Time zone

This 2019 time zone map gives an example of the way time zones are mapped out.

A time zone is a region of the globe that observes a uniform standard time for legal, commercial, and social purposes. Time zones tend to follow the boundaries of countries and their subdivisions instead of longitude, because it is convenient for areas in close commercial or other communication to keep the same time.

Most of the time zones on land are offset from Coordinated Universal Time (UTC) by a whole number of hours (UTC−12:00 to UTC+14:00), but a few zones are offset by 30 or 45 minutes (e.g. Newfoundland Standard Time is UTC−03:30, Nepal Standard Time is UTC+05:45, Indian Standard Time is UTC+05:30 and Myanmar Standard Time is UTC+06:30).

Some higher latitude and temperate zone countries use daylight saving time for part of the year, typically by adjusting local clock time by an hour. Many land time zones are skewed toward the west of the corresponding nautical time zones. This also creates a permanent daylight saving time effect.


Early timekeeping

Before clocks were invented, it was common practice to mark the time of day with apparent solar time (also called "true" solar time) – for example, the time on a sundial – which was typically different for every location and dependent on longitude.

When well-regulated mechanical clocks became widespread in the early 19th century,[1] each city began to use local mean solar time. Apparent and mean solar time can differ by up to around 15 minutes (as described by the equation of time) because of the elliptical shape of the Earth's orbit around the Sun (eccentricity) and the tilt of the Earth's axis (obliquity). Mean solar time has days of equal length, and the difference between the two sums to zero after a year.

Greenwich Mean Time (GMT) was established in 1675, when the Royal Observatory was built, as an aid to mariners to determine longitude at sea, providing a standard reference time while each city in England kept a different local time.

Railway time

Plaque commemorating the Railway General Time Convention of 1883 in North America

Local solar time became increasingly inconvenient as rail transport and telecommunications improved, because clocks differed between places by amounts corresponding to the differences in their geographical longitudes, which varied by four minutes of time for every degree of longitude. For example, Bristol is about 2.5 degrees west of Greenwich (East London), so when it is solar noon in Bristol, it is about 10 minutes past solar noon in London.[2] The use of time zones accumulates these differences into longer units, usually hours, so that nearby places can share a common standard for timekeeping.

The first adoption of a standard time was on December 1, 1847, in Great Britain by railway companies using GMT kept by portable chronometers. The first of these companies to adopt standard time was the Great Western Railway (GWR) in November 1840. 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 British clocks from this period have two minute hands—one for the local time, one for GMT.[3]

Improvements in worldwide communication 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 that adopted time would then differ markedly from the solar time to which people were accustomed.

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.[4]

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 junctions served by several railroads had a clock for each railroad, each showing a different time.[5]

1913 time zone map of the United States, showing boundaries very different from today

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 on the meridian 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.[6] 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",[7] 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 a year 85% of all cities with populations over 10,000, about 200 cities, were using standard time.[8] A notable exception was Detroit (which is about halfway 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 in the Standard Time Act of March 19, 1918.

Worldwide time zones

The first known person to conceive of a worldwide system of time zones was the Italian mathematician Quirico Filopanti. He introduced the idea 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. But his book attracted no attention until long after his death.[9][10]

Scottish-born Canadian Sir Sandford Fleming proposed a worldwide system of time zones in 1879. He advocated his system at several international conferences, and is credited with "the initial effort that led to the adoption of the present time meridians".[11] In 1876, his first proposal was for a global 24-hour clock, conceptually located at the centre 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".[12]

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. By 1929, most major countries had adopted hourly time zones. Nepal was the last country to adopt a standard offset, shifting slightly to UTC+5:45 in 1956.[13]

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, Myanmar, Sri Lanka, 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 of New Zealand, use quarter-hour deviations. Some countries, such as China and India, use a single time zone even though the extent of their territory far exceeds 15° of longitude.[14] Russia is traditionally divided into 11 time zones, but in 2011 the number was reduced to nine. Then-President Dmitry Medvedev said at the time that he would like to see even fewer in place.[15] Still, in 2014, the two removed time zones were reinstated, making the number of time zones 11 again.

Other Languages
Адыгэбзэ: Сыхьэт зонэ
Afrikaans: Tydsone
Alemannisch: Zeitzone
አማርኛ: ሰዓት ክልል
العربية: منطقة زمنية
aragonés: Zona horaria
অসমীয়া: সময় অঞ্চল
asturianu: Fusu horariu
Avañe'ẽ: Yvy arapehẽ
azərbaycanca: Saat qurşağı
Bân-lâm-gú: Sî-khu
Basa Banyumasan: Zona waktu
башҡортса: Сәғәт бүлкәте
беларуская: Часавы пояс
беларуская (тарашкевіца)‎: Часавы пас
भोजपुरी: टाइम जोन
български: Часова зона
Boarisch: Zeidzone
bosanski: Vremenska zona
brezhoneg: Rann-eur
català: Zona horària
čeština: Časové pásmo
Cymraeg: Cylchfa amser
dansk: Tidszone
davvisámegiella: Áigeavádat
Deutsch: Zeitzone
dolnoserbski: Casowa cona
eesti: Ajavöönd
Ελληνικά: Ζώνη ώρας
emiliàn e rumagnòl: Fûş orâri
español: Huso horario
Esperanto: Horzono
euskara: Ordu-eremu
føroyskt: Tíðarsonur
français: Fuseau horaire
Frysk: Tiidsône
furlan: Fûs orari
Gaeilge: Amchrios
Gaelg: Cryss hraa
Gàidhlig: Roinn-tìde
galego: Fuso horario
ગુજરાતી: સમય વિસ્તાર
客家語/Hak-kâ-ngî: Sṳ̀-khî
한국어: 시간대
հայերեն: Ժամային գոտի
हिन्दी: समय मण्डल
hornjoserbsce: Časowe pasmo
hrvatski: Vremenska zona
Ilokano: Sona ti oras
বিষ্ণুপ্রিয়া মণিপুরী: সময়র লয়া
Bahasa Indonesia: Zona waktu
interlingua: Fuso horari
íslenska: Tímabelti
italiano: Fuso orario
עברית: אזור זמן
ಕನ್ನಡ: ಸಮಯ ವಲಯ
къарачай-малкъар: Сагъат бёлге
Kiswahili: Kanda muda
Кыргызча: Убакыт аралыгы
latviešu: Laika josla
Lëtzebuergesch: Zäitzon
lietuvių: Laiko juosta
Limburgs: Tiedzaone
Livvinkarjala: Aiguvyöhykeh
lumbaart: Füs urari
magyar: Időzóna
македонски: Часовен појас
മലയാളം: സമയ മേഖല
მარგალური: ოსათე ორტყაფუ
Bahasa Melayu: Zon waktu
монгол: Цагийн бүс
မြန်မာဘာသာ: အချိန်ဇုန်
Nederlands: Tijdzone
нохчийн: Сахьтан аса
Norfuk / Pitkern: Tiemsoen
norsk: Tidssone
norsk nynorsk: Tidssone
Nouormand: Feusé horaire
Novial: Tempe-sone
occitan: Fus orari
олык марий: Шагат ӱштӧ
ଓଡ଼ିଆ: ସମୟ ମଣ୍ଡଳ
oʻzbekcha/ўзбекча: Vaqt mintaqasi
ਪੰਜਾਬੀ: ਸਮਾਂ ਖੇਤਰ
پنجابی: ویلہ تھاں
Papiamentu: Zona di tempu
ភាសាខ្មែរ: ល្វែងម៉ោង
Plattdüütsch: Tietrebeet
português: Fuso horário
qırımtatarca: Saat quşağı
română: Fus orar
Runa Simi: Pacha suyu
русиньскый: Часова зона
русский: Часовой пояс
саха тыла: Кэм курдааһына
संस्कृतम्: समयवलयः
Scots: Time zone
Seeltersk: Tiedzone
Sesotho sa Leboa: Time zone
sicilianu: Fusu orariu
Simple English: Time zone
سنڌي: وقت پٽو
slovenčina: Časové pásmo
slovenščina: Časovni pas
ślůnski: Czasowo strefa
српски / srpski: Временска зона
srpskohrvatski / српскохрватски: Vremenska zona
Sunda: Zona wanci
svenska: Tidszon
Tagalog: Sona ng oras
தமிழ்: நேர வலயம்
татарча/tatarça: Вакыт зонасы
తెలుగు: సమయప్రాంతం
Türkçe: Zaman dilimi
тыва дыл: Шак куржаа
українська: Часовий пояс
vèneto: Fuso orario
vepsän kel’: Aigvö
Tiếng Việt: Múi giờ
Võro: Aovüü
Winaray: Zona hin oras
吴语: 时区
ייִדיש: צייט זאנע
粵語: 時區
žemaitėška: Čiesa jousta
中文: 时区