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"UT1" redirects here. For other uses, see UT1 (disambiguation).
Not to be confused with Coordinated Universal Time.

Universal Time (UT or UT1) is a time standard based on Earth's rotation. While originally it was mean solar time at 0° longitude, precise measurements of the Sun are difficult. Therefore, UT1 is computed from a measure of the Earth's angle with respect to the International Celestial Reference Frame (ICRF), called the Earth Rotation Angle (ERA, which serves as a modern replacement for Greenwich Mean Sidereal Time). UT1 is the same everywhere on Earth. UT1 is required to follow the relationship

ERA = 2π(0.7790572732640 + 1.00273781191135448Tu) radians

where Tu = (Julian UT1 date - 2451545.0).

Contents

Prior to the introduction of standard time, each municipality throughout the clock-using 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 rail travel in Britain, which made it possible to travel fast enough over long distances to require continuous re-setting of timepieces as a train progressed in its daily run through several towns. Starting in 1847, Britain established Greenwich Mean Time, the mean solar time on the Prime Meridian at Greenwich, England, to solve this problem: all clocks in Britain were set to this time regardless of local solar noon. Using telescopes, GMT was calibrated to the mean solar time at the Royal Observatory, Greenwich in the UK. Chronometers or telegraphy were used to synchronize these clocks.

Standard time zones of the world (February 2021). The number at the bottom of each zone specifies the number of hours to add to UTC to convert it to the local time.

As international commerce increased, the need for an international standard of time measurement emerged. Several authors proposed a "universal" or "cosmic" time (see Time zone § Worldwide time zones). The development of Universal Time began at the International Meridian Conference. At the end of this conference, on 22 October 1884, the recommended base reference for world time, the "universal day", was announced to be the local mean solar time at the Royal Observatory in Greenwich, counted from 0 hours at Greenwich mean midnight. This agreed with the civil Greenwich Mean Time used on the island of Great Britain since 1847. In contrast, astronomical GMT began at mean noon, i.e. astronomical day X began at noon of civil day X. The purpose of this was to keep one night's observations under one date. The civil system was adopted as of 0 hours (civil) 1 January 1925. Nautical GMT began 24 hours before astronomical GMT, at least until 1805 in the Royal Navy, but persisted much later elsewhere because it was mentioned at the 1884 conference. Greenwich was chosen because by 1884 two-thirds of all nautical charts and maps already used it as their prime meridian.

During the period between 1848 and 1972, all of the major countries adopted time zones based on the Greenwich meridian.

In 1928, the term Universal Time (UT) was introduced by the International Astronomical Union to refer to GMT, with the day starting at midnight. The term was recommended 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. As the general public had always begun the day at midnight, the timescale continued to be presented to them as Greenwich Mean Time.

When introduced, broadcast time signals were based on UT, and hence on the rotation of the Earth. In 1955 the BIH adopted a proposal by William Markowitz, effective January 1, 1956, dividing UT into UT0 (UT as formerly computed), UT1 (UT0 corrected for polar motion) and UT2 (UT0 corrected for polar motion and seasonal variation). UT1 was the version sufficient for "many astronomical and geodetic applications", while UT2 was to be broadcast over radio to the public.

UT0 and UT2 soon became irrelevant due to the introduction of Coordinated Universal Time (UTC). Starting in 1956, WWV broadcast an atomic clock signal stepped by 20ms increments to bring it into agreement with UT1. The up to 20ms error from UT1 is on the same order of magnitude as the differences between UT0, UT1, and UT2. By 1960, the U.S. Naval Observatory, the Royal Greenwich Observatory, and the UK National Physical Laboratory had developed UTC, with a similar stepping approach. The 1960 URSI meeting recommended that all time services should follow the lead of the UK and US and broadcast coordinated time using a frequency offset from cesium aimed to match the predicted progression of UT2 with occasional steps as needed. Starting January 1, 1972, UTC was defined to follow UT1 within 0.9 seconds rather than UT2, marking the decline of UT2.

Modern civil time generally follows UTC. In some countries, the term Greenwich Mean Time persists in common usage to this day in reference to UT1, in civil timekeeping as well as in astronomical almanacs and other references. 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.

Adoption in various countries

The table shows the dates of adoption of time zones based on the Greenwich meridian, including half-hour zones.

Year Countries
1847 Great Britain
1880 Ireland (entire island)
1883 Canada, USA
1884 Serbia
1888 Japan
1892 Belgium, the Netherlands, S. Africa
1893 Italy, Germany, Austria-Hungary (railways)
1894 Bulgaria, Denmark, Norway, Switzerland, Romania, Turkey (railways)
1895 Australia, New Zealand, Natal
1896 Formosa (Taiwan)
1899 Puerto Rico, Philippines
1900 Sweden, Egypt, Alaska
1901 Spain
1902 Mozambique, Rhodesia
1903 Ts'intao, Tientsin
1904 China Coast, Korea, Manchuria, N. Borneo
1905 Chile
1906 India (except Calcutta), Ceylon (Sri Lanka), Seychelles
1907 Mauritius, Chagos
1908 Faroe Is., Iceland
1911 France, Algeria, Tunis, many French overseas possessions, British West Indies
1912 Portugal and overseas possessions, other French possessions, Samoa, Hawaii, Midway and Guam, Timor, Bismarck Arch., Jamaica, Bahamas Is.
1913 British Honduras, Dahomey
1914 Albania, Brazil, Colombia
1916 Greece, Poland, Turkey
Year Countries
1917 Iraq, Palestine
1918 Guatemala, Panama, Gambia, Gold Coast
1919 Latvia, Nigeria
1920 Argentina, Uruguay, Burma, Siam
1921 Finland, Estonia, Costa Rica
1922 Mexico
1924 Java, USSR
1925 Cuba
1928 China Inland
1930 Bermuda
1931 Paraguay
1932 Barbados, Bolivia, Dutch East Indies
1934 Nicaragua, E. Niger
By 1936 Labrador, Norfolk I.
By 1937 Cayman Is., Curaçao, Ecuador, Newfoundland
By 1939 Fernando Po, Persia
By 1940 Lord Howe I.
1940 The Netherlands
By 1948 Aden, Ascension I., Bahrain, British Somaliland, Calcutta, Dutch Guiana, Kenya, Federated Malay States, Oman, Straits Settlements, St. Helena, Uganda, Zanzibar
By 1953 Raratonga, South Georgia
By 1954 Cook Is.
By 1959 Maldive I. Republic
By 1961 Friendly Is., Tonga Is.
By 1962 Saudi Arabia
By 1964 Niue Is.
1972 Liberia

Apart from Nepal Standard Time (UTC+05:45), the Chatham Standard Time Zone (UTC+12:45) used in New Zealand's Chatham Islands and the officially unsanctioned Central Western Time Zone (UTC+8:45) used in Eucla, Western Australia and surrounding areas, all time zones in use are defined by an offset from UTC that is a multiple of half an hour, and in most cases a multiple of an hour.

Historically, Universal Time was computed from observing the position of the Sun in the sky. But astronomers found that it was more accurate to measure the rotation of the Earth by observing stars as they crossed the meridian each day. Nowadays, UT in relation to International Atomic Time (TAI) is determined by Very Long Baseline Interferometry (VLBI) observations of the positions of distant celestial objects (stars and quasars), a method which can determine UT1 to within 15 microseconds or better. Additional data sources include laser ranging of the Moon and artificial satellites, as well as the determination of GPS satellite orbits.

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.

The rotation of the Earth is somewhat irregular and also 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 modern 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 thus slightly irregular in its rate, astronomers introduced Ephemeris Time, which has since been replaced by Terrestrial Time (TT). Because Universal Time is determined by the Earth's rotation, which drifts away from more precise atomic-frequency standards, an adjustment (called a leap second) to this atomic time is needed since (as of 2019[update]) 'broadcast time' remains broadly synchronised with solar time. Thus, the civil broadcast standard for time and frequency usually follows International Atomic Time closely, but occasionally step (or "leap") in order to prevent them from drifting too far from mean solar time.

Barycentric Dynamical Time (TDB), a form of atomic time, is now used in the construction of the ephemerides of the planets and other solar system objects, for two main reasons. 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.

UT1 is the principal form of Universal Time. However, there are also several other infrequently-used time standards that are referred to as Universal Time, which agree within 0.03 seconds with UT1:

  • 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.
  • 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. UT1R is still in use in the technical literature but rarely used elsewhere.
  • 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
U T 2 = U T 1 + 0.022 sin ( 2 π t ) 0.012 cos ( 2 π t ) 0.006 sin ( 4 π t ) + 0.007 cos ( 4 π t ) seconds {\displaystyle 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}}}
where t is the time as fraction of the Besselian year.
  1. Despite its mandatory use on Great Western Railway stations from 1847 and thus widespread informal adoption, it was not until the Statutes (Definition of Time) Act 1880 that it became law.
  2. Voting took place on 13 October.
  3. legal in 1918 (Standard Time Act)
  4. Legal time reverted to Amsterdam time 1909; to Central European Time 1940,
  5. except Natal
  6. 24 hours of 60 minutes of 60 seconds.
  7. Continuation of this principle is under active debate in standards bodies. See Leap second#Future of leap seconds
  1. Seago, John H.; Seidelmann, P. Kenneth; Allen, Steve (5–7 October 2011). "Legislative Specifications for Coordinating with Universal Time"(PDF). Decoupling civil timekeeping from Earth rotation: proceedings of a colloquium exploring implications of redefining Coordinated Universal Time (UTC). Analytical Graphics, Inc., Exton, Pa.: American Astronautical Society. ISBN 978-0877035763.
  2. McCarthy & Seidelmann 2009, pp. 15–17, 62–64, 68–69, 76.
  3. Harry Rosehill (31 May 2017). "Why Britain Sets Its Clocks To London". Londonist.com. Retrieved25 November 2019.
  4. Howse 1997, ch. 4.
  5. Howse 1997, pp. 12, 137.
  6. Howse 1997, p. 133–137.
  7. Howse 1997, ch. 6.
  8. McCarthy & Seidelmann 2009, pp. 10–11.
  9. McCarthy & Seidelmann 2009, p. 14.
  10. Dick, Steven; McCarthy, Dennis (15 December 2018). "William Markowitz Obituary". U.S. Naval Observatory. Archived from the original on 2018-12-15.
  11. "On the Determination of Universal Time by the Time Services according to the Decisions of the General Assembly of the I.A.U. in Dublin"(PDF). Bulletin Horaire. July–August 1955. Archived(PDF) from the original on 2021-12-15.
  12. Arias, Guinot & Quinn 2003.
  13. Allen, Steve. "Seasonal Variation of Earth Rotation". www.ucolick.org.
  14. McCarthy & Seidelmann 2009, Ch. 14.
  15. Howse 1980, pp. 154–5. Names have not been updated.
  16. HM Nautical Almanac Office 2015.
  17. McCarthy & Seidelmann 2009, pp. 68–9.
  18. Urban & Seidelmann 2013, p. 175.
  19. McCarthy & Seidelmann 2009, Ch. 18.
  20. Urban & Seidelmann 2013, p. 7. Strictly speaking, a major producer of ephemerides, the Jet Propulsion Laboratory, uses a time scale they derive, Teph, which is functionally equivalent to TDB.
  21. Schlyter, Paul. "Time Scales: UT1, UTC, TAI, ET, TT, GPS time". stjarnhimlen.se. Retrieved24 May 2022.
  22. Urban & Seidelmann 2013, p. 81.
  23. IERS n.d.
  24. "A Brief Note on Time Systems". www.astronomy.ohio-state.edu. Retrieved24 May 2022.
  25. "Common Units and Conversions in Earth Orientation". IERS Rapid Service / Prediction Center, U.S. Naval Observatory.

This article incorporates public domain material from the General Services Administration document: "Federal Standard 1037C".

  • Time Lord by Clark Blaise: a biography of Sanford Fleming and the idea of standard time

Universal Time Article Talk Language Watch Edit 160 160 Redirected from Universal time UT1 redirects here For other uses see UT1 disambiguation Not to be confused with Coordinated Universal Time Universal Time UT or UT1 is a time standard based on Earth s rotation 1 While originally it was mean solar time at 0 longitude precise measurements of the Sun are difficult Therefore UT1 is computed from a measure of the Earth s angle with respect to the International Celestial Reference Frame ICRF called the Earth Rotation Angle ERA which serves as a modern replacement for Greenwich Mean Sidereal Time UT1 is the same everywhere on Earth UT1 is required to follow the relationship ERA 2p 0 7790572732640 1 00273781191135448Tu radians where Tu Julian UT1 date 2451545 0 2 Contents 1 History 1 1 Adoption in various countries 2 Measurement 3 Alternate versions 4 See also 5 Notes 6 Citations 7 References 8 External linksHistoryPrior to the introduction of standard time each municipality throughout the clock using 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 rail travel in Britain which made it possible to travel fast enough over long distances to require continuous re setting of timepieces as a train progressed in its daily run through several towns Starting in 1847 Britain established Greenwich Mean Time the mean solar time on the Prime Meridian at Greenwich England to solve this problem all clocks in Britain were set to this time regardless of local solar noon a Using telescopes GMT was calibrated to the mean solar time at the Royal Observatory Greenwich in the UK Chronometers or telegraphy were used to synchronize these clocks 4 Standard time zones of the world February 2021 The number at the bottom of each zone specifies the number of hours to add to UTC to convert it to the local time As international commerce increased the need for an international standard of time measurement emerged Several authors proposed a universal or cosmic time see Time zone Worldwide time zones The development of Universal Time began at the International Meridian Conference At the end of this conference on 22 October 1884 b the recommended base reference for world time the universal day was announced to be the local mean solar time at the Royal Observatory in Greenwich counted from 0 hours at Greenwich mean midnight 5 This agreed with the civil Greenwich Mean Time used on the island of Great Britain since 1847 In contrast astronomical GMT began at mean noon i e astronomical day X began at noon of civil day X The purpose of this was to keep one night s observations under one date The civil system was adopted as of 0 hours civil 1 January 1925 Nautical GMT began 24 hours before astronomical GMT at least until 1805 in the Royal Navy but persisted much later elsewhere because it was mentioned at the 1884 conference Greenwich was chosen because by 1884 two thirds of all nautical charts and maps already used it as their prime meridian 6 During the period between 1848 and 1972 all of the major countries adopted time zones based on the Greenwich meridian 7 In 1928 the term Universal Time UT was introduced by the International Astronomical Union to refer to GMT with the day starting at midnight 8 The term was recommended 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 9 As the general public had always begun the day at midnight the timescale continued to be presented to them as Greenwich Mean Time When introduced broadcast time signals were based on UT and hence on the rotation of the Earth In 1955 the BIH adopted a proposal by William Markowitz effective January 1 1956 dividing UT into UT0 UT as formerly computed UT1 UT0 corrected for polar motion and UT2 UT0 corrected for polar motion and seasonal variation UT1 was the version sufficient for many astronomical and geodetic applications while UT2 was to be broadcast over radio to the public 10 11 UT0 and UT2 soon became irrelevant due to the introduction of Coordinated Universal Time UTC Starting in 1956 WWV broadcast an atomic clock signal stepped by 20ms increments to bring it into agreement with UT1 12 The up to 20ms error from UT1 is on the same order of magnitude as the differences between UT0 UT1 and UT2 By 1960 the U S Naval Observatory the Royal Greenwich Observatory and the UK National Physical Laboratory had developed UTC with a similar stepping approach The 1960 URSI meeting recommended that all time services should follow the lead of the UK and US and broadcast coordinated time using a frequency offset from cesium aimed to match the predicted progression of UT2 with occasional steps as needed 13 Starting January 1 1972 UTC was defined to follow UT1 within 0 9 seconds rather than UT2 marking the decline of UT2 14 Modern civil time generally follows UTC In some countries the term Greenwich Mean Time persists in common usage to this day in reference to UT1 in civil timekeeping as well as in astronomical almanacs and other references 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 14 Adoption in various countries The table shows the dates of adoption of time zones based on the Greenwich meridian including half hour zones Year Countries 15 1847 Great Britain 3 1880 Ireland entire island 1883 Canada USA c 1884 Serbia1888 Japan1892 Belgium the Netherlands d S Africa e 1893 Italy Germany Austria Hungary railways 1894 Bulgaria Denmark Norway Switzerland Romania Turkey railways 1895 Australia New Zealand Natal1896 Formosa Taiwan 1899 Puerto Rico Philippines1900 Sweden Egypt Alaska1901 Spain1902 Mozambique Rhodesia1903 Ts intao Tientsin1904 China Coast Korea Manchuria N Borneo1905 Chile1906 India except Calcutta Ceylon Sri Lanka Seychelles1907 Mauritius Chagos1908 Faroe Is Iceland1911 France Algeria Tunis many French overseas possessions British West Indies1912 Portugal and overseas possessions other French possessions Samoa Hawaii Midway and Guam Timor Bismarck Arch Jamaica Bahamas Is 1913 British Honduras Dahomey1914 Albania Brazil Colombia1916 Greece Poland Turkey Year Countries1917 Iraq Palestine1918 Guatemala Panama Gambia Gold Coast1919 Latvia Nigeria1920 Argentina Uruguay Burma Siam1921 Finland Estonia Costa Rica1922 Mexico1924 Java USSR1925 Cuba1928 China Inland1930 Bermuda1931 Paraguay1932 Barbados Bolivia Dutch East Indies1934 Nicaragua E NigerBy 1936 Labrador Norfolk I By 1937 Cayman Is Curacao Ecuador NewfoundlandBy 1939 Fernando Po PersiaBy 1940 Lord Howe I 1940 The NetherlandsBy 1948 Aden Ascension I Bahrain British Somaliland Calcutta Dutch Guiana Kenya Federated Malay States Oman Straits Settlements St Helena Uganda ZanzibarBy 1953 Raratonga South GeorgiaBy 1954 Cook Is By 1959 Maldive I RepublicBy 1961 Friendly Is Tonga Is By 1962 Saudi ArabiaBy 1964 Niue Is 1972 Liberia Apart from Nepal Standard Time UTC 05 45 the Chatham Standard Time Zone UTC 12 45 used in New Zealand s Chatham Islands 16 and the officially unsanctioned Central Western Time Zone UTC 8 45 used in Eucla Western Australia and surrounding areas all time zones in use are defined by an offset from UTC that is a multiple of half an hour and in most cases a multiple of an hour MeasurementSee also Earth s rotation Measurement Historically Universal Time was computed from observing the position of the Sun in the sky But astronomers found that it was more accurate to measure the rotation of the Earth by observing stars as they crossed the meridian each day Nowadays UT in relation to International Atomic Time TAI is determined by Very Long Baseline Interferometry VLBI observations of the positions of distant celestial objects stars and quasars a method which can determine UT1 to within 15 microseconds or better 17 18 Additional data sources include laser ranging of the Moon and artificial satellites as well as the determination of GPS satellite orbits 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 19 The rotation of the Earth is somewhat irregular and also 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 modern mean solar day on the average to be slightly longer than the nominal 86 400 SI seconds the traditional number of seconds per day f As UT is thus slightly irregular in its rate astronomers introduced Ephemeris Time which has since been replaced by Terrestrial Time TT Because Universal Time is determined by the Earth s rotation which drifts away from more precise atomic frequency standards an adjustment called a leap second to this atomic time is needed since as of 2019 update broadcast time remains broadly synchronised with solar time g Thus the civil broadcast standard for time and frequency usually follows International Atomic Time closely but occasionally step or leap in order to prevent them from drifting too far from mean solar time Barycentric Dynamical Time TDB a form of atomic time is now used in the construction of the ephemerides of the planets and other solar system objects for two main reasons 20 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 Alternate versionsUT1 is the principal form of Universal Time 1 However there are also several other infrequently used time standards that are referred to as Universal Time which agree within 0 03 seconds with UT1 21 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 22 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 23 UT1R is still in use in the technical literature but rarely used elsewhere 24 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 byU T 2 U T 1 0 022 sin 2 p t 0 012 cos 2 p t 0 006 sin 4 p t 0 007 cos 4 p t seconds displaystyle 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 where t is the time as fraction of the Besselian year 25 dd See also World portal Airy mean time on Mars Earth orientation parameters List of international common standards Unix timeNotes Despite its mandatory use on Great Western Railway stations from 1847 and thus widespread informal adoption it was not until the Statutes Definition of Time Act 1880 that it became law 3 Voting took place on 13 October legal in 1918 Standard Time Act Legal time reverted to Amsterdam time 1909 to Central European Time 1940 except Natal 24 hours of 60 minutes of 60 seconds Continuation of this principle is under active debate in standards bodies See Leap second Future of leap secondsCitations a b Seago John H Seidelmann P Kenneth Allen Steve 5 7 October 2011 Legislative Specifications for Coordinating with Universal Time PDF Decoupling civil timekeeping from Earth rotation proceedings of a colloquium exploring implications of redefining Coordinated Universal Time UTC Analytical Graphics Inc Exton Pa American Astronautical Society ISBN 978 0877035763 McCarthy amp Seidelmann 2009 pp 15 17 62 64 68 69 76 a b Harry Rosehill 31 May 2017 Why Britain Sets Its Clocks To London Londonist com Retrieved 25 November 2019 Howse 1997 ch 4 Howse 1997 pp 12 137 Howse 1997 p 133 137 Howse 1997 ch 6 McCarthy amp Seidelmann 2009 pp 10 11 McCarthy amp Seidelmann 2009 p 14 Dick Steven McCarthy Dennis 15 December 2018 William Markowitz Obituary U S Naval Observatory Archived from the original on 2018 12 15 On the Determination of Universal Time by the Time Services according to the Decisions of the General Assembly of the I A U in Dublin PDF Bulletin Horaire July August 1955 Archived PDF from the original on 2021 12 15 Arias Guinot amp Quinn 2003 Allen Steve Seasonal Variation of Earth Rotation www ucolick org a b McCarthy amp Seidelmann 2009 Ch 14 Howse 1980 pp 154 5 Names have not been updated HM Nautical Almanac Office 2015 McCarthy amp Seidelmann 2009 pp 68 9 Urban amp Seidelmann 2013 p 175 McCarthy amp Seidelmann 2009 Ch 18 Urban amp Seidelmann 2013 p 7 Strictly speaking a major producer of ephemerides the Jet Propulsion Laboratory uses a time scale they derive Teph which is functionally equivalent to TDB Schlyter Paul Time Scales UT1 UTC TAI ET TT GPS time stjarnhimlen se Retrieved 24 May 2022 Urban amp Seidelmann 2013 p 81 IERS n d A Brief Note on Time Systems www astronomy ohio state edu Retrieved 24 May 2022 Common Units and Conversions in Earth Orientation IERS Rapid Service Prediction Center U S Naval Observatory References Common Units and Conversions in Earth Orientation IERS Rapid Service Prediction Center U S Naval Observatory Retrieved 16 June 2022 Arias E F Guinot B Quinn T J 29 May 2003 Rotation of the Earth and Time scales PDF ITU R Special Rapporteur Group Colloquium on the UTC Time Scale Earth Rotation Variations Due to Zonal Tides Paris Earth Orientation Center Retrieved 2 October 2011 Galison Peter 2003 Einstein s clocks Poincare s maps Empires of time New York W W Norton amp Co ISBN 0 393 02001 0 Discusses the history of time standardization Guinot Bernard July 2011 Solar time legal time time in use Metrologia 48 4 S181 S185 Bibcode 2011Metro 48S 181G doi 10 1088 0026 1394 48 4 S08 HM Nautical Almanac Office April 2015 World Time Zone Map Howse Derek 1980 Greenwich Time and the discovery of the longitude Oxford Univ Press pp 154 5 Names have not been updated Howse Derek 1997 Greenwich Time and the Longitude Phillip Wilson ISBN 0 85667 468 0 McCarthy Dennis D July 1991 Astronomical Time PDF Proceedings of the IEEE 79 7 915 920 doi 10 1109 5 84967 McCarthy Dennis Seidelmann P Kenneth 2009 TIME From Earth Rotation to Atomic Physics Weinheim Wiley VCH Verlag GmbH amp Co KGaA ISBN 978 3 527 40780 4 O Malley Michael 1996 Keeping watch A history of American time Washington DC Smithsonian ISBN 1 56098 672 7 Seidelmann P Kenneth 1992 Explanatory supplement to the Astronomical Almanac Mill Valley California University Science Books ISBN 0 935702 68 7 Urban Sean Seidelmann P Kenneth eds 2013 Explanatory Supplement to the Astronomical Almanac 3rd ed Mill Valley California University Science Books UT1R International Earth Rotation and Reference System Service Retrieved 6 March 2013 Terrestrial Time TT Astronomical Applications Department United States Naval Observatory Retrieved 16 June 2022 This article incorporates public domain material from the General Services Administration document Federal Standard 1037C External linksTime Lord by Clark Blaise a biography of Sanford Fleming and the idea of standard time Retrieved from https en wikipedia org w index php title Universal Time amp oldid 1093528250, wikipedia, wiki, book,

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