daylight saving time

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daylight saving time

(DST), time observed when clocks and other timepieces are set ahead so that the sun will rise and set later in the day as measured by civil timecivil time,
local time based on universal time. Civil time may be formally defined as mean solar time plus 12 hr; the civil day begins at midnight, while the mean solar day begins at noon.
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. The amount of daylight on a given dayday,
period of time for the earth to rotate once on its axis. The ordinary day, or solar day, is measured relative to the sun, being the time between successive passages of the sun over a stationary observer's celestial meridian.
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 of the year at a given latitude is fixed, but over the year the hours of sunrise and sunset vary from day to day. During the summer months, the sun rises earlier and sets later and there are more hours of daylight. If clocks and other timepieces are set ahead in the spring by some amount (usually one hour), the sun will rise and set later in the day as measured by those clocks. This provides more usable hours of daylight for activities that occur in the afternoon and evening, such as outdoor recreation. Daylight saving time can also be a means of conserving electrical and other forms of energy. In the fall, as the period of daylight grows shorter, clocks are set back to correspond to standard timestandard time,
civil time used within a given time zone. The earth is divided into 24 time zones, each of which is about 15° of longitude wide and corresponds to one hour of time. Within a zone all civil clocks are set to the same local solar time.
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Benjamin Franklin, when serving as U.S. minister to France, wrote an article recommending earlier opening and closing of shops to save the cost of lighting. In England, William Willett in 1907 began to urge the adoption of daylight saving time. During World War I the plan was adopted in England, Germany, France, and many other countries. In the United States, Robert Garland of Pittsburgh was a leading influence in securing the introduction and passage of a law (signed by President Wilson on Mar. 31, 1918) establishing daylight saving time in the United States. After World War I the law was repealed (1919). In World War II, however, national daylight saving time was reestablished by law on a year-round basis. National year-round daylight saving time was adopted as a fuel-saving measure during the energy crisis of the winter of 1973–74. In late 1974, standard time was reinstituted for the winter period. In 1987 federal legislation fixed the period of daylight saving time in the United States as the first Sunday (previously the last Sunday) in April to the last Sunday in October; it was expanded in 2005 (effective 2007) to extend from the second Sunday in March to the first Sunday in November. Arizona and Hawaii do not use daylight saving time.

daylight saving time

[¦dā‚līt ‚sāv·iŋ ‚tīm]
(astronomy)
A variation of zone time, usually 1 hour more advanced than standard time, frequently kept during the summer to make better use of daylight. Also known as summer time.
References in periodicals archive ?
Airlines oppose plan to extend daylight-saving time. The airline industry opposes a plan to extend daylight-saving time by two months, Air Transport Association spokesman Jack Evans said.
The lower house, however, failed to approve the decree to implement daylight-saving time for a seven-month period in 2002.
Reversing a decision by his Orthodox predecessor, Sharansky, who is observant but not Orthodox, said that daylight-saving time will be extended by 37 days this year.
The end of daylight-saving time is abrupt, but daylight has been seeping away since the beginning of summer - slowly at first, then quickly around the equinox, and from now until the solstice on at a slower pace.
Typically, daylight-saving time began on the first Sunday in April and ended on the last Sunday in October.
In a ruling certain to have national repercussions, Mexico's highest court (Suprema Corte de Justicia de la Nacion, SCJN) threw out the federal government's directive requiring Mexico City to abide by the federally imposed daylight-saving time.
Congress, in an effort to get us all to use less energy, passed a law two years ago adding four weeks to our daylight-saving time regimen.
While this was a setback for Fox, the president won a battle to implement daylight-saving time nationwide when Mexico City Mayor Andres Manuel Lopez Obrador dropped his opposition to the time change.
So, before you go to bed tonight, turn your clocks back one hour, and say good night to the old daylight-saving time schedule.
Mexico City authorities are questioning the federal government's decision to impose daylight-saving time, while the Yucatan government has challenged the administration's right to appoint members of the electoral body that would monitor the gubernatorial elections in May.
This Sunday marks the annual switch to daylight-saving time, and with it the need to set clocks ahead one hour.
The controversy regarding daylight-saving time has resurfaced in 2001, with many states resisting efforts by President Vicente Fox's administration to use the time change to conserve electrical power.