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{{Redirect2|UT1|UT|other uses of "UT1"|UT1 (disambiguation)|other uses of "UT"|UT (disambiguation)}}
This is a preview for the new '''MathML rendering mode''' (with SVG fallback), which is availble in production for registered users.
'''Universal Time''' ('''UT''') is a [[time standard]] based on the rotation of the Earth. It is a modern continuation of [[Greenwich Mean Time]] (GMT), i.e., the [[mean solar time]] on the [[Prime Meridian]] at [[Royal Observatory, Greenwich|Greenwich]], and GMT is sometimes used loosely as a synonym for [[UTC]]. In fact, the expression "Universal Time" is ambiguous, as there are several versions of it, the most commonly used being UTC and UT1 (see below). All of these versions of UT are based on the rotation of the Earth in relation to distant celestial objects ([[star]]s and [[quasar]]s), but with a scaling factor and other adjustments to make them closer to [[solar time]].


==Universal Time and standard time==
If you would like use the '''MathML''' rendering mode, you need a wikipedia user account that can be registered here [[https://en.wikipedia.org/wiki/Special:UserLogin/signup]]
Prior to the introduction of [[standard time]], each municipality throughout the civilized world set its official clock, if it had one, according to the local position of the Sun (see [[solar time]]). This served adequately until the introduction of the [[steam engine]], the telegraph, and [[railroad|rail]] travel, which made it possible to travel fast enough over long distances to require almost constant re-setting of [[clock|timepiece]]s as a [[train]] progressed in its daily run through several towns. Standard time, where all clocks in a large region are set to the same time, was established to solve this problem. [[marine chronometer|Chronometer]]s or [[telegraphy]] were used to synchronize these clocks.{{sfn|Howse|1997|loc=ch. 4}}
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[[Image:Standard time zones of the world.png|500px|thumb|right|Standard time zones of the world since September 20, 2011, instructions for converting UTC to or from local times are on the bottom, using addition or subtraction]]
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Standard time, as originally proposed by Scottish-Canadian Sir [[Sandford Fleming]] in 1879, divided the world into twenty-four [[time zone]]s, each one covering 15 degrees of longitude. All clocks within each zone would be set to the same time as the others, but differed by one hour from those in the neighboring zones. The local time at the [[Royal Greenwich Observatory]] in Greenwich, England was chosen as standard at the 1884 [[International Meridian Conference]], leading to the widespread use of Greenwich Mean Time to set local clocks. This location was chosen because by 1884 two-thirds of all [[nautical chart]]s and [[map]]s already used it as their [[prime meridian]].{{sfn|Howse|1997|loc=ch. 5}} The conference did not adopt Fleming's time zones because they were outside the purpose for which it was called, which was to choose a basis for universal time (as well as a prime meridian).
'''MathML'''
:<math forcemathmode="mathml">E=mc^2</math>


During the period between 1848 to 1972, all of the major countries adopted time zones based on the Greenwich meridian.{{sfn|Howse|1997|loc=ch. 6}}
<!--'''PNG'''  (currently default in production)
:<math forcemathmode="png">E=mc^2</math>


In 1935, the term ''Universal Time'' was recommended by the [[International Astronomical Union]] as a more precise term than [[Greenwich Mean Time]], because GMT could refer to either an [[astronomical day]] starting at noon or a civil day starting at midnight.{{sfn|McCarthy|Seidelmann|2009|p=14}} The term ''Greenwich Mean Time'' persists, however, in common usage to this day in reference to [[civil time]]keeping.
'''source'''
:<math forcemathmode="source">E=mc^2</math> -->


==Measurement==
<span style="color: red">Follow this [https://en.wikipedia.org/wiki/Special:Preferences#mw-prefsection-rendering link] to change your Math rendering settings.</span> You can also add a [https://en.wikipedia.org/wiki/Special:Preferences#mw-prefsection-rendering-skin Custom CSS] to force the MathML/SVG rendering or select different font families. See [https://www.mediawiki.org/wiki/Extension:Math#CSS_for_the_MathML_with_SVG_fallback_mode these examples].
Based on the rotation of the Earth, time can be measured by observing celestial bodies crossing the meridian every day. Astronomers found that it was more accurate to establish time by observing [[star]]s as they crossed a meridian rather than by observing the position of the [[Sun]] in the sky. Nowadays, UT in relation to [[International Atomic Time]] (TAI) is determined by [[Very Long Baseline Interferometry]] (VLBI) observations of distant [[quasar]]s, a method which can determine UT1 to within 4 milliseconds.{{sfn|McCarthy|Seidelmann|2009|pages=68&ndash;9}}{{sfn|Urban|Seidelmann|2013|page=175}}


[[File:Universal Dial Plate or Times of all Nations, 1854.jpg|thumb|left|An 1853 "Universal Dial Plate" showing the relative times of "all nations" before the adoption of universal time]]The rotation of the Earth and UT are monitored by the [[International Earth Rotation and Reference Systems Service]] (IERS). The [[International Astronomical Union]] also is involved in setting standards, but the final arbiter of broadcast standards is the [[International Telecommunication Union]] or ITU.{{sfn|McCarthy|Seidelmann|2009|loc=Ch. 18}}
==Demos==


The rotation of the Earth is somewhat irregular, and is very gradually slowing due to [[tidal acceleration]]. Furthermore, the length of the second was determined from observations of the [[Moon]] between 1750 and 1890. All of these factors cause the [[mean solar day]], on the average, to be slightly longer than the nominal 86,400 [[SI]] seconds, the traditional number of seconds per day. As UT is slightly irregular in its rate, astronomers introduced [[Ephemeris Time]], which has since been replaced by [[Terrestrial Time]] (TT). Because Universal Time is synchronous with night and day, and that more precise atomic-frequency standards drift away from this, however, UT is still used to produce a correction (called a [[leap second]]) to atomic time, in order to obtain a broadcast form of [[civil time]] that carries atomic frequency. Thus, civil broadcast standards for time and frequency usually follow [[International Atomic Time]] closely, but occasionally change discontinuously (or "leap") in order to prevent them from drifting too far from [[mean solar time]].
Here are some [https://commons.wikimedia.org/w/index.php?title=Special:ListFiles/Frederic.wang demos]:


[[Barycentric Dynamical Time]] (TDB), a form of atomic time, is now used in the construction of the ephemerides of the [[planet]]s and other solar system objects, for two main reasons.<ref>{{harvnb|Urban|Seidelmann|2013|page= 7}}. Strictly speaking, a major producer of ephemerides, the [[Jet Propulsion Laboratory]], uses a time scale they derive, T<sub>eph</sub>, which is functionally equivalent to TDB.</ref> First, these ephemerides are tied to optical and [[radar]] observations of planetary motion, and the TDB time scale is fitted so that [[Newton's laws of motion]], with corrections for [[general relativity]], are followed. Next, the time scales based on Earth's rotation are not uniform and therefore, are not suitable for predicting the motion of bodies in our solar system.


==Versions==
* accessibility:
There are several versions of Universal Time:
** Safari + VoiceOver: [https://commons.wikimedia.org/wiki/File:VoiceOver-Mac-Safari.ogv video only], [[File:Voiceover-mathml-example-1.wav|thumb|Voiceover-mathml-example-1]], [[File:Voiceover-mathml-example-2.wav|thumb|Voiceover-mathml-example-2]], [[File:Voiceover-mathml-example-3.wav|thumb|Voiceover-mathml-example-3]], [[File:Voiceover-mathml-example-4.wav|thumb|Voiceover-mathml-example-4]], [[File:Voiceover-mathml-example-5.wav|thumb|Voiceover-mathml-example-5]], [[File:Voiceover-mathml-example-6.wav|thumb|Voiceover-mathml-example-6]], [[File:Voiceover-mathml-example-7.wav|thumb|Voiceover-mathml-example-7]]
* '''UT0''' is Universal Time determined at an observatory by observing the diurnal motion of stars or extragalactic radio sources, and also from ranging observations of the Moon and artificial Earth satellites. The location of the observatory is considered to have fixed coordinates in a terrestrial reference frame (such as the [[International Terrestrial Reference Frame]]) but the position of the rotational axis of the Earth wanders over the surface of the Earth; this is known as [[polar motion]]. UT0 does not contain any correction for polar motion. The difference between UT0 and UT1 is on the order of a few tens of milliseconds. The designation UT0 is no longer in common use.{{sfn|Urban|Seidelmann|2013|page=81}}
** [https://commons.wikimedia.org/wiki/File:MathPlayer-Audio-Windows7-InternetExplorer.ogg Internet Explorer + MathPlayer (audio)]
* '''UT1''' is the principal form of Universal Time. While conceptually it is mean solar time at 0° longitude, precise measurements of the Sun are difficult. Hence, it is computed from observations of distant [[quasar]]s using long baseline interferometry, laser ranging of the [[Moon]] and artificial satellites, as well as the determination of [[Global Positioning System|GPS]] satellite orbits. UT1 is the same everywhere on Earth, and is proportional to the rotation angle of the Earth with respect to distant quasars, specifically, the [[International Celestial Reference Frame]] (ICRF), neglecting some small adjustments. The observations allow the determination of a measure of the Earth's angle with respect to the ICRF, called the Earth Rotation Angle (ERA, which serves as a modern replacement for [[Greenwich Sidereal Time|Greenwich Mean Sidereal Time]]). UT1 is required to follow the relationship
** [https://commons.wikimedia.org/wiki/File:MathPlayer-SynchronizedHighlighting-WIndows7-InternetExplorer.png Internet Explorer + MathPlayer (synchronized highlighting)]
::ERA = 2π(0.7790572732640 + 1.00273781191135448''T<sub>u</sub>'') radians
** [https://commons.wikimedia.org/wiki/File:MathPlayer-Braille-Windows7-InternetExplorer.png Internet Explorer + MathPlayer (braille)]
::where ''T<sub>u</sub>'' = (Julian UT1 date - 2451545.0){{Sfn|McCarthy|Seidelmann|2009|pp= 15&ndash;17, 62&ndash;64, 68&ndash;69, 76}}
** NVDA+MathPlayer: [[File:Nvda-mathml-example-1.wav|thumb|Nvda-mathml-example-1]], [[File:Nvda-mathml-example-2.wav|thumb|Nvda-mathml-example-2]], [[File:Nvda-mathml-example-3.wav|thumb|Nvda-mathml-example-3]], [[File:Nvda-mathml-example-4.wav|thumb|Nvda-mathml-example-4]], [[File:Nvda-mathml-example-5.wav|thumb|Nvda-mathml-example-5]], [[File:Nvda-mathml-example-6.wav|thumb|Nvda-mathml-example-6]], [[File:Nvda-mathml-example-7.wav|thumb|Nvda-mathml-example-7]].
* '''UT1R''' is a smoothed version of UT1, filtering out periodic variations due to tides. It includes 62 smoothing terms, with periods ranging from 5.6 days to 18.6 years.{{sfn|IERS|n.d.}}
** Orca: There is ongoing work, but no support at all at the moment [[File:Orca-mathml-example-1.wav|thumb|Orca-mathml-example-1]], [[File:Orca-mathml-example-2.wav|thumb|Orca-mathml-example-2]], [[File:Orca-mathml-example-3.wav|thumb|Orca-mathml-example-3]], [[File:Orca-mathml-example-4.wav|thumb|Orca-mathml-example-4]], [[File:Orca-mathml-example-5.wav|thumb|Orca-mathml-example-5]], [[File:Orca-mathml-example-6.wav|thumb|Orca-mathml-example-6]], [[File:Orca-mathml-example-7.wav|thumb|Orca-mathml-example-7]].
* '''UT2''' is a smoothed version of UT1, filtering out periodic seasonal variations. It is mostly of historic interest and rarely used anymore. It is defined by
** From our testing, ChromeVox and JAWS are not able to read the formulas generated by the MathML mode.
::<math>UT2 = UT1 + 0.022\cdot\sin(2\pi t) - 0.012\cdot\cos(2\pi t) - 0.006\cdot\sin(4\pi t) + 0.007\cdot\cos(4\pi t)\;\mbox{seconds}</math>
::where ''t'' is the time as fraction of the [[Year#Besselian year|Besselian year]].<ref>[http://www.usno.navy.mil/USNO/earth-orientation/eo-info/general/date-time-def Date and Time Definitions] n.d.</ref>
* '''UT2R''' is a smoothed version of UT1, incorporating both the seasonal corrections of UT2 and the tidal corrections of UT1R. It is the most smoothed form of Universal Time. Its non-uniformities reveal the unpredictable components of Earth rotation due to atmospheric weather, [[plate tectonics]] and currents in the interior of the Earth.{{citation needed|date=March 2013}}
* '''[[Coordinated Universal Time|UTC]]''' (Coordinated Universal Time) is an atomic timescale that approximates UT1. It is the international standard on which civil time is based. It ticks [[SI]] seconds, in step with [[International Atomic Time|TAI]]. It usually has 86,400 SI seconds per day but is kept within 0.9 seconds of UT1 by the introduction of occasional intercalary [[leap second]]s. {{As of|2013}}, these leaps have always been positive (the days which contained a leap second were 86,401 seconds long). Whenever a level of [[accuracy]] better than one second is not required, UTC can be used as an approximation of UT1. The difference between UT1 and UTC is known as [[DUT1]].{{sfn|McCarthy|Seidelmann|2009|loc=Ch. 14}}


==Adoption in various countries==
==Test pages ==
The table shows the dates of adoption of time zones based on the Greenwich meridian, including half-hour zones.
{|
! width=60 align=left | Year
!  align=left | Countries <ref>
{{harvnb|Howse|1980|pp=154&ndash;5}}. Names have not been updated.
</ref>
! width=60 align=left | Year
! align=left | Countries
! width=60 align=left | Year
! align=left | Countries
|-
| 1848 || Great Britain <ref>legal in 1880</ref>
| 1906 || India,<ref>except Calcutta</ref> Ceylon, Seychelles
| 1930 || Bermuda
|-
| 1879 || Sweden
| 1907 || Mauritius, Chagos
| 1931 || Paraguay
|-
| 1883 || Canada, USA <ref>legal in 1918</ref>
| 1908 || Faroe Is., Iceland
| 1932 || Barbados, Bolivia, Dutch East Indies
|-
| 1884 || Serbia
| 1911 || France, Algeria, Tunis,<ref>and many French overseas possessions,</ref> British West Indies
| 1934 || Nicaragua, E. Niger
|-
| 1888 || Japan
| 1912 || Portugal,<ref>and overseas possessions,</ref> other French possessions, Samoa, Hawaii, Midway and Guam, Timor, Bismarck Arch., Jamaica, Bahamas Is.
| By 1936 || Labrador, Norfolk I.
|-
| 1892 || Belgium, Holland,<ref>Legal time reverted to Amsterdam time 1909; to Central European Time 1940,</ref> S. Africa<ref>except Natal</ref>
| 1913 || British Honduras, Dahomey
| By 1937 || Cayman Is., Curaçao, Ecuador, Newfoundland
|-
| 1893 || Italy, Germany, Austria-Hungary (railways)
| 1914 || Albania, Brazil, Colombia
| By 1939 || Fernando Po, Persia
|-
| 1894 || Bulgaria, Denmark, Norway, Switzerland, Romania, Turkey (railways)
| 1916 || Greece, Ireland, Poland, Turkey
| 1940 || The Netherlands
|-
| 1895 || Australia, New Zealand, Natal
| 1917 || Iraq, Palestine
| By 1940 || Lord Howe I.
|-
| 1896 || Formosa (Taiwan)
| 1918 || Guatemala, Panama, Gambia, Gold Coast
| By 1948 || Aden, Ascension I., Bahrein, British Somaliland, Calcutta, Dutch Guiana, Kenya, Federated Malay States, Oman, Straits Settlements, St. Helena, Uganda, Zanzibar
|-
| 1899 || Puerto Rico, Philippines
| 1919 || Latvia, Nigeria
| By 1953 || Raratonga, South Georgia
|-
| 1900 || Sweden, Egypt, Alaska
| 1920 || Argentine, Uruguay, Burma, Siam
| By 1954 || Cook Is.
|-
| 1901 || Spain
| 1921 || Finland, Estonia, Costa Rica
| By 1959 || Maldive I. Republic
|-
| 1902 || Mozambique, Rhodesia
| 1922 || Mexico
| By 1961 || Friendly Is., Tonga Is.
|-
| 1903 || Ts'intao, Tientsin
| 1924 || Java, USSR
| By 1962 || Saudi Arabia
|-
| 1904 || China Coast, Korea, Manchuria, N. Borneo
| 1925 || Cuba
| By 1964 || Niue Is.
|-
| 1905 || Chile
| 1928 || China Inland
| 1972 || Liberia
|}


Apart from [[Nepal Time Zone]] (+5h 45m) and Chatham Isle (+12h 45m), all countries were keeping time within an even hour or half-hour of Greenwich.
To test the '''MathML''', '''PNG''', and '''source''' rendering modes, please go to one of the following test pages:
*[[Displaystyle]]
*[[MathAxisAlignment]]
*[[Styling]]
*[[Linebreaking]]
*[[Unique Ids]]
*[[Help:Formula]]


==See also==
*[[Inputtypes|Inputtypes (private Wikis only)]]
*[[List of international common standards]]
*[[Url2Image|Url2Image (private Wikis only)]]
*[[Unix time]]
==Bug reporting==
 
If you find any bugs, please report them at [https://bugzilla.wikimedia.org/enter_bug.cgi?product=MediaWiki%20extensions&component=Math&version=master&short_desc=Math-preview%20rendering%20problem Bugzilla], or write an email to math_bugs (at) ckurs (dot) de .
==Notes==
{{reflist}}
 
==References==
*{{cite web|url=http://www.usno.navy.mil/USNO/earth-orientation/eo-info/general/date-time-def|title=Date and Time Definitions|publisher=United States Naval Observatory|ref=harv | accessdate = 3 March 2013}}
*{{Anchor|ERC}}{{cite web|title= Earth Rotation Variations Due to Zonal Tides | publisher = Earth Orientation Center | location = Paris | accessdate = 2 October 2011 | url = http://hpiers.obspm.fr/eop-pc/models/UT1/UT1R_tab.html |ref=harv}}
*{{cite book|authorlink=Peter Galison |last=Galison|first=Peter |title=Einstein's clocks, Poincaré's maps: Empires of time|location=New York|publisher=W.W. Norton & Co|year=2003|isbn=0-393-02001-0|ref=harv}} Discusses the history of time standardization.
*{{cite book|title=Greenwich Time and the discovery of the longitude|first=Derek|last=Howse|year=1980|pages=154–5|publisher=Oxford Univ Press |ref=harv}}. Names have not been updated.
*{{cite book | last = Howse | first = Derek | title = Greenwich Time and the Longitude | year = 1997 | publisher = Phillip Wilson | isbn=0-85667-468-0 |ref=harv}}
*{{cite journal|first=Dennis D.|last=McCarthy| authorlink1=Dennis McCarthy (scientist)|url=http://www.cl.cam.ac.uk/~mgk25/volatile/astronomical-time.pdf|title=Astronomical Time|journal=Proceedings of the IEEE |volume=79 |issue=7|date=July 1991 |pages=915–920|doi=10.1109/5.84967 |ref=harv}}
*{{cite book | authorlink1=Dennis McCarthy (scientist)| last1 = McCarthy | first1=Dennis| last2= Seidelmann| first2= P. Kenneth| year= 2009| title=TIME&mdash;From Earth Rotation to Atomic Physics| place= Weinheim | publisher=Wiley-VCH Verlag GmbH & Co. KGaA. isbn=978-3-527-40780-4 |ref=harv}}
*{{cite book|last=O'Malley|first=Michael| title=Keeping watch: A history of American time|location=Washington DC| publisher=Smithsonian |year=1996| isbn=1-56098-672-7 |ref=harv}}
*{{cite book|last=Seidelmann|first=P. Kenneth|title=Explanatory supplement to the Astronomical Almanac|location=Mill Valley, California|publisher=University Science Books|year=1992|isbn=0-935702-68-7 |ref=harv}}
*{{cite book| editor1-last = Urban |editor1-first = Sean | editor2-last = Seidelmann | editor2-first = P. Kenneth | year = 2013 | title = Explanatory Supplement to the Astronomical Almanac | edition = 3rd | location = Mill Valley, California | publisher = University Science Books| ref=harv}}
*{{cite web|title=UT1R| url= http://hpiers.obspm.fr/eop-pc/models/UT1/UT1R_tab.html | publisher = International Earth Rotation and Reference System Service | accessdate = 6 March 2013 |ref={{harvid|IERS|n.d.}}}}
*{{cite web|title=What is TT?|url=http://aa.usno.navy.mil/faq/docs/TT.php/?searchterm=terrestrial_time|work=Naval Oceanography Portal|publisher=[[United States Naval Observatory]] | accessdate= 3 March 2013}}
{{FS1037C}}
 
==External links==
*[http://www.randomhouse.ca/catalog/display.pperl?isbn=9780676974737 ''Time Lord''] by Clark Blaise: a biography of Stanford Fleming and the idea of standard time
 
{{Time Topics}}
{{Time measurement and standards}}
 
[[Category:1883 in Canada]]
[[Category:Time scales]]
[[Category:Scottish inventions]]

Latest revision as of 23:52, 15 September 2019

This is a preview for the new MathML rendering mode (with SVG fallback), which is availble in production for registered users.

If you would like use the MathML rendering mode, you need a wikipedia user account that can be registered here [[1]]

  • Only registered users will be able to execute this rendering mode.
  • Note: you need not enter a email address (nor any other private information). Please do not use a password that you use elsewhere.

Registered users will be able to choose between the following three rendering modes:

MathML


Follow this link to change your Math rendering settings. You can also add a Custom CSS to force the MathML/SVG rendering or select different font families. See these examples.

Demos

Here are some demos:


Test pages

To test the MathML, PNG, and source rendering modes, please go to one of the following test pages:

Bug reporting

If you find any bugs, please report them at Bugzilla, or write an email to math_bugs (at) ckurs (dot) de .

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