Daylight saving time ( DST ; also summer time in British English—see Terminology ) is the practice of advancing clocks so that afternoons have more daylight and mornings have less. Typically clocks are adjusted forward one hour near the start of spring and are adjusted backward in autumn. Modern DST was first proposed in 1895 by George Vernon Hudson, a New Zealand entomologist. Many countries have used it since then; details vary by location and change occasionally.
The practice is controversial. Adding daylight to afternoons benefits retailing, sports, and other activities that exploit sunlight after working hours, but causes problems for farming, evening entertainment and other occupations tied to the sun. Traffic fatalities are reduced when there is extra afternoon daylight; its effect on health and crime is less clear. Although an early goal of DST was to reduce evening usage of incandescent lighting, formerly a primary use of electricity, modern heating and cooling usage patterns differ greatly, and research about how DST currently affects energy use is limited and often contradictory.
DST's occasional clock shifts present other challenges. They complicate timekeeping, and can disrupt meetings, travel, billing, recordkeeping, medical devices, heavy equipment, and sleep patterns. Often, software can adjust computer clocks automatically, but this can be limited and error-prone, particularly when DST rules change.
Origin
Although not punctual in the modern sense, ancient civilizations adjusted daily schedules to the sun more flexibly than modern DST does, often dividing daylight into twelve equal hours regardless of day length, so that each daylight hour was longer during summer. For example, Roman water clocks had different scales for different months of the year: at Rome's latitude the third hour from sunrise, hora tertia , started by modern standards at 09:02 solar time and lasted 44 minutes at the winter solstice, but at the summer solstice it started at 06:58 and lasted 75 minutes. After ancient times, equal-length civil hours eventually supplanted unequal, so civil time no longer varies by season. Unequal hours are still used in a few traditional settings, such as some Mount Athos monasteries and some Jewish ceremonies.
During his time as an American envoy to France, Benjamin Franklin, author of the proverb, "Early to bed, and early to rise, makes a man healthy, wealthy and wise", anonymously published a letter suggesting that Parisians economize on candles by rising earlier to use morning sunlight. This 1784 satire proposed taxing shutters, rationing candles, and waking the public by ringing church bells and firing cannons at sunrise. Franklin did not propose DST; like ancient Rome, 18th-century Europe did not keep precise schedules. However, this soon changed as rail and communication networks came to require a standardization of time unknown in Franklin's day.
Modern DST was first proposed by the New Zealand entomologist George Vernon Hudson, whose shift-work job gave him leisure time to collect insects, and made him aware of the value of after-hours daylight. In 1895 he presented a paper to the Wellington Philosophical Society proposing a two-hour daylight-saving shift, and after considerable interest was expressed in Christchurch, New Zealand he followed up in an 1898 paper. Many publications incorrectly credit DST's invention to the prominent English builder and outdoorsman William Willett, who independently conceived DST in 1905 during a pre-breakfast ride, when he observed with dismay how many Londoners slept through a large part of a summer day. An avid golfer, he also disliked cutting short his round at dusk. His solution was to advance the clock during the summer months, a proposal he published two years later.
As described in Politics below, Willett lobbied unsuccessfully for the proposal in the UK until his death in 1915, and Germany, its World War I allies, and their occupied zones were the first European nations to use Willett's invention, starting April 30, 1916, as a way to conserve coal during wartime. Britain, most of its allies, and many European neutrals soon followed suit. Russia and a few other countries waited until the next year; and the United States adopted it in 1918. Since then, the world has seen many enactments, adjustments, and repeals.
How it works
See also: Daylight saving time around the worldIn a typical case where a one-hour shift occurs at 02:00 local time, in spring the clock jumps forward from 02:00 standard time to 03:00 DST and that day has 23 hours, whereas in autumn the clock jumps backward from 02:00 DST to 01:00 standard time, repeating that hour, and that day has 25 hours. A digital display of local time does not read 02:00 exactly at the shift, but instead jumps from 01:59:59.9 either forward to 03:00:00.0 or backward to 01:00:00.0. In this example, a location observing UTC+10 during standard time is at UTC+11 during DST; conversely, a location at UTC−10 during standard time is at UTC−9 during DST.
Clock shifts are usually scheduled near a weekend midnight to lessen disruption to weekday schedules. A one-hour shift is customary, but Australia's Lord Howe Island uses a half-hour shift. Twenty-minute and two-hour shifts have been used in the past.
Coordination strategies differ when adjacent time zones shift clocks. The European Union shifts all at once, at 01:00 UTC; for example, Eastern European Time is always one hour ahead of Central European Time. Most of North America shifts at 02:00 local time, so its zones do not shift at the same time; for example, Mountain Time can be temporarily either zero or two hours ahead of Pacific Time. Australian districts go even further and do not always agree on start and end dates; for example, in 2008 most DST-observing areas shifted clocks forward on October 5 but Western Australia shifted on October 26.
Start and end dates vary with location and year. Since 1996 European Summer Time has been observed from the last Sunday in March to the last Sunday in October; previously the rules were not uniform across the European Union. Starting in 2007, most of the United States and Canada observe DST from the second Sunday in March to the first Sunday in November, almost two-thirds of the year. The 2007 U.S. change was part of the Energy Policy Act of 2005; previously, from 1987 through 2006, the start and end dates were the first Sunday in April and the last Sunday in October, and Congress retains the right to go back to the previous dates now that an energy-consumption study has been done.
Beginning and ending dates are the reverse in the southern hemisphere. For example, mainland Chile observes DST from the second Saturday in October to the second Saturday in March, with transitions at 24:00 local time. The time difference between the United Kingdom and mainland Chile may therefore be three, four, or five hours, depending on the time of year.
Western China, Iceland, and other areas skew time zones westward, in effect observing DST year-round without complications from clock shifts. For example, Saskatoon, Saskatchewan, is at 106° 39′ W longitude, slightly west of center of the idealized Mountain Time Zone (105° W) , bu
EngNet - EngNet Clocks - World Time Clock
EngNet Clocks - World Time Clock. Version 1.28. Windows 98/ME or Windows ... Free Tools and Software: Metric Conversion Chart - World Time Clock - Unit Converter
World Time Zone Clock Software - ZoneTick Time Zone Converter Download
ZoneTick World Time Zone Clock can replaces the regular system clock with several world time zone clock and time zone converter all in one.
World Time Clock Software - Kybtec World Clock, Paraben's World Clock ...
World Time Clock Software Listing. See the time all over the world on this attractive desktop world clock. Paraben's World Clock displays the time anywhere in the world on multiple ...
WorldTime Clock - World Time At Your Desktop
WorldTime Clock is an application displaying the local time in the any time zone around the world. WorldTime Clock has Appointment Management system and customizable look-and-feel.
Qlock - World Clock
World Clock ... Put our award winning real-time world map on your intranet / portal. business world time >
Desktop Version of World Time Clock & Map - Windows Software, Desktop ...
World Time Clock & Map - Offline Version. Desktop version of World Time Zones Map - softawre for Windows developed to check time around the world at one click! World Clock is a ...
World Clock - International Time Clock Software for your Computer ...
Sharp World Clock is perhaps the most sophisticated and beautiful International Clock and Desktop Clock - highly recommended for private and business use!
The World Time Server - correct, current, local
Get correct world time with accurate daylight saving clock adjustments for every zone. ... Copyright © 1998 - 2009 Chaos Software ...
ZoneTick World Time Zone Clock - Free software downloads and software ...
Time to kick the Windows clock up a notch? With the ability to display one or more clocks on the desktop or in the system tray, the skinnable ZoneTick World Time Zone lets you see ...
Best free world clock downloads. Display time from around the world ...
World clock software: Display time from around the world, Vista Clock - a Multifunctional Desktop Clock, Desktop clock calendar with world map and more.