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| Early timekeeping | |
| 3>
Before the invention of clocks, people marked the time of day with apparent solar time (or "true" solar time) – for example, the time on a sundial – which was typically different for every settlement.
When well-regulated mechanical clocks became widespread in the early 19th century,[citation needed] each city began to use some local mean solar time. Apparent and mean solar time can differ by up to around 15 minutes (as described by the equation of time) due to the non-circular shape of the Earth's orbit around the sun. Mean solar time has days of equal length, and the difference between the two averages to zero after a year.
Greenwich Mean Time (GMT) was established in 1675 when the Royal Observatory was built as an aid to (English) mariners to determine longitude at sea, providing a reference time at a point in history when each city in England kept a different local time.
[edit] Tags:Longitude,Apparent Solar Time,Sundial,Mean Solar Time,Equation Of Time,Greenwich Mean Time,Royal Observatory,England,Greenwich,Ru,Ca,Ne,De,Ee,Lt,Id,Us, | |
| Railroad time | |
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Plaque commemorating the Railway General Time Convention of 1883 in North America
The use of local solar time became increasingly awkward as railways and telecommunications improved, because clocks differed between places by an amount corresponding to the difference in their geographical longitude, which was usually not a convenient number.
The first time zone in the world was established on December 1, 1847, on the island of Great Britain by railway companies using GMT kept by portable chronometers. This quickly became known as Railway Time. About August 23, 1852, time signals were first transmitted by telegraph from the Royal Observatory, Greenwich. Even though 98% of Great Britain's public clocks were using GMT by 1855, it was not made Britain's legal time until August 2, 1880. Some old British clocks from this period have two minute hands—one for the local time, one for GMT.[1]
The increase in worldwide communication had further increased the need for interacting parties to communicate mutually comprehensible time references to one another. The problem of differing local times could be solved across larger areas by synchronizing clocks worldwide, but in many places the local time would then differ markedly from the solar time to which people were accustomed. Time zones were a compromise, relaxing the complex geographic dependence while still allowing local time to approximate the mean solar time.
On November 2, 1868, the then-British colony of New Zealand officially adopted a standard time to be observed throughout the colony, and was perhaps the first country to do so. It was based on the longitude 172°30′ East of Greenwich, that is 11 hours 30 minutes ahead of GMT. This standard was known as New Zealand Mean Time.
Timekeeping on the American railroads in the mid-19th century was somewhat confused. Each railroad used its own standard time, usually based on the local time of its headquarters or most important terminus, and the railroad's train schedules were published using its own time. Some major railroad junctions served by several different railroads had a separate clock for each railroad, each showing a different time; the main station in Pittsburgh, Pennsylvania, for example, kept six different times.
Charles F. Dowd proposed a system of one-hour standard time zones for American railroads about 1863, although he published nothing on the matter at that time and did not consult railroad officials until 1869. In 1870, he proposed four ideal time zones (having north–south borders), the first centered on Washington, D.C., but by 1872 the first was centered 75°W of Greenwich, with geographic borders (for example, sections of the Appalachian Mountains). Dowd's system was never accepted by American railroads. Instead, U.S. and Canadian railroads implemented a version proposed by William F. Allen, the editor of the Traveler's Official Railway Guide.[2] The borders of its time zones ran through railroad stations, often in major cities. For example, the border between its Eastern and Central time zones ran through Detroit, Buffalo, Pittsburgh, Atlanta, and Charleston. It was inaugurated on Sunday, November 18, 1883, also called "The Day of Two Noons",[3] when each railroad station clock was reset as standard-time noon was reached within each time zone. The zones were named Intercolonial, Eastern, Central, Mountain, and Pacific. Within one year, 85% of all cities with populations over 10,000, about 200 cities, were using standard time.[4] A notable exception was Detroit (which is about half-way between the meridians of eastern time and central time), which kept local time until 1900, then tried Central Standard Time, local mean time, and Eastern Standard Time before a May 1915 ordinance settled on EST and was ratified by popular vote in August 1916. The confusion of times came to an end when Standard zone time was formally adopted by the U.S. Congress on March 19, 1918, in the Standard Time Act.
U.S. Commissioner of Railroads William H. Armstrong gave the following account of the new railroad time system in his Report to the Secretary of the Interior for 1883.
The question of uniform time standards for railways of the United States has long attracted the attention of railway managers, but Mr. W. F. Allen, editor of the Traveler's Official Guide, and secretary of the time conventions, is entitled to the credit of having perfected the admirable system which was adopted by the general time convention of railway managers, held at Chicago, October 11, 1883, and ratified by the southern railway time convention, held at New York, October 17, 1883.
As this is a subject of great interest to the entire country, a brief synopsis of the general principles governing the proposed plan is deemed appropriate in this report.
Under the present system each railway is operated independently on the local time of some principal point or points on said road, but this plan was found to be highly objectionable, owing to the fact that some fifty standards, intersecting and interlacing each other, were in use throughout the country. By the plan which has been adopted this number will be reduced to four, the difference in time being one hour between each, viz, the 75th, 90th, 105th, and 120th degrees of longitude west from Greenwich. The adoption of these standards will not cause a difference of more than thirty minutes from the local time at any point which is now used as a standard. The new arrangement goes into effect November 18, 1883, and all changes of time are to occur at the termini of roads, or at the ends of divisions. The seventy-fifth meridian being almost precisely the central meridian for the system of roads now using standards based upon the time of the Eastern cities, and the ninetieth meridian being equally central for roads now running by the time of Western cities, the time of these meridians has been adopted for the territory which includes 90 per cent. of the whole railway system of the country. Nearly all of the larger cities have abolished local time and adopted that of the nearest standard meridian in use by the railways.[5][6][7]
[edit] Tags:Standard Time,Meridians,Railways,Telecommunications,Great Britain,Railway Companies,Chronometers,Railway Time,Telegraph,Royal Observatory, Greenwich,New Zealand,New Zealand Mean Time,Pittsburgh,Pennsylvania,Charles F. Dowd,Washington, D.c.,75°w Of Greenwich,Appalachian Mountains,Detroit,Buffalo,Atlanta,Charleston,Local Mean Time,U.s. Congress,William H. Armstrong,Meridian,Chicago,Fi,Lv,United States,New York, | |
| Worldwide time zones | |
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Although the first person to propose a worldwide system of time zones was the Italian mathematician Quirico Filopanti in his book Miranda! published in 1858, his idea was unknown outside the pages of his book until long after his death, so it did not influence the adoption of time zones during the 19th century. He proposed 24 hourly time zones, which he called "longitudinal days", the first centered on the meridian of Rome. He also proposed a universal time to be used in astronomy and telegraphy.[8][9]
Canadian Sir Sandford Fleming proposed a worldwide system of time zones in 1879. He advocated his system at several international conferences, thus is widely credited with their invention. In 1876, his first proposal was for a global 24-hour clock, conceptually located at the center of the Earth and not linked to any surface meridian. In 1879 he specified that his universal day would begin at the anti-meridian of Greenwich (180th meridian), while conceding that hourly time zones might have some limited local use. He also proposed his system at the International Meridian Conference in October 1884, but it did not adopt his time zones because they were not within its purview. The conference did adopt a universal day of 24 hours beginning at Greenwich midnight, but specified that it "shall not interfere with the use of local or standard time where desirable".
By about 1900, almost all time on Earth was in the form of standard time zones, only some of which used an hourly offset from GMT. Many applied the time at a local astronomical observatory to an entire country, without any reference to GMT. It took many decades before all time on Earth was in the form of time zones referred to some "standard offset" from GMT/UTC. Most major countries had adopted hourly time zones by 1929. Nepal was the last country to adopt a standard offset, shifting slightly to UTC+5:45 in 1986.
Today, all nations use standard time zones for secular purposes, but they do not all apply the concept as originally conceived. Newfoundland, India, Iran, Afghanistan, Venezuela, Burma, the Marquesas, as well as parts of Australia use half-hour deviations from standard time, and some nations, such as Nepal, and some provinces, such as the Chatham Islands, use quarter-hour deviations. Some countries, most notably China and India, use a single time zone, even though the extent of their territory far exceeds 15° of longitude. Before 1949, China used five time zones (see Time in China).
[edit] Tags:180th Meridian,Quirico Filopanti,Sandford Fleming,International Meridian Conference,Nepal,Newfoundland,India,Iran,Afghanistan,Venezuela,Burma,Marquesas,Chatham Islands,China,Time In China,Utc,Nl, | |
| Definition | |
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Before 1972, all time zones were specified as an offset from Greenwich Mean Time (GMT), which was the mean solar time at the meridian passing through the Royal Observatory in Greenwich, London, United Kingdom. Since 1972, all official time services have broadcast radio time signals synchronized to UTC, a form of atomic time that includes leap seconds to keep it within 0.9 seconds of this former GMT, now called UT1. Many countries now legally define their standard time relative to UTC, although some still legally refer to GMT, including the United Kingdom itself. UTC, also called Zulu time, is used everywhere on Earth by astronomers and others who need to state the time of an event unambiguously.
Time zones are based on Greenwich Mean Time (GMT)[citation needed], the mean solar time at longitude 0° (the Prime Meridian). The definition of GMT was recently changed[citation needed] – it was previously the same as UT1, a mean solar time calculated directly from the rotation of the Earth. As the rate of rotation of the Earth is not constant, the time derived from atomic clocks was adjusted to closely match UT1. In January 1972, however, the length of the second in both Greenwich Mean Time and atomic time was equalized. The readings of participating atomic clocks are averaged out to give a uniform time scale.
Because the length of the average day is a small fraction of a second more than 24 hours (slightly more than 86400 seconds), leap seconds are periodically inserted into Greenwich Mean Time to make it approximate to UT1. This new time system is also called Coordinated Universal Time (UTC). Leap seconds are inserted to keep UTC within 0.9 seconds of UT1. Because of the secular (long term) slowing down of the Earth's rotation, leap seconds will gradually need to be added more and more often. But on short time scales (from one year to the next) the rotation rate is irregular, so leap seconds are not added unless observations of Earth's rotation show that one is required. In this way, local times continue to correspond approximately to mean solar time, while the effects of variations in Earth's rotation rate are confined to simple step changes that can be more easily applied to the uniform time scale (International Atomic Time or TAI). All local times differ from TAI by an integral number of seconds. With the implementation of UTC, nations began to use it in the definition of their time zones. As of 2005, most nations had altered the definition of local time in this way.
In the United Kingdom, this involved redefining Greenwich Mean Time to make it the same as UTC.[10] British Summer Time (BST) is still one hour in advance of Greenwich Mean Time and is therefore also one hour in advance of Coordinated Universal Time. Thus Greenwich Mean Time is the local time at the Royal Observatory, Greenwich between 0100 hours GMT on the last Sunday in October and 0100 hours GMT on the last Sunday in March. Similar circumstances apply in many other places.
Looking to the future, leap seconds are considered by many to be a nuisance, and ways to abolish them are being considered. This means letting the time difference accumulate. One suggestion is to insert a "leap-hour" in about 5,000 years. For more on this discussion read Proposal to abolish leap seconds.
[edit] Tags:Coordinated Universal Time,London,United Kingdom,Leap Seconds,Prime Meridian,Ut1,Atomic Clocks,International Atomic Time,British Summer Time,Ki, | |
| UTC | |
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If the time is in UTC, add a "Z" directly after the time without a space. "Z" is the zone designator for the zero UTC offset. "09:30 UTC" is therefore represented as "09:30Z" or "0930Z". "14:45:15 UTC" would be "14:45:15Z" or "144515Z".
UTC time is also known as "Zulu" time, since "Zulu" is the ICAO spelling alphabet code word for "Z".
[edit] Tags:Icao Spelling Alphabet, | |
| Offsets from UTC | |
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Offsets from UTC are written in the format ±[hh]:[mm], ±[hh][mm], or ±[hh]. So if the time being described is one hour ahead of UTC (such as the time in Berlin during the winter), the zone designator would be "+01:00", "+0100", or simply "+01". This is appended to the time in the same way that 'Z' was above. The offset from UTC changes with daylight saving time, e.g. a time offset in Chicago, which is in the North American Central Time Zone, would be "−06:00" for the winter (Central Standard Time) and "−05:00" for the summer (Central Daylight Time).
[edit] Tags:Daylight Saving Time,Offsets From Utc,Berlin,−06:00,−05:00,+01:00, | |
| Abbreviations | |
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Time zones are often represented by abbreviations such as "EST, WST, CST" but these are not part of the international time and date standard ISO 8601 and their use as sole designator for a time zone is not recommended. Such designations can be ambiguous. For example, "BST", which is British Summer Time, was renamed "British Standard Time" between 1968 and 1971 when Central European Time was in force because legislators objected to calling it Central European Time. The same legislation affirmed that the Standard Time within the United Kingdom was, and would continue to be, Greenwich Mean Time.
[edit] Tags:Europe, | |
| UTC offsets worldwide | |
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Main article: List of time zones by UTC offset
Time zones map (Last update: December 31, 2011)
UTC−12:00 ...
UTC−07:00
UTC−06:00 ...
UTC−01:00
UTC±00:00 ...
UTC+05:45
UTC+06:00 ...
UTC+11:30
UTC+12:00 ...
UTC+14:00
Oceania / North America / Antarctica
North and South America / Antarctica
Europe / Africa / Asia / Antarctica
Asia / Antarctica
Asia / Oceania / Antarctica
No DST in summer
DST in summer
No DST in summer
DST in summer
No DST in summer
DST in summer
No DST in summer
DST in summer
No DST in summer
DST in summer
−12:00
−12:00
/−11:00
N: US-
−06:00
−06:00
/−05:00
N: US-
±00:00
IS
±00:00
/+01:00
N: GB, PT
+06:00
RU-, KZ--
+06:00
/+07:00
+12:00
KI-, RU-
+12:00
/+13:00
S: NZ-
+06:30
MM
+06:30
/+07:30
+12:45
+12:45
/+13:45
S: NZ
−11:00
−11:00
/−10:00
N: US-
−05:00
BO, CO, PA, PE
−05:00
/−04:00
N: CA-, CU, US-
+01:00
TN, CG, CD-, DZ, NE, NG
+01:00
/+02:00
N: AT, BA, BE, CH, CZ, DE, ES-, FR, HR, HU, IT, LI, LU, MK, NL, NO, SE, SI, SK
S: NA
+07:00
RU-, MN-, VN, LA, TH, KH, ID-
+07:00
/+08:00
+13:00
KI-
−04:30
VE
−10:00
−10:00
/−09:00
−04:00
−04:00
/−03:00
S: AQ-
+02:00
Europe: BY
+02:00
/+03:00
N: FI, EE, LV, LT, UA, BG, GR, MD, RO, TR
+08:00
CN, HK, ID-, MN-, MY, RU-, SG, TW,
+08:00
/+09:00
+14:00
KI-
−03:30
−03:30
/−02:30
S: CA-
−09:00
−09:00
/−08:00
−03:00
AR
−03:00
/−02:00
S: BR-
+03:00
Europe: BY, RU-, Africa: KE, SD, SO, SS, ER, Asia: IQ, SA
+03:00
/+04:00
+09:00
RU-, JP, KP, KR, ID-
+09:00
/+10:00
+03:30
+03:30
/+04:30
IR
+09:30
+09:30
/+10:30
AU-
−08:00
−08:00
/−07:00
N: CA-, US-, MX-
−02:00
−02:00
/−01:00
+04:00
RU-, GE
+04:00
/+05:00
+10:00
RU-
+10:00
/+11:00
+04:30
AF
−07:00
−07:00
/−06:00
N: CA-, US-, MX-
−01:00
−01:00
/±00:00
+05:00
KZ-, PK
+05:00
/+06:00
+11:00
RU-
+11:00
/+12:00
+05:30
IN
+11:30
NF
+05:45
NP
XX = ISO 3166-1 alpha-2 country code, XX- = parts of the country, N = North, S = South, UTC = Universal Coordinated Time, DST = Daylight Saving Time
[edit] Tags:Antarctica,Africa,−12:00,−11:00,±00:00,+06:00,+12:00,+13:00,+06:30,+12:45,+13:45,−10:00,−04:00,+02:00,+07:00,−04:30,−03:00,+03:00,+08:00,+14:00,−03:30,−02:30,−09:00,−02:00,+09:00,Jp,+03:30,+04:30,+09:30,+10:30,−08:00,−07:00,+04:00,+10:00,−01:00,+05:00,+11:00,+05:30,+11:30,+05:45,Iso 3166-1 Alpha-2,Universal Coordinated Time,Utc−12:00,Utc−07:00,Utc−06:00, | |
| List of UTC offsets | |
| 2>
These examples give the local time at various locations around the world when daylight saving time is not in effect:
Time zone
Example time
(ISO 8601 notation)
Example locations
Example locations that in summer use DST
UTC−12:00
2012-02-05T02:05:32-12:00
Baker Island, Howland Island (both uninhabited)
UTC−11:00
2012-02-05T03:05:32-11:00
American Samoa, Niue
UTC−10:00
2012-02-05T04:05:32-10:00
United States (Hawaii)
Most of French Polynesia, United States (Aleutian Islands)
UTC−09:30
2012-02-05T04:35:32-09:30
Marquesas Islands
UTC−09:00
2012-02-05T05:05:32-09:00
Gambier Islands
United States (most of Alaska)
UTC−08:00
2012-02-05T06:05:32-08:00
Canada (most of British Columbia), Mexico (Baja California), United States (California, most of Nevada, most of Oregon, Washington (state))
UTC−07:00
2012-02-05T07:05:32-07:00
Mexico (Sonora), United States (Arizona)
Canada (Alberta), Mexico (Chihuahua), United States (Colorado)
UTC−06:00
2012-02-05T08:05:32-06:00
Costa Rica, El Salvador, Ecuador (Galápagos Islands), Guatemala, Honduras, Mexico (most), Nicaragua,
Canada (Manitoba, Saskatchewan), United States (Illinois, most of Texas)
UTC−05:00
2012-02-05T09:05:32-05:00
Colombia, Cuba, Ecuador (continental), Haiti, Jamaica, Panama, Peru
Canada (most of Ontario, most of Quebec), United States (most of Florida, Georgia, Massachusetts, most of Michigan, New York, North Carolina, Ohio, Washington D.C.)
UTC−04:30
2012-02-05T09:35:32-04:30
Venezuela
UTC−04:00
2012-02-05T10:05:32-04:00
Bolivia, Brazil (Amazonas), Chile (continental), Dominican Republic, Canada (Nova Scotia), Paraguay, Puerto Rico, Trinidad and Tobago
Falkland Islands
UTC−03:30
2012-02-05T10:35:32-03:30
Canada (Newfoundland)
UTC−03:00
2012-02-05T11:05:32-03:00
Argentina
Brazil (BrasÃlia, Rio de Janeiro, São Paulo), most of Greenland, Uruguay
UTC−02:00
2012-02-05T12:05:32-02:00
Brazil (Fernando de Noronha), South Georgia and the South Sandwich Islands
UTC−01:00
2012-02-05T13:05:32-01:00
Portugal (Azores), Cape Verde
UTC±00:00
2012-02-05T14:05:32+00:00
Côte d'Ivoire, Faroe Islands, Ghana, Iceland, Senegal
Ireland, Portugal (continental and Madeira), Spain (Canary Islands), Morocco, United Kingdom
UTC+01:00
2012-02-05T15:05:32+01:00
Angola, Cameroon, Nigeria, Tunisia
Albania, Algeria, Austria, Belgium, Bosnia and Herzegovina, Spain (continental), Croatia, Czech Republic, Denmark, Germany, Hungary, Italy, Malta, Kinshasa, Kosovo, Macedonia, France (metropolitan), the Netherlands, Norway, Poland, Serbia, Slovakia, Slovenia, Sweden, Switzerland
UTC+02:00
2012-02-05T16:05:32+02:00
Libya, Egypt, Malawi, Mozambique, South Africa, Swaziland, Ukraine, Zambia, Zimbabwe
Bulgaria, Cyprus, Estonia, Finland, Greece, Israel, Jordan, Latvia, Lebanon, Lithuania, Moldova, Palestine, Romania, Syria, Turkey
UTC+03:00
2012-02-05T17:05:32+03:00
Belarus, Djibouti, Eritrea, Ethiopia, Iraq, Kenya, Madagascar, Russia (Kaliningrad Oblast), Saudi Arabia, South Sudan, Sudan, Somalia, South Sudan, Tanzania, Uganda, Yemen
UTC+03:30
2012-02-05T17:35:32+03:30
Iran
UTC+04:00
2012-02-05T18:05:32+04:00
Armenia, Azerbaijan, Georgia, Mauritius, Oman, Russia (European), Seychelles, United Arab Emirates
UTC+04:30
2012-02-05T18:35:32+04:30
Afghanistan
UTC+05:00
2012-02-05T19:05:32+05:00
Kazakhstan (West), Maldives, Pakistan, Uzbekistan
UTC+05:30
2012-02-05T19:35:32+05:30
India, Sri Lanka
UTC+05:45
2012-02-05T19:50:32+05:45
Nepal
UTC+06:00
2012-02-05T20:05:32+06:00
Kazakhstan (most), Bangladesh, Russia (Ural: Sverdlovsk Oblast, Chelyabinsk Oblast)
UTC+06:30
2012-02-05T20:35:32+06:30
Cocos Islands, Myanmar Tags:-12:00,Baker Island,Howland Island,Utc−11:00,-11:00,American Samoa,Niue,Utc−10:00,-10:00,Hawaii,French Polynesia,Aleutian Islands,Utc−09:30,-09:30,Marquesas Islands,Utc−09:00,-09:00,Gambier Islands,Alaska,Utc−08:00,-08:00,Canada,British Columbia,Mexico,Baja California,California,Nevada,Oregon,Washington (state),-07:00,Sonora,Arizona,Alberta,Chihuahua,Colorado,-06:00,Costa Rica,El Salvador,Galápagos Islands,Guatemala, | |
z³ote monety |