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Revision as of 19:42, 13 April 2006 by Reywas92 (talk | contribs) (→Observation of DST)(diff) ← Previous revision | Latest revision (diff) | Newer revision → (diff)Daylight saving time (DST), often referred to as daylight savings time, is a widely used system of adjusting the official local time forward, usually one hour, from its official winter standard time for the duration of the spring and summer months. This is intended to provide a better match between the hours of daylight and the active hours of work and school. The "saved" daylight is spent on evening activities which get more daylight, rather than being "wasted" while people sleep past dawn.
DST is most commonly used in temperate regions, due to the considerable variation in the amount of daylight versus darkness across the seasons in those regions.
Governments often tout it as an energy conservation measure, on the grounds that it allows more effective use of natural sunlight resource in summer time. Since there is less darkness in the "waking day", there is less use of electric lights. Some opponents reject this argument (see below, Criticism).
Europeans commonly refer to the system as summer time: Irish Summer Time, British Summer Time, and European Summer Time. This is reflected in the time zones names as well, e.g., Central European Time (CET) becomes Central European Summer Time (CEST).
Origin
It is sometimes asserted that DST was first proposed by Benjamin Franklin in a letter to the editors of the Journal of Paris. Read the full text. However, the article was humorous; Franklin was not proposing DST, but rather that people should get up and go to bed earlier.
It was first seriously proposed by William Willett in the "Waste of Daylight", published in 1907, but he was unable to get the British government to adopt it despite considerable lobbying.
The idea of daylight saving time was first put into practice by the German government during the First World War between April 30 and October 1, 1916. Shortly afterward, the United Kingdom followed suit, first adopting DST between May 21 and October 1, 1916. Then on March 19, 1918, the U.S. Congress established several time zones (which were already in use by railroads and most cities since 1883) and made daylight saving time official (which went into effect on March 31) for the remainder of World War I. It was observed for seven months in 1918 and 1919. The law, however, proved so unpopular (mostly because people rose and went to bed earlier than in current times) that it was later repealed.
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, and Arizona do not observe DST.
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.
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. However, beginning in 2007, the United States will begin observing DST on the second Sunday of March until the first Sunday in November, but if no energy savings can be shown from the extension after the U.S. Department of Energy completes a study of impact of the change, Congress may revert back to the schedule set in 1986 under Section 110 of the Energy Policy Act of 2005. Since 2002, the European Union has fixed the last Sunday in March and the last Sunday in October as start and end dates (European Summer Time).
In the southern hemisphere, the beginning and ending dates are switched; therefore, the time difference between the United Kingdom and Chile may be three, four, or five hours, depending on the time of year.
Usage and history by location
Africa
Egypt
Egypt operates Daylight-Saving Time between the last Friday in April and the last Thursday in September when the clocks are 3 hours ahead of Greenwich Mean Time (UTC+3).
Namibia
Namibia Daylight Saving Time begins on the first Sunday in September, and ends on the first Sunday in April.
Asia
China
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.
India
India used DST briefly during its wars with Pakistan and China.
Iran
As of 2006, Iran does not observe DST . In previous years, DST in Iran started on the first day of Farvardin (21-22 March) and ended on the first day of Mehr (23-24 September), in the Iranian calendar.
Israel
Israel observes DST starting on the last Friday before April 2 and ending on the Saturday (2AM Sunday) between Rosh Hashanah and Yom Kippur. Until 2005, the schedule was variable – the only requirement was that there be at least 150 days per year of DST – and was set out each year by the Ministry of the Interior.
Kyrgyzstan
Kyrgyzstan voted to stop observing it in 2005.
Pakistan
Pakistan experimented with DST in 2002 going from +5:00 to +6:00. It has not used DST since then.
Australasia
Australia
In Australia, daylight saving time is a state/territory-based initiative. Some states/territories implement it and some do not.
New South Wales, Victoria, Tasmania, Australian Capital Territory and South Australia apply daylight saving time. Tasmania starts DST earlier than the others, usually near the beginning of October.
Western Australia, Northern Territory and Queensland do not have daylight saving. Queensland experimented with it for a year or two in the early 1970s, and again in the 1990s, but it was not popular and was abandoned.
See the Australian time zones article or this site for maps and further information on standard and daylight saving time in Australia.
New Zealand
Main article: Time in New ZealandIn New Zealand, daylight saving time begins at 2 A.M. (standard time) on the first Sunday in October each year, and ends at 2 A.M.(standard time) on the third Sunday of March.
Europe
All countries in Europe but Iceland observe daylight-saving time and change on the same date and time: 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 (CET, 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 winter time in all zones. Thus in Moscow (local time = UTC+3 in winter, UTC+4 in summer), daylight-saving time commences at 23:00 UTC on the day before the last Sunday in March, and ends at 23:00 UTC on the day before the last Sunday in October.
Iceland
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. Polar or near-polar locations such as Iceland often opt out, as summer in these locations usually brings nearly uninterrupted daylight.
North America
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*.
* In 2007, the starting and ending dates for DST will change in the United States and parts of Canada (see below).
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 1988, they experimented with Double Daylight Time, when the clocks went ahead by two hours, instead of the usual one hour. Manitoba begins DST at 02:00, but switches back to standard time in October at 03:00.
Canada
Main article: Time in CanadaIn Canada, time is under provincial and territorial jurisdiction, not federal. The governments of Ontario, British Columbia, Manitoba, Quebec, Prince Edward Island, New Brunswick, Alberta and the Northwest Territories have pledged to change their daylight saving rules to match the new U.S. rules. In 2007, their DST will start on the second Sunday of March, and return to standard time on the first Sunday in November. The remaining provinces and territories will continue to change time on the first Sunday of April and last Sunday of October unless they change their legislation.
Saskatchewan
The province of Saskatchewan is the largest part of the country that does not use DST, that is, it does not adjust clocks in spring and fall. Saskatchewan is bisected by the 105° West meridian, the central meridian of the Mountain Standard Time Zone (UTC-7), yet clocks are kept at UTC-6 all year long. (This policy was implemented when the Saskatchewan Time Act was passed in 1966, to solve the problems that arose when time zones varied from town to town.) Thus, in the summer months Saskatchewan is in sync with Mountain Daylight Time and in the winter months it is in sync with Central Standard Time. Observationally, this is equivalent to the province being on Mountain Daylight Time year-round, or Central Standard Time year-round. Officially the province is considered to be part of the Central time zone.
The charter of the city of Lloydminster, which is bisected by the Saskatchewan–Alberta boundary, gives it a special exception (among areas in Saskatchewan) to use DST. Lloydminster and its immediately surrounding region in Saskatchewan use the same timekeeping routine used by Alberta, DST with Mountain Standard Time. Saskatchewan Government Relations gives further details on Saskatchewan's time policies. Local custom in Denare Beach and Creighton, SK, is to observe DST, thereby keeping the same time as nearby Manitoba communities.
Quebec
The eastern reaches of Quebec's North Shore, east of 63° West longitude, are in the Atlantic Time Zone, but do not observe DST (see exception, below). The effect is that in summer, their clocks match those of the rest of the province, which observes Eastern Daylight Time. In October, their clocks are rejoined by their Atlantic Standard Time neighbors. Although places east of 63° West are officially on Atlantic Time, local custom is to use Eastern Time as far east as the Natashquan River. Those communities observe DST, including all of Anticosti Island, which is bisected by the 63rd meridian.
British Columbia
Most of BC observes DST, but there is a large tract in east-central BC which does not, and it all falls in the Mountain Time Zone (most of BC is on Pacific Time). This includes Fort St. John, Charlie Lake, Taylor and Dawson Creek. The Crowsnest corridor between Creston and Yahk in the East Kootenays (southeastern BC) also keeps standard time year-round.
Nunavut
While the rest of Nunavut changes to DST, Southampton Island and thus Coral Harbour remain on Eastern Standard Time throughout the year.
Ontario
Secluded in the heart of northwestern Ontario, Pickle Lake and New Osnaburgh have no use for daylight saving time. To the south, Atikokan also ignores it, using Eastern Standard Time year-round, effectively adopting Central Daylight Time in summer. Southern Ontario including Toronto, however, does use DST.
Cuba
Since April 2004, Cuba has remained on DST. Cuba will end DST on October 29, 2006 and begin DST again on March 2007.
Mexico
Mexico adopted DST nationwide in 1996, even in its tropical regions, because of its increasing economic ties to the United States. The Mexican state of Sonora has not observed DST since 1998 because it borders on the U.S. state of Arizona, which also does not observe DST.
United States
The schedule for 2006 in the United States is that DST begins on the first Sunday in April (], 2006), and changes back to standard time on the last Sunday in October (October 29, 2006). Beginning in 2007, DST will start on the second Sunday in March, and change back to standard time on the first Sunday in November. Under Section 110 of the Energy Policy Act of 2005, the U.S. Department of Energy is required to study the impact of the daylight saving extension no later than nine months after the change takes effect. Congress has retained the right to revert back to the daylight saving schedule set in 1986 if it cannot be shown that there are significant energy savings from an extension of daylight saving time.
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. During this period, the official designation "War Time" was used for the year-round DST.
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, but the predominant national pattern was that the states and localities that did observe daylight saving time did so from the last Sunday in April to the last Sunday in September. In the mid-1950s, many states and localities in the northeastern United States began extending daylight saving time to the last Sunday in October. The absence of federal standardization 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).
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, effective in 1967. 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. On July 8, 1986, President Ronald Reagan signed the Federal Fire Prevention and Control Act of 1986 into law which amended the starting date of daylight saving time to the first Sunday in April, to take effect the following year.
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.
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 from the first Sunday in March to the last Sunday in November. 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. (See this article, for example.)
The extension was greeted with criticism by those concerned for the safety of children traveling to school in the dark before the late sunrise. In addition, the airline industry was especially concerned if daylight saving time was extended through to the last Sunday in November, as this is very often the Sunday after Thanksgiving. The Sunday after Thanksgiving is one of the busiest travel days at American airports, and could have resulted in much havoc among travelers who forgot that the clocks were changing that day.
If the original proposal to extend daylight saving time through the last Sunday in November had been adopted, the entire United States, with the exception of the states that exempted themselves, would have experienced the latest sunrises of the year during the month of November.
An additional issue raised by this extension is that it may require the reconfiguration of some computers. Many computers are programmed to adjust automatically for DST, but do so based on static tables stored directly on the computer itself. In order to change the dates and times at which the automatic jump to or from DST occurs, these tables must be modified, or the user must manually specify that the computer's clock should operate in Daylight Saving Time mode. One potential issue related to this (though difficult to quantify) is the amount of labor and money that may be spent correcting errors that arise due to a failure to update computers. Certain types of information systems (those that schedule future events with reference to UTC, for example) may encounter problems arising from a lack of synchronization unless both computers and databases are carefully updated.
Arizona
Arizona does not observe DST. However, the large Navajo Indian Reservation, which extends from Arizona into two adjacent states, does. The Hopi Indian Reservation, surrounded by the Navajo reservation but entirely in Arizona, does not. This has effects including, among other things, added confusion when communicating with friends and relatives in other states, as well as altering of television schedules. While most cable television services are nation-wide and observe DST, stations local to Arizona do not shift, leading to a shift of show schedules relative to each other.
The reasons are simple: Having everyone come home from work an hour earlier to turn on or turn down their apartment or home's central air conditioner would cost the state a prohibitively large amount of money. However, many homes on the reservations have only a swamp cooler, if even that.
Hawaii
Hawaii does not observe DST.
Indiana
DST has been a long-standing controversy in Indiana: not only is it a largely agricultural state, but it is also divided between the Eastern and Central time zones, and includes suburbs of cities in other states in both zones. Being out of sync with neighboring states and the national changing of clocks, supporters argued, had a negative economic impact on the state. Some supporters claimed that some businesses had located out-of-state due to time-related confusion. Opponents claimed that daylight saving time creates costs and inconvenience associated with changing clocks twice a year, and has little or no real value.
From 1991 until April 1, 2006, the state has had three time-zone/DST situations:
- 77 counties — most of the state — were on Eastern Standard Time and did not use DST.
- 5 northwestern counties near Chicago, Illinois, and 5 southwestern counties near Evansville, Indiana, were on Central Time and did use DST.
- 2 counties near Cincinnati, Ohio, and 3 counties near Louisville, Kentucky, were on Eastern time and not allowed to observe DST under the Uniform Time Act, but nevertheless did observe DST unofficially in order to remain synchronized with Louisville and Cincinnati.
On April 29, 2005, the Indiana legislature voted to begin observing daylight saving time statewide in 2006. The bill to observe DST also required the governor to request federal review of the time zone divisions in the state. As a result of the review, the United States Department of Transportation has moved eight more counties to the Central time zone, effective when DST begins on April 2, 2006. These are Starke and Pulaski Counties in the northwest; Daviess, Dubois, Knox, Martin, Perry, and Pike in the southwest. Currently, Pulaski and Martin counties reconsidered their bid to join the Central time zone and decided to formally request to be in the Eastern time zone. Pulaski County Commissioners and County Council both voted unanimously on Monday, February 6, 2006, to declare "home rule" and stay on Eastern time if a federal agency did not grant an appeal to change the time-zone ruling; however, the county conceded on Monday, March 27, 2006, accepting Central time officially, although many residents say that they will continue to observe Eastern time unofficially.
This Indiana Time Zone Map (a 13 KB PDF file) shows a graphical overview of what counties are on Central and Eastern Time Zones in the State of Indiana. Standard Time Zone Boundary in the State of Indiana (a 139 KB PDF file) has some history, public comments from each county, the final DOT determination, and the resulting time zone boundary. See also What Time is it in Indiana?
South America
Chile
Chile switches to DST at 24:00 (Midnight) on the second Saturday in October and reverts to Local Standard Time (LST) at 24:00 (Midnight) on the second Saturday the following March. The current law which affects the entire country was enacted in 1970, but it had observed the practice as early as 1927 when the country had been divided into two distinct time zones. In specific years the starting and ending dates have been modified for political or climatic reasons.
Brazil
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.
Rationales for DST
One of the major reasons given for observing DST is energy conservation. Theoretically, the amount of residential electricity needed in the evening hours is dependent both on when the sun sets and when people go to bed. Because people tend to observe the same bedtime year-round, by artificially moving sunset one hour later, the amount of energy used is theoretically reduced. United States Department of Transportation studies showed that DST reduces the country's electricity usage by one percent while it is in effect.
Part of the reason that it is normally observed in the late spring, summer, and early autumn instead of the winter months is that the amount of energy saved by experiencing sunset one hour later would be negated by the increased need for artificial morning lighting due to a later sunrise. During the summer most people would wake up after the sun rises, regardless of whether daylight saving time is in effect or not, so there is no increased need for morning lighting to offset the afternoon drop in energy usage.
Another perceived benefit of DST is increased opportunities for outdoor activities. Most people plan outdoor activities during the increased hours of sunlight. Other benefits cited include prevention of traffic injuries (by allowing more people to return home from work or school in daylight), and crime reduction (by reducing people's risk of being targets of crimes that are more common in dark areas).
When the U.S. went on extended DST in 1974 and 1975 in response to the 1973 energy crisis, Department of Transportation studies found that observing DST in March and April saved 10,000 barrels of oil a day, and prevented about 2,000 traffic injuries and 50 fatalities saving about U.S. $28 million in traffic costs. (Stats from ).
Criticism of DST
DST is not universally accepted and many localities do not observe it. Opponents claim that there is not enough benefit to justify the need to adjust clocks twice every year. The disruption in sleep patterns associated with setting clocks either forward or backward correlates with a spike in the number of severe auto accidents, as well as lost productivity as sleep-disrupted workers adjust to the schedule change. It is also noted that much effort is spent reminding everyone twice a year of the change, and thousands are inconvenienced by showing up at the wrong time when they forget. Since DST exchanges morning daylight for evening daylight, late sunrises occur when DST is in effect either too far before the vernal equinox or too far after the autumnal equinox and darkness in the morning can be undesirable for early risers like schoolchildren and workers who begin their workday at 8:00 AM or earlier.
There is also a question whether the decrease in lighting costs justifies the increase in summertime air conditioning costs. While many people use more sunlight under DST, most people also experience more heat, which prompts many people to turn on the air conditioner during the warmer afternoon hours. When air conditioning was not widely available, the change did save energy; however, air conditioning is much more widespread now than it was several decades ago. Air conditioning often uses more energy than artificial lighting. It was for this reason that Arizona rejected DST and opted to stay on standard time all year .
It is also speculated that one of the benefits—more afternoon sun—would also actually increase energy consumption as people get into their cars to enjoy more time for shopping and the like.
For example, during a North American time change, a fall night during which clocks are reset from 2 AM Daylight to 1 AM Standard Time, times between 1 AM and 2 AM will occur twice, causing confusion in transport schedules, payment systems, etc. On a more trivial note, this also means that people born during one of those two hours have no way to know which one it really was, unless someone such as a parent bothers to make a note of it; birth certificates rarely keep track of this. It is difficult to imagine anyone caring about this, but at least one aristocrat, Lord Balfour of the UK, has lodged a farfetched objection: "Supposing some unfortunate lady was confined with twins and the first child was born 10 minutes before 3 o'clock British Summer Time. ... the time of birth of the two children would be reversed. ... Such an alteration might conceivably affect the property and titles in that House."
Some studies do show that changing the clock increases the traffic accident rate. Following the spring shift to daylight saving time (when one hour of sleep is lost) there is a measurable increase in the number of traffic accidents that result in fatalities.
Some campaigners in Britain would like the country to stay on British Summer Time (BST) all year round, or in other words, adopt Central European Time and abolish BST. Alternatively, some would like Britain to adopt Central European Time and jump forward another hour during the summer (adopting a Single/Double Summer Time from Britain's perspective). This would make winter evenings longer, thereby reducing traffic accidents and cases of seasonal affective disorder. Opponents point to the longer hours of darkness on winter mornings, especially in Scotland, the north of England and Northern Ireland which might well cause an increase in road accidents. In response to this, there have been proposals to introduce legislation to put Scotland on a different time-zone to England and Wales.
DST is particularly unpopular among people working in agriculture because the animals do not observe it, and thus the people are placed out of synchronization with the rest of the community, including school times, broadcast schedules, and the like.
Other critics suggest that DST is, at its heart, government paternalism and that people rise in the morning as a matter of choice because many people enjoy nighttime hours and their jobs do not require them to make the most of daylight. Different people start their day at different times (office workers start their day later than factory workers, who start their day later than farm workers), regardless of daylight saving time.
Mnemonic
The mnemonic "spring forward, fall back" (also "spring ahead, fall back") tells us how to reset clocks when the time changes, regardless of hemisphere (although it has to be remembered that spring and autumn occur during different months in the northern and southern hemispheres). This uses the word "fall" to mean "autumn"; while this usage has died out in British English, it is still very common in North American English.
Associated practices
Fire safety officials in Australia, Canada, New Zealand, and the United States encourage citizens to use the two annual time changes as a reminder to check the batteries in home and office fire alarms and smoke detectors. For example, the Country Fire Authority of Victoria in Australia has been running a program called "Change Your Clock, Change Your Smoke Alarm Battery" for several years. This is especially important in autumn, just before the heating season causes an increase in home fires.
Computer systems
Most modern computer operating systems include the capability to automatically change the local time when daylight saving starts and finishes. See the Time zone article for general information on time zones and computer systems.
Microsoft Windows
The time zone database in Windows based computer systems only stores a single start and end rule for each zone, and daylight saving information is stored in the registry key HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Time Zones\
, under the TZI registry value. (In Windows XP Professional it's in the machines's policy hive in HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\Control\TimeZoneInformation\
) For example, DST ends on the last Sunday in October, regardless of year. When the actual rule changes (e.g. Australian DST ending one week later than usual in 2006, or DST being extended in the United States starting in 2007) a patch needs to be applied. In the case of a single year anomaly, a new time zone is created and used. Before the following year, the time zone will have to be switched back to the original. For permanent rule changes, the rule definition for the time zone can be changed without requiring a new time zone to be set up.
One of the problems of this approach is that software which uses time zone information will get incorrect results if referring to a year with rules that are different from those currently in the database. A good example is the Lotus Notes calendar system, which stores event times in UTC. Events created with calendar dates near DST start and end dates can have their local time interpretation changed after the time zone database is updated (i.e. after the OS patch is applied). Another issue was highlighted when the Australian government changed daylight saving time to end on April 2 instead of March 26 for the 2006 Commonwealth Games. Microsoft did not modify the start and end rule for the time zones affected, but instead added new timezones with the words "(Commonwealth Games)" which caused various issues with many software applications, including Microsoft Outlook and several accounting packages. Workarounds for the issue were to use the Microsoft utility timezone
to modify the start and finish of each effected timezone, then either reboot the computer or go into Date and Time in the Control Panel, click on the Time Zone tab and click on OK to force Windows to refresh its daylight saving time information.
Unix
Unix systems (including Linux and Mac OS X) allow a single time zone to have multiple DST rules to handle changes from year to year. As soon as a rule change is announced, it can be safely added to the system. All the standard library routines which calculate times access this database, so software that queries whether a particular date will have daylight saving in effect (for the time zone of the process) will get the correct answers as long as the time zone rule is correct for the year in question.
Java
Java uses a similar database to Unix, so rules for multiple years (not just the current year) can be represented. This database is separate from the underlying operating system time zone database, so it must also be updated when daylight saving rules change.
The name
In the normative form of the name, "daylight saving" is a compound adjective (part of which is a gerund) that modifies "time." A common variant is daylight savings time, which appears in some dictionaries, including The American Heritage Dictionary. In this form, the singular noun savings forms a compound adjective with daylight, in analogy with phrases like "retirement savings plan". Although this alternate form is frequently heard in speech, some consider it to be nonstandard. Sometimes compound adjectives are joined with a hyphen, but "daylight-saving time" is not a common usage, except in AP Style, a stylebook used by many journalists in the United States.
Hour Interchange
- When daylight saving time begins, the day loses one hour (hour interchange of -1)
- When daylight saving time ends, the day gains one hour (hour interchange of +1)
Notes
- "Directive 2000/84/EC of the European Parliament and of the Council of 19 January 2001 on summer-time arrangements". EU.int. Retrieved 2006-03-27.
- Ferguson, S.A. et al. (1995) Daylight saving time and motor vehicle crashes: the reduction in pedestrian and vehicle occupant fatalities. American Journal of Public Health 85, 92–95.
- Microsoft Download: Australian Daylight Savings Changes for Microsoft Products for the Year 2006; & MS-KB article 909915, "Microsoft products do not reflect Australian daylight saving time changes for the year 2006" - February 27, 2006
- Aussie Microsoft calendar mess. Office Watch, volume 11 no. 5, 25 January 2006.
See also
- British Summer Time
- European Summer Time
- Eastern Daylight Time
- Central Daylight Time
- Australian time zones
- List of countries that do not observe Daylight Saving Time
Books
- Prerau, David. Seize the Daylight: The Curious and Contentious Story of Daylight Saving Time (Thunder’s Mouth Press; ISBN 1-56025-655-9)
- Prerau, David. Saving the Daylight: Why We Put the Clocks Forward (Granta Books; ISBN 1-86207-796-7) — The Story of Summer Time/Daylight Saving time with a focus on the U.K.
- Downing, Michael. Spring Forward: The Annual Madness of Daylight Saving Time (Shoemaker & Hoard; ISBN 1-59376-053-1)
External links
- A Brief History of DST
- Congressional Research Service (CRS) Reports regarding DST
- DST by WebExhibits
- EU directive 2000/84/EC
- Saving Time, Saving Energy - United States DST schedule (including new rules starting in 2007), explanation, history
- Sources for daylight saving time data, including histories and predictions
- Summer Time by JR Stockton. With future changeover dates EU (until 2007 final, from then extrapolating)
- Sleep deficit and accidents
- National Association of Standard Time
- PhotoSydney: Daylight Saving examines daylight saving in Australia.
- www.TimeAndDate.com - Time calculation services
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