Time zones of Europe:

blue	Western European Time (UTC+0) Western European Summer Time (UTC+1)
red	Central European Time (UTC+1) Central European Summer Time (UTC+2)
yellow	Eastern European Time (UTC+2) Eastern European Summer Time (UTC+3)
green	Moscow Time (UTC+3) Moscow Summer Time (UTC+4)

Light colours indicate countries that do not observe summer time: Algeria, Iceland and Morocco

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. Western European Time ( WET, UTC+0, and commonly known as Greenwich Mean Time in the United Kingdom) is the Time zone Coordinated Universal Time, the basis for the world's civil time frequently referred to by the name of its predecessor Greenwich Mean Time Western Western European Summer Time ( WEST) is a summer Daylight saving time scheme 1 hour ahead of Coordinated Universal Time. UTC+1 is used in the following locations Central European Time West Africa Time Western European Summer Time Central European Time ( CET) is one of the names of the Time zone that is 1 hour ahead of Coordinated Universal Time. UTC+1 is used in the following locations Central European Time West Africa Time Western European Summer Time Central European Summer Time ( CEST) is one of the names of UTC+2 Time zone, 2 hours ahead of Coordinated Universal Time. UTC+2 corresponds to the following Time zones Eastern European Time Egypt Standard Time Central Africa Time Eastern European Time ( EET) is one of the names of UTC+2 Time zone, 2 hours ahead of Coordinated Universal Time. UTC+2 corresponds to the following Time zones Eastern European Time Egypt Standard Time Central Africa Time Eastern European Summer Time ( EEST) is one of the names of UTC+3 Time zone, 3 hours ahead of Coordinated Universal Time. UTC+3 is used in the following locations Moscow Time Eastern European Summer Time West Asian Summer Time Moscow Time (Моско́вское вре́мя is the Time zone for the city of Moscow, Russia and most of western Russia including Saint Petersburg UTC+3 is used in the following locations Moscow Time Eastern European Summer Time West Asian Summer Time Moscow Time (Моско́вское вре́мя is the Time zone for the city of Moscow, Russia and most of western Russia including Saint Petersburg UTC+4 time zone is used as Moscow Summer Time Iraq Summer Time Azerbaijan Time Single zone countries Daylight saving time ( DST Algeria ( ar [[Arabic]] الجزائر, Al Jaza'ir ælʤæˈzæːʔir Amazigh: ⴷⵥⴰⵢⴻⵔ Dzayer) officially the People's Iceland, officially the Republic of Iceland ( ( Ísland or Lýðveldið Ísland ( Morocco (المغرب "al-Maghrib" officially the Kingdom of Morocco (المملكة المغربية is a country located in North Africa Solar times are measures of the apparent position of the Sun on the Celestial sphere. The Royal Observatory Greenwich (formerly the Royal Greenwich Observatory or RGO) was commissioned in 1675 by King Charles II, with the London ( ˈlʌndən is the capital and largest urban area in the United Kingdom. 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. An atomic clock is a type of Clock that uses an Atomic resonance Frequency standard as its timekeeping element A time standard It is also used to refer to Universal Time (UT), which is the astronomical concept that directly replaced the original GMT. Astronomy (from the Greek words astron (ἄστρον "star" and nomos (νόμος "law" is the scientific study 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). Greenwich ( ˈɡrɛnɪtʃ GREN-itch /ˈɡrɛnɪdʒ/ GREN-idge or /ˈɡrɪnɪdʒ/ GRIN-idge is a district in south-east London, Western European Summer Time ( WEST) is a summer Daylight saving time scheme 1 hour ahead of Coordinated Universal Time.

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. The Sun (Sol is the Star at the center of the Solar System. The Prime Meridian is the meridian (line of Longitude) at which longitude is defined to be 0° In Physics, an orbit is the gravitationally curved path of one object around a point or another body for example the gravitational orbit of a planet around a star In Astronomy, axial tilt is the Inclination angle of a planet's rotational axis in relation to its orbital plane. This event may be up to 16 minutes away from noon GMT (this discrepancy is known as the equation of time). The equation of time is the difference over the course of a year between time as read from a Sundial and time as read from a Clock, measured in an ideal situation 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.

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.

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. 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 Longitude (ˈlɒndʒɪˌtjuːd or ˈlɒŋgɪˌtjuːd symbolized by the Greek character Lambda (λ is the east-west Geographic coordinate measurement 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. The Reverend Dr Nevil Maskelyne ( 6 October[[ 732]] &ndash 9 February[[ 811]] was the fifth English Astronomer Royal. Most time zones were based upon this reference as a number of hours and half-hours "ahead of GMT" or "behind GMT".

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. See also Kingdom of Great Britain Great Britain (Breatainn Mhòr Prydain Fawr Breten Veur Graet Breetain is the larger of the two main islands The British Railway Clearing House (RCH was an organisation set up to manage the allocation of revenue collected by numerous pre-grouping railway companies Railway time was the name given to the standardised time arrangement first applied by the Great Western Railway in England in November 1840 It was gradually adopted for other purposes, but a legal case in 1858 held "local mean time" to be the official time. 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, forming a uniform time scale at a specific longitude 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. The Isle of Man (Ellan Vannin ˈɛlʲən ˈvanɪn or Mann (Mannin) is a self-governing Crown dependency, located in the Irish Sea at the geographical The Bailiwick of Jersey ( Jèrriais: Jèrri) is a British Crown dependency off the coast of Normandy, France. The Bailiwick of Guernsey (Bailliage de Guernesey is a British Crown dependency in the English Channel off the coast of Normandy. Ireland adopted Greenwich Mean Time in 1916, supplanting Dublin Mean Time. UTC−025 was used in Ireland as Dublin Mean Time. Dublin Mean Time was introduced by the Statutes (Definition of Time Act 1880 (43 & 44 Vict ^[1] Hourly time signals from Greenwich Observatory were first broadcast on 5 February 1924. Events 1576 - Henry of Navarre converts to Roman Catholicism in order to ensure his right to the throne of France. Year 1924 ( MCMXXIV) was a Leap year starting on Tuesday (link will display the full calendar of the Gregorian calendar.

The daily rotation of the Earth is somewhat irregular (see ΔT) and is slowing down slightly. This article is about the time difference for the temperature difference see Psychrometrics. 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. New Year See also New Year The Ancient Romans began their consular year on January 1st since 153 BC Year 1972 ( MCMLXXII) was a Leap year starting on Saturday (link will display full calendar of the Gregorian calendar. UT1, introduced in 1928, represents earth rotation time. Rotation period Earth's rotation period relative to the Sun (its mean solar day is 86400 Seconds of mean solar time Leap seconds are added to or subtracted from UTC to keep it within 0. A leap second is a one- Second adjustment that keeps broadcast standards for time of day close to mean solar time. 9 seconds of UT1.

Indeed, even the Greenwich meridian itself is not quite what it used to be—defined by 'the centre of the transit instrument at the Observatory at Greenwich'. Although that instrument still survives in working order, it is no longer in use and now the meridian of origin of the world's longitude and time is not strictly defined in material form but from a statistical solution resulting from observations of all time-determination stations which the BIPM takes into account when co-ordinating the world's time signals. Nevertheless, the line in the old observatory's courtyard today differs no more than a few metres from that imaginary line which is now the Prime Meridian of the world. "^[2]

Time zone

Although civil time in the United Kingdom, e. In modern usage civil time refers to statutory time scales designated by civilian authorities or to local time indicated by clocks The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom, the UK or Britain,is a Sovereign state located 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. The Greenwich Time Signal ( GTS) popularly known as the pips, is a series of six short tones broadcast by many BBC radio stations at the end of each 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. Western European Summer Time ( WEST) is a summer Daylight saving time scheme 1 hour ahead of Coordinated Universal Time. In the United Kingdom, this is known as British Summer Time (BST); in the Republic of Ireland it is called Irish Summer Time (IST). Western European Summer Time ( WEST) is a summer Daylight saving time scheme 1 hour ahead of Coordinated Universal Time. Those countries marked in light blue keep their clocks on UTC/GMT/WET year round.

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. Geography (from Greek γεωγραφία - geografia) is the study of the Earth and its lands features inhabitants and phenomena 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. UTC+1 is used in the following locations Central European Time West Africa Time Western European Summer Time UTC−1 is used as offset for Cape Verde Greenland eastern Ittoqqortoormiit and surrounding g. , most of Portugal), or even UTC−2 (the westernmost part of Iceland). Portugal, officially the Portuguese Republic (República Portuguesa is a country on the Iberian Peninsula. Iceland, officially the Republic of Iceland ( ( Ísland or Lýðveldið Ísland ( 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. Lowestoft (ˈləʊstɒft/ /ˈləʊstəf is a town in Suffolk, East Anglia, England, lying between the eastern edge of The Broads National Park Suffolk (ˈsʌfək is a non-metropolitan county of historic origin in East Anglia, England. East Anglia is often used as a shorthand for the Kingdom of the East Angles. England is a Country which is part of the United Kingdom. Its inhabitants account for more than 83% of the total UK population whilst its mainland Following is a list of the "incongruencies":

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. Bjargtangar is the westernmost point of Iceland and is considered the westernmost point of Europe outside the mid-Atlantic archipelago of

Countries (or parts thereof) west of 7°30'W ("physical" UTC-1) that use UTC

• Canary Islands (Spain)
• Most of Portugal, incl. The Canary Islands ( English pronunciation kəˈnæriː ˈaɪləndz Spanish: Islas Canarias, ˈizlas kaˈnarjas are a Spanish Spain () or the Kingdom of Spain (Reino de España is a country located mostly in southwestern Europe on the Iberian Peninsula. Portugal, officially the Portuguese Republic (República Portuguesa is a country on the Iberian Peninsula. Lisbon, Porto, Braga, Aveiro, and Coimbra. Lisbon (Lisboa liʒˈboɐ is the Capital and largest city of Portugal. Braga (ˈBrag-uh a city and municipality in northwestern Portugal, is the capital of the district of Braga, the oldest archdiocese Aveiro (aˈvɐjɾu is a city of some 57000 people and a municipality in Portugal with a total area of 199 Coimbra (kuˈĩbɾɐ is a city and a municipality in Portugal, former capital of the country during the first dynasty period and home to the University of Coimbra (Only the easternmost part, incl. cities such as Bragança and Guarda, lies east of 7°30'W. Bragança ( pron bɾɐ'gɐ̃sɐ or locally; English language: Braganza) is a city and a municipality in north-eastern Portugal Guarda ( pron. 'gwaɾdɐ is a city and a municipality in Portugal with a total area of 712 ) The Madeira Islands, even further to the west, also employ UTC. History See also History of Madeira Pre-Portuguese times Pliny mentions certain Purple Islands the position of which with reference to the
• Western part of the Republic of Ireland, incl. Ireland ( Irish: Éire, ˈeːrʲə is a country in north-western Europe. the cities of Cork, Limerick, and Galway
• Westernmost tip of Northern Ireland, incl. Cork (Corcaigh is the second largest city in the Republic of Ireland and the island of Ireland 's third most populous city after Dublin and Belfast Limerick (pronounced /ˈlɪmrɪk/ Luimneach in Irish) is a city and the county seat of County Limerick in the Province of Munster Galway (Gaillimh is the only city in the province of Connacht in Ireland. Northern Ireland (Tuaisceart Éireann Ulster Scots: Norlin Airlann) is a Country within the United Kingdom, lying in the northeast of the capital of County Fermanagh, Enniskillen
• Extreme westerly portion of the Outer Hebrides, west of Scotland; for instance, Vatersay, an inhabited island in the Outer Hebrides and the westernmost settlement in the whole of Great Britain, lies at 7°54'W. County Fermanagh (fɚr'mænɘ Contae Fhear Manach or Fear Manach ('Men of Monach'in Irish) is the westernmost of the six counties that form Northern Enniskillen ( is the county town (and largest town in County Fermanagh and the west of Northern Ireland. The Outer Hebrides, ( officially known for local government purposes by the Gaelic name Na h-Eileanan Siar) comprise an island Scotland ( Gaelic: Alba) is a Country in northwest Europethat occupies the northern third of the island of Great Britain. Vatersay ( Scottish Gaelic: Bhatarsaigh) is an inhabited Island in the Outer Hebrides of Scotland. The Outer Hebrides, ( officially known for local government purposes by the Gaelic name Na h-Eileanan Siar) comprise an island See also Kingdom of Great Britain Great Britain (Breatainn Mhòr Prydain Fawr Breten Veur Graet Breetain is the larger of the two main islands If uninhabited islands and/or rocks are to be taken into account then St Kilda, west of the Outer Hebrides, at 8°58'W, and Rockall, at 13°41'W, should also be included. An uninhabited island is an Island that has yet to be (or is not currently populated by Humans Uninhabited islands are often used in movies or stories for shipwrecked St Kilda (Hiort is an isolated Archipelago 64 kilometres (40 mi west-northwest of North Uist in the North Atlantic Ocean. The Outer Hebrides, ( officially known for local government purposes by the Gaelic name Na h-Eileanan Siar) comprise an island Rockall is a small uninhabited rocky Islet in the north Atlantic Ocean, and one of the sea areas named in the Shipping Forecast broadcast on BBC
• Westernmost island of the Faroe Islands (autonomous region of the Danish Kingdom), Mykines
• Iceland, including Reykjavík

Major metropolitan areas

• Belfast, Northern Ireland, United Kingdom
• Birmingham, England, United Kingdom
• Bristol, England, United Kingdom
• Cardiff, Wales, United Kingdom
• Casablanca, Morocco
• Dublin, Ireland
• Edinburgh, Scotland, United Kingdom
• Aberdeen, Scotland, United Kingdom
• Glasgow, Scotland, United Kingdom
• Liverpool, England, United Kingdom
• Leeds, England, United Kingdom
• Lisbon, Portugal
• London, England, United Kingdom
• Manchester, England, United Kingdom
• Sheffield, England, United Kingdom
• Porto, Portugal
• Reykjavík, Iceland
• Accra, Ghana
• Dakar, Senegal

See also

• WWV (radio station) — United States' time signal service
• CHU (radio station) — Canada's time signal service
• BPM (time service) — China's national time signal service
• DCF77 — Germany's time signal service
• VNG — Australia's national time signal service
• Marine chronometer — synchronised with GMT, and used by ships to calculate their longitude
• 24-hour watch — 24-hour wristwatch
• Swatch Internet Time — alternative, decimal measure of time
• Sandringham Time

Notes

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. Events 46 BC - Titus Labienus defeats Julius Caesar in the Battle of Ruspina. 2008 ( MMVIII) is the current year in accordance with the Gregorian calendar, a Leap year that started on Tuesday of the Common

External links

• Greenwich Mean Time
• NIST — World Time Scales
• International Earth Rotation and Reference Systems Service
• World Clock — Current Local Times
• Royal Observatory Greenwich
• The original BBC World Service GMT time signal in mp3 format