Daylight saving time (DST), also daylight savings time or daylight time and summer time, is the practice of advancing clocks during summer months so that evening daylight lasts longer, while sacrificing normal sunrise times. Typically, regions that use daylight saving time adjust clocks forward one hour close to the start of spring and adjust them backward in the autumn. In effect, DST causes a lost hour of sleep in the spring and an extra hour of sleep in the fall.
The North American Central Time Zone (CT) is a time zone in parts of Canada, the United States, Mexico, Central America, some Caribbean Islands, and part of the Eastern Pacific Ocean.
The Mountain Time Zone of North America keeps time by subtracting seven hours from Coordinated Universal Time (UTC) when standard time is in effect, and by subtracting six hours during daylight saving time (UTC−06:00). The clock time in this zone is based on the mean solar time at the 105th meridian west of the Greenwich Observatory. In the United States, the exact specification for the location of time zones and the dividing lines between zones is set forth in the Code of Federal Regulations at 49 CFR 71.
The Uniform Time Act of 1966, Pub.L. 89–387, 80 Stat. 107, enacted April 13, 1966, was a Law of the United States to "promote the adoption and observance of uniform time within the standard time zones" prescribed by the Standard Time Act of 1918. Its intended effect was to simplify the official pattern of where and when daylight saving time (DST) is applied within the U.S. Prior to this law, each state had its own scheme for when DST would begin and end, and in some cases, which parts of the state should use it.
The Atlantic Time Zone is a geographical region that keeps standard time—called Atlantic Standard Time (AST)—by subtracting four hours from Coordinated Universal Time (UTC), resulting in UTC−04:00. During part of the year, some portions of the zone observe daylight saving time, referred to as Atlantic Daylight Time (ADT), by moving their clocks forward one hour to result in UTC−03:00. The clock time in this zone is based on the mean solar time of the 60th meridian west of the Greenwich Observatory.
Australia uses three main time zones: Australian Western Standard Time, Australian Central Standard Time, and Australian Eastern Standard Time. Time is regulated by the individual state governments, some of which observe daylight saving time (DST). Australia's external territories observe different time zones.
The UTC offset is the difference in hours and minutes from Coordinated Universal Time (UTC) for a particular place and date. It is generally shown in the format ±[hh]:[mm], ±[hh][mm], or ±[hh]. So if the time being described is one hour ahead of UTC, the UTC offset would be "+01:00", "+0100", or simply "+01".
Iran Standard Time (IRST) or Iran Time (IT) is the time zone used in Iran. Iran uses a UTC offset UTC+03:30. IRST is defined by the 52.5 degrees east meridian, the same meridian which defines the Iranian calendar and is the official meridian of Iran.
The time zone in Germany is Central European Time and Central European Summer Time. Daylight saving time is observed from the last Sunday in March to the last Sunday in October. The doubled hour during the switch back to standard time is named 2A and 2B.
Mexico uses four main time zones since February 2015. Most of the country observes Daylight Saving Time.
- Zona Sureste covers the state of Quintana Roo is UTC-05:00 year round. It is the equivalent of U.S. Eastern Standard Time.
- Zona Centro covers the eastern three-fourths of Mexico, including Mexico City, Guadalajara and Monterrey. For most of the year, it is the equivalent of U.S. Central Time.
- Zona Pacífico covers the states of Baja California Sur, Chihuahua, Nayarit, Sinaloa, and Sonora. The state of Sonora, like the U.S. state of Arizona, does not observe daylight saving time. For most of the year, it is the equivalent of U.S. Mountain Time.
- Zona Noroeste covers the state of Baja California. It is identical to U.S. Pacific Time, including the daylight saving time schedule.
Daylight saving time in the United States is the practice of setting the clock forward by one hour during the warmer part of the year, so that evenings have more daylight and mornings have less. Most areas of the United States observe daylight saving time (DST), the exceptions being Arizona, Hawaii, and the overseas territories of American Samoa, Guam, the Northern Mariana Islands, Puerto Rico, and the United States Virgin Islands. The Uniform Time Act of 1966 established the system of uniform Daylight Saving Time throughout the US.
Europe spans seven primary time zones, excluding summer time offsets. Most European countries use summer time and harmonise their summer time adjustments; see Summer time in Europe for details.
Samoa uses UTC+13:00 as standard time and UTC+14:00 as daylight saving time, which it observes during summer in the Southern Hemisphere. In 2011, daylight saving time ended on Saturday, 2 April 2011, 04:00 local daylight time and started on Saturday, 24 September 2011, 03:00 local standard time. Due to its location in the South Pacific Ocean, Samoa traditionally did not observe daylight saving time. Initially planned for 2009, the introduction of daylight saving time in Samoa was postponed for one year due to the aftermath of the 2009 Samoa tsunami.
The choice of whether to use daylight saving time (DST) in Australia is a matter for the individual states and territories. However, during World War I and World War II all states and territories had daylight saving by federal acts under section 51 of the constitution (defence). In 1968 Tasmania became the first state since the war to practise daylight saving. In 1971, New South Wales, Victoria, Queensland, South Australia, and the Australian Capital Territory followed Tasmania by observing daylight saving time. Western Australia and the Northern Territory did not. Queensland abandoned daylight saving time in 1972. Queensland and Western Australia have observed daylight saving over the past 40 years from time to time on trial bases.
Pakistan has experimented with Daylight Saving Time (DST) a number of times since 2002, shifting local time from UTC+05:00 to UTC+06:00 during various summer periods, having the effect of making Pakistan counter-intuitively half an hour ahead of India during those times, even though India is generally to its east.
Daylight saving time in the Americas is the arrangement in the Americas by which clocks are advanced by one hour in spring and moved back in autumn, to make the most of seasonal daylight. The practice is widespread in North America, with most of Canada, Mexico, and the United States participating, but much less so in South America.
As of 2017, daylight saving time is used in the following Asian countries:
Portugal has two time zones and observes daylight saving time. Continental Portugal and Madeira use UTC+00:00, while the Azores use UTC–01:00. Daylight saving time is observed nationwide from the last Sunday in March to the last Sunday in October, so that every year, continental Portugal and Madeira temporarily use UTC+01:00, and the Azores temporarily use UTC+00:00.
Most areas in Europe and North America observe daylight saving time (DST), while most areas of Africa and Asia do not. In South America, most countries in the north of the continent near the Equator do not observe DST, while Paraguay and most of Chile do. The practice of observing daylight saving time in Oceania is also mixed, with New Zealand and parts of southeastern Australia observing DST, while most other areas do not.
Bosnia and Herzegovina uses a single time zone, denoted as Central European Time. It also observes summer time, shifting to Central European Summer Time.
