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Encyclopedia > Greenwich mean time
Greenwich clock with standard measurements
Greenwich clock with standard measurements

Greenwich Mean Time (GMT) is a term originally referring to mean solar time at the Royal Observatory, Greenwich in London. It is now often used to refer to Coordinated Universal Time (UTC) when this is viewed as a time zone, although strictly UTC is an atomic time scale which only approximates GMT in the old sense. It is also used to refer to Universal Time (UT), which is the astronomical concept that directly replaced the original GMT. In the community of Greenwich, GMT (in the form of UTC) is the official time only during winter (during summer the time in Greenwich is British Summer Time rather than GMT). GMT may mean: Greenwich Mean Time Generic Mapping Tools Giant Magellan Telescope GMT Games GMT, an imprint/sub-label of Aozora Records GMT, A hard rock band from the UK Category: ... Image File history File links Time_zones_of_Europe. ... Image File history File links Time_zones_of_Europe. ... Time zones of Europe: Light colours indicate countries that do not observe summer time Western European Time (WET, UTC+0) is the time zone covering parts of western and northwestern Europe, including the following countries and regions: Canary Islands, since 1946 (rest of Spain is CET, i. ... -12 | -11 | -10 | -9:30 | -9 | -8 | -7 | -6 | -5 | -4 | -3:30 | -3 | -2:30 | -2 | -1 | -0:25 | UTC (0) | +0:20 | +0:30 | +1 | +2 | +3 | +3:30 | +4 | +4:30 | +4:51 | +5 | +5:30 | +5:40 | +5:45 | +6 | +6:30 | +7 | +7:20 | +7... BST redirects here. ... Central European Time West Africa Time British Summer Time* Irish Summer Time* Western European Summer Time* Category: ... Time zones of Europe: Light colours indicate countries that do not observe summer time Central European Time (CET) is one of the names of the time zone that is 1 hour ahead of Coordinated Universal Time. ... Central European Time West Africa Time British Summer Time* Irish Summer Time* Western European Summer Time* Category: ... Time zones of Europe: Light colours indicate countries that do not observe summer time Central European Summer Time (CEST) is one of the names of UTC+2 time zone, 2 hours ahead of Coordinated Universal Time. ... Eastern European Time Central Africa Time Israel Standard Time South Africa Standard Time Central European Summer Time West Africa Summer Time Category: ... Time zones of Europe: Light colours indicate countries not observing daylight saving Eastern European Time (EET) is one of the names of UTC+2 time zone, 2 hours ahead of Coordinated Universal Time. ... Eastern European Time Central Africa Time Israel Standard Time South Africa Standard Time Central European Summer Time West Africa Summer Time Category: ... Eastern European Summer Time (EEST) is one of the names of UTC+3 time zone, 3 hours ahead of Coordinated Universal Time. ... -12 | -11 | -10 | -9:30 | -9 | -8 | -7 | -6 | -5 | -4 | -3:30 | -3 | -2:30 | -2 | -1 | -0:25 | UTC (0) | +0:20 | +0:30 | +1 | +2 | +3 | +3:30 | +4 | +4:30 | +4:51 | +5 | +5:30 | +5:40 | +5:45 | +6 | +6:30 | +7 | +7:20 | +7... Time zones of Europe: Light colours indicate countries not observing daylight saving Moscow Time (Russian: ) is the time zone for the city of Moscow, Russia and most of western Russia, including Saint Petersburg, Russia. ... -12 | -11 | -10 | -9:30 | -9 | -8 | -7 | -6 | -5 | -4 | -3:30 | -3 | -2:30 | -2 | -1 | -0:25 | UTC (0) | +0:20 | +0:30 | +1 | +2 | +3 | +3:30 | +4 | +4:30 | +4:51 | +5 | +5:30 | +5:40 | +5:45 | +6 | +6:30 | +7 | +7:20 | +7... Time zones of Europe: Light colours indicate countries not observing daylight saving Moscow Time (Russian: ) is the time zone for the city of Moscow, Russia and most of western Russia, including Saint Petersburg, Russia. ... Moscow Summer Time Category: ... Although DST is common in Europe and North America, most of the worlds people do not use it. ... Solar time is based on the idea that when the sun reaches its highest point in the sky, it is noon. ... Royal Observatory, Greenwich. ... This article is about the capital of England and the United Kingdom. ... UTC redirects here. ... Timezone and TimeZone redirect here. ... “Nuclear Clock” redirects here. ... A time scale specifies divisions of time. ... Universal Time (UT) is a timescale based on the rotation of the Earth. ... Astronomy, which etymologically means law of the stars, (from Greek: αστρονομία = άστρον + νόμος) is a science involving the observation and explanation of events occurring outside Earth and its atmosphere. ... This article is about Greenwich in England. ... Time zones of Europe: Light colours indicate countries not observing daylight saving British Summer Time (BST) is the changing of the clocks in effect in the United Kingdom and Irish Summer Time (IST) in Republic of Ireland between the last Sunday in March and the last Sunday in October each...


Noon Greenwich Mean Time is not necessarily the moment when the sun crosses the Greenwich meridian (and reaches its highest point in the sky in Greenwich) because of Earth's uneven speed in its elliptic orbit and its axial tilt. This event may be up to 16 minutes away from noon GMT (this discrepancy is known as the equation of time). The fictitious mean sun is the annual average of this nonuniform motion of the true Sun, necessitating the inclusion of mean in Greenwich Mean Time. Sol redirects here. ... The Prime Meridian, Greenwich The Prime Meridian is the meridian (line of longitude) passing through the Royal Greenwich Observatory, Greenwich, England; it is the meridian at which longitude is 0 degrees. ... Two bodies with a slight difference in mass orbiting around a common barycenter. ... In astronomy, axial tilt is the inclination angle of a planets rotational axis in relation to a perpendicular to its orbital plane. ... The equation of time is the difference, over the course of a year, between time as read from a sundial and a clock. ...


Historically the term GMT has been used with two different conventions for numbering hours. The old astronomical convention (before 1925) was to refer to noon as zero hours, whereas the civil convention during the same period was to refer to midnight as zero hours. The latter is modern astronomical and civil convention. The more specific terms UT and UTC do not share this ambiguity, always referring to midnight as zero hours.

Contents

History

As the United Kingdom grew into an advanced maritime nation, British mariners kept at least one timepiece on GMT in order to calculate their longitude from the Greenwich meridian, which was by convention considered to have longitude zero degrees. This did not affect shipboard time itself, which was still solar time. This, combined with mariners from other nations drawing from Nevil Maskelyne's method of lunar distances based on observations at Greenwich, eventually led to GMT being used world-wide as a reference time independent of location. Most time zones were based upon this reference as a number of hours and half-hours "ahead of GMT" or "behind GMT". A maritime nation is any nation which borders the sea and utilizes it for any of the following: commerce and transport, war, to define a territorial boundary, or for any maritime activity (activities using the sea to convey or produce an end result). ... Longitude is the east-west geographic coordinate measurement most commonly utilized in cartography and global navigation. ... Nevil Maskelyne. ... In celestial navigation, lunar distance is in the angle of the Moons centre from the Sun or from the bright stars. ...


Greenwich Mean Time was adopted across the island of Great Britain by the Railway Clearing House in 1847, and by almost all railway companies by the following year from which the term "railway time" is derived. It was gradually adopted for other purposes, but a legal case in 1858 held "local mean time" to be the official time. This changed in 1880, when GMT was legally adopted throughout the island of Great Britain. GMT was adopted on the Isle of Man in 1883, Jersey in 1898 and Guernsey in 1913. Ireland adopted Greenwich Mean Time in 1916, supplanting Dublin Mean Time.[1] Hourly time signals from Greenwich Observatory were first broadcast on 5 February 1924. The British Railway Clearing House (RCH) was set up in 1842 in offices in Seymour Street, London. ... Madras Time was a time zone set up in 1802 by John Goldingham, the first official astronomer of the British East India Company in India. ... A legal case is a dispute between opposing parties resolved by a court, or by some equivalent legal process. ... Local mean time is a form of solar time that corrects the variations of local apparent time. ... -12 | -11 | -10 | -9:30 | -9 | -8 | -7 | -6 | -5 | -4 | -3:30 | -3 | -2:30 | -2 | -1 | -0:25 | UTC (0) | +0:20 | +0:30 | +1 | +2 | +3 | +3:30 | +4 | +4:30 | +4:51 | +5 | +5:30 | +5:40 | +5:45 | +6 | +6:30 | +7 | +7:20 | +7... is the 36th day of the year in the Gregorian calendar. ... For the rap album, see 1924 (album). ...


The daily rotation of the Earth is somewhat irregular (see ΔT) and is slowing down slightly. Atomic clocks constitute a much more stable timebase. On 1 January 1972, GMT was replaced as the international time reference by Coordinated Universal Time, maintained by an ensemble of atomic clocks around the world. UT1, introduced in 1928, represents earth rotation time. Leap seconds are added to or subtracted from UTC to keep it within 0.9 seconds of UT1. Delta T and delta-T are ASCII substitutes for the formal ΔT, which is Terrestrial Time minus Universal Time. ... is the 1st day of the year in the Gregorian calendar. ... Year 1972 (MCMLXXII) was a leap year starting on Saturday (link will display full calendar) of the Gregorian calendar. ... Universal Time (UT) is a timescale based on the rotation of the Earth. ... The Earths rotation is the rotation of the solid earth around its own axis, which is called Earths axis or rotation axis. ... A leap second is a one-second adjustment to civil time in order to keep it close to the mean solar time. ...


The international prime meridian is no longer precisely the Greenwich meridian, but remains close to it (5.31"E). Location of the Prime Meridian Image:Prime Meridian. ...


Time zone

Although civil time in the United Kingdom, e.g., the Greenwich Time Signal, is in practice now based on UTC, the winter time scale, which is equal to UTC, is still popularly called GMT. Civil time in the UK is legally (but not practically) still based on astronomical GMT, not UTC. Those countries marked in dark blue on the map above use Western European Summer Time and advance their clock one hour in summer. In the United Kingdom, this is known as British Summer Time (BST); in the Republic of Ireland it is called Irish Summer Time (IST). Those countries marked in light blue keep their clocks on UTC/GMT/WET year round. Civil time is another name for mean solar time reckoned from midnight. ... Graph of the six pips The Greenwich Time Signal (abbreviated GTS) or BBC pips is a time code heard on some BBC radio stations at the start of the hour, most notably on Radio 4 and the World Service. ... BST redirects here. ... Time zones of Europe: Light colours indicate countries not observing daylight saving British Summer Time (BST) is the changing of the clocks in effect in the United Kingdom and Irish Summer Time (IST) in Republic of Ireland between the last Sunday in March and the last Sunday in October each...


Anomalies

Since political, in addition to purely geographical, criteria are used in the drawing of time zones, it follows that actual time zones do not precisely adhere to meridian lines. The GMT time zone, were it drawn by purely geographical terms, would consist of exactly the area between meridians 7°30'W and 7°30'E. As a result, there are European locales that despite lying in an area with a "physical" UTC time, actually use another time zone (UTC+1 in particular); contrariwise, there are European areas that use UTC, even though their "physical" time zone is UTC-1 (e.g., most of Portugal), or even UTC−2 (the westernmost part of Iceland).Actually, because the UTC time zone in Europe is "shifted" to the west, Lowestoft in Suffolk, East Anglia, England at only 1°45'E is the easternmost settlement in Europe in which UTC is applied. Following is a list of the "incongruencies": For the books called Geography by Ancient Greek authors, see Geographia (Ptolemy) and Geographica (Strabo) For the magazine of the Royal Geographical Society, see Geographical (magazine) Geography is the study of the earth and its features, inhabitants, and phenomena. ... Central European Time West Africa Time British Summer Time* Irish Summer Time* Western European Summer Time* Category: ... −12 | −11 | −10 | −9:30 | −9 | −8 | −7 | −6 | −5 | −4 | −3:30 | −3 | −2:30 | −2 | −1 | −0:25 | UTC (0) | +0:20 | +0:30 | +1 | +2 | +3 | +3:30 | +4 | +4:30 | +4:51 | +5 | +5:30 | +5:40 | +5:45 | +6 | +6:30 | +7 | +7:20 | +7... , Lowestoft (pronounced ) is a town in Suffolk, East Anglia, England, lying between the eastern edge of The Broads National Park at Oulton Broad and the North Sea. ... Suffolk (pronounced ) is a large historic and modern non-metropolitan county in East Anglia, England. ... Norfolk and Suffolk, the core area of East Anglia. ... For other uses, see England (disambiguation). ...

Countries (or parts thereof) west of 22°30'W ("physical" UTC-2) that use UTC
  • The westernmost part of Iceland, incl. the northwest peninsula and its main town of Ísafjörður, which is west of 22°30'W, uses UTC. Bjargtangar, Iceland is the westernmost point in which UTC is applied.
Countries (or parts thereof) west of 7°30'W ("physical" UTC-1) that use UTC

Location of Ísafjörður in Iceland (upper left) Constituency Northwest Area 270 km² ( 104. ... Bjargtangar is the westernmost point of Iceland and the westernmost point of Europe. ... This article is about the islands in the Atlantic Ocean. ... For other uses, see Lisbon (disambiguation). ... Oporto redirects here. ... For other uses, see Braga (disambiguation). ... Location    - Country  Portugal  - Region Centro  - Subregion Baixo Vouga  - District or A.R. Aveiro Mayor Élio Maia  - Party PSD-CDS Area 199. ... Location    - Country  Portugal  - Region Centro  - Subregion Baixo Mondego  - District or A.R. Coimbra Mayor Carlos Encarnação  - Party PSD Area 319. ... Location    - Country Portugal    - Region Norte  - Subregion Alto Trás-os-Montes  - District or A.R. Bragança Mayor António Nunes  - Party PSD Area 1,173. ... Location    - Country  Portugal  - Region Centro  - Subregion Beira Interior Norte  - District or A.R. Guarda Mayor Joaquim Valente  - Party PS Area 712. ... Location Motto of the autonomous region: Das ilhas, as mais belas e livres (Portuguese: Of the islands, the most beautiful and free) Official language Portuguese Capital Funchal Other towns Porto Santo, Machico, Santa Cruz, Câmara de Lobos, Santana, Ribeira Brava, Caniço Area 797 km² Population  - Total (1991)  - Density... This article is about the city in the Republic of Ireland. ... This article is about the city. ... WGS-84 (GPS) Coordinates: , Irish Grid Reference M300256 Statistics Province: Connacht County: Dáil Éireann: Galway West European Parliament: North-West Dialling Code: 091 Postal District(s): G Area: 50. ... Northern Ireland (Irish: , Ulster Scots: Norlin Airlann) is a constituent country of the United Kingdom lying in the northeast of the island of Ireland, covering 5,459 square miles (14,139 km², about a sixth of the islands total area). ... Statistics Province: Ulster County Town: Enniskillen Area: 1,691 km² Population (est. ... For other uses, see Enniskillen (disambiguation). ... Na h-Eileanan Siar (Western Isles) redirects here. ... This article is about the country. ... Location of Vatersay Vatersay Bay, Vatersay. ... Na h-Eileanan Siar (Western Isles) redirects here. ... An uninhabited island is an island that has yet to be (or is not currently) populated by humans. ... Mercator projection map of the St. ... Na h-Eileanan Siar (Western Isles) redirects here. ... Rockall, a small, isolated rocky islet in the North Atlantic Ocean Rockall is a small, uninhabited, rocky islet in the North Atlantic, and one of the sea areas named in the Shipping Forecast broadcast on BBC Radio 4. ... For other uses, see Denmark (disambiguation). ... There are two place names that have the name Mykines: Mykines, Faroe Islands, an island in the Faroe Islands Mykines, a village on that island. ... Location in Iceland Coordinates: , Constituency Government  - Mayor (Borgarstjóri) Dagur B. Eggertsson Area  - City 274. ...

Major metropolitan areas

This article is about the city in Northern Ireland. ... Northern Ireland (Irish: , Ulster Scots: Norlin Airlann) is a constituent country of the United Kingdom lying in the northeast of the island of Ireland, covering 5,459 square miles (14,139 km², about a sixth of the islands total area). ... This article is about the British city. ... For other uses, see England (disambiguation). ... This article is about the English city. ... This article is about the capital city of Wales. ... This article is about the country. ... For other uses, see Casablanca (disambiguation). ... For other uses, see Dublin (disambiguation). ... For other uses, see Edinburgh (disambiguation). ... This article is about the country. ... For other uses, see Aberdeen (disambiguation). ... For other uses, see Glasgow (disambiguation). ... For other uses, see Liverpool (disambiguation). ... For other uses, see Leeds (disambiguation) and Leeds City (disambiguation). ... For other uses, see Lisbon (disambiguation). ... This article is about the capital of England and the United Kingdom. ... This article is about the City of Manchester in England. ... For other uses, see Sheffield (disambiguation). ... Oporto redirects here. ... Location in Iceland Coordinates: , Constituency Government  - Mayor (Borgarstjóri) Dagur B. Eggertsson Area  - City 274. ... Accra, population 1,970,400 (2005), is the capital of Ghana. ... (City of Dakar, divided into 19 communes darrondissement) City proper (commune) Région Dakar Département Dakar Mayor Pape Diop (PDS) (since 2002) Area 82. ...

See also

WWV Transmitter Building WWV is the callsign of NISTs shortwave radio station located in Fort Collins, Colorado. ... For other uses, see Chu. ... BPM is the Peoples Republic of Chinas national time signal service, operated by the Chinese Academy of Sciences. ... DCF77 is a longwave time signal radio station. ... VNG was Australias national time signal service, and operated on 2500, 5000, 8638, 12984, and 16000 kHz. ... A marine chronometer is a timekeeper precise enough to be used as a portable time standard, used to determine longitude by means of celestial navigation. ... The Glycine Airman I, a 24-hour watch built by Glycine Watch SA of Switzerland. ... Swatch Internet Time is a concept introduced in 1998 and marketed by the Swatch corporation as an alternative, decimal measure of time. ... Sandringham time is the name given to the idiosyncratic alterations that King Edward VII made to the timekeeping at the royal estate of Sandringham. ...

Notes

  1. ^ Myers, Joseph. (2007). History of legal time in Britain. Retrieved January 4, 2008.

is the 4th day of the year in the Gregorian calendar. ... 2008 (MMVIII) is the current year, a leap year that started on Tuesday of the Anno Domini (or common era), in accordance to the Gregorian calendar. ...

References

  • Howse, Derek. (1997). Greenwich time and the longitude. London: Philip Wilson.
  • Myers, Joseph. (2007). History of legal time in Britain. Retrieved January 4, 2008.

is the 4th day of the year in the Gregorian calendar. ... 2008 (MMVIII) is the current year, a leap year that started on Tuesday of the Anno Domini (or common era), in accordance to the Gregorian calendar. ...

External links

A tropical year is the length of time that the Sun, as viewed from the Earth, takes to return to the same position along the ecliptic (its path among the stars on the celestial sphere). ... For other uses, see Equinox (disambiguation). ... “Summer solstice” redirects here. ... This article is about days of the week. ... This article details various mathematical algorithms to calculate the day of the week for any particular date in the past or future. ... The days of the year are sometimes designated letters A, B, C, D, E, F and G in a cycle of 7 as an aid for finding the day of week of a given calendar date and in calculating Easter. ... The International Commission on Stratigraphy concerns itself with stratigraphy on a global scale. ... Diagram of geological time scale. ... Dating material drawn from the archaeological record can made by a direct study of a artifact or may be deduced by association with materials found in the context the item is drawn from or inferred by its point of discovery in the sequence relative to datable contexts. ... The precession of Earths axis of rotation with respect to inertial space is also called the precession of the equinoxes. ... Sidereal time is time measured by the apparent diurnal motion of the vernal equinox, which is very close to, but not identical with, the motion of stars. ... // Galactic time NGC 4414, a typical spiral galaxy alike our Milky Way Galactic time, not to confuse with siderial time, is the time that is described by our spin relative to the center of the galaxy. ... Look up fortnight in Wiktionary, the free dictionary. ... The term jiffy (or jiffie) is used in different applications for various different short periods of time, usually 1/60 of a second. ... Lustrum was a sacrifice for expiation and purification offered by one of the censors of Rome in name of the Roman people at the close of the taking of the census, and which took place after a period of five years, so that the name came to denote a period... A saeculum is a length of time roughly equal to the lifetime of a person, or about 90 years. ... A shake is an informal unit of time equal to 10 nanoseconds, or 10-8 seconds. ... A tide is an obsolete or archaic term for time, period or season, such as eventide, shrovetide, Eastertide, etc. ... For the novel by Michael Crichton, see Timeline (novel). ... A duration is an amount of time or a particular time interval. ... In computer science and computer programming, system time represents a computer systems notion of the passing of time. ... // Definition and history Psychologists have investigated mental chronometry for over 100 years. ... The time value of money is the premise that an investor prefers to receive a payment of a fixed amount of money today, rather than an equal amount in the future, all else being equal. ... Look up timekeeper in Wiktionary, the free dictionary. ...

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Note that LMT is not, in general, the same as the the civil time (standard time) at a location since the civil time is the same for all locations in that zone and is the LMT for the zone's standard longitude.
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Greenwich Sidereal Time (GST or ST0) is the local sidereal time on the Greenwich meridian.
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