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Daylight saving time (also called DST, or Summer Time) is the local time a country adopts for a portion of the year, usually an hour forward from its standard official time.

It is a system intended to "save" daylight (as opposed to wasting it by sleeping, say, while the sun shines). The official time is adjusted forward during the spring and summer months, so that the active hours of work and school will better match the hours of daylight.

It is sometimes asserted that DST was first proposed by Benjamin Franklin in a letter to the editors of the Journal of Paris. However, the article was humourous and, in any case, 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 was first put into practice by the German government during the First World War between the 30th of April, 1916 and the 1st of October, 1916. Shortly afterwards, the United Kingdom followed suit, first adopting DST between the 21st of May, 1916 and the 1st of October, 1916. Then on March 19, 1918 the United States Congress established several time zones and made daylight saving time permanent.

DST is not universally accepted; many localities do not observe it. Nevertheless, proponents claim that DST helps more than it hurts. The primary claim is that it reduces energy consumption. Opponents claim that there's not enough benefit to justify needing to adjust clocks twice per year. The disruption in sleep patterns associated with setting clocks forward, and thereby "losing" an hour, correlates with a spike in the number of severe auto accidents.

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.

DST is a long-standing controversy in Indiana, not only as an agricultural state, but also because the meridian separating the eastern and central time zones divides the state. In the past, neighboring communities sometimes ended up one or even two hours apart. In the current compromise, the state has three kinds of time zone: 77 counties, most of the state, are on Eastern Standard Time but do not use DST; 7 counties near Chicago and 3 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 use DST.

For fairly obvious reasons, DST is a temperate zone practice: day lengths in the tropics do not vary enough to justify 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, but it commonly begins in the Northern Hemisphere at 2:00 AM on either the first Sunday in April or the last Sunday in March, and ends at 2:00 AM on the last Sunday in October. In the Southern Hemisphere, the beginning and ending dates are switched.

The mnemonic "Spring forward, Fall back", tells how to reset clocks when the time switches.

The expression Daylight savings time (with the extra s) is a common alternate form, considered a usage error by some.

Daylight-saving time first went into effect in the United States on February 9, 1942 as a wartime measure to conserve resources needed to fight World War II.

See also British Summer Time

External Links

• Straightforward, good-looking discussion of DST, suitable for anybody of about age ten or over
• DST changeover times throughout the world
• World Time Server
• Time Zone Converter
• Sleep deficit and accidents

Links about changing or abolishing DST:

• End Daylight Saving Time web page, with petition
• Daylight saving humor