Since Howland Island and Baker Island constitute the world's westernmost landmasses in relation to the International Date Line, making them the last places on Earth where any date exists, they are sometimes assigned a theoretical 12th timezone called Anywhere on Earth (AOE). They will become active again after the next clock change as Daylight Saving Time begins or ends.
Since 1967, the US Department of Transportation (DOT) has been responsible for governing time zones in the country. In addition, the uninhabited atolls of Baker Island (AOE) and Wake Island (WAIT) add to the timezone count, making 11 the total number of time zones in the US.
Arizona, Puerto Rico, Hawaii, U.S. Virgin Islands and American Samoa do not observe Daylight Saving Time. Read more about the new federal law that took effect in March 2007 which extended Daylight Saving Time by four weeks.
Region on Earth that has a uniform standard time for legal, commercial, and social purposes A timezone is a designated area of the global 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 strictly following longitude because it is convenient for areas in close commercial or other communication to keep the same time. France, including its overseas territories, has the most time zones of any country, with a total of 12.
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. This also creates permanent daylight saving time effect.
When well-regulated mechanical clocks became widespread in the early 19th century, 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 accumulated 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.
Plaque commemorating the Railway General Time Convention of 1883 in North AmericaLocal 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, England 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.
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 in November 1840, 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 (GDR) in November 1840. About August 23, 1852, time signals were first transmitted by telegraph from the Royal Observatory, Greenwich.
1913 timezone map of the United States, showing boundaries very different from today Charles F. Down 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).
Instead, U.S. and Canadian railroads implemented 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 was inaugurated on Sunday, November 18, 1883, also called “The Day of Two Moons”, when each railroad station clock was reset as standard- time noon was reached within each timezone.
The zones were named Intercolonial, Eastern, Central, Mountain, and Pacific. The confusion of times came to an end when Standard onetime was formally adopted by the U.S. Congress in the Standard Time Act of March 19, 1918.
The first known person to conceive of a worldwide system of time zones was the Italian mathematician Chirico Flippant. He proposed 24 hourly time zones, which he called “longitudinal days”, the first centered on the meridian of Rome.
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”.
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 when desirable”.
World map of time zones in 1928By about 1900, almost all inhabited places on Earth had adopted one or other standard timezone ; but only some of these 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/UTC. By 1929, the majority of countries had adopted hourly time zones, though a number of countries from Iran to Australia had time zones with a 30-minute offset.
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, 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 timezone even though the extent of their territory far exceeds 15° of longitude; other countries, such as Spain or 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 the western reaches of China. Russia is traditionally divided into 11 time zones, but in 2010 the number was reduced to nine.
Then-President Dmitry Mercedes said at the time that he would like to see even fewer in place. ISO 8601 is an international standard that defines methods of representing dates and times in textual form, including specifications for representing time zones.
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 and their use as sole designated for a timezone is discouraged. It is also a widely used variant of ACST (Australian Central Standard Time, UTC+9:30).
For example, the New York Stock Exchange opens at 09:30 (EST, UTC offset=05:00). Since the 1920s a nautical standard time system has been in operation for ships on the high seas.
Nautical time zones are an ideal form of the terrestrial timezone system. The 15° gore that is offset from GMT or UT1 (not UTC) by twelve hours is bisected by the nautical date line into two 7.5° gores that differ from GMT by ±12 hours.
A nautical date line is implied but not explicitly drawn on timezone maps. It follows the 180th meridian except where it is interrupted by territorial waters adjacent to land, forming gaps: it is a pole-to-pole dashed line.
A ship within the territorial waters of any nation would use that nation's standard time, but would revert to nautical standard time upon leaving its territorial waters. Ships going in shuttle traffic over a timezone border often keep the same timezone all the time, to avoid confusion about work, meal, and shop opening hours.
Still the timetable for port calls must follow the land timezone. In practice, zone boundaries are often drawn much farther to the west with often irregular boundaries, and some locations base their time on meridians located far to the east.
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 the war. Similarly, prior to World War II, the Netherlands observed “Amsterdam Time “, which was twenty minutes ahead of Greenwich Mean Time.
In the mid 1970s the Netherlands, as with other European states, began observing daylight saving (summer) time. In the Northern Hemisphere, there is a tendency to draw timezone boundaries far to the west of their meridians.
Another reason for this is that similar working day schedules around the world have led to people rising on average at 07:00 clock time and going to bed at 23:00 clock time. Many of these locations also use DST, adding yet another nautical timezone to the east.
As a result, in summer, solar noon in the Spanish town of Music occurs at 14:37 clock time, indeed very close to awake time noon (15:00). This westernmost area of continental Spain never experiences sunset before 18:00 clock time, even in midwinter, despite its lying more than 40 degrees north of the equator.
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 the same meridian but north of the Arctic Circle, has an annual event on August 9 to celebrate two sunsets in the same 24-hour day, one shortly after midnight at the start of the day, and the other shortly before midnight at the end of the day.
This typically involves advancing clocks by an hour near the start of spring and adjusting back in autumn (“spring forward”, “fall back”). Modern DST was first proposed in 1907 and was in widespread use in 1916 as a wartime measure aimed at conserving coal.
Despite, many countries have used it off and on since then; details vary by location and change occasionally. Most countries around the equator do not observe daylight saving time, since the seasonal difference in sunlight is minimal.
(See the article on daylight saving time for more details on this aspect). More internationally oriented websites may show times in UTC only or using an arbitrary timezone.
For example, the international English-language version of CNN includes GMT and Hong Kong Time, whereas the US version shows Eastern 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.
Calendar systems nowadays usually tie their time stamps to UTC, and show them differently on computers that are in different time zones. 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 timezone.
There is also an option in newer versions of Microsoft Outlook to enter the timezone in which an event will happen, but often not in other calendar systems. Calendaring software must also deal with daylight saving time (DST).
In Microsoft Outlook, time stamps are therefore stored and communicated without DST offsets. Hence, an appointment in London at noon in the summer will be represented as 12:00 (UTC+00:00) even though the event will actually take place at 13:00 UTC.
In fact, many systems, including anything using the GNU C Library, can make use of this database. The system registry contains timezone information that includes the offset from UTC and rules that indicate the start and end dates for daylight saving in each zone.
Terminal Servers allow remote computers to redirect their timezone settings to the Terminal Server so that users see the correct time for their timezone in their desktop/application sessions. Terminal Services uses the server base time on the Terminal Server and the client timezone information to calculate the time in the session.
While most application software will use the underlying operating system for timezone information, the Java Platform, from version 1.3.1, has maintained its own timezone database. As an alternative to the timezone information bundled with the Java Platform, programmers may choose to use the Soda- Time library.
However, due to size constraint, some implementations or distributions do not include it. The Daytime object in Perl supports all time zones in the Olson DB and includes the ability to get, set and convert between time zones.
The Daytime objects and related functions have been compiled into the PHP core since 5.2. As noted there, the most current timezone database can be implemented via the PEEL timezone db.
The standard module date time included with Python stores and operates on the timezone information class info. The third party PTZ module provides access to the full DIANA timezone database.
VisualWorks provides a Timezone class that supports up to two annually recurring offset transitions, which are assumed to apply to all years (same behavior as Windows time zones). Squeak provides a Timezone class that does not support any offset transitions.
For full support of the TZ database (zone info) in a Small talk application (including support for any number of annually recurring offset transitions, and support for different intra-term offset transition rules in different years) the third party, open-source, ANSI-Smalltalk-compliant Chronic Date/ Time Library is available for use with any of the following Small talk dialects: VisualWorks, Squeak, Gemstone, or Dolphin. Orbiting spacecraft typically experience many sunrises and sunsets in a 24-hour period, or in the case of Apollo program astronauts travelling to the moon, none.
A common practice for space exploration is to use the Earth-based timezone of the launch site or mission control. The International Space Station normally uses Greenwich Mean Time (GMT).
Timekeeping on Mars can be more complex, since the planet has a solar day of approximately 24 hours and 39 minutes, known as a sol. Earth controllers for some Mars missions have synchronized their sleep/wake cycles with the Martian day, because solar-powered rover activity on the surface was tied to periods of light and dark.
“How India's single time zone is hurting its people”. Malik Again, economist at Cornell University (January 15, 2019).
“Doorstep: Sunset Time and Human Capital Production” (Job Market Paper). Time Bandits: The countries rebelling against GMT” (Video).
^ International conference held at Washington for the Purpose of Fixing a Prime Meridian and a Universal Day. , Washington, D. C., 1884, p. 201, retrieved July 23, 2018 ^ Time Zone & Clock Changes in Kathmandu, Nepal”.
^ “Russian clocks to retreat again in winter, 11 time zones return”. ^ Hill, John C., Thomas F. Regard, Gerard Riordan.
^ How time zone normalization works in Microsoft Outlook. Google Calendar Help (as of Oct. 2015) “The Open Group Base Specifications Issue 7, section 4.16 Seconds Since the Epoch”.