Daylight saving time

Daylight saving time (also called DST, or summer time) is the portion of the year in which a region's local time is advanced by (usually) one hour from its official standard time. It is most common in temperate regions.

Observation of DST

Daylight saving time is generally a temperate zone practice; day lengths in the tropics do not vary enough to justify DST. Hawaii, the only U.S. state in the tropics, does not observe DST. However, Mexico has adopted DST nationwide, even in its tropical regions, because of its increasing economic ties to the United States. The Mexican state of Sonora does not observe DST because it borders on the U.S. state of Arizona which also does not observe DST (except in the large Navajo Indian Reservation in northeastern Arizona). Polar or near-polar locations such as Iceland often opt out as well, as summer in these locations usually brings nearly uninterrupted daylight.

Related Topics:
Temperate - Tropics - Hawaii - Mexico - Sonora - Arizona - Navajo Indian Reservation - Iceland

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The amount of the time shift varies, but one hour is the most common. The dates of the beginning and ending of DST also vary by country. With a few exceptions, switchovers between standard time and daylight saving time generally occur in the early morning hours of a Sunday morning, presumably because doing so then causes less disruption than a change on a weekday would.

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DST commonly begins in the Northern Hemisphere on either the first Sunday in April or the last Sunday in March, and ends on the last Sunday in October. In the Southern Hemisphere, the beginning and ending dates are switched (thus the time difference between, e.g., the United Kingdom and Chile may be three, four, or five hours).

Related Topics:
Northern Hemisphere - Southern Hemisphere - United Kingdom - Chile

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North America generally follows the same procedure, going by local time in each zone, each time zone switching at 02:00 LST (local standard time) to 03:00 LDT (local daylight time) on the first Sunday in April, and again from 02:00 LDT to 01:00 LST on the last Sunday in October. The Canadian province of Newfoundland and Labrador is an exception in that the time changes take place at 00:01 local standard time and 00:01 local daylight time respectively. Also, in 1990, they experimented with Double Daylight Time, when the clocks went ahead by two hours, instead of the usual one hour. The Energy Policy Act of 2005, signed by President George W. Bush will extend DST, which might prompt neighboring countries with integrated economies and schedules (especially Canada and Mexico) to adopt these changes as well.

Related Topics:
North America - Newfoundland and Labrador - 1990 - Energy Policy Act of 2005 - George W. Bush

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All countries in Europe, except Iceland as already noted, observe daylight-saving time and change on the same date: moving clocks forward one hour on the last Sunday in March and back one hour on the last Sunday in October. In the West European (UTC), Central European (UTC+1), and East European (UTC+2) time zones the change is simultaneous: on both dates the clocks are changed everywhere at 01:00 UTC, i.e. from local times of 01:00/02:00/03:00 to 02:00/03:00/04:00 in March, and vice versa in October. (See also: European Summer Time). In Russia, however, although the changeover dates are the same, clocks are moved forward or back at 02:00 local time in all zones. Thus in Moscow (local time = UTC+3 in winter, UTC+4 in summer), daylight-saving time commences at 05:00 UTC on the last Sunday in March, and ends at 06:00 UTC on the last Sunday in October.

Related Topics:
Europe - Iceland - UTC - European Summer Time - Russia

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With Iceland observing UTC all year round, despite being at a longitude which would indicate UTC-1, the country may be said to be on continuous DST.

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Egypt switches to DST on midnight of the last Thursday of April, since the weekend holiday for most Egyptians is on Friday, thus giving workers and students a chance to adjust.

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Israel adopts Daylight Saving Time on the last Friday before April 2 at 02:00, and returns to standard time at 02:00 of the Sunday of the month of Tishrei between Rosh Hashanah and Yom Kippur. Israel's Daylight Saving Time rules have changed repeatedly in recent years; there has been trouble reaching a consensus regarding Gregorian calendar end dates for DST as they are dependant on Jewish Holidays, which follow the lunar Hebrew calendar. For more on this subject, see Israeli Daylight Savings Law.

Related Topics:
Israel - Tishrei - Rosh Hashanah - Yom Kippur - Gregorian calendar - Jewish Holidays - Lunar - Hebrew calendar - Israeli Daylight Savings Law

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The People's Republic of China experimented with DST from 1986, but abandoned it in the 1990s. The PRC now uses one universal time zone for all of the nation from Urumqi in the northwest to Fujian in the southeast; the size of the nation was a major factor why DST was not considered practical in China.

Related Topics:
People's Republic of China - 1986 - 1990s - Urumqi - Fujian

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Australia has a mixed implementation of daylight saving time. During winter it has three time zones, but when daylight saving time is in effect, it has five time zones (mostly differing by 30 minutes) ranging from UTC+8 to UTC+11. Although there have been several referenda on the topic, Western Australia, the Northern Territory and Queensland have not adopted the practice. As a result, the tropical regions of the country do not observe daylight saving. Interestingly, during daylight saving time, South Australia observes a time later than Queensland, despite the latter being almost entirely further east. Tasmania starts DST earlier than the rest of the country, usually at the start of October.

Related Topics:
Australia - Referenda - Western Australia - Northern Territory - Queensland - South Australia - Tasmania

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Cuba always starts its DST on April 1 but the end date varies.

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Brazil adopted DST for the first time in 1931, but uninterruptedly since 1985 in southern states (south, southeast regions and states of Goiás and Mato Grosso do Sul). Starting and ending dates are variable: normally, Brazilian DST starts at 00:00 on an October (rarely November) Sunday and ends at 00:00 on a February Sunday.

Related Topics:
Brazil - 1931 - 1985 - Goiás - Mato Grosso do Sul

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Pakistan experimented with DST in 2002 going from +5:00 to +6:00. It has not used DST since then. India used DST briefly during its wars with Pakistan and China.

Related Topics:
Pakistan - 2002 - India

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The Canadian province of Saskatchewan is the only part of that country (other than northeastern British Columbia and Southampton Island) that does not use DST. However, the charter of the city of Lloydminster, which is bisected by the Saskatchewan–Alberta border, gives it the special exception of using DST. Lloydminster and its immediately surrounding region in Saskatchewan use DST with Mountain Standard Time, which is the time used by Alberta.

Related Topics:
Saskatchewan - British Columbia - Southampton Island - Lloydminster - Alberta - Mountain Standard Time

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In the US

Daylight saving time was reinstated in the United States on February 9, 1942, again as a wartime measure to conserve resources. This remained in effect until World War II began winding down and the requirement was removed on September 30, 1945.

Related Topics:
United States - February 9 - 1942 - World War II - September 30 - 1945

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From 1945 to 1966, U.S. federal law did not address daylight saving time. States and localities were free to observe daylight saving time or not. This resulted in a patchwork where some areas observed DST while adjacent areas did not, and it was not unheard of to have to reset one's clock several times during a relatively short trip (e.g., bus drivers operating between Moundsville, West Virginia, and Steubenville, Ohio had to reset their watches seven times over 35 miles).

Related Topics:
1945 - 1966 - Moundsville, West Virginia - Steubenville, Ohio

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The U.S. federal Uniform Time Act of 1966 mandated that daylight saving time begin nationwide on the last Sunday of April and end on the last Sunday of October. Any state that wanted to be exempt from daylight saving time could do so by passing a state law, provided that it exempt the entire state. The law was amended in 1972 to permit states that straddle a time zone boundary to exempt the entire area of the state lying in one time zone. The law was amended again in 1986 to begin daylight saving time on the first Sunday in April, to take effect the following year.

Related Topics:
Uniform Time Act - April - October - 1972 - 1986 - Sunday

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In response to the 1973 energy crisis, daylight saving in the United States was begun earlier in both 1974 and 1975, commencing on the first Sunday in January (January 6) in the former year and the last Sunday in February (February 23) in the latter.

Related Topics:
1973 energy crisis - 1974 - 1975 - Sunday - January - January 6 - February - February 23

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Starting March 11, 2007, daylight saving time will be extended another four to five weeks, from the second Sunday of March to the first Sunday of November. The change was introduced by the Energy Policy Act of 2005; the House had originally approved a motion that would have extended DST even further. Proponents claimed that the extension would save "the equivalent of" 10,000 barrels of oil per day, but this figure was based on U.S. Department of Energy information from the 1970s, the accuracy and relevance of which the DoE no longer stands by. There is very little recent research on what the actual positive effects, if any, might be. http://news.nationalgeographic.com/news/2005/07/0728_050728_daylight.html

Related Topics:
March 11 - 2007 - Energy Policy Act of 2005 - House - Barrel - Oil - U.S. Department of Energy - 1970s

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The extension, which puts the U.S. out of step with other countries in North America (for example Canada), was greeted by criticism from the airline industry http://www.airlines.org/ga/files/ATA_DST_Letter.pdf, observant Jews http://www.beliefnet.com/story/171/story_17135_1.html, and those concerned for the safety of children traveling to school in the dark before the late sunrise http://www.gainesville.com/apps/pbcs.dll/article?AID=/20050723/WIRE/207230308/1117/news. Many businesses will have to reprogram or replace devices such as time clocks, security systems, and timed safes; traffic lights must be adjusted to properly recognize rush hour. Devices that use atomic time from radio clocks will adjust automatically, but such devices are rare, and it is difficult to receive the signals inside buildings. Many devices, such as VCRs, cannot be updated at all and will need to be manually adjusted twice a year.

Related Topics:
Canada - Jews - Sunrise - Time clock - Security system - Timed safe - Traffic light - Rush hour - Atomic time - Radio clock - Building - VCR

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DST and the state of Indiana

DST is a long-standing controversy in Indiana, not only as an agricultural state, but also because the border separating the Eastern and Central time zones divides the state. In the past, neighboring communities sometimes ended up one or even two hours apart. Being out-of-sync with neighboring states and the national changing of clocks, it is argued, has a negative economic impact on the state. It has been demonstrated that some businesses have located outside of the state once the confusion related to not changing clocks is discovered. In the current compromise, the state has three kinds of time zones:

Related Topics:
Indiana - Time zone

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• 77 counties, most of the state, are on Eastern Standard Time but do not use DST;
• 5 counties near Chicago, Illinois and 5 counties in the southwestern corner of the state are on Central Standard Time and do use DST; and
• 2 counties near Cincinnati, Ohio and 3 counties near Louisville, Kentucky are on Eastern Standard time but do observe DST. Their observance of DST is unofficial in this case, as a strict reading of the Uniform Time Act would not allow for this situation, but by observing DST, they remain synchronized with the greater Louisville and Cincinnati metropolitan areas.

On April 29, 2005, the Indiana legislature voted to begin observing daylight-saving time in 2006. Currently, the state is in the Eastern time zone; however, its time zone is currently under federal reviewhttp://www.indystar.com/apps/pbcs.dll/article?AID=/20050429/NEWS02/504290510. There was further controversy after this passed, as some people that supported it initially had thought that the time would fall back an extra hour in winter instead of going ahead an extra hour in summer.

Related Topics:
April 29 - 2005

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