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Greenwich Mean Time
Greenwich Mean Time (GMT), or Universal Time (UT), mean solar time on the prime meridian. Universal Time does not increase uniformly and is therefore unsatisfactory for theoretical astronomical and frequency control purposes. Ephemeris Time, based on atomic clocks rather than solar time and coordinated from Paris, has taken the place of UT for purely scientific purposes but Greenwich, at longitude zero, remains the prime meridian for all navigational purposes. By the middle of the 19th century some dozen prime meridians were in use for navigational charts and many more for the calculation of time.
In October 1884 an international intergovernmental conference met in Washington, DC, with the purpose of fixing a Prime Meridian and Universal Day. After many months of probably fairly leisurely deliberation the conference agreed to recommend to the governments represented that they should adopt the meridian passing through the transit instrument at the Observatory of Greenwich as the initial meridian for longitude; that the longitude should be counted in two directions from this meridian; and that the universal day should be a mean solar day to begin for all the world at mean midnight at the initial meridian. In due course the recommendations were universally adopted, as was the time zone convention based on Greenwich. Astronomers by and large prefer the term Universal Time to Greenwich Mean Time but for most nautical and navigational work GMT still prevails. Howse, D. , Greenwich Time and the Discovery of Longitude (1980). ——‘The Centenary of the Adoption of Greenwich as the Zero Meridian’, Journal of Navigation, 38 (1985), 191. Mike Richey |
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"Greenwich Mean Time." The Oxford Companion to Ships and the Sea. 2006. Encyclopedia.com. 28 May. 2012 <http://www.encyclopedia.com>. "Greenwich Mean Time." The Oxford Companion to Ships and the Sea. 2006. Encyclopedia.com. (May 28, 2012). http://www.encyclopedia.com/doc/1O225-GreenwichMeanTime.html "Greenwich Mean Time." The Oxford Companion to Ships and the Sea. 2006. Retrieved May 28, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O225-GreenwichMeanTime.html |
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Greenwich Mean Time
Greenwich Mean Time (GMT) The mean solar time on the Greenwich Meridian of longitude, which was defined to pass through the Airy Transit Circle at Greenwich in England and was adopted internationally as the zero of longitude at a conference in Washington in 1884. Its acceptance was facilitated by the overwhelming use of the Greenwich Meridian in navigation and the adoption, in the USA and Canada, of time zones based on Greenwich. Originally different towns in Great Britain kept their own local time, varying according to longitude. In the mid-19th century Greenwich time was adopted by railways throughout Britain for the sake of uniformity. However, it was only in 1880 that Greenwich Mean Time became the legal time throughout Great Britain. The international reference time-scale for civil use is now based on atomic clocks but is subject to step adjustments (leap seconds) to keep it close to mean solar time on the Greenwich Meridian. The formal name of the time-scale is UTC (a language-independent abbreviation of coordinated universal time) but it is still widely known as Greenwich Mean Time.
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"Greenwich Mean Time." A Dictionary of World History. 2000. Encyclopedia.com. 28 May. 2012 <http://www.encyclopedia.com>. "Greenwich Mean Time." A Dictionary of World History. 2000. Encyclopedia.com. (May 28, 2012). http://www.encyclopedia.com/doc/1O48-GreenwichMeanTime.html "Greenwich Mean Time." A Dictionary of World History. 2000. Retrieved May 28, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O48-GreenwichMeanTime.html |
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Greenwich mean time
Greenwich mean time or Greenwich meridian time (GMT), the former name for mean solar time at the original site of the Royal Observatory in Greenwich, England, which is located on the prime meridian . In 1925 the numbering system was changed to make GMT equivalent to civil time at the prime meridian, and in 1928 the International Astronomical Union changed the designation of the standard time of the prime meridian to universal time (UT), which is now in general use. |
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"Greenwich mean time." The Columbia Encyclopedia, 6th ed.. 2011. Encyclopedia.com. 28 May. 2012 <http://www.encyclopedia.com>. "Greenwich mean time." The Columbia Encyclopedia, 6th ed.. 2011. Encyclopedia.com. (May 28, 2012). http://www.encyclopedia.com/doc/1E1-GreenwTm.html "Greenwich mean time." The Columbia Encyclopedia, 6th ed.. 2011. Retrieved May 28, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1E1-GreenwTm.html |
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Greenwich Mean Time
Greenwich Mean Time (GMT) The mean solar time on the Greenwich meridian, now more generally known astronomically as Universal Time (UT). It is the Greenwich hour angle of the mean sun + 12 hours, as the day starts at midnight.
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"Greenwich Mean Time." A Dictionary of Astronomy. 1997. Encyclopedia.com. 28 May. 2012 <http://www.encyclopedia.com>. "Greenwich Mean Time." A Dictionary of Astronomy. 1997. Encyclopedia.com. (May 28, 2012). http://www.encyclopedia.com/doc/1O80-GreenwichMeanTime.html "Greenwich Mean Time." A Dictionary of Astronomy. 1997. Retrieved May 28, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O80-GreenwichMeanTime.html |
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Greenwich Mean Time
Green·wich Mean Time (abbr.: GMT) (also Green·wich time) the mean solar time at the Greenwich meridian, adopted as the standard time in a zone that includes the British Isles. |
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"Greenwich Mean Time." The Oxford Pocket Dictionary of Current English. 2009. Encyclopedia.com. 28 May. 2012 <http://www.encyclopedia.com>. "Greenwich Mean Time." The Oxford Pocket Dictionary of Current English. 2009. Encyclopedia.com. (May 28, 2012). http://www.encyclopedia.com/doc/1O999-greenwichmeantime.html "Greenwich Mean Time." The Oxford Pocket Dictionary of Current English. 2009. Retrieved May 28, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O999-greenwichmeantime.html |
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GMT
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"GMT." A Dictionary of Astronomy. 1997. Encyclopedia.com. 28 May. 2012 <http://www.encyclopedia.com>. "GMT." A Dictionary of Astronomy. 1997. Encyclopedia.com. (May 28, 2012). http://www.encyclopedia.com/doc/1O80-GMT.html "GMT." A Dictionary of Astronomy. 1997. Retrieved May 28, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O80-GMT.html |
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GMT
GMT • abbr. Greenwich Mean Time. |
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Cite this article
"GMT." The Oxford Pocket Dictionary of Current English. 2009. Encyclopedia.com. 28 May. 2012 <http://www.encyclopedia.com>. "GMT." The Oxford Pocket Dictionary of Current English. 2009. Encyclopedia.com. (May 28, 2012). http://www.encyclopedia.com/doc/1O999-gmt.html "GMT." The Oxford Pocket Dictionary of Current English. 2009. Retrieved May 28, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O999-gmt.html |
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Greenwich Mean Time
Greenwich Mean Time former term for Universal Time.
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"Greenwich Mean Time." The Oxford Essential Dictionary of the U.S. Military. 2001. Encyclopedia.com. 28 May. 2012 <http://www.encyclopedia.com>. "Greenwich Mean Time." The Oxford Essential Dictionary of the U.S. Military. 2001. Encyclopedia.com. (May 28, 2012). http://www.encyclopedia.com/doc/1O63-GreenwichMeanTime.html "Greenwich Mean Time." The Oxford Essential Dictionary of the U.S. Military. 2001. Retrieved May 28, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O63-GreenwichMeanTime.html |
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GMT
GMT Abbreviation of Greenwich Mean Time
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"GMT." World Encyclopedia. 2005. Encyclopedia.com. 28 May. 2012 <http://www.encyclopedia.com>. "GMT." World Encyclopedia. 2005. Encyclopedia.com. (May 28, 2012). http://www.encyclopedia.com/doc/1O142-GMT.html "GMT." World Encyclopedia. 2005. Retrieved May 28, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O142-GMT.html |
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GMT
GMT Greenwich Mean Time
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FRAN ALEXANDER , PETER BLAIR , JOHN DAINTITH , ALICE GRANDISON , VALERIE ILLINGWORTH , ELIZABETH MARTIN , ANNE STIBBS , JUDY PEARSALL , and SARA TULLOCH. "GMT." The Oxford Dictionary of Abbreviations. 1998. Encyclopedia.com. 28 May. 2012 <http://www.encyclopedia.com>. FRAN ALEXANDER , PETER BLAIR , JOHN DAINTITH , ALICE GRANDISON , VALERIE ILLINGWORTH , ELIZABETH MARTIN , ANNE STIBBS , JUDY PEARSALL , and SARA TULLOCH. "GMT." The Oxford Dictionary of Abbreviations. 1998. Encyclopedia.com. (May 28, 2012). http://www.encyclopedia.com/doc/1O25-GMT.html FRAN ALEXANDER , PETER BLAIR , JOHN DAINTITH , ALICE GRANDISON , VALERIE ILLINGWORTH , ELIZABETH MARTIN , ANNE STIBBS , JUDY PEARSALL , and SARA TULLOCH. "GMT." The Oxford Dictionary of Abbreviations. 1998. Retrieved May 28, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O25-GMT.html |
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