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135-461: Australia uses three main time zones : Australian Eastern Standard Time ( AEST ; UTC+10:00 ), Australian Central Standard Time ( ACST ; UTC+09:30 ) and Australian Western Standard Time ( AWST ; UTC+08:00 ). Time is regulated by the individual state governments , some of which observe daylight saving time (DST). Daylight saving time (+1 hour) is used between the first Sunday in October and
270-713: A Federal Court may be filed based on the local time. The effect of this is that if there had been a failure to file a legal document on time in an eastern State, that document can sometimes still be filed (within two hours) in Western Australia. The 18 zones for Australia as given by zone.tab of the IANA time zone database . Columns marked * are from the zone.tab. Queensland has had a particularly involved debate over daylight saving time, with public opinion geographically divided. The state's first trial of DST lasted one year, from 31 October 1971 to 27 February 1972. In 1973
405-521: A prospectus for the issue of stock in a company would usually set the closing time for offers at some location (e.g. Sydney) as the time when offers must be received, regardless of the source of the offer. Similarly, tenders for their sale of stock usually set out the time at a given location by which they must be received to be considered. Another example is the Australian Securities Exchange which operates on Sydney time. On
540-564: A C library based on the BSD C library, or the System V Release 4 C library, can make use of this database. Windows -based computer systems prior to Windows 95 and Windows NT used local time, but Windows 95 and later, and Windows NT, base system time on UTC. They allow a program to fetch the system time as UTC, represented as a year, month, day, hour, minute, second, and millisecond; Windows 95 and later, and Windows NT 3.5 and later, also allow
675-417: A break with the common international practice of setting one-hour intervals between adjacent time zones, South Australia advanced Central Standard Time by thirty minutes after lobbying by businesses who wanted to be closer to Melbourne time and cricketers and footballers who wanted more daylight to practice in the evenings. It also meant that South Australia became one of only a few places in the world which uses
810-553: A close approximation to UT1 , UTC occasionally has discontinuities where it changes from one linear function of TAI to another. These discontinuities take the form of leap seconds implemented by a UTC day of irregular length. Discontinuities in UTC occurred only at the end of June or December. However, there is provision for them to happen at the end of March and September as well as a second preference. The International Earth Rotation and Reference Systems Service (IERS) tracks and publishes
945-444: A convenient time, usually at night, not exactly when they cross a certain longitude. Some ships simply remain on the time of the departing port during the whole trip. Ideal time zones, such as nautical time zones, are based on the mean solar time of a particular meridian in the middle of that zone with boundaries located 7.5 degrees east and west of the meridian. In practice, however, many time zone boundaries are drawn much farther to
1080-453: A mean solar day in the mid‑19th century. In earlier centuries, the mean solar day was shorter than 86,400 SI seconds, and in more recent centuries it is longer than 86,400 seconds. Near the end of the 20th century, the length of the mean solar day (also known simply as "length of day" or "LOD") was approximately 86,400.0013 s. For this reason, UT is now "slower" than TAI by the difference (or "excess" LOD) of 1.3 ms/day. The excess of
1215-418: A mean solar day to lengthen by one second (at a rate of 2 ms per century). This rate fluctuates within the range of 1.7–2.3 ms/cy. While the rate due to tidal friction alone is about 2.3 ms/cy, the uplift of Canada and Scandinavia by several metres since the last ice age has temporarily reduced this to 1.7 ms/cy over the last 2,700 years. The correct reason for leap seconds, then,
1350-478: A meridian drifting eastward faster and faster. Thus, the time system will lose its fixed connection to the geographic coordinates based on the IERS meridian . The difference between UTC and UT would reach 0.5 hours after the year 2600 and 6.5 hours around 4600. ITU-R Study Group 7 and Working Party 7A were unable to reach consensus on whether to advance the proposal to the 2012 Radiocommunications Assembly;
1485-422: A minute is usually 60, but with an occasional leap second , it may be 61 or 59 instead. Thus, in the UTC time scale, the second and all smaller time units (millisecond, microsecond, etc.) are of constant duration, but the minute and all larger time units (hour, day, week, etc.) are of variable duration. Decisions to introduce a leap second are announced at least six months in advance in "Bulletin C" produced by
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#17328021501421620-417: A negative vote of 54.6 per cent in the 2009 referendum , the highest percentage for all four of these referendums. Each referendum followed a trial period during which the state observed DST. The first three followed a one-year trial, while the 2006 Western Australian Daylight Saving Bill (No. 2) 2006 instituted a trial of DST beginning on 3 December 2006, and lasting for three years. Some towns located near
1755-516: A particular time zone can be determined by adding or subtracting the number of hours and minutes specified by the UTC offset , which ranges from UTC−12:00 in the west to UTC+14:00 in the east (see List of UTC offsets ). The time zone using UTC is sometimes denoted UTC+00:00 or by the letter Z —a reference to the equivalent nautical time zone (GMT), which has been denoted by a Z since about 1950. Time zones were identified by successive letters of
1890-694: A result of the International Telecommunication Union and the International Astronomical Union wanting to use the same abbreviation in all languages. The compromise that emerged was UTC , which conforms to the pattern for the abbreviations of the variants of Universal Time (UT0, UT1, UT2, UT1R, etc.). McCarthy described the origin of the abbreviation: In 1967 the CCIR adopted the names Coordinated Universal Time and Temps Universel Coordonné for
2025-547: A shift of the sun's movements relative to civil time, with the difference increasing quadratically with time (i.e., proportional to elapsed centuries squared). This is analogous to the shift of seasons relative to the yearly calendar that results from the calendar year not precisely matching the tropical year length. This would be a change in civil timekeeping, and would have a slow effect at first, but becoming drastic over several centuries. UTC (and TAI) would be more and more ahead of UT; it would coincide with local mean time along
2160-423: A single time zone even though the extent of their territory far exceeds the ideal 15° of longitude for one hour; other countries, such as Spain and Argentina , use standard hour-based offsets, but not necessarily those that would be determined by their geographical location. The consequences, in some areas, can affect the lives of local citizens, and in extreme cases contribute to larger political issues, such as in
2295-476: A source of error). UTC does not change with a change of seasons, but local time or civil time may change if a time zone jurisdiction observes daylight saving time (summer time). For example, local time on the east coast of the United States is five hours behind UTC during winter, but four hours behind while daylight saving is observed there. In 1928, the term Universal Time ( UT ) was introduced by
2430-442: A standard clock not on the geoid, or in rapid motion, will not maintain synchronicity with UTC. Therefore, telemetry from clocks with a known relation to the geoid is used to provide UTC when required, on locations such as those of spacecraft. It is impossible to compute the exact time interval elapsed between two UTC timestamps without consulting a table showing how many leap seconds occurred during that interval. By extension, it
2565-401: A system of hourly standard time zones for North American railroads, 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 on meridian 75° west of Greenwich , with natural borders such as sections of
2700-487: A time standard. Amateur radio operators often schedule their radio contacts in UTC, because transmissions on some frequencies can be picked up in many time zones. UTC divides time into days, hours, minutes, and seconds . Days are conventionally identified using the Gregorian calendar , but Julian day numbers can also be used. Each day contains 24 hours and each hour contains 60 minutes. The number of seconds in
2835-443: A time zone may use a different offset for part of the year, typically one hour ahead during spring and summer , a practice known as daylight saving time (DST). In the table below, the locations that use daylight saving time (DST) are listed in their UTC offset when DST is not in effect. When DST is in effect, approximately during spring and summer, their UTC offset is increased by one hour (except for Lord Howe Island , where it
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#17328021501422970-680: A time-zone meridian located outside of its geographical boundaries. Attempts to undo this change in 1986 and 1994 failed. In 1911, when the Northern Territory was separated from South Australia and placed under the jurisdiction of the Federal Government, the Territory kept Central Standard Time. Likewise, when the ACT and Jervis Bay Territory were broken off from New South Wales, they retained Eastern Standard Time. Since 1899,
3105-420: A value to be chosen for the length of the atomic second that would accord with the celestial laws of motion. The coordination of time and frequency transmissions around the world began on 1 January 1960. UTC was first officially adopted in 1963 as CCIR Recommendation 374, Standard-Frequency and Time-Signal Emissions , and "UTC" became the official abbreviation of Coordinated Universal Time in 1967. In 1961,
3240-445: A worldwide system of time zones in 1876 - see Sandford Fleming § Inventor of worldwide standard time . The proposal divided the world into twenty-four time zones labeled A-Y (skipping J), each one covering 15 degrees of longitude. All clocks within each zone would be set to the same time as the others, but differed by one hour from those in the neighboring zones. He advocated his system at several international conferences, including
3375-656: Is about 10 minutes before solar noon in Bristol , which is about 2.5 degrees to the west. The Royal Observatory, Greenwich , founded in 1675, established Greenwich Mean Time (GMT), the mean solar time at that location, as an aid to mariners to determine longitude at sea, providing a standard reference time while each location in England kept a different time. In the 19th century, as transportation and telecommunications improved, it became increasingly inconvenient for each location to observe its own solar time. In November 1840,
3510-478: Is added directly after the time without a separating space. "Z" is the zone designator for the zero UTC offset. "09:30 UTC" is therefore represented as "09:30Z" or "0930Z". Likewise, "14:45:15 UTC" is written as "14:45:15Z" or "144515Z". UTC time is also known as "Zulu" time, since "Zulu" is a phonetic alphabet code word for the letter "Z". Offsets from UTC are written in the format ±hh:mm, ±hhmm, or ±hh (either hours ahead or behind UTC). For example, if
3645-451: Is affected by the leap seconds introduced in UTC). Time zones are usually defined as differing from UTC by an integer number of hours, although the laws of each jurisdiction would have to be consulted if sub-second accuracy was required. Several jurisdictions have established time zones that differ by an odd integer number of half-hours or quarter-hours from UT1 or UTC. Current civil time in
3780-497: Is also a widely used variant of ACST ( Australian Central Standard Time , UTC+09:30). Conversion between time zones obeys the relationship in which each side of the equation is equivalent to UTC. The conversion equation can be rearranged to For example, the New York Stock Exchange opens at 09:30 ( EST , UTC offset= −05:00). In California ( PST , UTC offset= −08:00) and India ( IST , UTC offset= +05:30),
3915-541: Is an abbreviation for the time laboratory. The time of events may be provisionally recorded against one of these approximations; later corrections may be applied using the International Bureau of Weights and Measures (BIPM) monthly publication of tables of differences between canonical TAI/UTC and TAI( k )/UTC( k ) as estimated in real-time by participating laboratories. (See the article on International Atomic Time for details.) Because of time dilation ,
4050-481: Is approximately +1.7 ms per century. At the end of the 21st century, LOD will be roughly 86,400.004 s, requiring leap seconds every 250 days. Over several centuries, the frequency of leap seconds will become problematic. A change in the trend of the UT1 – UTC values was seen beginning around June 2019 in which instead of slowing down (with leap seconds to keep the difference between UT1 and UTC less than 0.9 seconds)
4185-613: Is in the North American Central Time Zone , is " −06:00 " for the winter (Central Standard Time) and " −05:00 " for the summer (Central Daylight Time). Time zones are often represented by alphabetic abbreviations such as "EST", "WST", and "CST", but these are not part of the international time and date standard ISO 8601 . Such designations can be ambiguous; for example, "CST" can mean (North American) Central Standard Time (UTC−06:00), Cuba Standard Time (UTC−05:00) and China Standard Time (UTC+08:00), and it
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4320-682: Is increased by 30 minutes). For example, during the DST period California observes UTC−07:00 and the United Kingdom observes UTC+01:00 . The apparent position of the Sun in the sky, and thus solar time , varies by location due to the spherical shape of the Earth. This variation corresponds to four minutes of time for every degree of longitude , so for example when it is solar noon in London , it
4455-604: Is not officially recognised, but is marked by official road signs. It is tracked in the tz database , the record of time zones for computers, as "Australia/Eucla". A number of small towns in Outback Western Australia also follow UTC+09:30 rather than UTC+08. These towns include Blackstone, Irrunytju, Warakurna, Wanarn, Kiwirrkurra, and Tjukurla. The Indian Pacific train has its own time zone—a so-called "train time" when travelling between Kalgoorlie , Western Australia and Port Augusta , South Australia—which
4590-485: Is not possible to compute the precise duration of a time interval that ends in the future and may encompass an unknown number of leap seconds (for example, the number of TAI seconds between "now" and 2099-12-31 23:59:59). Therefore, many scientific applications that require precise measurement of long (multi-year) intervals use TAI instead. TAI is also commonly used by systems that cannot handle leap seconds. GPS time always remains exactly 19 seconds behind TAI (neither system
4725-407: Is not the current difference between actual and nominal LOD, but rather the accumulation of this difference over a period of time: Near the end of the 20th century, this difference was about 1 / 800 of a second per day; therefore, after about 800 days, it accumulated to 1 second (and a leap second was then added). In the graph of DUT1 above, the excess of LOD above
4860-557: Is often used to avoid ambiguity with the time zone abbreviations "CST" and "EST" referring to the Central and Eastern Time Zones in North America. Though the governments of the states and territories have the power to legislate variations in time, the standard time within each of these is set related to Coordinated Universal Time (UTC) as determined by the International Bureau of Weights and Measures and set by section 8AA of
4995-413: Is slightly longer than 86,400 SI seconds so occasionally the last minute of a UTC day is adjusted to have 61 seconds. The extra second is called a leap second. It accounts for the grand total of the extra length (about 2 milliseconds each) of all the mean solar days since the previous leap second. The last minute of a UTC day is permitted to contain 59 seconds to cover the remote possibility of
5130-441: Is the effective successor to Greenwich Mean Time (GMT) in everyday usage and common applications. In specialized domains such as scientific research, navigation, and timekeeping, other standards such as UT1 and International Atomic Time (TAI) are also used alongside UTC. UTC is based on TAI, which is a weighted average of hundreds of atomic clocks worldwide. UTC is within about one second of mean solar time at 0° longitude,
5265-467: Is to allow the more efficient use of afternoon sunlight. Some of these locations also use daylight saving time (DST), further increasing the difference to local solar time. As a result, in summer, solar noon in the Spanish city of Vigo occurs at 14:41 clock time. This westernmost area of continental Spain never experiences sunset before 18:00 clock time, even in winter, despite lying 42 degrees north of
5400-599: Is updated whenever time zone or daylight saving time rules change. Oracle provides an updater tool for this purpose. As an alternative to the information bundled with the Java Platform, programmers may choose to use the Joda-Time library. This library includes its own data based on the IANA time zone database. As of Java 8 there is a new date and time API that can help with converting times. Traditionally, there
5535-403: Is usually converted to local time when displayed to the user, and times specified by the user in local time are converted to Unix time. The conversion takes into account the time zone and daylight saving time rules; by default the time zone and daylight saving time rules are set up when the system is configured, though individual processes can specify time zones and daylight saving time rules using
Time in Australia - Misplaced Pages Continue
5670-468: Is very slowly decreasing because of tidal deceleration ; this increases the length of the mean solar day . The length of the SI ;second was calibrated on the basis of the second of ephemeris time and can now be seen to have a relationship with the mean solar day observed between 1750 and 1892, analysed by Simon Newcomb . As a result, the SI second is close to 1 / 86400 of
5805-761: The Appalachian Mountains . Dowd's system was never accepted by North American railroads. Chief meteorologist at the United States Weather Bureau Cleveland Abbe divided the United States into four standard time zones for consistency among the weather stations. In 1879, he published a paper titled Report on Standard Time . In 1883, he convinced North American railroad companies to adopt his time-zone system. In 1884, Britain, which had already adopted its own standard time system for England, Scotland, and Wales, helped gather international consent for global time. In time,
5940-589: The Australian Capital Territory use Eastern Standard Time. Daylight saving time is not currently used in Western Australia, the Northern Territory, or Queensland. The Cocos (Keeling) Islands uses UTC+06:30 year round, Christmas Island uses UTC+07:00 year round, while Norfolk Island uses UTC+11:00 as standard time and UTC+12:00 as daylight saving time. The standardisation of time in Australia began in 1892, when surveyors from
6075-592: The Bureau International de l'Heure began coordinating the UTC process internationally (but the name Coordinated Universal Time was not formally adopted by the International Astronomical Union until 1967). From then on, there were time steps every few months, and frequency changes at the end of each year. The jumps increased in size to 0.1 seconds. This UTC was intended to permit a very close approximation to UT2. In 1967,
6210-665: The Daylight Saving for South East Queensland (DS4SEQ) political party was officially registered, to advocate for the use of a two-time-zone system for DST in Queensland, with most of the state (in land area) using standard time. This party contested the March 2009 Queensland State election with 32 candidates, and it received about one per cent of the statewide primary vote. In early 2010, the DS4SEQ political party approached
6345-583: The Eyre Highway (including Eucla , Cocklebiddy , Madura , Mundrabilla and Border Village , just over the border into South Australia), follow "CWT" instead of Western Australian time. The total population of that area is estimated at 200 people. This area did not change when South Australia introduced DST. During the Western Australian trial of DST from 2006 to 2009, this area also sets its clocks ahead one hour during summer. This time zone
6480-494: The IANA time zone database and includes the ability to get, set and convert between time zones. The DateTime objects and related functions have been compiled into the PHP core since 5.2. This includes the ability to get and set the default script time zone, and DateTime is aware of its own time zone internally. PHP.net provides extensive documentation on this. As noted there, the most current time zone database can be implemented via
6615-580: The International Earth Rotation and Reference Systems Service . The leap seconds cannot be predicted far in advance due to the unpredictable rate of the rotation of Earth. Nearly all UTC days contain exactly 86,400 SI seconds with exactly 60 seconds in each minute. UTC is within about one second of mean solar time (such as UT1 ) at 0° longitude , (at the IERS Reference Meridian ). The mean solar day
6750-705: The International Meridian Conference , where it received some consideration. The system has not been directly adopted, but some maps divide the world into 24 time zones and assign letters to them, similarly to Fleming's system. By about 1900, almost all inhabited places on Earth had adopted a standard time zone, but only some of them 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 zones were based on some standard offset from GMT or Coordinated Universal Time (UTC). By 1929,
6885-569: The Marine Research Centre and the Parks and Wildlife office on the island remain on Eastern Standard Time. Resort manager Alistair Cooray says no-one is sure how the time zone came about. 'I believe it started in the late '50s early '60s as a way to give the guests a bit more daylight time on the island and no-one knows for sure though. ' " Lord Howe Island , part of the state of New South Wales but 600 kilometres (370 miles) east of
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#17328021501427020-697: The National Measurement Act 1960 of the Commonwealth . Australia has kept a version of the UTC atomic time scale since the 1990s, but Greenwich Mean Time (GMT) remained the formal basis for the standard times of all of the states until 2005. In November 2004, the state and territory attorneys-general endorsed a proposal from the Australian National Measurement Institute to adopt UTC as the standard of all Australian standard times, thereby eliminating
7155-471: The PECL timezonedb. Coordinated Universal Time Coordinated Universal Time ( UTC ) is the primary time standard globally used to regulate clocks and time. It establishes a reference for the current time, forming the basis for civil time and time zones . UTC facilitates international communication, navigation, scientific research, and commerce. UTC has been widely embraced by most countries and
7290-546: The SI second was redefined in terms of the frequency supplied by a caesium atomic clock. The length of second so defined was practically equal to the second of ephemeris time. This was the frequency that had been provisionally used in TAI since 1958. It was soon decided that having two types of second with different lengths, namely the UTC second and the SI second used in TAI, was a bad idea. It
7425-576: The Standard Time Act of March 19, 1918. Italian mathematician Quirico Filopanti introduced the idea of a worldwide system of time zones in his book Miranda! , published in 1858. He proposed 24 hourly time zones, which he called "longitudinal days", the first centred on the meridian of Rome . He also proposed a universal time to be used in astronomy and telegraphy. However, his book attracted no attention until long after his death. Scottish -born Canadian Sir Sandford Fleming proposed
7560-513: The TZ environment variable . This allows users in multiple time zones, or in the same time zone but with different daylight saving time rules, to use the same computer, with their respective local times displayed correctly to each user. Time zone and daylight saving time rule information most commonly comes from the IANA time zone database . In fact, many systems, including anything using the GNU C Library ,
7695-936: The UT1 variant of universal time . See the " Current number of leap seconds " section for the number of leap seconds inserted to date. The first leap second occurred on 30 June 1972. Since then, leap seconds have occurred on average about once every 19 months, always on 30 June or 31 December. As of July 2022 , there have been 27 leap seconds in total, all positive, putting UTC 37 seconds behind TAI. A study published in March 2024 in Nature concluded that accelerated melting of ice in Greenland and Antarctica due to climate change has decreased Earth's rotational velocity, affecting UTC adjustments and causing problems for computer networks that rely on UTC. Earth's rotational speed
7830-631: The WWV time signals, named for the shortwave radio station that broadcasts them. In 1960, the U.S. Naval Observatory, the Royal Greenwich Observatory, and the UK National Physical Laboratory coordinated their radio broadcasts so that time steps and frequency changes were coordinated, and the resulting time scale was informally referred to as "Coordinated Universal Time". In a controversial decision,
7965-400: The independent member, Peter Wellington , to introduce a private member's bill for DST. Since Wellington agreed with the principles of the DS4SEQ proposal, specifically the dual-time-zone system, he drafted the Daylight Saving for South East Queensland Referendum Bill 2010 and he submitted this bill to Queensland Parliament on 14 April 2010. Wellington called for a referendum to be held at
8100-598: The 25th century, four leap seconds are projected to be required every year, so the current quarterly options would be insufficient. In April 2001, Rob Seaman of the National Optical Astronomy Observatory proposed that leap seconds be allowed to be added monthly rather than twice yearly. In 2022 a resolution was adopted by the General Conference on Weights and Measures to redefine UTC and abolish leap seconds, but keep
8235-541: The American government, influenced in part by Abbe's 1879 paper, adopted the time-zone system. It was a version proposed by William F. Allen, the editor of the Traveler's Official Railway Guide . 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
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#17328021501428370-663: The Australian mainland in the Pacific Ocean, uses UTC+10:30 during the winter months (30 minutes ahead of the eastern states), but advances to UTC+11:00 in summer (the same time as the rest of New South Wales). A compromise between Western and Central time (UTC+08:45, without DST), unofficially known as Central Western Standard Time , is used in one area in the southeastern corner of Western Australia and one roadhouse in South Australia. Towns east of Caiguna on
8505-718: The British Great Western Railway started using GMT kept by portable chronometers . This practice was soon followed by other railway companies in Great Britain and became known as railway time . Around August 23, 1852, time signals were first transmitted by telegraph from the Royal Observatory. By 1855, 98% of Great Britain's public clocks were using GMT, but it was not made the island's legal time until August 2, 1880. Some British clocks from this period have two minute hands, one for
8640-475: The Committee on Daylight Saving analysed this trial and the effects of daylight saving on different demographics, and ultimately concluded not to adopt daylight saving time. The committee's reasons include Queensland's unsuitable geography and a lack of broad support from denizens. Later, another introduction of DST was trialled from 29 October 1989 to 4 March 1990, overseen by the daylight saving task force. At
8775-603: The DUT1 correction (UT1 − UTC) for applications requiring a closer approximation of UT1 than UTC now provided. The current version of UTC is defined by International Telecommunication Union Recommendation (ITU-R TF.460-6), Standard-frequency and time-signal emissions , and is based on International Atomic Time (TAI) with leap seconds added at irregular intervals to compensate for the accumulated difference between TAI and time measured by Earth's rotation . Leap seconds are inserted as necessary to keep UTC within 0.9 seconds of
8910-461: The Earth rotating faster, but that has not yet been necessary. The irregular day lengths mean fractional Julian days do not work properly with UTC. Since 1972, UTC may be calculated by subtracting the accumulated leap seconds from International Atomic Time (TAI), which is a coordinate time scale tracking notional proper time on the rotating surface of the Earth (the geoid ). In order to maintain
9045-551: The Earth's rotation has sped up, causing this difference to increase. If the trend continues, a negative leap second may be required, which has not been used before. This may not be needed until 2025. Some time in the 22nd century, two leap seconds will be required every year. The current practice of only allowing leap seconds in June and December will be insufficient to maintain a difference of less than 1 second, and it might be decided to introduce leap seconds in March and September. In
9180-512: The English and French names with the acronym UTC to be used in both languages. The name "Coordinated Universal Time (UTC)" was approved by a resolution of IAU Commissions 4 and 31 at the 13th General Assembly in 1967 (Trans. IAU, 1968). Time zones around the world are expressed using positive, zero, or negative offsets from UTC , as in the list of time zones by UTC offset . The westernmost time zone uses UTC−12 , being twelve hours behind UTC;
9315-540: The International Astronomical Union to refer to GMT, with the day starting at midnight. Until the 1950s, broadcast time signals were based on UT, and hence on the rotation of the Earth. In 1955, the caesium atomic clock was invented. This provided a form of timekeeping that was both more stable and more convenient than astronomical observations. In 1956, the U.S. National Bureau of Standards and U.S. Naval Observatory started to develop atomic frequency time scales; by 1959, these time scales were used in generating
9450-506: The LOD over the nominal 86,400 s accumulates over time, causing the UTC day, initially synchronised with the mean sun, to become desynchronised and run ahead of it. Near the end of the 20th century, with the LOD at 1.3 ms above the nominal value, UTC ran faster than UT by 1.3 ms per day, getting a second ahead roughly every 800 days. Thus, leap seconds were inserted at approximately this interval, retarding UTC to keep it synchronised in
9585-608: The New York Stock Exchange opens at These calculations become more complicated near the time switch to or from daylight saving time, as the UTC offset for the area becomes a function of UTC time. The time differences may also result in different dates. For example, when it is 22:00 on Monday in Egypt (UTC+02:00), it is 01:00 on Tuesday in Pakistan (UTC+05:00). The table "Time of day by zone" gives an overview on
9720-459: The Northern Territory, which it governed); and by 10 hours in Queensland, New South Wales, Victoria, and Tasmania. The three time zones became known as Western Standard Time , Central Standard Time , and Eastern Standard Time . Broken Hill in the far west of New South Wales (strictly speaking, the county of Yancowinna ) also adopted Central Standard Time due to it being connected at the time by rail to Adelaide but not Sydney . In May 1899, in
9855-595: The Terminal Server so that users see the correct time for their time zone in their desktop/application sessions. Terminal Services uses the server base time on the Terminal Server and the client time zone information to calculate the time in the session. While most application software will use the underlying operating system for time zone and daylight saving time rule information, the Java Platform , from version 1.3.1, has maintained its own database of time zone and daylight saving time rule information. This database
9990-534: The US version shows Eastern Time . US Eastern Time and Pacific Time are also used fairly commonly on many US-based English-language websites with global readership. The format is typically based in the W3C Note "datetime". Email systems and other messaging systems ( IRC chat , etc.) time-stamp messages using UTC, or else include the sender's time zone as part of the message, allowing the receiving program to display
10125-455: The UTC second equal to the TAI second. This CCIR Recommendation 460 "stated that (a) carrier frequencies and time intervals should be maintained constant and should correspond to the definition of the SI second ; (b) step adjustments, when necessary, should be exactly 1 s to maintain approximate agreement with Universal Time (UT); and (c) standard signals should contain information on the difference between UTC and UT." As an intermediate step at
10260-561: The UTC system. If only milliseconds precision is needed, clients can obtain the current UTC from a number of official internet UTC servers. For sub-microsecond precision, clients can obtain the time from satellite signals. UTC is also the time standard used in aviation , e.g. for flight plans and air traffic control . In this context it is frequently referred to as Zulu time, as described below. Weather forecasts and maps all use UTC to avoid confusion about time zones and daylight saving time. The International Space Station also uses UTC as
10395-560: The alphabet and the Greenwich time zone was marked by a Z as it was the point of origin. The letter also refers to the "zone description" of zero hours, which has been used since 1920 (see time zone history ). Since the NATO phonetic alphabet word for Z is "Zulu", UTC is sometimes known as "Zulu time". This is especially true in aviation, where "Zulu" is the universal standard. This ensures that all pilots, regardless of location, are using
10530-464: The article on daylight saving time for more details on this aspect.) Web servers presenting web pages primarily for an audience in a single time zone or a limited range of time zones typically show times as a local time, perhaps with UTC time in brackets. More internationally oriented websites may show times in UTC only or using an arbitrary time zone. For example, the international English-language version of CNN includes GMT and Hong Kong Time, whereas
10665-469: The begin and end dates of daylight saving time are changed, calendar entries should stay the same in local time, even though they may shift in UTC time. Unix-like systems, including Linux and macOS , keep system time in Unix time format, representing the number of seconds (excluding leap seconds ) that have elapsed since 00:00:00 Coordinated Universal Time (UTC) on Thursday, January 1, 1970. Unix time
10800-604: The border between New South Wales and Queensland (with the majority of the airport on the Gold Coast and a small portion of it in Tweed Heads ), uses Australian Eastern Standard Time (AEST) throughout the airport all year round, despite New South Wales observing daylight savings (which Queensland does not observe). Time zone A time zone is an area which observes a uniform standard time for legal , commercial and social purposes. Time zones tend to follow
10935-480: The border of another state or territory use a different time zone to the rest of their own state or territory and may follow the bordering state or territory's time zone instead. The most well-known example of this is Broken Hill and the surrounding area, which, despite being located in New South Wales, use the same time zone as South Australia year-round. Additionally, Gold Coast Airport , which straddles
11070-527: The boundaries between countries and their subdivisions instead of strictly following longitude , because it is convenient for areas in frequent communication to keep the same time. Each time zone is defined by a standard offset from Coordinated Universal Time (UTC). The offsets range from UTC−12:00 to UTC+14:00 , and are usually a whole number of hours, but a few zones are offset by an additional 30 or 45 minutes, such as in India and Nepal . Some areas in
11205-549: The calendar events are assumed to take place in the time zone the computer or smartphone was on when creating the event. The event can be shown at the wrong time. For example, if a New Yorker plans to meet someone in Los Angeles at 9 am, and makes a calendar entry at 9 am (which the computer assumes is New York time), the calendar entry will be at 6 am if taking the computer's time zone. Calendaring software must also deal with daylight saving time (DST). If, for political reasons,
11340-557: The chairman of Study Group 7 elected to advance the question to the 2012 Radiocommunications Assembly (20 January 2012), but consideration of the proposal was postponed by the ITU until the World Radio Conference in 2015. This conference, in turn, considered the question, but no permanent decision was reached; it only chose to engage in further study with the goal of reconsideration in 2023. A proposed alternative to
11475-441: The civil second constant and equal to the SI second, so that sundials would slowly get further and further out of sync with civil time. The leap seconds will be eliminated by 2035. The resolution does not break the connection between UTC and UT1, but increases the maximum allowable difference. The details of what the maximum difference will be and how corrections will be implemented is left for future discussions. This will result in
11610-490: The current year, and so this section generally only refers to the legislation. In New South Wales and Western Australia, the starting and ending dates, if any, are to be set by legislation. Australian Western Central Standard Time (AWCST) UTC+8:45 The choice of whether to use DST is a matter for the governments of the individual states and territories. However, during World War I and World War II all states and territories used daylight saving time (DST). In 1968 Tasmania became
11745-551: The currently used prime meridian , and is not adjusted for daylight saving time . The coordination of time and frequency transmissions around the world began on 1 January 1960. UTC was first officially adopted as a standard in 1963 and "UTC" became the official abbreviation of Coordinated Universal Time in 1967. The current version of UTC is defined by the International Telecommunication Union . Since adoption, UTC has been adjusted several times, notably adding leap seconds in 1972. Recent years have seen significant developments in
11880-473: The difference between UTC and Universal Time, DUT1 = UT1 − UTC, and introduces discontinuities into UTC to keep DUT1 in the interval (−0.9 s, +0.9 s). As with TAI, UTC is only known with the highest precision in retrospect. Users who require an approximation in real time must obtain it from a time laboratory, which disseminates an approximation using techniques such as GPS or radio time signals . Such approximations are designated UTC( k ), where k
12015-552: The easternmost time zone uses UTC+14 , being fourteen hours ahead of UTC. In 1995, the island nation of Kiribati moved those of its atolls in the Line Islands from UTC−10 to UTC+14 so that Kiribati would all be on the same day. UTC is used in many Internet and World Wide Web standards. The Network Time Protocol (NTP), designed to synchronise the clocks of computers over the Internet, transmits time information from
12150-526: The effects of slight variations in the rate of rotation of the Earth that are inherent in mean solar time . All jurisdictions have adopted the UTC standard, starting on 1 September 2005. In Victoria, South Australia, Tasmania and the ACT, the starting and ending dates of daylight saving times are officially determined by proclamations , declarations, or regulation made by the State Governor or responsible minister. Such instruments may be valid for only
12285-483: The end of 1971, there was a final irregular jump of exactly 0.107758 TAI seconds, making the total of all the small time steps and frequency shifts in UTC or TAI during 1958–1971 exactly ten seconds, so that 1 January 1972 00:00:00 UTC was 1 January 1972 00:00:10 TAI exactly, and a whole number of seconds thereafter. At the same time, the tick rate of UTC was changed to exactly match TAI. UTC also started to track UT1 rather than UT2. Some time signals started to broadcast
12420-469: The equator. Near the summer solstice , Vigo has sunset times after 22:00, similar to those of Stockholm , which is in the same time zone and 17 degrees farther north. Stockholm has much earlier sunrises, though. In the United States, the reasons were more historical and business-related. In Midwestern states, like Indiana and Michigan , those living in Indianapolis and Detroit wanted to be on
12555-633: The first Sunday in April in jurisdictions in the south and south-east: Standard time was introduced in the 1890s when all of the Australian colonies adopted it. Before the switch to standard time zones, each local city or town was free to determine its local time, called local mean time . Now, Western Australia uses Western Standard Time; South Australia and the Northern Territory use Central Standard Time; while New South Wales , Queensland , Tasmania , Victoria , Jervis Bay Territory , and
12690-415: The first Sunday in October, and ended it later, on the first Sunday of April. On 12 April 2007, New South Wales, Victoria, Tasmania, and the ACT agreed to common beginning and ending dates for DST from 2008. DST in these states and South Australia began on the first Sunday in October and ended on the first Sunday in April. Western Australia was then the only state to use DST from the last Sunday in October to
12825-504: The first state to use DST in peacetime, followed in 1971 by New South Wales, Victoria, Queensland, South Australia, and the Australian Capital Territory. Queensland abandoned DST in 1972. Western Australia and the Northern Territory did not adopt it. Queensland and Western Australia have occasionally used DST since then during trial periods. The main DST zones are the following: During the usual periods of DST,
12960-509: The frequency for the caesium transition , newly established, with the ephemeris second . The ephemeris second is a unit in the system of time that, when used as the independent variable in the laws of motion that govern the movement of the planets and moons in the solar system, enables the laws of motion to accurately predict the observed positions of solar system bodies. Within the limits of observable accuracy, ephemeris seconds are of constant length, as are atomic seconds. This publication allowed
13095-399: The frequency of the signals was initially set to match the rate of UT, but then kept at the same frequency by the use of atomic clocks and deliberately allowed to drift away from UT. When the divergence grew significantly, the signal was phase shifted (stepped) by 20 ms to bring it back into agreement with UT. Twenty-nine such steps were used before 1960. In 1958, data was published linking
13230-449: The greatest terrestrial time zone difference on Earth, with a 3.5 hour difference between Afghanistan's UTC+4:30 and China's UTC+08:00 . Many countries, and sometimes just certain regions of countries, adopt daylight saving time (DST), also known as summer time, during part of the year. This typically involves advancing clocks by an hour near the start of spring and adjusting back in autumn ("spring forward", "fall back"). Modern DST
13365-448: The last Sunday in March, but it abolished DST in 2009. Unlike the rest of New South Wales, Broken Hill and the surrounding region ( Yancowinna County ) observes Australian Central Standard Time (UTC+09:30), a time zone it shares with nearby South Australia and the Northern Territory. Heron Island , 72 km (45 mi) off the coast off Gladstone in Queensland, has two time zones: the island resort follows DST all year round, whereas
13500-519: The local time and one for GMT. On November 2, 1868, the British Colony of New Zealand officially adopted a standard time to be observed throughout the colony. It was based on 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 North American railroads in the 19th century was complex. Each railroad used its own standard time, usually based on
13635-413: The local time of its headquarters or most important terminus, and the railroad's train schedules were published using its own time. Some junctions served by several railroads had a clock for each railroad, each showing a different time. Because of this a number of accidents occurred when trains from different companies using the same tracks mistimed their passings. Around 1863, Charles F. Dowd proposed
13770-435: The long term. The actual rotational period varies on unpredictable factors such as tectonic motion and has to be observed, rather than computed. Just as adding a leap day every four years does not mean the year is getting longer by one day every four years, the insertion of a leap second every 800 days does not indicate that the mean solar day is getting longer by a second every 800 days. It will take about 50,000 years for
13905-554: The majority of countries had adopted hourly time zones, though some countries such as Iran , India , Myanmar and parts of Australia had time zones with a 30-minute offset. Nepal was the last country to adopt a standard offset, shifting slightly to UTC+05:45 in 1986. All nations currently use standard time zones for secular purposes, but not all of them apply the concept as originally conceived. Several countries and subdivisions use half-hour or quarter-hour deviations from standard time. Some countries, such as China and India , use
14040-653: The message's date and time of sending in the recipient's local time. Database records that include a time stamp typically use UTC, especially when the database is part of a system that spans multiple time zones. The use of local time for time-stamping records is not recommended for time zones that implement daylight saving time because once a year there is a one-hour period when local times are ambiguous. Calendar systems nowadays usually tie their time stamps to UTC, and show them differently on computers that are in different time zones. That works when having telephone or internet meetings. It works less well when travelling, because
14175-416: The necessary support for working with all (or almost all) possible local times based on the various time zones. Internally, operating systems typically use UTC as their basic time-keeping standard , while providing services for converting local times to and from UTC, and also the ability to automatically change local time conversions at the start and end of daylight saving time in the various time zones. (See
14310-480: The next state election on the introduction of DST into southeastern Queensland under the dual-time-zone system. In response to this bill, Premier Anna Bligh announced a community consultation process, which resulted in over 74,000 respondents participating, 64 per cent of whom voted in favour of a trial, and 63 per cent of whom were in favour of holding a referendum. The decision announced by the Premier on 7 June 2010
14445-494: The nominal 86,400 s corresponds to the downward slope of the graph between vertical segments. (The slope became shallower in the 1980s, 2000s and late 2010s to 2020s because of slight accelerations of Earth's rotation temporarily shortening the day.) Vertical position on the graph corresponds to the accumulation of this difference over time, and the vertical segments correspond to leap seconds introduced to match this accumulated difference. Leap seconds are timed to keep DUT1 within
14580-409: The only major changes in Australian time zones have been setting of clocks half an hour later than Eastern time (GMT plus 10:30) on the territory of Lord Howe Island , and Norfolk Island changing from UTC+11:30 to UTC+11:00 on 4 October 2015. When abbreviating "Australian Central Time" and "Australian Eastern Time", in domestic contexts the leading "Australian" may be omitted; however, the prefix "A"
14715-429: The other hand, Federal legislation yields to state-regulated standard times in many diverse situations. For example, it yields in setting the normal working times of Federal employees, the recognition of public holidays, etc. The Federal government also relies on local times for Federal elections, so that the polls in Western Australia close two or three hours after those in the eastern states. Also, documents to be filed in
14850-611: The positive vote being strongest in the southeastern region (e.g. in Brisbane ). The holiday islands in the Whitsundays ( Hayman , Lindeman and Hamilton ) continued to observe DST in defiance of the Standard Time Act (The "Australia/Lindeman" Timezone in the tz database is based on this). However the practice was abandoned two years later in 1995. Heron Island, 72 km off the coast off Gladstone, has two time zones:
14985-639: The rate of skin cancer in the state, an assertion for which there is no evidence, according to the Queensland Cancer Fund. In October 2007, the government-commissioned research was presented to Anna Bligh , who had replaced Peter Beattie as the Premier of Queensland ; she ruled out holding a new referendum, despite the report indicating that 59 per cent of the residents of Queensland and 69 per cent of those in southeastern Queensland to be in favour of adopting daylight saving. In December 2008,
15120-416: The realm of UTC, particularly in discussions about eliminating leap seconds from the timekeeping system because leap seconds occasionally disrupt timekeeping systems worldwide. The General Conference on Weights and Measures adopted a resolution to alter UTC with a new system that would eliminate leap seconds by 2035. The official abbreviation for Coordinated Universal Time is UTC . This abbreviation comes as
15255-798: The resort follows DST all year round, whereas "the Marine Research Centre and the Parks and Wildlife office on the island remain on Eastern Standard Time". Since the late 1900s, there have been a number of petitions submitted to the Legislative Assembly of Queensland , lobbying for the introduction of daylight saving time or for another referendum to be held. A petition in 2006 was signed by 62,232 people. In response to these petitions, then Queensland Premier Peter Beattie commissioned research to find out if it should be re-introduced into Queensland. Around this time, Beattie predicted that daylight saving in Queensland would increase
15390-638: The same 24-hour clock , thus avoiding confusion when flying between time zones. See the list of military time zones for letters used in addition to Z in qualifying time zones other than Greenwich. On electronic devices which only allow the time zone to be configured using maps or city names, UTC can be selected indirectly by selecting cities such as Accra in Ghana or Reykjavík in Iceland as they are always on UTC and do not currently use daylight saving time (which Greenwich and London do, and so could be
15525-493: The same meridian but north of the Arctic Circle, has two sunsets on the same day in early August, one shortly after midnight at the start of the day, and the other shortly before midnight at the end of the day. China extends as far west as 73°E , but all parts of it use UTC+08:00 ( 120°E ), so solar "noon" can occur as late as 15:00 in western portions of China such as Xinjiang . The Afghanistan-China border marks
15660-419: The same time zone as New York to simplify communications and transactions. A more extreme example is Nome, Alaska , which is at 165°24′W longitude – just west of center of the idealized Samoa Time Zone ( 165°W ). Nevertheless, Nome observes Alaska Time ( 135°W ) with DST so it is slightly more than two hours ahead of the sun in winter and over three in summer. Kotzebue, Alaska , also near
15795-626: The six colonies in Australia met in Melbourne for the Intercolonial Conference of Surveyors. The delegates accepted the recommendation of the 1884 International Meridian Conference to adopt Greenwich Mean Time (GMT) as the basis for standard time. The colonies enacted time zone legislation, which took effect in February 1895. The clocks were set ahead of GMT by 8 hours in Western Australia; by 9 hours in South Australia (and
15930-465: The system time to be fetched as a count of 100 ns units since 1601-01-01 00:00:00 UTC. The system registry contains time zone information that includes the offset from UTC and rules that indicate the start and end dates for daylight saving in each zone. Interaction with the user normally uses local time, and application software is able to calculate the time in various zones. Terminal Servers allow remote computers to redirect their time zone settings to
16065-428: The task force's recommendation, the trial was extended from one to three years. The Legislative Assembly voted to hold a referendum on DST at the trial's conclusion in 1992, which was defeated with a 54.5 per cent negative vote. The referendum result displayed a distinct trend—that public opinion on DST in Queensland is geographically divided, with the negative vote being strongest in northern and western districts, while
16200-476: The three standard time zones in Australia become five zones. This includes the areas that do not observe DST: Western Australia (UTC+08:00), the Northern Territory (UTC+09:30), and Queensland (UTC+10:00). The change to and from DST takes place at 02:00 local standard time the appropriate Sunday. Until 2008, DST usually began on the last Sunday in October, and ended on the last Sunday in March. However, Tasmania, given its latitude further south, began DST earlier, on
16335-529: The time being described is one hour ahead of UTC (such as the time in Germany during the winter), the zone designator would be " +01:00 ", "+0100", or simply "+01". This numeric representation of time zones is appended to local times in the same way that alphabetic time zone abbreviations (or "Z", as above) are appended. The offset from UTC changes with daylight saving time , e.g. a time offset in Chicago , which
16470-548: The time relations between different zones. Since the 1920s, a nautical standard time system has been in operation for ships on the high seas . As an ideal form of the terrestrial time zone system, nautical time zones consist of gores of 15° offset from GMT by a whole number of hours. A nautical date line follows the 180th meridian, bisecting one 15° gore into two 7.5° gores that differ from GMT by ±12 hours. However, in practice each ship may choose what time to observe at each location. Ships may decide to adjust their clocks at
16605-475: The usual date, which was 29 October 2000. In 2006, all of the states that followed DST (the above states and South Australia) delayed their return to Standard Times by one week, because of the 2006 Commonwealth Games held in Melbourne in March. DST ended on 2 April 2006. There are situations in which a nationwide time is in effect. In the case of business activities, a national time can be used. For example,
16740-489: The vertical range depicted by the adjacent graph. The frequency of leap seconds therefore corresponds to the slope of the diagonal graph segments, and thus to the excess LOD. Time periods when the slope reverses direction (slopes upwards, not the vertical segments) are times when the excess LOD is negative, that is, when the LOD is below 86,400 s. As the Earth's rotation continues to slow, positive leap seconds will be required more frequently. The long-term rate of change of LOD
16875-471: The war. Similarly, prior to World War II, the Netherlands observed "Amsterdam Time", which was twenty minutes ahead of Greenwich Mean Time. They were obliged to follow German time during the war, and kept it thereafter. In the mid-1970s the Netherlands, as other European states, began observing daylight saving (summer) time. One reason to draw time zone boundaries far to the west of their ideal meridians
17010-576: The west, and some countries are located entirely outside their ideal time zones. For example, even though the Prime Meridian (0°) passes through Spain and France , they use the mean solar time of 15 degrees east ( Central European Time ) rather than 0 degrees (Greenwich Mean Time). France previously used GMT, but was switched to CET (Central European Time) during the German occupation of the country during World War II and did not switch back after
17145-562: The western reaches of China. In Russia, which has 11 time zones , two time zones were removed in 2010 and reinstated in 2014. ISO 8601 is a standard established by the International Organization for Standardization defining methods of representing dates and times in textual form, including specifications for representing time zones. If a time is in Coordinated Universal Time (UTC), a "Z"
17280-463: Was Detroit (located about halfway between the meridians of Eastern and Central time), which kept local time until 1900, then tried Central Standard Time, local mean time , and Eastern Standard Time (EST) 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 time zones were formally adopted by the U.S. Congress in
17415-408: Was also dissatisfaction with the frequent jumps in UTC (and SAT). In 1968, Louis Essen , the inventor of the caesium atomic clock, and G. M. R. Winkler both independently proposed that steps should be of 1 second only. to simplify future adjustments. This system was eventually approved as leap seconds in a new UTC in 1970 and implemented in 1972, along with the idea of maintaining
17550-582: Was at UTC+09:00 hours during November 2005 when DST was observed in the eastern and southern states. Australia's external territories follow different time zones. In 2000, all of the eastern jurisdictions that normally observe DST—New South Wales, Victoria, the ACT, and Tasmania—began DST early because of the Summer Olympic Games held in Sydney. These jurisdictions moved to DST on 27 August 2000. South Australians did not change their clocks until
17685-415: Was first proposed in 1907 and was in widespread use in 1916 as a wartime measure aimed at conserving coal . Despite controversy , many countries have used it off and on since then; details vary by location and change occasionally. Countries around the equator usually do not observe daylight saving time, since the seasonal difference in sunlight there is minimal. Many computer operating systems include
17820-403: Was inaugurated on Sunday, November 18, 1883, also called "The Day of Two Noons", when each railroad station clock was reset as standard-time noon was reached within each time zone. The North American zones were named Intercolonial, Eastern, Central, Mountain, and Pacific. Within a year 85% of all cities with populations over 10,000 (about 200 cities) were using standard time. A notable exception
17955-478: Was that her Government would not support the bill because rural Queenslanders were overwhelmingly opposed to DST. The Bill was defeated in Queensland Parliament on 15 June 2011. Western Australia has also had a particularly involved debate over DST, with the issue being put to a referendum four times: in 1975, 1984, 1992, and 2009. All of these proposals to adopt DST were defeated. Voters registered
18090-408: Was thought better for time signals to maintain a consistent frequency, and that this frequency should match the SI second. Thus it would be necessary to rely on time steps alone to maintain the approximation of UT. This was tried experimentally in a service known as "Stepped Atomic Time" (SAT), which ticked at the same rate as TAI and used jumps of 0.2 seconds to stay synchronised with UT2. There
18225-669: Was very little in the way of time zone support for JavaScript . Essentially the programmer had to extract the UTC offset by instantiating a time object, getting a GMT time from it, and differencing the two. This does not provide a solution for more complex daylight saving variations, such as divergent DST directions between northern and southern hemispheres. ECMA-402, the standard on Internationalization API for JavaScript, provides ways of formatting Time Zones. However, due to size constraint, some implementations or distributions do not include it. The DateTime object in Perl supports all entries in
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