in the 22nd century, two leap seconds will be required every year.
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

.Thereafter there will need to be the possibility of leap seconds at the end of any month.^ In UTC, however, about once every year or two there is an extra second, called a "leap second."
  • Date (Java 2 Platform SE 5.0) 10 February 2010 14:44 UTC java.sun.com [Source type: Reference]

^ (Various of the example leap seconds would have been better scheduled either a month earlier or later.
  • A Proposal to Upgrade UTC 26 January 2010 1:27 UTC iraf.noao.edu [Source type: FILTERED WITH BAYES]

^ Leap seconds are usually added at the end of either June or December.
  • Time Standards 10 February 2010 14:44 UTC www.beaglesoft.com [Source type: FILTERED WITH BAYES]

.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.^ When there is talk about a 1 or 1.5 year cadence of leap seconds, what is really meant is a 6 month sampling rate.
  • A Proposal to Upgrade UTC 26 January 2010 1:27 UTC iraf.noao.edu [Source type: FILTERED WITH BAYES]

^ Thereafter there will need to be the possibility of leap seconds at the end of any month.
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

^ Intercalation · Leap second · Leap year .
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

[19]
.In a few tens of thousands of years (the timing is 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.^ Time is precious, but truth is more precious than time.
  • Time - The Physics Hypertextbook 10 February 2010 14:44 UTC physics.info [Source type: FILTERED WITH BAYES]

^ Intercalation · Leap second · Leap year .
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

^ In a few tens of thousands of years (the timing is 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.
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

.It would be possible to then continue with double leaps, but this becomes increasingly untenable.^ It would be possible to then continue with double leaps, but this becomes increasingly untenable.
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

.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.^ Continued leap seconds or a much larger DUT1 range - both have a cost.
  • A Proposal to Upgrade UTC 26 January 2010 1:27 UTC iraf.noao.edu [Source type: FILTERED WITH BAYES]

^ 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.
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

^ This function returns the current time in seconds.

.There is a proposal to redefine UTC and abolish leap seconds, such that sundials would slowly get further out of sync with civil time.^ There is a proposal to redefine UTC and abolish leap seconds, such that sundials would slowly get further out of sync with civil time .
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

^ UTC might be redefined without Leap Seconds " .
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

^ 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.
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

[20] .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.^ 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.
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

^ UTC does not change with a change of seasons, but local time or civil time may change if a time zone jurisdiction observes daylight saving time or summer time .
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

^ Civil Dusk The time at which the sun is 6 degrees below the horizon in the evening.
  • Glossary - NOAA's National Weather Service 10 February 2010 14:44 UTC www.nws.noaa.gov [Source type: FILTERED WITH BAYES]

.This would be a major practical change in civil timekeeping, but would take effect slowly over several centuries.^ This would be a major practical change in civil timekeeping, but would take effect slowly over several centuries.
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

^ There is a proposal to redefine UTC and abolish leap seconds, such that sundials would slowly get further out of sync with civil time .
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

^ Even if we have not changed our system, society has enough slop in its timekeeping that people will slowly shift without even knowing it.
  • A Proposal to Upgrade UTC 26 January 2010 1:27 UTC iraf.noao.edu [Source type: FILTERED WITH BAYES]

An ITU study group was to have voted 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.
.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.^ Leap seconds are used to allow UTC to closely track UT1 , which is mean solar time at the Royal Observatory, Greenwich .
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

^ 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.
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

^ There are other time and date systems as well; for example, the time scale used by the satellite-based global positioning system (GPS) is synchronized to UTC but is not adjusted for leap seconds.
  • Date (Java 2 Platform SE 5.0) 10 February 2010 14:44 UTC java.sun.com [Source type: Reference]

[21]

Uses

.UTC is the time system used for many Internet and World Wide Web standards.^ UTC is also the time system used in aviation .
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

^ UTC is the time system used for many Internet and World Wide Web standards.
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

^ Most Amateur radio operators refer to it as UTC. UTC uses 24-hour (military) time notation and is based on the local standard time on the 0 longitude meridian which runs through Greenwich, England, hence, Greenwich Mean Time.
  • UTC - Coordinated Universal Time Explained - UTC Conversion Chart - WWV Frequencies 10 February 2010 14:44 UTC www.hamuniverse.com [Source type: FILTERED WITH BAYES]

In particular, the Network Time Protocol, which is designed to synchronise the clocks of many computers over the Internet (usually to that of a known accurate atomic clock), uses UTC.
.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.^ Several radio stations worldwide transmit precise time signals 2 .
  • Coordinated Universal Time (UTC) 10 February 2010 14:44 UTC www.spacearchive.info [Source type: FILTERED WITH BAYES]

^ Several radio stations worldwide transmit precise time signals on HF bands and other frequencies.
  • UTC - Coordinated Universal Time Explained - UTC Conversion Chart - WWV Frequencies 10 February 2010 14:44 UTC www.hamuniverse.com [Source type: FILTERED WITH BAYES]

^ 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.
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

.In the past, the FCC required all amateur radio operators in the United States to log their radio conversations.^ In the past, the FCC required all amateur radio operators in the United States to log their radio conversations.
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

^ 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.
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

^ In the EU, all time zones change at the same moment ( in the United.States, each time zone switches at a different time.
  • Time Standards 10 February 2010 14:44 UTC www.beaglesoft.com [Source type: FILTERED WITH BAYES]

.International broadcasters such as the BBC World Service also use UTC when publishing their schedules and announcing times during broadcasts.^ International time, UTC, is based on the average of the world's atomic clocks.
  • Keeping time › Science Features (ABC Science) 10 February 2010 14:44 UTC www.abc.net.au [Source type: FILTERED WITH BAYES]

^ World Clock Deluxe is a powerful and easy-to-use time tool.
  • MaBaSoft | News 10 February 2010 14:44 UTC www.mabasoft.net [Source type: News]

^ However, by international agreement, the term UTC is recommended for all general timekeeping applications, and use of the term GMT is discouraged.
  • Time Standards 10 February 2010 14:44 UTC www.beaglesoft.com [Source type: FILTERED WITH BAYES]

.UTC is also the time system used in aviation.^ UTC is also the time system used in aviation .
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

^ There are other time and date systems as well; for example, the time scale used by the satellite-based global positioning system (GPS) is synchronized to UTC but is not adjusted for leap seconds.
  • Date (Java 2 Platform SE 5.0) 10 February 2010 14:44 UTC java.sun.com [Source type: Reference]

^ UTC uses 24-hour (military) time notation and is based on the local standard time on the 0° longitude meridian which runs through Greenwich, England.
  • Coordinated Universal Time (UTC) 10 February 2010 14:44 UTC www.spacearchive.info [Source type: FILTERED WITH BAYES]

[22] .Weather forecastings, flight plans, air traffic control clearances, and maps all use UTC (also colloquially referred to as "Zulu Time") to avoid confusion about time zones and daylight saving time.^ Understanding and using Zulu time ".
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

^ Pacific Daylight Saving Time 5:30 p.m.
  • Product Presentations - HumanWare USA 10 February 2010 14:44 UTC www.humanware.com [Source type: FILTERED WITH BAYES]

^ The corresponding daylight saving time information indicates that the daylight saving time is not used in this region.
  • IMAGE PICKUP APPARATUS AND TIME CORRECTION METHOD - Patent application 10 February 2010 14:44 UTC www.faqs.org [Source type: Reference]

.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.^ UTC is also the time system used in aviation .
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

^ (UTC clock at top of this page provided by World Time Server ) .
  • UTC - Coordinated Universal Time Explained - UTC Conversion Chart - WWV Frequencies 10 February 2010 14:44 UTC www.hamuniverse.com [Source type: FILTERED WITH BAYES]

^ 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.
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

.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.^ UTC might be redefined without Leap Seconds " .
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

^ 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.
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

^ Leap seconds are the difference between the mean solar time in 1820 (determined by "Newcomb's Table of the Sun" which in 1954 was agreed to be 86,400 secs/days) and the caesium atomic clock which is 86,400.002 secs/day.
  • Keeping time › Science Features (ABC Science) 10 February 2010 14:44 UTC www.abc.net.au [Source type: FILTERED WITH BAYES]

.Therefore, many scientific applications that require precise measurement of long (multi-year) intervals use TAI instead.^ Therefore, many scientific applications that require precise measurement of long (multi-year) intervals use TAI instead.
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

^ Many electronic navigation and communication systems—including the global positioning system, which can tell people exactly where they are on the planet—depend on extremely precise measurements of time intervals.
  • Time Standards 10 February 2010 14:44 UTC www.beaglesoft.com [Source type: FILTERED WITH BAYES]

^ To help reduce the chance that a restart will be required, stop all affected services and close all applications that may use the affected files prior to installing the security update.
  • Microsoft Security Bulletin MS06-061: Vulnerabilities in Microsoft XML Core Services Could Allow Remote Code Execution (924191) 10 February 2010 14:44 UTC www.microsoft.com [Source type: Reference]

.TAI is also commonly used by systems that can not handle leap seconds.^ TAI is also commonly used by systems that can not handle leap seconds.
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

^ There are other time and date systems as well; for example, the time scale used by the satellite-based global positioning system (GPS) is synchronized to UTC but is not adjusted for leap seconds.
  • Date (Java 2 Platform SE 5.0) 10 February 2010 14:44 UTC java.sun.com [Source type: Reference]

^ 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.
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

.A fixed 19-second offset from TAI also gives GPS time.^ A fixed 19-second offset from TAI also gives GPS time .
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

^ It has the same rate as INTERNATIONAL ATOMIC TIME (TAI), from which it differs by an integral number of seconds, called leap seconds.

^ There are also reports of GPS receivers experiencing intermittent errors in the displayed time amounting to entire seconds.
  • Coordinated Universal Time (UTC) 10 February 2010 14:44 UTC www.spacearchive.info [Source type: FILTERED WITH BAYES]

.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 ambiguous.^ 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 ambiguous.
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

^ 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.
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

^ In UTC, however, about once every year or two there is an extra second, called a "leap second."
  • Date (Java 2 Platform SE 5.0) 10 February 2010 14:44 UTC java.sun.com [Source type: Reference]

[23]
.UTC has been adopted as legal time in the Title 15 of the US Code, section 261b.^ UTC has been adopted as legal time in the Title 15 of the US Code , section 261b.
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

^ The code is divided h ie rarchically into titles (there are 50), chapters and sections.
  • SBF Glossary: UR to .uy 26 January 2010 1:27 UTC www.plexoft.com [Source type: FILTERED WITH BAYES]

^ Vb.NET sample code: Returns the Coordinated Universal Time (UTC) offset for the specified local time.
  • FAQ's - IsNegativeInfinity,IsPositiveInfinity,IsInfinity,Write, Year, Create, GetDaylightChanges, Start, Change, TimeZone, DaylightTime, Local, Display, Standard, 10 February 2010 14:44 UTC www.eggheadcafe.com [Source type: Reference]

Time zones

.Time zones usually differ from UTC by an integral number of hours,[24] 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 or quarter-hours from UT1 or UTC. .
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

^ The exact number of hours depends on the time zones.
  • Lying about Santa: The Irrelevance of Proof to the Holiday Spirit | Media/Culture | ReligionDispatches 10 February 2010 14:44 UTC religiondispatches.org [Source type: General]

^ Main articles: Time zone and List of time zones Time zones usually differ from UTC by an integral number of hours, [ 24 ] although the laws of each jurisdiction would have to be consulted if sub-second accuracy was required.
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

Several jurisdictions established time zones that differ by an integer number of half-hours or quarter-hours from UT1 or 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).^ 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.
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

^ For other uses, see UTC (disambiguation) .
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

^ UTC is also the time system used in aviation .
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

.Since the NATO phonetic alphabet and amateur radio word for Z is "Zulu", UTC is sometimes known as Zulu time.^ Since the NATO phonetic alphabet and amateur radio word for Z is "Zulu", UTC is sometimes known as Zulu time .
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

^ Zulu time : This is the same as UTC. .
  • NSDL AVC HOME 26 January 2010 1:27 UTC www.nsdl.arm.gov [Source type: Academic]

^ 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.
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

.This is especially true in aviation, where Zulu is the universal standard.^ This is especially true in aviation, where Zulu is the universal standard.
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

[25] .This ensures all pilots regardless of location are using the same 24-hour clock, thus avoiding confusion when flying between time zones.^ This ensures all pilots regardless of location are using the same 24-hour clock , thus avoiding confusion when flying between time zones.
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

^ Weather forecastings , flight plans , air traffic control clearances, and maps all use UTC (also colloquially referred to as "Zulu Time") to avoid confusion about time zones and daylight saving time .
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

^ 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.
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

[26] .See list of military time zones for letters used in addition to Z in qualifying time zones other than Greenwich.^ The hardware (e.g., millicode) of the environment uses this information and/or other information within the processing environment to update the information in the hardware system timing area.
  • DIRECTLY OBTAINING BY APPLICATION PROGRAMS INFORMATION USABLE IN DETERMINING CLOCK ACCURACY - Patent application 10 February 2010 14:44 UTC www.faqs.org [Source type: Reference]

^ Also, the timing information can be stored in areas of memory other than the hardware system timing area, or in storage.
  • DIRECTLY OBTAINING BY APPLICATION PROGRAMS INFORMATION USABLE IN DETERMINING CLOCK ACCURACY - Patent application 10 February 2010 14:44 UTC www.faqs.org [Source type: Reference]

^ This update also includes other DST-related changes, time zone-related changes, and settings-related changes.
  • August 2009 cumulative time zone update for Microsoft Windows operating systems 10 February 2010 14:44 UTC support.microsoft.com [Source type: FILTERED WITH BAYES]

.UTC does not change with a change of seasons, but local time or civil time may change if a time zone jurisdiction observes daylight saving time or summer time.^ UTC does not change with a change of seasons, but local time or civil time may change if a time zone jurisdiction observes daylight saving time or summer time .
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

^ Pacific Daylight Saving Time 5:30 p.m.
  • Product Presentations - HumanWare USA 10 February 2010 14:44 UTC www.humanware.com [Source type: FILTERED WITH BAYES]

^ Central Daylight Saving Time 12 a.m.
  • Product Presentations - HumanWare USA 10 February 2010 14:44 UTC www.humanware.com [Source type: FILTERED WITH BAYES]

.For example, UTC is 5 hours ahead of local time on the east coast of the United States during the winter but 4 hours ahead during the summer.^ For example, UTC is 5 hours ahead of local time on the east coast of the United States during the winter but 4 hours ahead during the summer.
  • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

^ Valid timing modes for IBM's z/Architecture include, for instance, local timing mode, ETR (External Time Reference) timing mode, STP timing mode; [0031] b) System Timing State 404--This field indicates the timing state of the system.
  • DIRECTLY OBTAINING BY APPLICATION PROGRAMS INFORMATION USABLE IN DETERMINING CLOCK ACCURACY - Patent application 10 February 2010 14:44 UTC www.faqs.org [Source type: Reference]

^ In step ST3, the control unit 31 calculates the local time.
  • IMAGE PICKUP APPARATUS AND TIME CORRECTION METHOD - Patent application 10 February 2010 14:44 UTC www.faqs.org [Source type: Reference]

See also

Bibliography

.
  • Allan, David W., Neil Ashby, Clifford C. Hodge: The Science of Timekeeping.^ Allan, David W., Neil Ashby, Clifford C. Hodge: The Science of Timekeeping.
    • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

    .Hewlett Packard Application Note 1289, 1997.
  • ITU-R Recommendation TF.460-4: Standard-frequency and time-signal emissions.^ ITU-R Recommendation TF.460-4 : Standard-frequency and time-signal emissions.
    • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

    ^ Hewlett Packard Application Note 1289, 1997.
    • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

    ^ In 1956, the U.S. National Bureau of Standards started to use atomic frequency standards in generating the WWV time signals, named for the shortwave radio station which broadcasts them.
    • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

    .International Telecommunication Union.^ This is the group whose charter is to advise the International Telecommunications Union (ITU) on whether UTC should be redefined.
    • A Proposal to Upgrade UTC 26 January 2010 1:27 UTC iraf.noao.edu [Source type: FILTERED WITH BAYES]

    ^ Coordinated Universal Time is abbreviated UTC. The International Telecommunication Union wanted Coordinated Universal Time to have a single abbreviation for all languages.
    • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

    ^ International Telecommunication Union .
    • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

    .(Annex I of this document contains the official definition of UTC.)
  • McCarthy, Dennis D.: "Astronomical Time". Proc.^ (Annex I of this document contains the official definition of UTC.) McCarthy, Dennis D.: "Astronomical Time".
    • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

    ^ UTC was officially initiated at the start of 1961 (but the name Coordinated Universal Time was not adopted by the International Astronomical Union until 1967).
    • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

    ^ MM-ddTHH:mm:ss) date does not contain any time zone information, the time zone of the returned string is Coordinated Universal Time (UTC), represented as Greenwich Mean Time (GMT).

    .IEEE
    79, No.^ IEEE 79, No.
    • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

    .7 (July 1991): 915–920.
  • Nelson, G.K., Lombardi, M.A., and Okayama, D. T. 2005. NIST Time and Frequency Radio Stations: WWV, WWVH, and WWVB (PDF) (Special Publication 250-67).^ Nelson, Lombardi and Okayama 2005:46 ^ " Bulletin C: Relationship Between TAI and UTC ".
    • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

    ^ 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.
    • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

    ^ 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. .
    • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

    .National Institute of Standards and Technology.
  • Nelson, Robert A. and McCarthy, Dennis D. (13 September 2005).^ My favorite NTP server is time.nist.gov at the Time and Frequency Division of the National Institute of Standards and Technology in Boulder, Colorado.
    • Time - The Physics Hypertextbook 10 February 2010 14:44 UTC physics.info [Source type: FILTERED WITH BAYES]

    ^ Nelson, Robert A. and McCarthy, Dennis D. (13 September 2005).
    • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

    ^ See National Institute of Standards and Technology Time and frequency FAQ , accessed 5 October 2008, for the origin of this abbreviation.
    • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

    .Coordinated Universal Time (UTC) and the Future of the Leap Second. Presented at meeting of Civil GPS Interface Committee.^ Although the Date class is intended to reflect coordinated universal time (UTC), it may not do so exactly, depending on the host environment of the Java Virtual Machine.
    • Date (Java 2 Platform SE 5.0) 10 February 2010 14:44 UTC java.sun.com [Source type: Reference]

    ^ Wednesday, November 4, 2009 21:00 (UTC) Coordinated Universal Time 2 p.m.
    • Product Presentations - HumanWare USA 10 February 2010 14:44 UTC www.humanware.com [Source type: FILTERED WITH BAYES]

    ^ The long time stamp represents the difference, measured in milliseconds, between the current time (Coordinated Universal Time (UTC) or Greenwich Mean Time (GMT)) and the standard base time.

    .United States Coast Guard.^ USCG United States Coast Guard .
    • SBF Glossary: UR to .uy 26 January 2010 1:27 UTC www.plexoft.com [Source type: FILTERED WITH BAYES]

    .Retrieved 7 August 2009.
  • Nelson, McCarthy, et al.^ Nelson, McCarthy, et al.
    • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

    ^ Retrieved 7 August 2009.
    • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

    ^ Retrieved 21 August 2009.
    • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

    ."The leap second: its history and possible future" (PDF).^ Coordinated Universal Time (UTC) and the Future of the Leap Second.
    • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

    ^ Thereafter there will need to be the possibility of leap seconds at the end of any month.
    • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

    ^ A leap second is issued as soon as possible (presumably to provide "slack" later).
    • A Proposal to Upgrade UTC 26 January 2010 1:27 UTC iraf.noao.edu [Source type: FILTERED WITH BAYES]

    .Metrologia 38 (2001): 509–529.
  • Seidelman, P.K. (ed).^ Any leap-hour would occur many centuries from now; according to Nelson et al.'s Figure 7 (Metrologia, 2001, 38,509-529), we should only accumulate 140 seconds by 2100.
    • A Proposal to Upgrade UTC 26 January 2010 1:27 UTC iraf.noao.edu [Source type: FILTERED WITH BAYES]

    .Explanatory Supplement to the Astronomical Almanac.^ Explanatory Supplement to the Astronomical Almanac .
    • Boston University School of Theology Archives 10 February 2010 14:44 UTC sthweb.bu.edu [Source type: FILTERED WITH BAYES]

    Sausalito, CA: University Science Books. 1992.

Notes

  1. ^ See National Institute of Standards and Technology Time and frequency FAQ, accessed 5 October 2008, for the origin of this abbreviation.
  2. ^ "Leap Seconds". Time Service Dept., U.S. Naval Observatory. http://tycho.usno.navy.mil/leapsec.html. Retrieved 4 January 2009. 
  3. ^ a b Universal Time. United States Naval Observatory. Retrieved on 1 February 2009.
  4. ^ "World Time Scales". physics.nist.gov. http://physics.nist.gov/GenInt/Time/world.html. Retrieved 28 May 2009. 
  5. ^ "Why is UTC used as the acronym for Coordinated Universal Time instead of CUT?". http://www.boulder.nist.gov/timefreq/general/misc.htm#Anchor-14550. Retrieved 2 June 2007. 
  6. ^ Federal Aviation Administration (2008). Pilot's Handbook of Aeronautical Knowledge. Retrieved 21 August 2009.
  7. ^ "History of TAI−UTC". Time Service Dept., U.S. Naval Observatory. ftp://maia.usno.navy.mil/ser7/tai-utc.dat. Retrieved 4 January 2009. 
  8. ^ "Bulletin C". IERS EOP PC, Observatoire de Paris. http://hpiers.obspm.fr/iers/bul/bulc/bulletinc.dat. Retrieved 4 January 2009. 
  9. ^ E.F. Arias et al, "Rotation of the Earth and Time Scales", Bureau International des Poids et Mesures.
  10. ^ a b Markowitz, W. et al. (August 1958). "Frequency of cesium in terms of Ephemeris Time" (PDF). Physical Review Letters 1 (3): 105–7. doi:10.1103/PhysRevLett.1.105. http://www.leapsecond.com/history/1958-PhysRev-v1-n3-Markowitz-Hall-Essen-Parry.pdf. Retrieved 18 October 2008. 
  11. ^ a b c (equal to 1 part in 1010): Wm. Markowitz(1988) "Comparisons of ET(Solar), ET(Lunar), UT and TDT", in (eds.) A K Babcock & G A Wilkins, The Earth's Rotation and Reference Frames for Geodesy and Geophysics, IAU Symposia #128 (1988), at pp 413–418.
  12. ^ Nelson & McCarthy 13 September 2005, 15
  13. ^ Nelson, McCarthy et al. 2001, 515.
  14. ^ Essen, L. (1968). "Time Scales" (PDF). Metrologica 4 (4): 161–5. doi:10.1088/0026-1394/4/4/003. http://www.leapsecond.com/history/1968-Metrologia-v4-n4-Essen.pdf. Retrieved 18 October 2008. 
  15. ^ Seidelmann 1995:85–87.
  16. ^ Nelson, Lombardi and Okayama 2005:46
  17. ^ "Bulletin C: Relationship Between TAI and UTC". IERS EOP PC, Observatoire de Paris. http://hpiers.obspm.fr/eoppc/bul/bulc/UTC-TAI.history. Retrieved 4 January 2009. 
  18. ^ 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.
  19. ^ "UTC is doomed". http://www.ucolick.org/~sla/leapsecs/utcdoomed. Retrieved 2 June 2007. 
  20. ^ "UTC might be redefined without Leap Seconds". http://www.ucolick.org/~sla/leapsecs/. Retrieved 2 June 2007. 
  21. ^ "A Proposal to Upgrade UTC". http://iraf.noao.edu/~seaman/leap/. Retrieved 2 June 2007. 
  22. ^ AOPA Aviation Time. AOPA's PATH to Aviation. Retrieved on 25 February 2007.
  23. ^ "A Few Facts Concerning GMT, UT, and the RGO". http://www.apparent-wind.com/gmt-explained.html. Retrieved 19 August 2007. 
  24. ^ Seidelmann, (1992), 7
  25. ^ Military & Civilian Time Designations
  26. ^ Williams, Jack (17 May 2005). "Understanding and using Zulu time". USA Today. http://www.usatoday.com/weather/zulu.htm. Retrieved 25 February 2007. 

External links


Wiktionary

Up to date as of January 15, 2010

Definition from Wiktionary, a free dictionary

English

Proper noun

Singular
Coordinated Universal Time
Plural
-
Coordinated Universal Time
.
  1. A high-precision atomic time standard.^ Coordinated Universal Time Coordinated Universal Time (UTC) is a high-precision atomic time standard.
    • World Time. The time around the World, World time zones and UTC. 10 February 2010 14:44 UTC 247clocks.com [Source type: News]

    ^ It takes into account relativistic effects and is based on International Atomic Time (TAI), which is a high-precision standard using several hundred atomic clocks worldwide.

    ^ The "Atomic Web Clock" from the U.S. government's National Institute of Standards and Technology (NIST) provides the current local time .
    • What is Coordinated Universal Time? - Definition from Whatis.com - see also: GMT, UTC, CUT, Universal Time Coordinated, Universal Coordinated Time 10 February 2010 14:44 UTC searchcio-midmarket.techtarget.com [Source type: Academic]

    Abbreviation: UTC

Simple English

Time zones of Europe in relation to UTC:
blue Western European Time (UTC+0)
Western European Summer Time (UTC+1)
red Central European Time (UTC+1)
Central European Summer Time (UTC+2)
yellow Eastern European Time (UTC+2)
Eastern European Summer Time (UTC+3)
green Moscow Time (UTC+3)
Moscow Summer Time (UTC+4)
Light colours indicate countries not observing summer time

Coordinated Universal Time (UTC) is the standard time zone of the world. The standard before was Greenwich Mean Time (GMT). UTC and GMT are almost the same. It is also called civil time and Zulu time.

Some websites, like Wikipedia, use UTC because it does not make any country look more important than the others. It offers one time for all the internet (the same time can be used by people all over the world).

Timezones are often named by how many hours they are different from UTC time. For example, UTC -5 (United States east coast) is 5 hours behind UTC. If the time is 07:00 UTC, the local time is 02:00 in New York (UTC -5) and 10:00 in Moscow (UTC +3).

07:00 UTC is also written more simply as 0700Z (or 07:00Z).

Note that UTC uses the 24-hour clock. That means there is no 'AM' or 'PM'. For example, 4:00PM would be 16:00 or 1600.

When this page loaded, it was Friday, 2011 February 25, 03:18 in UTC

When this page loaded, it was Friday, 2011 February 25, 03:18Z

Other websites

frr:UTC



Citable sentences

Up to date as of December 17, 2010

Here are sentences from other pages on Coordinated Universal Time, which are similar to those in the above article.








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