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Coordinated Universal Time</a></h1></div> <div class="searchform"> <form action="javascript:jumpiter()" style="display:inline;"> <table style="text-align:center; margin:0 auto; width:310px; border:0; border-collapse:collapse;" cellspacing="0" cellpadding="0"> <tr><td width="235"><input type="text" id="search-box" style="padding-left:3px" name="s" value="" onfocus="if(this.value==this.defaultValue)this.value='';" maxlength="100"></td> <td><a class="btn" onclick="jumpiter()">Get All</a></td></tr></table></form></div> </div> <div id="headerdown"> <div style="float:left; margin:2px 0 0 0"> <script>function fbs_click() {u=location.href;t=document.title;window.open('http://www.facebook.com/sharer.php?u='+encodeURIComponent(u)+'&t='+encodeURIComponent(t),'sharer','toolbar=0,status=0,width=626,height=436');return false;}</script><a rel="nofollow" href="http://www.facebook.com/share.php?u=<;url>" onclick="return fbs_click()" target="_blank"><img border="0" src="http://4.bp.blogspot.com/-luohbbGvls0/UZa5XZT-ylI/AAAAAAAAHxU/5e8GLTXP6EE/s320/f-share.png" width="57" height="18" alt="Share on Facebook" /></a> </div> <div class="expandable"> <span>Language</span> <ul class="expandabletabs"> <li><a href="http://www.mashpedia.com">English</a></li> <li><a href="http://es.mashpedia.com">Español</a></li> </ul> </div> </div> </div> <div id="tabs-1"> <div class="abstract">  <div id="mw-content-text" lang="en" dir="ltr" class="mw-content-ltr"><div class="dablink">"UTC" redirects here. For other uses, see <a href="UTC_(disambiguation)" title="UTC (disambiguation)">UTC (disambiguation)</a>.</div> <p><b>Coordinated Universal Time</b> (<b>UTC</b>) is the primary <a href="Time_standard" title="Time standard">time standard</a> by which the world regulates clocks and time. It is one of several closely related successors to <a href="Greenwich_Mean_Time" title="Greenwich Mean Time">Greenwich Mean Time (GMT)</a>. For most purposes, UTC is synonymous with GMT, but GMT is no longer precisely defined by the scientific community.</p> <table id="toc" class="toc"> <tr> <td> <div id="toctitle"> <h2>Contents</h2> </div> <ul> <li class="toclevel-1 tocsection-1"><a href="#Background"><span class="tocnumber">1</span> <span class="toctext">Background</span></a></li> <li class="toclevel-1 tocsection-2"><a href="#Uses"><span class="tocnumber">2</span> <span class="toctext">Uses</span></a></li> <li class="toclevel-1 tocsection-3"><a href="#Abbreviation"><span class="tocnumber">3</span> <span class="toctext">Abbreviation</span></a></li> <li class="toclevel-1 tocsection-4"><a href="#Mechanism"><span class="tocnumber">4</span> <span class="toctext">Mechanism</span></a> <ul> <li class="toclevel-2 tocsection-5"><a href="#Time_zones"><span class="tocnumber">4.1</span> <span class="toctext">Time zones</span></a></li> <li class="toclevel-2 tocsection-6"><a href="#Daylight_saving"><span class="tocnumber">4.2</span> <span class="toctext">Daylight saving</span></a></li> </ul> </li> <li class="toclevel-1 tocsection-7"><a href="#History"><span class="tocnumber">5</span> <span class="toctext">History</span></a></li> <li class="toclevel-1 tocsection-8"><a href="#Rationale"><span class="tocnumber">6</span> <span class="toctext">Rationale</span></a></li> <li class="toclevel-1 tocsection-9"><a href="#Future"><span class="tocnumber">7</span> <span class="toctext">Future</span></a></li> <li class="toclevel-1 tocsection-10"><a href="#See_also"><span class="tocnumber">8</span> <span class="toctext">See also</span></a></li> <li class="toclevel-1 tocsection-11"><a href="#Notes"><span class="tocnumber">9</span> <span class="toctext">Notes</span></a></li> <li class="toclevel-1 tocsection-12"><a href="#References"><span class="tocnumber">10</span> <span class="toctext">References</span></a></li> <li class="toclevel-1 tocsection-13"><a href="#External_links"><span class="tocnumber">11</span> <span class="toctext">External links</span></a></li> </ul> </td> </tr> </table> <h2><span class="mw-headline" id="Background">Background</span> <span class="mw-editsection">[<a href="/w/index.php?title=Coordinated_Universal_Time&action=edit&section=1" title="Edit section: Background">edit</a>]</span></h2> <p>The UTC was officially formalized in 1963 by the International Radio Consultative Committee in Recommendation 374,<sup id="cite_ref-FOOTNOTEMcCarthySeidelmann2009227_1-0" class="reference"><a href="#cite_note-FOOTNOTEMcCarthySeidelmann2009227-1"><span>[</span>1<span>]</span></a></sup> having been initiated by several national time laboratories. The system was adjusted several times until <a href="Leap_seconds" title="Leap seconds" class="mw-redirect">leap seconds</a> were adopted in 1972 to simplify future adjustments. A number of proposals have been made to replace UTC with a new system which would eliminate leap seconds but no consensus has yet been reached.</p> <p>The current version of UTC is defined by <a href="International_Telecommunications_Union" title="International Telecommunications Union" class="mw-redirect">International Telecommunications Union</a> Recommendation (ITU-R TF.460-6), <i>Standard-frequency and time-signal emissions</i>.<sup id="cite_ref-FOOTNOTEITU_Radiocommunication_Assembly2002_2-0" class="reference"><a href="#cite_note-FOOTNOTEITU_Radiocommunication_Assembly2002-2"><span>[</span>2<span>]</span></a></sup> and is based on <a href="International_Atomic_Time" title="International Atomic Time">International Atomic Time</a> (TAI) with <a href="Leap_second" title="Leap second">leap seconds</a> added at irregular intervals to compensate for the slowing of <a href="Earth%27s_rotation" title="Earth's rotation">Earth's rotation</a>.<sup id="cite_ref-FOOTNOTETime_Service_Dept.c._2009_3-0" class="reference"><a href="#cite_note-FOOTNOTETime_Service_Dept.c._2009-3"><span>[</span>3<span>]</span></a></sup> Leap seconds keep UTC within 0.9 seconds of <a href="Universal_Time#Versions" title="Universal Time">UT1</a>.<sup id="cite_ref-FOOTNOTENational_Institute_of_Standards_and_Technology2012_4-0" class="reference"><a href="#cite_note-FOOTNOTENational_Institute_of_Standards_and_Technology2012-4"><span>[</span>4<span>]</span></a></sup> In the 41 years up to and including 2012, a total of 25 leap seconds have been added; the most recent was added on 30 June 2012.</p> <p>If high precision is not required, the general term Universal Time (UT) may be used.<sup id="cite_ref-FOOTNOTEUnited_States_Naval_Observatoryn.d._5-0" class="reference"><a href="#cite_note-FOOTNOTEUnited_States_Naval_Observatoryn.d.-5"><span>[</span>5<span>]</span></a></sup> The term <a href="Greenwich_Mean_Time" title="Greenwich Mean Time">Greenwich Mean Time</a> (GMT) does not have a precise definition at the sub-second level, but it is often considered equivalent to UTC or UT1. Saying "GMT" often implies either UTC or UT1 when used within informal or casual contexts. In technical contexts, usage of "GMT" is avoided; the unambiguous terminology "UTC" or "UT1" is preferred.<sup id="cite_ref-FOOTNOTEUnited_States_Naval_Observatoryn.d._5-1" class="reference"><a href="#cite_note-FOOTNOTEUnited_States_Naval_Observatoryn.d.-5"><span>[</span>5<span>]</span></a></sup></p> <h2><span class="mw-headline" id="Uses">Uses</span> <span class="mw-editsection">[<a href="/w/index.php?title=Coordinated_Universal_Time&action=edit&section=2" title="Edit section: Uses">edit</a>]</span></h2> <p><a href="Time_zone" title="Time zone">Time zones</a> around the world are expressed as positive or negative offsets from UTC, as in the <a href="List_of_time_zones_by_UTC_offset" title="List of time zones by UTC offset" class="mw-redirect">list of time zones by UTC offset</a>.</p> <p>UTC is the time standard used for many <a href="Internet" title="Internet">internet</a> and <a href="World_Wide_Web" title="World Wide Web">World Wide Web</a> standards. The <a href="Network_Time_Protocol" title="Network Time Protocol">Network Time Protocol</a>, designed to synchronise the clocks of computers over the Internet, encodes times using the UTC system.<sup id="cite_ref-FOOTNOTEHow_NTP_Works2011_6-0" class="reference"><a href="#cite_note-FOOTNOTEHow_NTP_Works2011-6"><span>[</span>6<span>]</span></a></sup></p> <p>Computer servers, online services and other entities that rely on having a universally accepted time use UTC as it is more specific than GMT. If only limited precision is needed, clients can obtain the current UTC time from a number of official Internet UTC servers. For sub-microsecond precision, clients can obtain the time from satellite signals.</p> <p>UTC is also the time standard used in <a href="Aviation" title="Aviation">aviation</a><sup id="cite_ref-FOOTNOTEAviation_Time2006_7-0" class="reference"><a href="#cite_note-FOOTNOTEAviation_Time2006-7"><span>[</span>7<span>]</span></a></sup>, e.g., for <a href="Flight_plan" title="Flight plan">flight plans</a> and <a href="Air_traffic_control" title="Air traffic control">air traffic control</a> clearances. <a href="Weather_forecasting" title="Weather forecasting">Weather forecasts</a> and maps all use UTC to avoid confusion about time zones and <a href="Daylight_saving_time" title="Daylight saving time">daylight saving time</a>.</p> <p><a href="Amateur_radio" title="Amateur radio">Amateur radio</a> operators often schedule their radio contacts in UTC, because transmissions on some frequencies can be picked up by many timezones.<sup id="cite_ref-FOOTNOTEHorzepa2010_8-0" class="reference"><a href="#cite_note-FOOTNOTEHorzepa2010-8"><span>[</span>8<span>]</span></a></sup></p> <h2><span class="mw-headline" id="Abbreviation">Abbreviation</span> <span class="mw-editsection">[<a href="/w/index.php?title=Coordinated_Universal_Time&action=edit&section=3" title="Edit section: Abbreviation">edit</a>]</span></h2> <table class="wikitable" style="margin:.5em; float:right;"> <caption>Compromise abbreviation</caption> <tr> <th>Source</th> <th>Initials</th> <th>Words</th> </tr> <tr> <td>English</td> <td>CUT</td> <td>Coordinated Universal Time</td> </tr> <tr> <td>French</td> <td>TUC</td> <td>Temps Universel Coordonné</td> </tr> <tr> <td>compromise</td> <td>UTC</td> <td style="width:300px">unofficial English: "Universal Time Coordinated";<sup id="cite_ref-FOOTNOTEUniversal_Timen.d._9-0" class="reference"><a href="#cite_note-FOOTNOTEUniversal_Timen.d.-9"><span>[</span>9<span>]</span></a></sup> unofficial French: "Universel Temps Coordonné"<sup id="cite_ref-10" class="reference"><a href="#cite_note-10"><span>[</span>10<span>]</span></a></sup></td> </tr> </table> <p>The official abbreviation for Coordinated Universal Time is <i>UTC</i>. This abbreviation arose from a desire by the <a href="International_Telecommunication_Union" title="International Telecommunication Union">International Telecommunication Union</a> and the <a href="International_Astronomical_Union" title="International Astronomical Union">International Astronomical Union</a> to use the same abbreviation in all languages. <a href="English_language" title="English language">English</a> speakers originally proposed <i>CUT</i> (for "coordinated universal time"), while <a href="French_language" title="French language">French</a> speakers proposed <i>TUC</i> (for "temps universel coordonné"). The compromise that emerged was <i>UTC</i>,<sup id="cite_ref-FOOTNOTENational_Institute_of_Standards_and_Technology2011_11-0" class="reference"><a href="#cite_note-FOOTNOTENational_Institute_of_Standards_and_Technology2011-11"><span>[</span>11<span>]</span></a></sup> which conforms to the pattern for the abbreviations of the variants of <a href="Universal_Time" title="Universal Time">Universal Time</a> (UT0, UT1, UT2, UT1R, etc.).<sup id="cite_ref-FOOTNOTEIAU_resolutions1976_12-0" class="reference"><a href="#cite_note-FOOTNOTEIAU_resolutions1976-12"><span>[</span>12<span>]</span></a></sup></p> <h2><span class="mw-headline" id="Mechanism">Mechanism</span> <span class="mw-editsection">[<a href="/w/index.php?title=Coordinated_Universal_Time&action=edit&section=4" title="Edit section: Mechanism">edit</a>]</span></h2> <p>UTC divides time into days, hours, minutes and seconds. Days are conventionally identified using the <a href="Gregorian_calendar" title="Gregorian calendar">Gregorian calendar</a>, but <a href="Julian_day" title="Julian day">Julian day numbers</a> can also be used. Each day contains 24 hours and each hour contains 60 minutes. The number of seconds in a minute is usually 60, but may very rarely be 61 or 59.<sup id="cite_ref-FOOTNOTEITU_Radiocommunication_Assembly20023_13-0" class="reference"><a href="#cite_note-FOOTNOTEITU_Radiocommunication_Assembly20023-13"><span>[</span>13<span>]</span></a></sup> Thus, in the UTC time scale, the second and all smaller time units (millisecond, microsecond, etc.) are of constant duration, but the minute and all larger time units (hour, day, week, etc.) are of variable duration. Decisions to introduce a leap second are announced at least 8 weeks in advance in "Bulletin C" produced by the <a href="International_Earth_Rotation_and_Reference_Systems_Service" title="International Earth Rotation and Reference Systems Service">International Earth Rotation and Reference Systems Service</a>.<sup id="cite_ref-FOOTNOTEInternational_Earth_Rotation_and_Reference_Systems_Service2011_14-0" class="reference"><a href="#cite_note-FOOTNOTEInternational_Earth_Rotation_and_Reference_Systems_Service2011-14"><span>[</span>14<span>]</span></a></sup><sup id="cite_ref-FOOTNOTEMcCarthySeidelmann2009229_15-0" class="reference"><a href="#cite_note-FOOTNOTEMcCarthySeidelmann2009229-15"><span>[</span>15<span>]</span></a></sup> The leap seconds cannot be predicted far in advance due to the unpredictable rate of rotation of the earth.<sup id="cite_ref-FOOTNOTEMcCarthySeidelmann2009chapter_4_16-0" class="reference"><a href="#cite_note-FOOTNOTEMcCarthySeidelmann2009chapter_4-16"><span>[</span>16<span>]</span></a></sup></p> <p>Nearly all UTC days contain exactly 86,400 <a href="International_System_of_Units" title="International System of Units">SI</a> <a href="Second" title="Second">seconds</a>, with exactly 60 seconds in each minute. However, because the <a href="Mean_solar_day" title="Mean solar day" class="mw-redirect">mean solar day</a> is slightly longer than 86,400 SI seconds, occasionally the last minute of a UTC day is adjusted to have 61 seconds. The extra second is called a <a href="Leap_second" title="Leap second">leap second</a>. It accounts for the grand total of the extra length (about 2 milliseconds each) of all the mean solar days since the previous leap second. The last minute of a UTC day is permitted 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 irregular day lengths mean that fractional <a href="Julian_day" title="Julian day">Julian days</a> do not work properly with UTC.</p> <p>Since 1972 UTC is calculated by subtracting the accumulated leap seconds from International Atomic Time (TAI), which is a <a href="Coordinate_time" title="Coordinate time">coordinate time</a> scale tracking notional <a href="Proper_time" title="Proper time">proper time</a> on the rotating surface of the <a href="Earth" title="Earth">Earth</a> (the <a href="Geoid" title="Geoid">geoid</a>). In order to maintain a close approximation to <a href="Universal_Time" title="Universal Time">UT1</a> (equivalent to <a href="Greenwich_Mean_Time" title="Greenwich Mean Time">GMT</a> before 1960), UTC occasionally has <a href="Classification_of_discontinuities" title="Classification of discontinuities">discontinuities</a> where it changes from one linear function of TAI to another. These discontinuities take the form of leap seconds implemented by a UTC day of irregular length. Discontinuities in UTC have occurred only at the end of a <a href="Gregorian_calendar" title="Gregorian calendar">Gregorian</a> month.<sup id="cite_ref-FOOTNOTEHistory_of_TAI-UTCc._2009_17-0" class="reference"><a href="#cite_note-FOOTNOTEHistory_of_TAI-UTCc._2009-17"><span>[</span>17<span>]</span></a></sup> The <a href="International_Earth_Rotation_and_Reference_Systems_Service" title="International Earth Rotation and Reference Systems Service">International Earth Rotation and Reference Systems Service</a> (IERS) tracks and publishes the difference between UTC and Universal Time, <a href="DUT1" title="DUT1">DUT1</a> = UT1 – UTC, and introduces discontinuities into UTC to keep DUT1 in the <a href="Interval_(mathematics)" title="Interval (mathematics)">interval</a> (−0.9 s, +0.9 s). Since 1972 the discontinuities have consisted only of a leap of one second at the end of 30 June or 31 December.<sup id="cite_ref-FOOTNOTEMcCarthySeidelmann2009217.2C_227.E2.80.93231_18-0" class="reference"><a href="#cite_note-FOOTNOTEMcCarthySeidelmann2009217.2C_227.E2.80.93231-18"><span>[</span>18<span>]</span></a></sup></p> <p>As with TAI, UTC is only known with the highest precision in retrospect. Users who require an approximation in real time must obtain it from a time laboratory, which disseminates an approximation using techniques such as <a href="GPS" title="GPS" class="mw-redirect">GPS</a> or radio <a href="Time_signal" title="Time signal">time signals</a>. Such approximations are designated UTC(k), where k is an abbreviation for the time laboratory.<sup id="cite_ref-FOOTNOTEMcCarthySeidelmann2009209_19-0" class="reference"><a href="#cite_note-FOOTNOTEMcCarthySeidelmann2009209-19"><span>[</span>19<span>]</span></a></sup> The time of events may be provisionally recorded against one of these approximations; later corrections may be applied using the <a href="International_Bureau_of_Weights_and_Measures" title="International Bureau of Weights and Measures">International Bureau of Weights and Measures</a> (BIPM) monthly publication of tables of differences between canonical TAI/UTC and TAI(k)/UTC(k) as estimated in real time by participating laboratories. (See the article on <a href="International_Atomic_Time" title="International Atomic Time">International Atomic Time</a> for details.)</p> <p>Because of <a href="Time_dilation" title="Time dilation">time dilation</a>, a standard clock not on the <a href="Geoid" title="Geoid">geoid</a>, or in rapid motion, will not maintain synchronicity with UTC. Therefore, <a href="Telemetry" title="Telemetry">telemetry</a> from clocks with a known relation to the geoid is used to provide UTC when required, on locations such as those of spacecraft.</p> <p>UTC is a discontinuous timescale, so it is not possible to compute the exact <a href="Time" title="Time">time interval</a> elapsed between two UTC timestamps without consulting a table that describes how many leap seconds occurred during that interval. Therefore, many scientific applications that require precise measurement of long (multi-year) intervals use <a href="International_Atomic_Time" title="International Atomic Time">TAI</a> instead. TAI is also commonly used by systems that cannot handle leap seconds. A fixed 19‑second offset from TAI also gives <a href="GPS_time" title="GPS time" class="mw-redirect">GPS time</a>.</p> <p>For most common and legal-trade purposes, the fractional second difference between UTC and UT (<a href="GMT" title="GMT" class="mw-redirect">GMT</a>) is inconsequentially small, so UTC is often called GMT (for instance, by the <a href="BBC" title="BBC">BBC</a>).<sup id="cite_ref-FOOTNOTELangley1999_20-0" class="reference"><a href="#cite_note-FOOTNOTELangley1999-20"><span>[</span>20<span>]</span></a></sup></p> <h3><span class="mw-headline" id="Time_zones">Time zones</span> <span class="mw-editsection">[<a href="/w/index.php?title=Coordinated_Universal_Time&action=edit&section=5" title="Edit section: Time zones">edit</a>]</span></h3> <div class="rellink relarticle mainarticle">Main articles: <a href="Time_zone" title="Time zone">Time zone</a> and <a href="List_of_time_zones" title="List of time zones" class="mw-redirect">List of time zones</a></div> <p>Time zones are usually defined to differ from UTC by an integer number of hours,<sup id="cite_ref-FOOTNOTESeidelmann19927_21-0" class="reference"><a href="#cite_note-FOOTNOTESeidelmann19927-21"><span>[</span>21<span>]</span></a></sup> although the laws of each jurisdiction would have to be consulted if sub-second accuracy was required. Several jurisdictions have established time zones that differ by an integer number of half-hours or quarter-hours from UT1 or UTC.</p> <p>The UTC time zone is sometimes denoted by the letter <b>Z</b>—a reference to the equivalent <a href="Time_zone#Nautical_time_zones" title="Time zone">nautical time zone</a> (<a href="GMT" title="GMT" class="mw-redirect">GMT</a>), which has been denoted by a <b>Z</b> since about 1950. The letter also refers to the "zone description" of <b>zero</b> hours, which has been used since 1920 (see <a href="Time_zone#History" title="Time zone">time zone history</a>). Since the <a href="ICAO_spelling_alphabet" title="ICAO spelling alphabet" class="mw-redirect">NATO phonetic alphabet</a> word for <b>Z</b> is "Zulu", UTC is sometimes known as <b>Zulu time</b>. This is especially true in aviation, where Zulu is the universal standard.<sup id="cite_ref-FOOTNOTEMilitary_.26_Civilian_Time_Designationsn.d._22-0" class="reference"><a href="#cite_note-FOOTNOTEMilitary_.26_Civilian_Time_Designationsn.d.-22"><span>[</span>22<span>]</span></a></sup> This ensures all pilots regardless of location are using the same <a href="24-hour_clock" title="24-hour clock">24-hour clock</a>, thus avoiding confusion when flying between time zones.<sup id="cite_ref-FOOTNOTEWilliams2005_23-0" class="reference"><a href="#cite_note-FOOTNOTEWilliams2005-23"><span>[</span>23<span>]</span></a></sup> See <a href="List_of_military_time_zones" title="List of military time zones">list of military time zones</a> for letters used in addition to Z in qualifying time zones other than Greenwich.</p> <p>On electronic devices that only allow the current time zone to be configured using maps or city names, UTC can be selected indirectly by selecting <a href="Reykjav%C3%ADk" title="Reykjavík">Reykjavík</a>, <a href="Iceland" title="Iceland">Iceland</a>, which is always on UTC time and does not use <a href="Daylight_saving" title="Daylight saving" class="mw-redirect">daylight saving</a>.<sup id="cite_ref-FOOTNOTEIceland2011_24-0" class="reference"><a href="#cite_note-FOOTNOTEIceland2011-24"><span>[</span>24<span>]</span></a></sup></p> <h3><span class="mw-headline" id="Daylight_saving">Daylight saving</span> <span class="mw-editsection">[<a href="/w/index.php?title=Coordinated_Universal_Time&action=edit&section=6" title="Edit section: Daylight saving">edit</a>]</span></h3> <p>UTC does not change with a change of seasons, but <a href="Local_time" title="Local time" class="mw-redirect">local time</a> or <a href="Civil_time" title="Civil time">civil time</a> may change if a time zone jurisdiction observes <a href="Daylight_saving_time" title="Daylight saving time">daylight saving time</a> (summer time). For example, local time on the east coast of the United States is five hours behind UTC during winter, but four hours behind while daylight saving is observed there.<sup id="cite_ref-FOOTNOTEStandard_time2010_25-0" class="reference"><a href="#cite_note-FOOTNOTEStandard_time2010-25"><span>[</span>25<span>]</span></a></sup></p> <h2><span class="mw-headline" id="History">History</span> <span class="mw-editsection">[<a href="/w/index.php?title=Coordinated_Universal_Time&action=edit&section=7" title="Edit section: History">edit</a>]</span></h2> <p>At the 1884 <a href="International_Meridian_Conference" title="International Meridian Conference">International Meridian Conference</a> held in Washington, D.C., the local mean solar time at the <a href="Royal_Observatory,_Greenwich" title="Royal Observatory, Greenwich">Royal Observatory, Greenwich</a> in <a href="England" title="England">England</a> was chosen to define the Universal day, counted from 0 hours at mean midnight. This agreed with civil <a href="Greenwich_Mean_Time" title="Greenwich Mean Time">Greenwich Mean Time</a> (GMT), used on the island of Great Britain since 1847. In contrast, astronomical GMT began at mean noon, 12 hours <i>after</i> mean midnight of the same date until 1 January 1925, whereas nautical GMT began at mean noon, 12 hours <i>before</i> mean midnight of the same date, at least until 1805 in the <a href="Royal_Navy" title="Royal Navy">Royal Navy</a>, but persisted much later elsewhere because it was mentioned at the 1884 conference. In 1884 the Greenwich Meridian was used for two-thirds of all charts and maps as their <a href="Prime_Meridian" title="Prime Meridian" class="mw-redirect">Prime Meridian</a>.<sup id="cite_ref-FOOTNOTEHowse1997133.E2.80.93137_26-0" class="reference"><a href="#cite_note-FOOTNOTEHowse1997133.E2.80.93137-26"><span>[</span>26<span>]</span></a></sup> In 1928, the term Universal Time (UT) was introduced by the <a href="International_Astronomical_Union" title="International Astronomical Union">International Astronomical Union</a> to refer to GMT with the day starting at midnight.<sup id="cite_ref-FOOTNOTEMcCarthySeidelmann200910.E2.80.9311_27-0" class="reference"><a href="#cite_note-FOOTNOTEMcCarthySeidelmann200910.E2.80.9311-27"><span>[</span>27<span>]</span></a></sup> Until the 1950s, broadcast <a href="Time_signal" title="Time signal">time signals</a> were based on UT, and hence on the rotation of the Earth.</p> <p>In 1955 the <a href="Caesium" title="Caesium">caesium</a> <a href="Atomic_clock" title="Atomic clock">atomic clock</a> was invented. This provided a form of timekeeping that was both more stable and more convenient than astronomical observations. In 1956 the U.S. <a href="National_Bureau_of_Standards" title="National Bureau of Standards" class="mw-redirect">National Bureau of Standards</a> and <a href="U.S._Naval_Observatory" title="U.S. Naval Observatory" class="mw-redirect">U.S. Naval Observatory</a> started to develop atomic frequency time scales; by 1959 these time scales were used in generating the <a href="WWV_(radio_station)" title="WWV (radio station)">WWV</a> time signals, named for the shortwave radio station that broadcasts them. In 1960 the U.S. Naval Observatory, the Royal Greenwich Observatory, and the UK National Physical Laboratory coordinated their radio broadcasts so time steps and frequency changes were coordinated, and the resulting time scale was informally referred to as "Coordinated Universal Time".<sup id="cite_ref-FOOTNOTEMcCarthySeidelmann2009226.E2.80.93227_28-0" class="reference"><a href="#cite_note-FOOTNOTEMcCarthySeidelmann2009226.E2.80.93227-28"><span>[</span>28<span>]</span></a></sup></p> <p>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 <a href="Millisecond" title="Millisecond">ms</a> to bring it back into agreement with UT. Twenty-nine such steps were used before 1960.<sup id="cite_ref-FOOTNOTEAriasGuinotQuinn2003_29-0" class="reference"><a href="#cite_note-FOOTNOTEAriasGuinotQuinn2003-29"><span>[</span>29<span>]</span></a></sup></p> <p>In 1958 data was published linking the frequency for the <a href="/w/index.php?title=Caesium_transition&action=edit&redlink=1" class="new" title="Caesium transition (page does not exist)">caesium transition</a>, newly established, with the ephemeris second. The ephemeris second is the duration of time that, when used as the independent variable in the laws of motion that govern the movement of the planets and moons in the solar system, cause the laws of motion to accurately predict the observed positions of solar system bodies. Within the limits of observing accuracy, ephemeris seconds are of constant length, as are atomic seconds. This publication allowed a value to be chosen for the length of the atomic second that would work properly with the celestial laws of motion.<sup id="cite_ref-FOOTNOTEMarkowitzHallEssenParry1958_30-0" class="reference"><a href="#cite_note-FOOTNOTEMarkowitzHallEssenParry1958-30"><span>[</span>30<span>]</span></a></sup></p> <p>UTC was officially initiated at the start of 1961 (but the name Coordinated Universal Time was not adopted by the <a href="International_Astronomical_Union" title="International Astronomical Union">International Astronomical Union</a> until 1967).<sup id="cite_ref-FOOTNOTENelsonMcCarthy200515_31-0" class="reference"><a href="#cite_note-FOOTNOTENelsonMcCarthy200515-31"><span>[</span>31<span>]</span></a></sup><sup id="cite_ref-FOOTNOTENelsonMcCarthy2001515_32-0" class="reference"><a href="#cite_note-FOOTNOTENelsonMcCarthy2001515-32"><span>[</span>32<span>]</span></a></sup> 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 jumps increased in size to 100 ms, with only one 50 ms jump having ever occurred. This UTC was intended to permit a very close approximation of UT2, within around 0.1 s.</p> <p>In 1967, the <a href="SI" title="SI" class="mw-redirect">SI</a> second was redefined in terms of the frequency supplied by a caesium atomic clock. The length of second so defined was practically equal to the second of <a href="Ephemeris_time" title="Ephemeris time">ephemeris time</a>.<sup id="cite_ref-FOOTNOTEMarkowitz1988_33-0" class="reference"><a href="#cite_note-FOOTNOTEMarkowitz1988-33"><span>[</span>33<span>]</span></a></sup> This was the frequency that had been provisionally used in TAI since 1958. It was soon recognised that having two types of second with different lengths, namely the UTC second and the SI second used in TAI, was a bad idea. It was thought that it would be better for time signals to maintain a consistent frequency, and that that frequency should match the SI second. Thus it would be necessary to rely on time steps alone to maintain the approximation of UT. This was tried experimentally in a service known as "Stepped Atomic Time" (SAT), which ticked at the same rate as TAI and used jumps of 200 ms to stay synchronised with UT2.<sup id="cite_ref-FOOTNOTEMcCarthySeidelmann2009227_1-1" class="reference"><a href="#cite_note-FOOTNOTEMcCarthySeidelmann2009227-1"><span>[</span>1<span>]</span></a></sup></p> <p>There was also dissatisfaction with the frequent jumps in UTC (and SAT). In 1968, <a href="Louis_Essen" title="Louis Essen">Louis Essen</a>, the inventor of the caesium atomic clock, and G. M. R. Winkler both independently proposed that steps should be of 1 s only.<sup id="cite_ref-FOOTNOTEEssen1968161.E2.80.935_34-0" class="reference"><a href="#cite_note-FOOTNOTEEssen1968161.E2.80.935-34"><span>[</span>34<span>]</span></a></sup> This system was eventually approved, along with the idea of maintaining the UTC second equal to the TAI second. At the end of 1971, there was a final irregular jump of exactly 0.107758 TAI seconds, 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 <a href="Integer" title="Integer">integer number</a> of seconds. At the same time, the tick rate of UTC was changed to exactly match TAI. UTC also started to track UT1 rather than UT2. Some time signals started to broadcast the DUT1 correction (UT1 − UTC) for applications requiring a closer approximation of UT1 than UTC now provided.<sup id="cite_ref-FOOTNOTESeidelmann199285.E2.80.9387_35-0" class="reference"><a href="#cite_note-FOOTNOTESeidelmann199285.E2.80.9387-35"><span>[</span>35<span>]</span></a></sup><sup id="cite_ref-FOOTNOTENelsonLombardiOkayama200546_36-0" class="reference"><a href="#cite_note-FOOTNOTENelsonLombardiOkayama200546-36"><span>[</span>36<span>]</span></a></sup></p> <p>The first <a href="Leap_second" title="Leap second">leap second</a> 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. As of 1 July 2012, 00:00:00 UTC, there have been 25 leap seconds in total, all positive, putting UTC 35 seconds behind TAI.</p> <h2><span class="mw-headline" id="Rationale">Rationale</span> <span class="mw-editsection">[<a href="/w/index.php?title=Coordinated_Universal_Time&action=edit&section=8" title="Edit section: Rationale">edit</a>]</span></h2> <div class="thumb tleft"> <div class="thumbinner" style="width:252px;"><a target="_blank" href="http://commons.wikimedia.org/wiki/File:Leapsecond.ut1-utc.svg" class="image"><img alt="" src="//upload.wikimedia.org/wikipedia/commons/thumb/f/fb/Leapsecond.ut1-utc.svg/250px-Leapsecond.ut1-utc.svg.png" width="250" height="200" class="thumbimage" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/f/fb/Leapsecond.ut1-utc.svg/375px-Leapsecond.ut1-utc.svg.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/f/fb/Leapsecond.ut1-utc.svg/500px-Leapsecond.ut1-utc.svg.png 2x" /></a> <div class="thumbcaption"> <div class="magnify"><a target="_blank" href="http://commons.wikimedia.org/wiki/File:Leapsecond.ut1-utc.svg" class="internal" title="Enlarge"><img src="//bits.wikimedia.org/static-1.22wmf3/skins/common/images/magnify-clip.png" width="15" height="11" alt="" /></a></div> Graph showing the difference <a href="DUT1" title="DUT1">DUT1</a> between UT1 and UTC (in seconds). Vertical segments correspond to leap seconds.</div> </div> </div> <p>The Earth's <a href="Rotational_speed" title="Rotational speed">rotational speed</a> is very slowly decreasing due to <a href="Tidal_acceleration" title="Tidal acceleration">tidal deceleration</a>, causing the <a href="Solar_time" title="Solar time">mean solar day</a> to increase in length. The length of the SI second was calibrated on the basis of the second of <a href="Ephemeris_time" title="Ephemeris time">ephemeris time</a><sup id="cite_ref-FOOTNOTEMarkowitzHallEssenParry1958_30-1" class="reference"><a href="#cite_note-FOOTNOTEMarkowitzHallEssenParry1958-30"><span>[</span>30<span>]</span></a></sup><sup id="cite_ref-FOOTNOTEMarkowitz1988_33-1" class="reference"><a href="#cite_note-FOOTNOTEMarkowitz1988-33"><span>[</span>33<span>]</span></a></sup> and can now be seen to have a relationship with the mean solar day observed between 1750 and 1892, analysed by <a href="Simon_Newcomb" title="Simon Newcomb">Simon Newcomb</a>. As a result, the SI second is close to 1/86,400 of a mean solar day in the mid‑19th century<sup id="cite_ref-FOOTNOTEMcCarthySeidelmann200987_37-0" class="reference"><a href="#cite_note-FOOTNOTEMcCarthySeidelmann200987-37"><span>[</span>37<span>]</span></a></sup>. In earlier centuries the mean solar day was shorter than 86,400 SI seconds, and in more recent centuries it is longer than 86,400 seconds. Near the end of the 20th century the length of the mean solar day (also known simply as "length of day" or "LOD") was approximately 86,400.0013 s.<sup id="cite_ref-FOOTNOTEMcCarthySeidelmann200954_38-0" class="reference"><a href="#cite_note-FOOTNOTEMcCarthySeidelmann200954-38"><span>[</span>38<span>]</span></a></sup> For this reason, UT is now "slower" than TAI by the difference (or "excess" LOD) of 1.3 ms/day.</p> <p>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. Near the end of the 20th century, with the LOD at 1.3 ms above the nominal value, UTC ran faster than UT by 1.3 ms per day, getting a second ahead roughly every 800 days. Thus, leap seconds were inserted at approximately this interval, retarding UTC to keep it synchronised in the long term.<sup id="cite_ref-39" class="reference"><a href="#cite_note-39"><span>[</span>39<span>]</span></a></sup> Note that the actual <a href="Rotation_period" title="Rotation period">rotational period</a> varies on unpredictable factors such as <a href="Plate_tectonics" title="Plate tectonics">tectonic motion</a> and has to be observed, rather than computed.</p> <p>Just as adding a leap day every four years does not mean the year is getting longer by one day every four years, the insertion of a leap second every 800 days does not indicate that the mean solar day is getting longer by a second every 800 days. Rather, 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 rate fluctuates within the range of 1.7–2.3 ms/cy. While the rate due to <a href="Tidal_friction" title="Tidal friction" class="mw-redirect">tidal friction</a> alone is about 2.3 ms/cy, the uplift of <a href="Canada" title="Canada">Canada</a> and <a href="Scandinavia" title="Scandinavia">Scandinavia</a> by several metres since the last <a href="Ice_Age" title="Ice Age" class="mw-redirect">Ice Age</a> has temporarily reduced this to 1.7 ms/cy over the last 2,700 years.<sup id="cite_ref-FOOTNOTEStephensonMorrison1995_40-0" class="reference"><a href="#cite_note-FOOTNOTEStephensonMorrison1995-40"><span>[</span>40<span>]</span></a></sup> The correct reason for leap seconds, then, is not the current difference between actual and nominal LOD, but rather the <i>accumulation</i> of this difference over a period of time: Near the end of the 20th century, this difference was about 1/800 of a second per day; therefore, after about 800 days, it accumulated to 1 second (and a leap second was then added).</p> <p>For example, assume you start counting the seconds from the <a href="Unix_time" title="Unix time">Unix epoch</a> of 1970-01-01T00:00:00 UTC with an atomic clock. At midnight on that day (as measured on UTC), your counter registers 0 s. After Earth has made one full rotation with respect to the mean Sun, your counter will register approximately 86,400.002 s (the precise value will vary depending on <a href="Plate_tectonics" title="Plate tectonics">plate tectonic</a> conditions). Based on your counter, you can calculate that the date is 1970-01-02T00:00:00 UT1. After 500 rotations, your counter will register 43,200,001 s. Since 86,400 s × 500 is 43,200,000 s, you will calculate that the date is 1971-05-16T00:00:01 UTC, while it is only 1971-05-16T00:00:00 UT1. If you had added a leap second on December 31, 1970, retarding your counter by 1 s, then the counter would have a value of 43,200,000 s at 1971-05-16T00:00:00 UT1, and allow you to calculate the correct date.</p> <p>In the graph of <a href="DUT1" title="DUT1">DUT1</a> above, the excess of LOD above the nominal 86,400 s corresponds to the downward slope of the graph between vertical segments. (Note that the slope became shallower in the 2000s, due to a slight acceleration of the Earth's crust temporarily shortening the day.) Vertical position on the graph corresponds to the accumulation of this difference over time, and the vertical segments correspond to leap seconds introduced to match this accumulated difference. Leap seconds are timed to keep DUT1 within the vertical range depicted by this graph. The frequency of leap seconds therefore corresponds to the slope of the diagonal graph segments, and thus to the excess LOD.</p> <h2><span class="mw-headline" id="Future">Future</span> <span class="mw-editsection">[<a href="/w/index.php?title=Coordinated_Universal_Time&action=edit&section=9" title="Edit section: Future">edit</a>]</span></h2> <div class="rellink boilerplate seealso">See also: <a href="Leap_second" title="Leap second">Leap second</a></div> <p>As the Earth's rotation continues to slow, positive leap seconds will be required more frequently. The long-term <a href="Derivative" title="Derivative">rate of change</a> of LOD is approximately +1.7 ms per century. At the end of the 21st century LOD will be roughly 86,400.004 s, requiring leap seconds every 250 days. Over several centuries, the frequency of leap seconds will become problematic.</p> <p>Some time in the 22nd century, two leap seconds will be required every year. The current use of only the leap second opportunities in June and December will be insufficient, and the March and September options will have to be used. In the 25th century, four leap seconds will be required every year, so the current quarterly options will be insufficient. Thereafter there will need to be the possibility of leap seconds at the end of any month. In about two thousand years even that will become insufficient, and there will have to be leap seconds that are not at the end of a month.<sup id="cite_ref-FOOTNOTEAllen2011a_41-0" class="reference"><a href="#cite_note-FOOTNOTEAllen2011a-41"><span>[</span>41<span>]</span></a></sup></p> <p>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. It would be possible to then continue with double leaps, but this becomes increasingly untenable.</p> <p>Both the one-leap-second-per-month<sup id="cite_ref-FOOTNOTEFinklemanAllenSeagoSeaman2011_42-0" class="reference"><a href="#cite_note-FOOTNOTEFinklemanAllenSeagoSeaman2011-42"><span>[</span>42<span>]</span></a></sup> and one-leap-second-per-day milestones are considered (by different theorists<sup class="noprint Inline-Template" style="white-space:nowrap;">[<i><a href="Wikipedia:Avoid_weasel_words" title="Wikipedia:Avoid weasel words" class="mw-redirect"><span title="The material near this tag may use weasel words or too-vague attribution. (December 2009)">who?</span></a></i>]</sup>) 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.</p> <p>There is a proposal to redefine UTC and abolish leap seconds, such that <a href="Sundial" title="Sundial">sundials</a> would slowly get further out of sync with <a href="Civil_time" title="Civil time">civil time</a>.<sup id="cite_ref-FOOTNOTEAllen2011b_43-0" class="reference"><a href="#cite_note-FOOTNOTEAllen2011b-43"><span>[</span>43<span>]</span></a></sup> The resulting gradual shift of the sun's movements relative to civil time is analogous to the shift of <a href="Season" title="Season">seasons</a> relative to the yearly calendar that results from the calendar year not precisely matching the <a href="Tropical_year" title="Tropical year">tropical year</a> length. This would be a major practical change in civil timekeeping, but would take effect slowly over several centuries. <a href="ITU-R" title="ITU-R">ITU‑R</a> Study Group 7 and Working Party 7A were unable to reach consensus on whether to advance the proposal to the 2012 Radiocommunications Assembly; the chairman of Study Group 7 elected to advance the question to the 2012 Radiocommunications Assembly (20 January 2012)<sup id="cite_ref-FOOTNOTESeidelmannSeago2011S190_44-0" class="reference"><a href="#cite_note-FOOTNOTESeidelmannSeago2011S190-44"><span>[</span>44<span>]</span></a></sup>, but consideration of the proposal was postponed by the ITU until the World Radio Conference in 2015.<sup id="cite_ref-FOOTNOTELeap_decision_postponed2012_45-0" class="reference"><a href="#cite_note-FOOTNOTELeap_decision_postponed2012-45"><span>[</span>45<span>]</span></a></sup></p> <p>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.<sup id="cite_ref-FOOTNOTESeaman2003_46-0" class="reference"><a href="#cite_note-FOOTNOTESeaman2003-46"><span>[</span>46<span>]</span></a></sup></p> <h2><span class="mw-headline" id="See_also">See also</span> <span class="mw-editsection">[<a href="/w/index.php?title=Coordinated_Universal_Time&action=edit&section=10" title="Edit section: See also">edit</a>]</span></h2> <ul> <li><a href="Ephemeris_time" title="Ephemeris time">Ephemeris time</a></li> <li><a href="IERS_Reference_Meridian" title="IERS Reference Meridian">IERS Reference Meridian</a></li> <li><a href="ISO_8601" title="ISO 8601">ISO 8601</a></li> <li><a href="Terrestrial_Time" title="Terrestrial Time">Terrestrial Time</a></li> <li><a href="World_Radiocommunication_Conference" title="World Radiocommunication Conference">World Radiocommunication Conference</a></li> </ul> <h2><span class="mw-headline" id="Notes">Notes</span> <span class="mw-editsection">[<a href="/w/index.php?title=Coordinated_Universal_Time&action=edit&section=11" title="Edit section: Notes">edit</a>]</span></h2> <div class="reflist references-column-width" style="-moz-column-width: 30em; -webkit-column-width: 30em; column-width: 30em; list-style-type: decimal;"> <ol class="references"> <li id="cite_note-FOOTNOTEMcCarthySeidelmann2009227-1"><span class="mw-cite-backlink">^ <a href="#cite_ref-FOOTNOTEMcCarthySeidelmann2009227_1-0"><sup><i><b>a</b></i></sup></a> <a href="#cite_ref-FOOTNOTEMcCarthySeidelmann2009227_1-1"><sup><i><b>b</b></i></sup></a></span> <span class="reference-text"><a href="#CITEREFMcCarthySeidelmann2009">McCarthy & Seidelmann 2009</a>, p. 227.</span></li> <li id="cite_note-FOOTNOTEITU_Radiocommunication_Assembly2002-2"><span class="mw-cite-backlink"><b><a href="#cite_ref-FOOTNOTEITU_Radiocommunication_Assembly2002_2-0">^</a></b></span> <span class="reference-text"><a href="#CITEREFITU_Radiocommunication_Assembly2002">ITU Radiocommunication Assembly 2002</a>.</span></li> <li id="cite_note-FOOTNOTETime_Service_Dept.c._2009-3"><span class="mw-cite-backlink"><b><a href="#cite_ref-FOOTNOTETime_Service_Dept.c._2009_3-0">^</a></b></span> <span class="reference-text"><a href="#CITEREFTime_Service_Dept.c._2009">Time Service Dept. c. 2009</a>.</span></li> <li id="cite_note-FOOTNOTENational_Institute_of_Standards_and_Technology2012-4"><span class="mw-cite-backlink"><b><a href="#cite_ref-FOOTNOTENational_Institute_of_Standards_and_Technology2012_4-0">^</a></b></span> <span class="reference-text"><a href="#CITEREFNational_Institute_of_Standards_and_Technology2012">National Institute of Standards and Technology 2012</a>.</span></li> <li id="cite_note-FOOTNOTEUnited_States_Naval_Observatoryn.d.-5"><span class="mw-cite-backlink">^ <a href="#cite_ref-FOOTNOTEUnited_States_Naval_Observatoryn.d._5-0"><sup><i><b>a</b></i></sup></a> <a href="#cite_ref-FOOTNOTEUnited_States_Naval_Observatoryn.d._5-1"><sup><i><b>b</b></i></sup></a></span> <span class="reference-text"><a href="#CITEREFUnited_States_Naval_Observatoryn.d.">United States Naval Observatory n.d.</a>.</span></li> <li id="cite_note-FOOTNOTEHow_NTP_Works2011-6"><span class="mw-cite-backlink"><b><a href="#cite_ref-FOOTNOTEHow_NTP_Works2011_6-0">^</a></b></span> <span class="reference-text"><a href="#CITEREFHow_NTP_Works2011">How NTP Works 2011</a>.</span></li> <li id="cite_note-FOOTNOTEAviation_Time2006-7"><span class="mw-cite-backlink"><b><a href="#cite_ref-FOOTNOTEAviation_Time2006_7-0">^</a></b></span> <span class="reference-text"><a href="#CITEREFAviation_Time2006">Aviation Time 2006</a>.</span></li> <li id="cite_note-FOOTNOTEHorzepa2010-8"><span class="mw-cite-backlink"><b><a href="#cite_ref-FOOTNOTEHorzepa2010_8-0">^</a></b></span> <span class="reference-text"><a href="#CITEREFHorzepa2010">Horzepa 2010</a>.</span></li> <li id="cite_note-FOOTNOTEUniversal_Timen.d.-9"><span class="mw-cite-backlink"><b><a href="#cite_ref-FOOTNOTEUniversal_Timen.d._9-0">^</a></b></span> <span class="reference-text"><a href="#CITEREFUniversal_Timen.d.">Universal Time n.d.</a>.</span></li> <li id="cite_note-10"><span class="mw-cite-backlink"><b><a href="#cite_ref-10">^</a></b></span> <span class="reference-text"><span class="citation web">BelleSerene. <a rel="nofollow" class="external text" href="http://www.ybw.com/forums/archive/index.php/t-202760.html">"French time: "heure légale""</a>. Yachting and Boating World Forums<span class="reference-accessdate">. Retrieved 5 August 2011</span>.</span><span title="ctx_ver=Z39.88-2004&rfr_id=info%3Asid%2Fen.wikipedia.org%3ACoordinated+Universal+Time&rft.au=BelleSerene&rft.aulast=BelleSerene&rft.btitle=French+time%3A+%22heure+l%C3%A9gale%22&rft.genre=book&rft_id=http%3A%2F%2Fwww.ybw.com%2Fforums%2Farchive%2Findex.php%2Ft-202760.html&rft.pub=Yachting+and+Boating+World+Forums&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook" class="Z3988"><span style="display:none;"> </span></span></span></li> <li id="cite_note-FOOTNOTENational_Institute_of_Standards_and_Technology2011-11"><span class="mw-cite-backlink"><b><a href="#cite_ref-FOOTNOTENational_Institute_of_Standards_and_Technology2011_11-0">^</a></b></span> <span class="reference-text"><a href="#CITEREFNational_Institute_of_Standards_and_Technology2011">National Institute of Standards and Technology 2011</a>.</span></li> <li id="cite_note-FOOTNOTEIAU_resolutions1976-12"><span class="mw-cite-backlink"><b><a href="#cite_ref-FOOTNOTEIAU_resolutions1976_12-0">^</a></b></span> <span class="reference-text"><a href="#CITEREFIAU_resolutions1976">IAU resolutions 1976</a>.</span></li> <li id="cite_note-FOOTNOTEITU_Radiocommunication_Assembly20023-13"><span class="mw-cite-backlink"><b><a href="#cite_ref-FOOTNOTEITU_Radiocommunication_Assembly20023_13-0">^</a></b></span> <span class="reference-text"><a href="#CITEREFITU_Radiocommunication_Assembly2002">ITU Radiocommunication Assembly 2002</a>, p. 3.</span></li> <li id="cite_note-FOOTNOTEInternational_Earth_Rotation_and_Reference_Systems_Service2011-14"><span class="mw-cite-backlink"><b><a href="#cite_ref-FOOTNOTEInternational_Earth_Rotation_and_Reference_Systems_Service2011_14-0">^</a></b></span> <span class="reference-text"><a href="#CITEREFInternational_Earth_Rotation_and_Reference_Systems_Service2011">International Earth Rotation and Reference Systems Service 2011</a>.</span></li> <li id="cite_note-FOOTNOTEMcCarthySeidelmann2009229-15"><span class="mw-cite-backlink"><b><a href="#cite_ref-FOOTNOTEMcCarthySeidelmann2009229_15-0">^</a></b></span> <span class="reference-text"><a href="#CITEREFMcCarthySeidelmann2009">McCarthy & Seidelmann 2009</a>, p. 229.</span></li> <li id="cite_note-FOOTNOTEMcCarthySeidelmann2009chapter_4-16"><span class="mw-cite-backlink"><b><a href="#cite_ref-FOOTNOTEMcCarthySeidelmann2009chapter_4_16-0">^</a></b></span> <span class="reference-text"><a href="#CITEREFMcCarthySeidelmann2009">McCarthy & Seidelmann 2009</a>, chapter 4.</span></li> <li id="cite_note-FOOTNOTEHistory_of_TAI-UTCc._2009-17"><span class="mw-cite-backlink"><b><a href="#cite_ref-FOOTNOTEHistory_of_TAI-UTCc._2009_17-0">^</a></b></span> <span class="reference-text"><a href="#CITEREFHistory_of_TAI-UTCc._2009">History of TAI-UTC c. 2009</a>.</span></li> <li id="cite_note-FOOTNOTEMcCarthySeidelmann2009217.2C_227.E2.80.93231-18"><span class="mw-cite-backlink"><b><a href="#cite_ref-FOOTNOTEMcCarthySeidelmann2009217.2C_227.E2.80.93231_18-0">^</a></b></span> <span class="reference-text"><a href="#CITEREFMcCarthySeidelmann2009">McCarthy & Seidelmann 2009</a>, pp. 217, 227–231.</span></li> <li id="cite_note-FOOTNOTEMcCarthySeidelmann2009209-19"><span class="mw-cite-backlink"><b><a href="#cite_ref-FOOTNOTEMcCarthySeidelmann2009209_19-0">^</a></b></span> <span class="reference-text"><a href="#CITEREFMcCarthySeidelmann2009">McCarthy & Seidelmann 2009</a>, p. 209.</span></li> <li id="cite_note-FOOTNOTELangley1999-20"><span class="mw-cite-backlink"><b><a href="#cite_ref-FOOTNOTELangley1999_20-0">^</a></b></span> <span class="reference-text"><a href="#CITEREFLangley1999">Langley 1999</a>.</span></li> <li id="cite_note-FOOTNOTESeidelmann19927-21"><span class="mw-cite-backlink"><b><a href="#cite_ref-FOOTNOTESeidelmann19927_21-0">^</a></b></span> <span class="reference-text"><a href="#CITEREFSeidelmann1992">Seidelmann 1992</a>, p. 7.</span></li> <li id="cite_note-FOOTNOTEMilitary_.26_Civilian_Time_Designationsn.d.-22"><span class="mw-cite-backlink"><b><a href="#cite_ref-FOOTNOTEMilitary_.26_Civilian_Time_Designationsn.d._22-0">^</a></b></span> <span class="reference-text"><a href="#CITEREFMilitary_.26_Civilian_Time_Designationsn.d.">Military & Civilian Time Designations n.d.</a>.</span></li> <li id="cite_note-FOOTNOTEWilliams2005-23"><span class="mw-cite-backlink"><b><a href="#cite_ref-FOOTNOTEWilliams2005_23-0">^</a></b></span> <span class="reference-text"><a href="#CITEREFWilliams2005">Williams 2005</a>.</span></li> <li id="cite_note-FOOTNOTEIceland2011-24"><span class="mw-cite-backlink"><b><a href="#cite_ref-FOOTNOTEIceland2011_24-0">^</a></b></span> <span class="reference-text"><a href="#CITEREFIceland2011">Iceland 2011</a>.</span></li> <li id="cite_note-FOOTNOTEStandard_time2010-25"><span class="mw-cite-backlink"><b><a href="#cite_ref-FOOTNOTEStandard_time2010_25-0">^</a></b></span> <span class="reference-text"><a href="#CITEREFStandard_time2010">Standard time 2010</a>.</span></li> <li id="cite_note-FOOTNOTEHowse1997133.E2.80.93137-26"><span class="mw-cite-backlink"><b><a href="#cite_ref-FOOTNOTEHowse1997133.E2.80.93137_26-0">^</a></b></span> <span class="reference-text"><a href="#CITEREFHowse1997">Howse 1997</a>, pp. 133–137.</span></li> <li id="cite_note-FOOTNOTEMcCarthySeidelmann200910.E2.80.9311-27"><span class="mw-cite-backlink"><b><a href="#cite_ref-FOOTNOTEMcCarthySeidelmann200910.E2.80.9311_27-0">^</a></b></span> <span class="reference-text"><a href="#CITEREFMcCarthySeidelmann2009">McCarthy & Seidelmann 2009</a>, pp. 10–11.</span></li> <li id="cite_note-FOOTNOTEMcCarthySeidelmann2009226.E2.80.93227-28"><span class="mw-cite-backlink"><b><a href="#cite_ref-FOOTNOTEMcCarthySeidelmann2009226.E2.80.93227_28-0">^</a></b></span> <span class="reference-text"><a href="#CITEREFMcCarthySeidelmann2009">McCarthy & Seidelmann 2009</a>, pp. 226–227.</span></li> <li id="cite_note-FOOTNOTEAriasGuinotQuinn2003-29"><span class="mw-cite-backlink"><b><a href="#cite_ref-FOOTNOTEAriasGuinotQuinn2003_29-0">^</a></b></span> <span class="reference-text"><a href="#CITEREFAriasGuinotQuinn2003">Arias, Guinot & Quinn 2003</a>.</span></li> <li id="cite_note-FOOTNOTEMarkowitzHallEssenParry1958-30"><span class="mw-cite-backlink">^ <a href="#cite_ref-FOOTNOTEMarkowitzHallEssenParry1958_30-0"><sup><i><b>a</b></i></sup></a> <a href="#cite_ref-FOOTNOTEMarkowitzHallEssenParry1958_30-1"><sup><i><b>b</b></i></sup></a></span> <span class="reference-text"><a href="#CITEREFMarkowitzHallEssenParry1958">Markowitz et al. 1958</a>.</span></li> <li id="cite_note-FOOTNOTENelsonMcCarthy200515-31"><span class="mw-cite-backlink"><b><a href="#cite_ref-FOOTNOTENelsonMcCarthy200515_31-0">^</a></b></span> <span class="reference-text"><a href="#CITEREFNelsonMcCarthy2005">Nelson & McCarthy 2005</a>, p. 15.</span></li> <li id="cite_note-FOOTNOTENelsonMcCarthy2001515-32"><span class="mw-cite-backlink"><b><a href="#cite_ref-FOOTNOTENelsonMcCarthy2001515_32-0">^</a></b></span> <span class="reference-text"><a href="#CITEREFNelsonMcCarthy2001">Nelson & McCarthy 2001</a>, p. 515.</span></li> <li id="cite_note-FOOTNOTEMarkowitz1988-33"><span class="mw-cite-backlink">^ <a href="#cite_ref-FOOTNOTEMarkowitz1988_33-0"><sup><i><b>a</b></i></sup></a> <a href="#cite_ref-FOOTNOTEMarkowitz1988_33-1"><sup><i><b>b</b></i></sup></a></span> <span class="reference-text"><a href="#CITEREFMarkowitz1988">Markowitz 1988</a>.</span></li> <li id="cite_note-FOOTNOTEEssen1968161.E2.80.935-34"><span class="mw-cite-backlink"><b><a href="#cite_ref-FOOTNOTEEssen1968161.E2.80.935_34-0">^</a></b></span> <span class="reference-text"><a href="#CITEREFEssen1968">Essen 1968</a>, pp. 161–5.</span></li> <li id="cite_note-FOOTNOTESeidelmann199285.E2.80.9387-35"><span class="mw-cite-backlink"><b><a href="#cite_ref-FOOTNOTESeidelmann199285.E2.80.9387_35-0">^</a></b></span> <span class="reference-text"><a href="#CITEREFSeidelmann1992">Seidelmann 1992</a>, pp. 85–87.</span></li> <li id="cite_note-FOOTNOTENelsonLombardiOkayama200546-36"><span class="mw-cite-backlink"><b><a href="#cite_ref-FOOTNOTENelsonLombardiOkayama200546_36-0">^</a></b></span> <span class="reference-text"><a href="#CITEREFNelsonLombardiOkayama2005">Nelson, Lombardi & Okayama 2005</a>, p. 46.</span></li> <li id="cite_note-FOOTNOTEMcCarthySeidelmann200987-37"><span class="mw-cite-backlink"><b><a href="#cite_ref-FOOTNOTEMcCarthySeidelmann200987_37-0">^</a></b></span> <span class="reference-text"><a href="#CITEREFMcCarthySeidelmann2009">McCarthy & Seidelmann 2009</a>, p. 87.</span></li> <li id="cite_note-FOOTNOTEMcCarthySeidelmann200954-38"><span class="mw-cite-backlink"><b><a href="#cite_ref-FOOTNOTEMcCarthySeidelmann200954_38-0">^</a></b></span> <span class="reference-text"><a href="#CITEREFMcCarthySeidelmann2009">McCarthy & Seidelmann 2009</a>, p. 54.</span></li> <li id="cite_note-39"><span class="mw-cite-backlink"><b><a href="#cite_ref-39">^</a></b></span> <span class="reference-text"><a href="#CITEREFMcCarthySeidelmann2009">McCarthy & Seidelmann 2009</a>, p. 230. Average for period from 1 January 1991 through 1 January 2009. The average could change considerably depending on exactly what period is chosen to average over.</span></li> <li id="cite_note-FOOTNOTEStephensonMorrison1995-40"><span class="mw-cite-backlink"><b><a href="#cite_ref-FOOTNOTEStephensonMorrison1995_40-0">^</a></b></span> <span class="reference-text"><a href="#CITEREFStephensonMorrison1995">Stephenson & Morrison 1995</a>.</span></li> <li id="cite_note-FOOTNOTEAllen2011a-41"><span class="mw-cite-backlink"><b><a href="#cite_ref-FOOTNOTEAllen2011a_41-0">^</a></b></span> <span class="reference-text"><a href="#CITEREFAllen2011a">Allen 2011a</a>.</span></li> <li id="cite_note-FOOTNOTEFinklemanAllenSeagoSeaman2011-42"><span class="mw-cite-backlink"><b><a href="#cite_ref-FOOTNOTEFinklemanAllenSeagoSeaman2011_42-0">^</a></b></span> <span class="reference-text"><a href="#CITEREFFinklemanAllenSeagoSeaman2011">Finkleman et al. 2011</a>.</span></li> <li id="cite_note-FOOTNOTEAllen2011b-43"><span class="mw-cite-backlink"><b><a href="#cite_ref-FOOTNOTEAllen2011b_43-0">^</a></b></span> <span class="reference-text"><a href="#CITEREFAllen2011b">Allen 2011b</a>.</span></li> <li id="cite_note-FOOTNOTESeidelmannSeago2011S190-44"><span class="mw-cite-backlink"><b><a href="#cite_ref-FOOTNOTESeidelmannSeago2011S190_44-0">^</a></b></span> <span class="reference-text"><a href="#CITEREFSeidelmannSeago2011">Seidelmann & Seago 2011</a>, p. S190.</span></li> <li id="cite_note-FOOTNOTELeap_decision_postponed2012-45"><span class="mw-cite-backlink"><b><a href="#cite_ref-FOOTNOTELeap_decision_postponed2012_45-0">^</a></b></span> <span class="reference-text"><a href="#CITEREFLeap_decision_postponed2012">Leap decision postponed 2012</a>.</span></li> <li id="cite_note-FOOTNOTESeaman2003-46"><span class="mw-cite-backlink"><b><a href="#cite_ref-FOOTNOTESeaman2003_46-0">^</a></b></span> <span class="reference-text"><a href="#CITEREFSeaman2003">Seaman 2003</a>.</span></li> </ol> </div> <h2><span class="mw-headline" id="References">References</span> <span class="mw-editsection">[<a href="/w/index.php?title=Coordinated_Universal_Time&action=edit&section=12" title="Edit section: References">edit</a>]</span></h2> <div class="refbegin references-column-width" style="-moz-column-width: 30em; -webkit-column-width: 30em; column-width: 30em;"> <ul> <li><span id="CITEREFAllanAshbyHodge1997" class="citation book">Allan, David W.; Ashby, Neil; Hodge, Clifford C. 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Retrieved 18 July 2011</span>.</span><span title="ctx_ver=Z39.88-2004&rfr_id=info%3Asid%2Fen.wikipedia.org%3ACoordinated+Universal+Time&rft.au=Allen%2C+Steve&rft.aufirst=Steve&rft.aulast=Allen&rft.btitle=UTC+is+doomed&rft.date=2011a&rft.genre=book&rft_id=http%3A%2F%2Fwww.ucolick.org%2F~sla%2Fleapsecs%2Futcdoomed&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook" class="Z3988"><span style="display:none;"> </span></span></li> <li><span id="CITEREFAllen2011b" class="citation web">Allen, Steve (2011b). <a rel="nofollow" class="external text" href="http://www.ucolick.org/~sla/leapsecs/">"UTC might be redefined without Leap Seconds"</a><span class="reference-accessdate">. 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London: Philip Wilson. <a href="International_Standard_Book_Number" title="International Standard Book Number">ISBN</a> <a href="Special:BookSources/0-85667-468-0" title="Special:BookSources/0-85667-468-0">0-85667-468-0</a>.</span><span title="ctx_ver=Z39.88-2004&rfr_id=info%3Asid%2Fen.wikipedia.org%3ACoordinated+Universal+Time&rft.aufirst=Derek&rft.au=Howse%2C+Derek&rft.aulast=Howse&rft.btitle=Greenwich+Time+and+the+Longitude&rft.date=1997&rft.genre=book&rft.isbn=0-85667-468-0&rft.place=London&rft.pub=Philip+Wilson&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook" class="Z3988"><span style="display:none;"> </span></span></li> <li><span id="CITEREFHow_NTP_Works2011" class="citation web"><a rel="nofollow" class="external text" href="http://www.eecis.udel.edu/~mills/ntp/html/warp.html">"How NTP Works"</a>. <i>NTP: The Network Time Protocol</i>. 28 July 2011.</span><span title="ctx_ver=Z39.88-2004&rfr_id=info%3Asid%2Fen.wikipedia.org%3ACoordinated+Universal+Time&rft.atitle=How+NTP+Works&rft.date=28+July+2011&rft.genre=article&rft_id=http%3A%2F%2Fwww.eecis.udel.edu%2F~mills%2Fntp%2Fhtml%2Fwarp.html&rft.jtitle=NTP%3A+The+Network+Time+Protocol&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal" class="Z3988"><span style="display:none;"> </span></span> See heading "NTP Timescale and Data Formats".</li> <li><span id="CITEREFIAU_resolutions1976" class="citation web"><a rel="nofollow" class="external text" href="http://www.iau.org/static/resolutions/IAU1976_French.pdf">"IAU resolutions adopted at the XVIth General Assembly, Grenoble, France, 1976"</a>. 1976.</span><span title="ctx_ver=Z39.88-2004&rfr_id=info%3Asid%2Fen.wikipedia.org%3ACoordinated+Universal+Time&rft.btitle=IAU+resolutions+adopted+at+the+XVIth+General+Assembly%2C+Grenoble%2C+France%2C+1976&rft.date=1976&rft.genre=book&rft_id=http%3A%2F%2Fwww.iau.org%2Fstatic%2Fresolutions%2FIAU1976_French.pdf&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook" class="Z3988"><span style="display:none;"> </span></span> Resolution no. 3 by Commissions 4 (Ephemerides/Ephémérides) and 31 (Time/L'Heure) (near the end of the document) "recommend that the following notations be used in all languages", UT0(i), UT1(i), UT2(i), UTC, UTC(i), UT, where (i) is institution "i".</li> <li><span id="CITEREFIceland2011" class="citation web"><a rel="nofollow" class="external text" href="http://wwp.greenwichmeantime.com/time-zone/europe/iceland/">"Iceland"</a>. 2011.</span><span title="ctx_ver=Z39.88-2004&rfr_id=info%3Asid%2Fen.wikipedia.org%3ACoordinated+Universal+Time&rft.btitle=Iceland&rft.date=2011&rft.genre=book&rft_id=http%3A%2F%2Fwwp.greenwichmeantime.com%2Ftime-zone%2Feurope%2Ficeland%2F&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook" class="Z3988"><span style="display:none;"> </span></span></li> <li><span id="CITEREFInternational_Bureau_of_Weights_and_Measures2011" class="citation journal"><a href="International_Bureau_of_Weights_and_Measures" title="International Bureau of Weights and Measures">International Bureau of Weights and Measures</a> (10 October 2011). <a rel="nofollow" class="external text" href="ftp://ftp2.bipm.org/pub/tai/publication/cirt.285"><i>Circular T</i></a> (285).</span><span title="ctx_ver=Z39.88-2004&rfr_id=info%3Asid%2Fen.wikipedia.org%3ACoordinated+Universal+Time&rft.au=International+Bureau+of+Weights+and+Measures&rft.aulast=International+Bureau+of+Weights+and+Measures&rft.btitle=Circular+T&rft.date=10+October+2011&rft.genre=book&rft_id=ftp%3A%2F%2Fftp2.bipm.org%2Fpub%2Ftai%2Fpublication%2Fcirt.285&rft.issue=285&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook" class="Z3988"><span style="display:none;"> </span></span></li> <li><span id="CITEREFInternational_Earth_Rotation_and_Reference_Systems_Service2011" class="citation web"><a href="International_Earth_Rotation_and_Reference_Systems_Service" title="International Earth Rotation and Reference Systems Service">International Earth Rotation and Reference Systems Service</a> (19 July 2011). <a rel="nofollow" class="external text" href="http://www.iers.org/IERS/EN/Publications/Bulletins/bulletins.html">"IERS Bulletins"</a>.</span><span title="ctx_ver=Z39.88-2004&rfr_id=info%3Asid%2Fen.wikipedia.org%3ACoordinated+Universal+Time&rft.au=International+Earth+Rotation+and+Reference+Systems+Service&rft.aulast=International+Earth+Rotation+and+Reference+Systems+Service&rft.btitle=IERS+Bulletins&rft.date=19+July+2011&rft.genre=book&rft_id=http%3A%2F%2Fwww.iers.org%2FIERS%2FEN%2FPublications%2FBulletins%2Fbulletins.html&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook" class="Z3988"><span style="display:none;"> </span></span></li> <li><span id="CITEREFITU_Radiocommunication_Assembly2002" class="citation web">ITU Radiocommunication Assembly (2002). <a rel="nofollow" class="external text" href="http://www.itu.int/dms_pubrec/itu-r/rec/tf/R-REC-TF.460-6-200202-I!!PDF-E.pdf">"Standard-frequency and time-signal emissions"</a>. 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January 19, 2012.</span><span title="ctx_ver=Z39.88-2004&rfr_id=info%3Asid%2Fen.wikipedia.org%3ACoordinated+Universal+Time&rft.atitle=Leap+second+decision+is+postponed&rft.date=January+19%2C+2012&rft.genre=article&rft_id=http%3A%2F%2Fwww.bbc.co.uk%2Fnews%2Fscience-environment-16625614&rft.jtitle=BBC+News&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal" class="Z3988"><span style="display:none;"> </span></span></li> <li><span id="CITEREFMcCarthy.2C_Dennis_D.1991" class="citation journal"><a href="Dennis_McCarthy_(scientist)" title="Dennis McCarthy (scientist)">McCarthy, Dennis D.</a> (July 1991). <a rel="nofollow" class="external text" href="http://www.cl.cam.ac.uk/~mgk25/volatile/astronomical-time.pdf">"Astronomical Time"</a> (PDF). <i>Proc. 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Dordrecht: Kluwer Academic Publishers. pp. 413–418. <a href="Bibcode" title="Bibcode">Bibcode</a>:<a rel="nofollow" class="external text" href="http://adsabs.harvard.edu/abs/1988IAUS..128..413M">1988IAUS..128..413M</a>.</span><span title="ctx_ver=Z39.88-2004&rfr_id=info%3Asid%2Fen.wikipedia.org%3ACoordinated+Universal+Time&rft.atitle=The+Earth%27s+Rotation+and+Reference+Frames+for+Geodesy+and+Geophysicss%3A+Proceedings+of+the+128th+Symposium+of+the+International+Astronomical+Union%2C+held+in+Coolfont%2C+West+Virginia%2C+U.S.A.%2C+20%E2%80%9324+October+1986&rft.aufirst=Wm.&rft.aulast=Markowitz&rft.au=Markowitz%2C+Wm.&rft.btitle=Comparisons+of+ET%28Solar%29%2C+ET%28Lunar%29%2C+UT+and+TDT&rft.date=1988&rft.genre=bookitem&rft_id=info%3Abibcode%2F1988IAUS..128..413M&rft.pages=413%E2%80%93418&rft.place=Dordrecht&rft.pub=Kluwer+Academic+Publishers&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook" class="Z3988"><span style="display:none;"> </span></span></li> <li><span id="CITEREFMilitary_.26_Civilian_Time_Designationsn.d." class="citation web"><a rel="nofollow" class="external text" href="http://wwp.greenwichmeantime.com/info/timezone.htm">"Military & Civilian Time Designations"</a>. wwp.</span><span title="ctx_ver=Z39.88-2004&rfr_id=info%3Asid%2Fen.wikipedia.org%3ACoordinated+Universal+Time&rft.btitle=Military+%26+Civilian+Time+Designations&rft.genre=book&rft_id=http%3A%2F%2Fwwp.greenwichmeantime.com%2Finfo%2Ftimezone.htm&rft.pub=wwp&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook" class="Z3988"><span style="display:none;"> </span></span></li> <li><span id="CITEREFNational_Institute_of_Standards_and_Technology2011" class="citation web"><a href="National_Institute_of_Standards_and_Technology" title="National Institute of Standards and Technology">National Institute of Standards and Technology</a> (18 January 2011). <a rel="nofollow" class="external text" href="http://www.nist.gov/pml/div688/utcnist.cfm#cut">"Frequently asked questions (FAQ)"</a><span class="reference-accessdate">. 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height="40" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/f/f8/Wiktionary-logo-en.svg/55px-Wiktionary-logo-en.svg.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/f/f8/Wiktionary-logo-en.svg/73px-Wiktionary-logo-en.svg.png 2x" /></td> <td class="mbox-text plainlist" style="">Look up <i><b><a href="//en.wiktionary.orgUTC" class="extiw" title="wiktionary:UTC">UTC</a></b></i> in Wiktionary, the free dictionary.</td> </tr> </table> <ul> <li><a rel="nofollow" class="external text" href="http://www.cl.cam.ac.uk/~mgk25/time/zeitgesetz.en.html">Definition of Coordinated Universal Time in German law–ZeitG §1 (3)</a></li> <li><a rel="nofollow" class="external text" href="http://hpiers.obspm.fr/eop-pc/earthor/utc/TAI-UTC_tab.html">International Earth Rotation Service; list of differences between TAI and UTC from 1961 to present</a></li> <li><a rel="nofollow" class="external text" href="http://www.usno.navy.mil/USNO/time/master-clock/systems-of-time">U.S. Naval Observatory: Systems of Time</a></li> <li><a rel="nofollow" class="external text" href="http://www.w3.org/TR/NOTE-datetime">W3C Specification about UTC Date and Time</a> and <a href="IETF" title="IETF" class="mw-redirect">IETF</a> <a href="Internet_standard" title="Internet standard" class="mw-redirect">Internet standard</a> <a class="external mw-magiclink-rfc" rel="nofollow" href="//tools.ietf.org/html/rfc3339">RFC 3339</a>, based on <a href="ISO_8601" title="ISO 8601">ISO 8601</a></li> <li><a rel="nofollow" class="external text" href="http://www.ipses.com/prod/timing/UTC-GPS.php?language=en">Standard of time definition: UTC, GPS, LORAN and TAI</a></li> </ul> <table cellspacing="0" class="navbox" style="border-spacing:0;"> <tr> <td style="padding:2px;"> <table cellspacing="0" class="nowraplinks hlist collapsible collapsed navbox-inner" style="border-spacing:0;background:transparent;color:inherit;"> <tr> <th scope="col" class="navbox-title" colspan="3" style="background:#ee9;;"> <div class="noprint plainlinks hlist navbar mini"> <ul> <li class="nv-view"><a href="Template:Time_topics" title="Template:Time topics"><span title="View this template" style=";background:#ee9;;background:none transparent;border:none;;">v</span></a></li> <li class="nv-talk"><a href="Template_talk:Time_topics" title="Template talk:Time topics"><span title="Discuss this template" style=";background:#ee9;;background:none transparent;border:none;;">t</span></a></li> <li class="nv-edit"><a class="external text" href="//en.wikipedia.org/w/index.php?title=Template:Time_topics&action=edit"><span title="Edit this template" style=";background:#ee9;;background:none transparent;border:none;;">e</span></a></li> </ul> </div> <div style="font-size:110%;"><a href="Time" title="Time">Time</a></div> </th> </tr> <tr style="height:2px;"> <td></td> </tr> <tr> <th scope="row" class="navbox-group" style="background:#dd9;;">Key concepts</th> <td class="navbox-list navbox-odd" style="text-align:left;border-left-width:2px;border-left-style:solid;width:100%;padding:0px;"> <div style="padding:0em 0.25em;"> <ul> <li><a href="Past" title="Past">Past</a> <ul> <li><a href="History" title="History">history</a></li> <li><a href="Deep_time" title="Deep time">deep time</a></li> </ul> </li> <li><a href="Present" title="Present">Present</a></li> <li><a href="Future" title="Future">Future</a> <ul> <li><a href="Futures_studies" title="Futures studies">futurology</a></li> </ul> </li> <li><a href="Eternity" title="Eternity">Eternity</a> <ul> <li><a href="Arguments_for_eternity" title="Arguments for eternity">arguments for</a></li> </ul> </li> <li><a href="Immortality" title="Immortality">Immortality</a></li> </ul> </div> </td> <td class="navbox-image" rowspan="15" style="width:0%;padding:0px 0px 0px 2px;"> <div><a target="_blank" href="http://commons.wikimedia.org/wiki/File:Wooden_hourglass_3.jpg" class="image" title="Wooden hourglass"><img alt="Wooden hourglass" src="//upload.wikimedia.org/wikipedia/commons/thumb/7/70/Wooden_hourglass_3.jpg/76px-Wooden_hourglass_3.jpg" width="76" height="154" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/7/70/Wooden_hourglass_3.jpg/114px-Wooden_hourglass_3.jpg 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/7/70/Wooden_hourglass_3.jpg/152px-Wooden_hourglass_3.jpg 2x" /></a><br /> <a target="_blank" href="http://commons.wikimedia.org/wiki/File:Portal-puzzle.svg" class="image" title="Portal:Time"><img alt="Portal:Time" src="//upload.wikimedia.org/wikipedia/en/thumb/f/fd/Portal-puzzle.svg/16px-Portal-puzzle.svg.png" width="16" height="14" srcset="//upload.wikimedia.org/wikipedia/en/thumb/f/fd/Portal-puzzle.svg/24px-Portal-puzzle.svg.png 1.5x, //upload.wikimedia.org/wikipedia/en/thumb/f/fd/Portal-puzzle.svg/32px-Portal-puzzle.svg.png 2x" /></a> <b><a href="Portal:Time" title="Portal:Time">Time portal</a></b></div> </td> </tr> <tr style="height:2px;"> <td></td> </tr> <tr> <th scope="row" class="navbox-group" style="background:#dd9;;"> <div style="padding:0.1em 0;line-height:1.2em;">Measurement and<br /> <a href="Time_standard" title="Time standard">standards</a></div> </th> <td class="navbox-list navbox-even" style="text-align:left;border-left-width:2px;border-left-style:solid;width:100%;padding:0px;"> <div style="padding:0em 0.25em;"></div> <table cellspacing="0" class="nowraplinks navbox-subgroup" style="border-spacing:0;"> <tr> <th scope="row" class="navbox-group" style="width:7.4em;padding-left:0em;padding-right:0em;font-weight:normal;background:#dd9;;"> <div style="padding:0em 0.75em;"><a href="Chronometry" title="Chronometry">Chronometry</a></div> </th> <td class="navbox-list navbox-odd" style="text-align:left;border-left-width:2px;border-left-style:solid;padding:0px;"> <div style="padding:0em 0.25em;"> <ul> <li><b><strong class="selflink">UTC</strong></b></li> <li><a href="Universal_Time" title="Universal Time">UT</a></li> <li><a href="International_Atomic_Time" title="International Atomic Time">TAI</a></li> <li><a href="Unit_of_time" title="Unit of time">Unit of time</a></li> <li><a href="Hour" title="Hour">Hour</a></li> <li><a href="Minute" title="Minute">Minute</a></li> <li><b><a href="Second" title="Second">Second</a></b></li> <li><a href="Sidereal_time" title="Sidereal time">Sidereal time</a></li> <li><a href="Solar_time" title="Solar time">Solar time</a></li> <li><a href="Time_zone" title="Time zone">Time zone</a></li> <li><a href="Metric_time" title="Metric time">Metric time</a></li> <li><a href="Decimal_time" title="Decimal time">Decimal time</a></li> <li><a href="Hexadecimal_time" title="Hexadecimal time">Hexadecimal time</a></li> </ul> </div> </td> </tr> <tr style="height:2px;"> <td></td> </tr> <tr> <th scope="row" class="navbox-group" style="width:7.4em;padding-left:0em;padding-right:0em;font-weight:normal;background:#dd9;;"> <div style="padding:0em 0.75em;"><a href="Clock" title="Clock">Clock</a></div> </th> <td class="navbox-list navbox-even" style="text-align:left;border-left-width:2px;border-left-style:solid;padding:0px;"> <div style="padding:0em 0.25em;"> <ul> <li><a href="12-hour_clock" title="12-hour clock">12-hour clock</a></li> <li><a href="24-hour_clock" title="24-hour clock">24-hour clock</a></li> <li><a href="Astrarium" title="Astrarium">Astrarium</a></li> <li><a href="History_of_timekeeping_devices" title="History of timekeeping devices">History of timekeeping devices</a></li> <li><a href="Horology" title="Horology">Horology</a></li> <li><a href="Marine_chronometer" title="Marine chronometer">Marine chronometer</a></li> <li><a href="Sundial" title="Sundial">Sundial</a></li> <li><a href="Water_clock" title="Water clock">Water clock</a></li> </ul> </div> </td> </tr> <tr style="height:2px;"> <td></td> </tr> <tr> <th scope="row" class="navbox-group" style="width:7.4em;padding-left:0em;padding-right:0em;font-weight:normal;background:#dd9;;"> <div style="padding:0em 0.75em;"><a href="Calendar" title="Calendar">Calendar</a></div> </th> <td class="navbox-list navbox-odd" style="text-align:left;border-left-width:2px;border-left-style:solid;padding:0px;"> <div style="padding:0em 0.25em;"> <ul> <li><a href="Day" title="Day">Day</a></li> <li><a href="Week" title="Week">Week</a></li> <li><a href="Month" title="Month">Month</a></li> <li><a href="Year" title="Year">Year</a></li> <li><a href="Tropical_year" title="Tropical year">Tropical year</a></li> <li><a href="Decade" title="Decade">Decade</a></li> <li><a href="Century" title="Century">Century</a></li> <li><a href="Millennium" title="Millennium">Millennium</a></li> <li><a href="Gregorian_calendar" title="Gregorian calendar">Gregorian</a></li> <li><a href="Islamic_calendar" title="Islamic calendar">Islamic</a></li> <li><a href="Julian_calendar" title="Julian calendar">Julian</a></li> <li><a href="Solar_Hijri" title="Solar Hijri" class="mw-redirect">Solar Hijri</a></li> <li><a href="Maya_calendar" title="Maya calendar">Mayan</a></li> <li><a href="Intercalation_(timekeeping)" title="Intercalation (timekeeping)">Intercalation</a></li> <li><a href="Leap_second" title="Leap second">Leap second</a></li> <li><a href="Leap_year" title="Leap year">Leap year</a></li> </ul> </div> </td> </tr> </table> </td> </tr> <tr style="height:2px;"> <td></td> </tr> <tr> <th scope="row" class="navbox-group" style="background:#dd9;;"> <div style="padding:0.1em 0;line-height:1.2em;"><a href="Chronology" title="Chronology">Chronology</a> / <a href="History" title="History">history</a> /<br /> archaeology / geology</div> </th> <td class="navbox-list navbox-odd" style="text-align:left;border-left-width:2px;border-left-style:solid;width:100%;padding:0px;"> <div style="padding:0em 0.25em;"> <ul> <li><a href="Astronomical_chronology" title="Astronomical chronology">Astronomical chronology</a> / <a href="Calendar_era" title="Calendar era">Calendar era</a></li> <li><a href="Chronicle" title="Chronicle">Chronicle</a></li> <li><a href="Timeline" title="Timeline">Timeline</a></li> <li><a href="Periodization" title="Periodization">Periodization</a></li> <li><a href="Regnal_year" title="Regnal year">Regnal year</a></li> <li><a href="Big_History" title="Big History">Big History</a> / <a href="Dating_methodologies_in_archaeology" title="Dating methodologies in archaeology">Dating methodologies</a> / <a href="Geologic_time_scale" title="Geologic time scale">Geological time</a></li> <li><a href="Geochronology" title="Geochronology">Geochronology</a></li> <li><a href="Geological_history_of_Earth" title="Geological history of Earth">Geological history</a></li> <li><a href="Deep_time" title="Deep time">Deep time</a></li> <li><a href="Eon_(geology)" title="Eon (geology)" class="mw-redirect">Eon</a></li> <li><a href="Era_(geology)" title="Era (geology)">Era</a></li> <li><a href="Period_(geology)" title="Period (geology)">Period</a></li> <li><a href="Epoch_(geology)" title="Epoch (geology)">Epoch</a></li> <li><a href="Age_(geology)" title="Age (geology)">Age</a></li> <li><a href="Chron" title="Chron" class="mw-redirect">Chron</a></li> </ul> </div> </td> </tr> <tr style="height:2px;"> <td></td> </tr> <tr> <th scope="row" class="navbox-group" style="background:#dd9;;">Religion and mythology</th> <td class="navbox-list navbox-even" style="text-align:left;border-left-width:2px;border-left-style:solid;width:100%;padding:0px;"> <div style="padding:0em 0.25em;"> <ul> <li><a href="Dreamtime" title="Dreamtime">Dreamtime</a></li> <li><a href="K%C4%81la_(time)" title="Kāla (time)">Kāla</a></li> <li><a href="Kalachakra" title="Kalachakra">Kalachakra</a></li> <li><a href="Prophecy" title="Prophecy">Prophecy</a></li> <li><a href="Time_and_fate_deities" title="Time and fate deities">Time and fate deities</a></li> <li><a href="Wheel_of_time" title="Wheel of time">Wheel of time</a></li> </ul> </div> </td> </tr> <tr style="height:2px;"> <td></td> </tr> <tr> <th scope="row" class="navbox-group" style="background:#dd9;;"><a href="Philosophy_of_space_and_time" title="Philosophy of space and time">Philosophy</a></th> <td class="navbox-list navbox-odd" style="text-align:left;border-left-width:2px;border-left-style:solid;width:100%;padding:0px;"> <div style="padding:0em 0.25em;"> <ul> <li><a href="A-series_and_B-series" title="A-series and B-series">A-series and B-series</a></li> <li><a href="B-theory_of_time" title="B-theory of time">B-theory of time</a></li> <li><a href="Causality" title="Causality">Causality</a></li> <li><a href="Duration_(philosophy)" title="Duration (philosophy)">Duration</a></li> <li><a href="Endurantism" title="Endurantism">Endurantism</a></li> <li><a href="Eternal_return" title="Eternal return">Eternal return</a></li> <li><a href="Eternalism_(philosophy_of_time)" title="Eternalism (philosophy of time)">Eternalism</a></li> <li><a href="Event_(philosophy)" title="Event (philosophy)">Event</a></li> <li><a href="Perdurantism" title="Perdurantism">Perdurantism</a></li> <li><a href="Presentism_(philosophy_of_time)" title="Presentism (philosophy of time)">Presentism</a></li> <li><a href="Temporal_finitism" title="Temporal finitism">Temporal finitism</a></li> <li><a href="Temporal_parts" title="Temporal parts">Temporal parts</a></li> <li><i><a href="The_Unreality_of_Time" title="The Unreality of Time">The Unreality of Time</a></i></li> </ul> </div> </td> </tr> <tr style="height:2px;"> <td></td> </tr> <tr> <th scope="row" class="navbox-group" style="background:#dd9;;"><a href="Time_in_physics" title="Time in physics">Physics</a></th> <td class="navbox-list navbox-even" style="text-align:left;border-left-width:2px;border-left-style:solid;width:100%;padding:0px;"> <div style="padding:0em 0.25em;"> <ul> <li><a href="Absolute_time_and_space" title="Absolute time and space">Absolute time and space</a></li> <li><a href="Arrow_of_time" title="Arrow of time">Arrow of time</a></li> <li><a href="Chronon" title="Chronon">Chronon</a></li> <li><a href="Coordinate_time" title="Coordinate time">Coordinate time</a></li> <li><a href="Planck_epoch" title="Planck epoch">Planck epoch</a></li> <li><a href="Planck_time" title="Planck time">Planck time</a></li> <li><a href="Proper_time" title="Proper time">Proper time</a></li> <li><a href="Rate_(mathematics)" title="Rate (mathematics)">Rate</a></li> <li><a href="Spacetime" title="Spacetime">Spacetime</a></li> <li><a href="Theory_of_relativity" title="Theory of relativity">Theory of relativity</a></li> <li><a href="Time_dilation" title="Time dilation">Time dilation</a> <ul> <li><a href="Gravitational_time_dilation" title="Gravitational time dilation">gravitational</a></li> </ul> </li> <li><a href="Time_domain" title="Time domain">Time domain</a></li> <li><a href="T-symmetry" title="T-symmetry">T-symmetry</a></li> </ul> </div> </td> </tr> <tr style="height:2px;"> <td></td> </tr> <tr> <th scope="row" class="navbox-group" style="background:#dd9;;"> <div style="padding:0.1em 0;line-height:1.2em;">Biology / psychology /<br /> sociology / economics /<br /> accounting / management</div> </th> <td class="navbox-list navbox-odd" style="text-align:left;border-left-width:2px;border-left-style:solid;width:100%;padding:0px;"> <div style="padding:0em 0.25em;"> <ul> <li><a href="Chronobiology" title="Chronobiology">Chronobiology</a></li> <li><a href="Circadian_rhythm" title="Circadian rhythm">Circadian rhythms</a> / <a href="Mental_chronometry" title="Mental chronometry">Mental chronometry</a></li> <li><a href="Specious_present" title="Specious present">Specious present</a></li> <li><a href="Time_perception" title="Time perception">Time perception</a> / <a href="Time_discipline" title="Time discipline">Time discipline</a> / <a href="Time_use_research" title="Time use research">Time use research</a></li> <li><a href="Time_value_of_money" title="Time value of money">Time value of money</a></li> <li><a href="Time-based_currency" title="Time-based currency">Time-based currency</a></li> <li><a href="Time_banking" title="Time banking">Time banking</a></li> <li><a href="Term_(time)" title="Term (time)">Term</a> / <a href="Accounting_period" title="Accounting period">Accounting period</a></li> <li><a href="Fiscal_year" title="Fiscal year">Fiscal year</a> / <a href="Time_management" title="Time management">Time management</a></li> <li><a href="Punctuality" title="Punctuality">Punctuality</a></li> <li><a href="Procrastination" title="Procrastination">Procrastination</a></li> <li><a href="Time_clock" title="Time clock">Time clock</a></li> <li><a href="Timesheet" title="Timesheet">Timesheet</a></li> <li><a href="Time_tracking_software" title="Time tracking software">Time tracking software</a></li> </ul> </div> </td> </tr> <tr style="height:2px;"> <td></td> </tr> <tr> <th scope="row" class="navbox-group" style="background:#dd9;;">Related topics</th> <td class="navbox-list navbox-even" style="text-align:left;border-left-width:2px;border-left-style:solid;width:100%;padding:0px;"> <div style="padding:0em 0.25em;"> <ul> <li><i><a href="Carpe_diem" title="Carpe diem">Carpe diem</a></i></li> <li><a href="Clock_position" title="Clock position">Clock position</a></li> <li><a href="Space" title="Space">Space</a></li> <li><a href="System_time" title="System time">System time</a></li> <li><i><a href="Tempus_fugit" title="Tempus fugit">Tempus fugit</a></i></li> <li><a href="Time_capsule" title="Time capsule">Time capsule</a></li> <li><a href="Time_signature" title="Time signature">Time signature</a></li> <li><a href="Time_travel" title="Time travel">Time travel</a></li> </ul> </div> </td> </tr> </table> </td> </tr> </table> <table cellspacing="0" class="navbox" style="border-spacing:0;"> <tr> <td style="padding:2px;"> <table cellspacing="0" class="nowraplinks collapsible collapsed navbox-inner" style="border-spacing:0;background:transparent;color:inherit;"> <tr> <th scope="col" class="navbox-title" colspan="2"> <div class="noprint plainlinks hlist navbar mini"> <ul> <li class="nv-view"><a href="Template:Time_measurement_and_standards" title="Template:Time measurement and standards"><span title="View this template" style=";;background:none transparent;border:none;;">v</span></a></li> <li class="nv-talk"><a href="Template_talk:Time_measurement_and_standards" title="Template talk:Time measurement and standards"><span title="Discuss this template" style=";;background:none transparent;border:none;;">t</span></a></li> <li class="nv-edit"><a class="external text" href="//en.wikipedia.org/w/index.php?title=Template:Time_measurement_and_standards&action=edit"><span title="Edit this template" style=";;background:none transparent;border:none;;">e</span></a></li> </ul> </div> <div style="font-size:110%;">Time measurement and <a href="Time_standard" title="Time standard">standards</a></div> </th> </tr> <tr style="height:2px;"> <td></td> </tr> <tr> <th scope="row" class="navbox-group">Major subjects</th> <td class="navbox-list navbox-odd hlist" style="text-align:left;border-left-width:2px;border-left-style:solid;width:100%;padding:0px;"> <div style="padding:0em 0.25em;"> <ul> <li><b><a href="Time" title="Time">Time</a></b></li> <li><a href="Chronometry" title="Chronometry">Chronometry</a></li> <li><a href="Orders_of_magnitude_(time)" title="Orders of magnitude (time)">Orders of magnitude</a></li> <li><a href="Metrology" title="Metrology">Metrology</a></li> </ul> </div> </td> </tr> <tr style="height:2px;"> <td></td> </tr> <tr> <th scope="row" class="navbox-group">International standards</th> <td class="navbox-list navbox-even hlist" style="text-align:left;border-left-width:2px;border-left-style:solid;width:100%;padding:0px;"> <div style="padding:0em 0.25em;"> <ul> <li><b><strong class="selflink">UTC</strong></b></li> <li><a href="UTC_offset" title="UTC offset">UTC offset</a></li> <li><a href="Universal_Time" title="Universal Time">UT</a></li> <li><a href="%CE%94T" title="ΔT">ΔT</a></li> <li><a href="DUT1" title="DUT1">DUT1</a></li> <li><a href="International_Earth_Rotation_and_Reference_Systems_Service" title="International Earth Rotation and Reference Systems Service">IERS</a></li> <li><a href="ISO_31-1" title="ISO 31-1">ISO 31-1</a></li> <li><a href="ISO_8601" title="ISO 8601">ISO 8601</a></li> <li><a href="International_Atomic_Time" title="International Atomic Time">TAI</a></li> <li><a href="12-hour_clock" title="12-hour clock">12-hour clock</a></li> <li><a href="24-hour_clock" title="24-hour clock">24-hour clock</a></li> <li><a href="Barycentric_Coordinate_Time" title="Barycentric Coordinate Time">Barycentric Coordinate Time</a></li> <li><a href="Civil_time" title="Civil time">Civil time</a></li> <li><a href="Daylight_saving_time" title="Daylight saving time">Daylight saving time</a></li> <li><a href="Geocentric_Coordinate_Time" title="Geocentric Coordinate Time">Geocentric Coordinate Time</a></li> <li><a href="International_Date_Line" title="International Date Line">International Date Line</a></li> <li><a href="Leap_second" title="Leap second">Leap second</a></li> <li><a href="Solar_time" title="Solar time">Solar time</a></li> <li><a href="Terrestrial_Time" title="Terrestrial Time">Terrestrial Time</a></li> <li><a href="Time_zone" title="Time zone">Time zone</a></li> </ul> </div> </td> </tr> <tr style="height:2px;"> <td></td> </tr> <tr> <th scope="row" class="navbox-group">Obsolete standards</th> <td class="navbox-list navbox-odd hlist" style="text-align:left;border-left-width:2px;border-left-style:solid;width:100%;padding:0px;"> <div style="padding:0em 0.25em;"> <ul> <li><a href="Barycentric_Dynamical_Time" title="Barycentric Dynamical Time">Barycentric Dynamical Time</a></li> <li><a href="Ephemeris_time" title="Ephemeris time">Ephemeris time</a></li> <li><a href="Greenwich_Mean_Time" title="Greenwich Mean Time">Greenwich Mean Time</a></li> <li><a href="Prime_meridian" title="Prime meridian">Prime meridian</a></li> </ul> </div> </td> </tr> <tr style="height:2px;"> <td></td> </tr> <tr> <th scope="row" class="navbox-group"><a href="Time_in_physics" title="Time in physics">Time in physics</a></th> <td class="navbox-list navbox-even hlist" style="text-align:left;border-left-width:2px;border-left-style:solid;width:100%;padding:0px;"> <div style="padding:0em 0.25em;"> <ul> <li><a href="Absolute_time_and_space" title="Absolute time and space">Absolute time and space</a></li> <li><a href="Spacetime" title="Spacetime">Spacetime</a></li> <li><a href="Chronon" title="Chronon">Chronon</a></li> <li><a href="Continuous_signal" title="Continuous signal">Continuous time</a></li> <li><a href="Coordinate_time" title="Coordinate time">Coordinate time</a></li> <li><a href="Cosmological_decade" title="Cosmological decade">Cosmological decade</a></li> <li><a href="Discrete_time" title="Discrete time">Discrete time</a></li> <li><a href="Planck_epoch" title="Planck epoch">Planck epoch</a></li> <li><a href="Planck_time" title="Planck time">Planck time</a></li> <li><a href="Proper_time" title="Proper time">Proper time</a></li> <li><a href="Theory_of_relativity" title="Theory of relativity">Theory of relativity</a></li> <li><a href="Time_dilation" title="Time dilation">Time dilation</a></li> <li><a href="Gravitational_time_dilation" title="Gravitational time dilation">Gravitational time dilation</a></li> <li><a href="Time_domain" title="Time domain">Time domain</a></li> <li><a href="T-symmetry" title="T-symmetry">T-symmetry</a></li> </ul> </div> </td> </tr> <tr style="height:2px;"> <td></td> </tr> <tr> <th scope="row" class="navbox-group"><a href="Horology" title="Horology">Horology</a></th> <td class="navbox-list navbox-odd hlist" style="text-align:left;border-left-width:2px;border-left-style:solid;width:100%;padding:0px;"> <div style="padding:0em 0.25em;"> <ul> <li><b><a href="Clock" title="Clock">Clock</a></b></li> <li><a href="Astrarium" title="Astrarium">Astrarium</a></li> <li><a href="Atomic_clock" title="Atomic clock">Atomic clock</a></li> <li><a href="Complication_(horology)" title="Complication (horology)">Complication</a></li> <li><a href="Equation_of_time" title="Equation of time">Equation of time</a></li> <li><a href="History_of_timekeeping_devices" title="History of timekeeping devices">History of timekeeping devices</a></li> <li><a href="Hourglass" title="Hourglass">Hourglass</a></li> <li><a href="Marine_chronometer" title="Marine chronometer">Marine chronometer</a></li> <li><a href="Marine_sandglass" title="Marine sandglass">Marine sandglass</a></li> <li><a href="Radio_clock" title="Radio clock">Radio clock</a></li> <li><a href="Sundial" title="Sundial">Sundial</a></li> <li><a href="Watch" title="Watch">Watch</a></li> <li><a href="Water_clock" title="Water clock">Water clock</a></li> </ul> </div> </td> </tr> <tr style="height:2px;"> <td></td> </tr> <tr> <th scope="row" class="navbox-group"><b><a href="Calendar" title="Calendar">Calendar</a></b></th> <td class="navbox-list navbox-even hlist" style="text-align:left;border-left-width:2px;border-left-style:solid;width:100%;padding:0px;"> <div style="padding:0em 0.25em;"> <ul> <li><a href="Astronomical_year_numbering" title="Astronomical year numbering">Astronomical</a></li> <li><a href="Dominical_letter" title="Dominical letter">Dominical letter</a></li> <li><a href="Epact" title="Epact">Epact</a></li> <li><a href="Equinox" title="Equinox">Equinox</a></li> <li><a href="Gregorian_calendar" title="Gregorian calendar">Gregorian</a></li> <li><a href="Hebrew_calendar" title="Hebrew calendar">Hebrew</a></li> <li><a href="Hindu_calendar" title="Hindu calendar">Hindu</a></li> <li><a href="Intercalation_(timekeeping)" title="Intercalation (timekeeping)">Intercalation</a></li> <li><a href="Islamic_calendar" title="Islamic calendar">Islamic</a></li> <li><a href="Julian_calendar" title="Julian calendar">Julian</a></li> <li><a href="Leap_year" title="Leap year">Leap year</a></li> <li><a href="Lunar_calendar" title="Lunar calendar">Lunar</a></li> <li><a href="Lunisolar_calendar" title="Lunisolar calendar">Lunisolar</a></li> <li><a href="Seven-day_week" title="Seven-day week">Seven-day week</a></li> <li><a href="Solar_calendar" title="Solar calendar">Solar</a></li> <li><a href="Solstice" title="Solstice">Solstice</a></li> <li><a href="Tropical_year" title="Tropical year">Tropical year</a></li> <li><a href="Weekday_determination" title="Weekday determination" class="mw-redirect">Weekday determination</a></li> <li><a href="Weekday_names" title="Weekday names" class="mw-redirect">Weekday names</a></li> </ul> </div> </td> </tr> <tr style="height:2px;"> <td></td> </tr> <tr> <th scope="row" class="navbox-group">Archaeology and geology</th> <td class="navbox-list navbox-odd hlist" style="text-align:left;border-left-width:2px;border-left-style:solid;width:100%;padding:0px;"> <div style="padding:0em 0.25em;"> <ul> <li><a href="Dating_methodologies_in_archaeology" title="Dating methodologies in archaeology">Dating methodologies</a></li> <li><a href="Geologic_time_scale" title="Geologic time scale">Geologic time scale</a></li> <li><a href="International_Commission_on_Stratigraphy" title="International Commission on Stratigraphy">International Commission on Stratigraphy</a></li> </ul> </div> </td> </tr> <tr style="height:2px;"> <td></td> </tr> <tr> <th scope="row" class="navbox-group"><a href="Astronomical_chronology" title="Astronomical chronology">Astronomical chronology</a></th> <td class="navbox-list navbox-even hlist" style="text-align:left;border-left-width:2px;border-left-style:solid;width:100%;padding:0px;"> <div style="padding:0em 0.25em;"> <ul> <li><a href="Galactic_year" title="Galactic year">Galactic year</a></li> <li><a href="Nuclear_time_scale" title="Nuclear time scale" class="mw-redirect">Nuclear time scale</a></li> <li><a href="Precession_(astronomy)" title="Precession (astronomy)" class="mw-redirect">Precession</a></li> <li><a href="Sidereal_time" title="Sidereal time">Sidereal time</a></li> </ul> </div> </td> </tr> <tr style="height:2px;"> <td></td> </tr> <tr> <th scope="row" class="navbox-group"><a href="Unit_of_time" title="Unit of time">Units of time</a></th> <td class="navbox-list navbox-odd hlist" style="text-align:left;border-left-width:2px;border-left-style:solid;width:100%;padding:0px;"> <div style="padding:0em 0.25em;"> <ul> <li><a href="Century" title="Century">Century</a></li> <li><a href="Day" title="Day">Day</a></li> <li><a href="Decade" title="Decade">Decade</a></li> <li><a href="Fortnight" title="Fortnight">Fortnight</a></li> <li><a href="Hour" title="Hour">Hour</a></li> <li><a href="Jiffy_(time)" title="Jiffy (time)">Jiffy</a></li> <li><a href="Lustrum" title="Lustrum">Lustrum</a></li> <li><a href="Millennium" title="Millennium">Millennium</a></li> <li><a href="Minute" title="Minute">Minute</a></li> <li><a href="Month" title="Month">Month</a></li> <li><a href="Paksha" title="Paksha">Paksha</a></li> <li><a href="Saeculum" title="Saeculum">Saeculum</a></li> <li><a href="Second" title="Second">Second</a></li> <li><a href="Shake_(unit)" title="Shake (unit)">Shake</a></li> <li><a href="Tide_(time)" title="Tide (time)">Tide</a></li> <li><a href="Week" title="Week">Week</a></li> <li><a href="Year" title="Year">Year</a></li> </ul> </div> </td> </tr> <tr style="height:2px;"> <td></td> </tr> <tr> <th scope="row" class="navbox-group">Related topics</th> <td class="navbox-list navbox-even hlist" style="text-align:left;border-left-width:2px;border-left-style:solid;width:100%;padding:0px;"> <div style="padding:0em 0.25em;"> <ul> <li><a href="Chronology" title="Chronology">Chronology</a></li> <li><a href="Duration_(philosophy)" title="Duration (philosophy)">Duration</a></li> <li><a href="Mental_chronometry" title="Mental chronometry">Mental chronometry</a></li> <li><a href="Metric_time" title="Metric time">Metric time</a></li> <li><a href="System_time" title="System time">System time</a></li> <li><a href="Time_value_of_money" title="Time value of money">Time value of money</a></li> <li><a href="Timekeeper" title="Timekeeper">Timekeeper</a></li> </ul> </div> </td> </tr> </table> </td> </tr> </table> <table cellspacing="0" class="navbox" style="border-spacing:0;"> <tr> <td style="padding:2px;"> <table cellspacing="0" class="nowraplinks collapsible autocollapse navbox-inner" style="border-spacing:0;background:transparent;color:inherit;"> <tr> <th scope="col" class="navbox-title" colspan="2"> <div class="noprint plainlinks hlist navbar mini"> <ul> <li class="nv-view"><a href="Template:Timezones" title="Template:Timezones" class="mw-redirect"><span title="View this template" style=";;background:none transparent;border:none;;">v</span></a></li> <li class="nv-talk"><a href="Template_talk:Timezones" title="Template talk:Timezones" class="mw-redirect"><span title="Discuss this template" style=";;background:none transparent;border:none;;">t</span></a></li> <li class="nv-edit"><a class="external text" href="//en.wikipedia.org/w/index.php?title=Template:Timezones&action=edit"><span title="Edit this template" style=";;background:none transparent;border:none;;">e</span></a></li> </ul> </div> <div style="font-size:110%;"><strong class="selflink">Coordinated Universal Time</strong> (UTC)</div> </th> </tr> <tr style="height:2px;"> <td></td> </tr> <tr> <th scope="row" class="navbox-group"><a href="UTC_offset" title="UTC offset">UTC offset</a> for <a href="Standard_time" title="Standard time">standard time</a> and<br /> <a href="Daylight_saving_time" title="Daylight saving time">Daylight saving time</a> (DST)<br /> <i>Italics: historical only</i></th> <td class="navbox-list navbox-odd hlist" style="text-align:left;border-left-width:2px;border-left-style:solid;width:100%;padding:0px;"> <div style="padding:0em 0.25em;"></div> <table cellspacing="0" class="nowraplinks navbox-subgroup" style="border-spacing:0;"> <tr> <th scope="row" class="navbox-group" style="padding-left:0em;padding-right:0em;;"> <div style="padding:0em 0.75em;"><a href="180th_meridian" title="180th meridian">180°</a> to < <a href="90th_meridian_west" title="90th meridian west">90°W</a></div> </th> <td class="navbox-list navbox-odd" style="text-align:left;border-left-width:2px;border-left-style:solid;width:100%;padding:0px;"> <div style="padding:0em 0.25em;"> <ul> <li><a href="UTC%E2%88%9212:00" title="UTC−12:00">−12:00</a></li> <li><i><a href="/w/index.php?title=UTC%E2%88%9211:30&action=edit&redlink=1" class="new" title="UTC−11:30 (page does not exist)">−11:30</a></i></li> <li><a href="UTC%E2%88%9211:00" title="UTC−11:00">−11:00</a></li> <li><i><a href="UTC%E2%88%9210:30" title="UTC−10:30">−10:30</a></i></li> <li><a href="UTC%E2%88%9210:00" title="UTC−10:00">−10:00</a></li> <li><a href="UTC%E2%88%9209:30" title="UTC−09:30">−09:30</a></li> <li><a href="UTC%E2%88%9209:00" title="UTC−09:00">−09:00</a></li> <li><i><a href="UTC%E2%88%9208:30" title="UTC−08:30">−08:30</a></i></li> <li><a href="UTC%E2%88%9208:00" title="UTC−08:00">−08:00</a></li> <li><a href="UTC%E2%88%9207:00" title="UTC−07:00">−07:00</a></li> </ul> </div> </td> </tr> <tr style="height:2px;"> <td></td> </tr> <tr> <th scope="row" class="navbox-group" style="padding-left:0em;padding-right:0em;;"> <div style="padding:0em 0.75em;"><a href="90th_meridian_west" title="90th meridian west">90°W</a> to < <a href="IERS_Reference_Meridian" title="IERS Reference Meridian">0°</a></div> </th> <td class="navbox-list navbox-even" style="text-align:left;border-left-width:2px;border-left-style:solid;width:100%;padding:0px;"> <div style="padding:0em 0.25em;"> <ul> <li><a href="UTC%E2%88%9206:00" title="UTC−06:00">−06:00</a></li> <li><a href="UTC%E2%88%9205:00" title="UTC−05:00">−05:00</a></li> <li><a href="UTC%E2%88%9204:30" title="UTC−04:30">−04:30</a></li> <li><a href="UTC%E2%88%9204:00" title="UTC−04:00">−04:00</a></li> <li><a href="UTC%E2%88%9203:30" title="UTC−03:30">−03:30</a></li> <li><a href="UTC%E2%88%9203:00" title="UTC−03:00">−03:00</a></li> <li><a href="UTC%E2%88%9202:30" title="UTC−02:30">−02:30</a></li> <li><a href="UTC%E2%88%9202:00" title="UTC−02:00">−02:00</a></li> <li><a href="UTC%E2%88%9201:00" title="UTC−01:00">−01:00</a></li> <li><i><a href="UTC%E2%88%9200:44" title="UTC−00:44">−00:44</a></i></li> <li><i><a href="UTC%E2%88%9200:25" title="UTC−00:25" class="mw-redirect">−00:25</a></i></li> </ul> </div> </td> </tr> <tr style="height:2px;"> <td></td> </tr> <tr> <th scope="row" class="navbox-group" style="padding-left:0em;padding-right:0em;;"> <div style="padding:0em 0.75em;"><a href="IERS_Reference_Meridian" title="IERS Reference Meridian">0°</a> to < <a href="90th_meridian_east" title="90th meridian east">90°E</a></div> </th> <td class="navbox-list navbox-odd" style="text-align:left;border-left-width:2px;border-left-style:solid;width:100%;padding:0px;"> <div style="padding:0em 0.25em;"> <ul> <li><a href="UTC%C2%B100:00" title="UTC±00:00">±00:00</a></li> <li><i><a href="UTC%2B00:20" title="UTC+00:20">+00:20</a></i></li> <li><i><a href="UTC%2B00:30" title="UTC+00:30">+00:30</a></i></li> <li><a href="UTC%2B01:00" title="UTC+01:00">+01:00</a></li> <li><i><a href="UTC%2B01:24" title="UTC+01:24" class="mw-redirect">+01:24</a></i></li> <li><i><a href="UTC%2B01:30" title="UTC+01:30">+01:30</a></i></li> <li><a href="UTC%2B02:00" title="UTC+02:00">+02:00</a></li> <li><i><a href="UTC%2B02:30" title="UTC+02:30">+02:30</a></i></li> <li><a href="UTC%2B03:00" title="UTC+03:00">+03:00</a></li> <li><a href="UTC%2B03:30" title="UTC+03:30">+03:30</a></li> <li><a href="UTC%2B04:00" title="UTC+04:00">+04:00</a></li> <li><a href="UTC%2B04:30" title="UTC+04:30">+04:30</a></li> <li><i><a href="UTC%2B04:51" title="UTC+04:51">+04:51</a></i></li> <li><a href="UTC%2B05:00" title="UTC+05:00">+05:00</a></li> <li><a href="UTC%2B05:30" title="UTC+05:30">+05:30</a></li> <li><i><a href="UTC%2B05:40" title="UTC+05:40">+05:40</a></i></li> <li><a href="UTC%2B05:45" title="UTC+05:45">+05:45</a></li> </ul> </div> </td> </tr> <tr style="height:2px;"> <td></td> </tr> <tr> <th scope="row" class="navbox-group" style="padding-left:0em;padding-right:0em;;"> <div style="padding:0em 0.75em;"><a href="90th_meridian_east" title="90th meridian east">90°E</a> to < <a href="180th_meridian" title="180th meridian">180°</a></div> </th> <td class="navbox-list navbox-even" style="text-align:left;border-left-width:2px;border-left-style:solid;width:100%;padding:0px;"> <div style="padding:0em 0.25em;"> <ul> <li><a href="UTC%2B06:00" title="UTC+06:00">+06:00</a></li> <li><a href="UTC%2B06:30" title="UTC+06:30">+06:30</a></li> <li><a href="UTC%2B07:00" title="UTC+07:00">+07:00</a></li> <li><i><a href="UTC%2B07:20" title="UTC+07:20">+07:20</a></i></li> <li><i><a href="UTC%2B07:30" title="UTC+07:30">+07:30</a></i></li> <li><a href="UTC%2B08:00" title="UTC+08:00">+08:00</a></li> <li><i><a href="UTC%2B08:30" title="UTC+08:30">+08:30</a></i></li> <li><a href="UTC%2B08:45" title="UTC+08:45">+08:45</a></li> <li><a href="UTC%2B09:00" title="UTC+09:00">+09:00</a></li> <li><a href="UTC%2B09:30" title="UTC+09:30">+09:30</a></li> <li><i><a href="UTC%2B09:45" title="UTC+09:45">+09:45</a></i></li> <li><a href="UTC%2B10:00" title="UTC+10:00">+10:00</a></li> <li><a href="UTC%2B10:30" title="UTC+10:30">+10:30</a></li> <li><a href="UTC%2B11:00" title="UTC+11:00">+11:00</a></li> <li><a href="UTC%2B11:30" title="UTC+11:30">+11:30</a></li> </ul> </div> </td> </tr> <tr style="height:2px;"> <td></td> </tr> <tr> <th scope="row" class="navbox-group" style="padding-left:0em;padding-right:0em;;"> <div style="padding:0em 0.75em;">(<a href="180th_meridian" title="180th meridian">180°</a> to < <a href="90th_meridian_west" title="90th meridian west">90°W</a>)</div> </th> <td class="navbox-list navbox-odd" style="text-align:left;border-left-width:2px;border-left-style:solid;width:100%;padding:0px;"> <div style="padding:0em 0.25em;"> <ul> <li><a href="UTC%2B12:00" title="UTC+12:00">+12:00</a></li> <li><a href="UTC%2B12:45" title="UTC+12:45">+12:45</a></li> <li><a href="UTC%2B13:00" title="UTC+13:00">+13:00</a></li> <li><a href="UTC%2B13:45" title="UTC+13:45">+13:45</a></li> <li><a href="UTC%2B14:00" title="UTC+14:00">+14:00</a></li> </ul> </div> </td> </tr> </table> </td> </tr> <tr style="height:2px;"> <td></td> </tr> <tr> <th scope="row" class="navbox-group"><a href="Time_zone" title="Time zone">Time zone</a> data sources</th> <td class="navbox-list navbox-even hlist" style="text-align:left;border-left-width:2px;border-left-style:solid;width:100%;padding:0px;"> <div style="padding:0em 0.25em;"><a href="Tz_database" title="Tz database">tz database</a></div> </td> </tr> <tr style="height:2px;"> <td></td> </tr> <tr> <th scope="row" class="navbox-group"><a href="Lists_of_time_zones" title="Lists of time zones">Lists of time zones</a></th> <td class="navbox-list navbox-odd hlist" style="text-align:left;border-left-width:2px;border-left-style:solid;width:100%;padding:0px;"> <div style="padding:0em 0.25em;"> <ul> <li><a href="List_of_time_zones_by_country" title="List of time zones by country">Time zones by country</a></li> <li><a href="List_of_time_zones_by_UTC_offset" title="List of time zones by UTC offset" class="mw-redirect">Time zones by UTC offset</a></li> <li><a href="List_of_tz_database_time_zones" title="List of tz database time zones">tz database time zones</a></li> <li><a href="List_of_military_time_zones" title="List of military time zones">Military time zones</a></li> <li><a href="List_of_time_zone_abbreviations" title="List of time zone abbreviations">Time zone abbreviations</a></li> <li><a href="Daylight_saving_time_by_region_and_country" title="Daylight saving time by region and country" class="mw-redirect">Daylight saving 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