Daylight saving time (DST), also known as daylight savings time or daylight time, and summer time, is the practice of advancing clocks during warmer months so that darkness falls at a later clock time. The typical implementation of DST is to set clocks forward by one hour in the spring and set clocks back by one hour in autumn to return to standard time. As a result, there is one 23-hour day in late winter or early spring and one 25-hour day in the autumn.
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 Eastern Time Zone (ET) is a time zone encompassing part or all of 23 states in the eastern part of the United States, parts of eastern Canada, the state of Quintana Roo in Mexico, Panama and Colombia, mainland Ecuador, Peru, and a small portion of westernmost Brazil in South America, along with certain Caribbean and Atlantic islands.
Time in the United States, by law, is divided into nine standard time zones covering the states, territories and other US possessions, with most of the United States observing daylight saving time (DST) for approximately the spring, summer, and fall months. The time zone boundaries and DST observance are regulated by the Department of Transportation. Official and highly precise timekeeping services (clocks) are provided by two federal agencies: the National Institute of Standards and Technology (NIST) ; and the United States Naval Observatory (USNO). The clocks run by these services are kept synchronized with each other as well as with those of other international timekeeping organizations.
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. AST is observed in parts of North America, some Caribbean islands, and parts of South America. 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.
There are eleven time zones in Russia, which currently observe times ranging from UTC+02:00 to UTC+12:00. Daylight saving time (DST) has not been used in Russia since 26 October 2014. From 27 March 2011 to 26 October 2014, permanent DST was used.
Canada is divided into six time zones, based on proposals by Scottish Canadian railway engineer Sandford Fleming, who pioneered the use of the 24-hour clock, the world's time zone system, and a standard prime meridian. Most of Canada operates on standard time from the first Sunday in November to the second Sunday in March and daylight saving time the rest of the year.
Time in Chile is divided into three time zones. Most of Continental Chile uses the time offset UTC−04:00 in winter time and UTC−03:00 in summer time, while the Magallanes and Chilean Antarctica region uses the time offset UTC-03:00 the whole year. Additionally, Easter Island uses the time offset UTC−06:00 in winter time and UTC−05:00 in summer time
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.
Mexico uses four main time zones since February 2015. Most of the country observes Daylight Saving Time (DST).
- 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. For most of the year, it is the equivalent of U.S. Mountain Time. The state of Sonora, like the adjacent U.S. state of Arizona, does not observe DST.
- Zona Noroeste covers the state of Baja California. It is identical to U.S. Pacific Time, including the DST schedule.
Daylight saving time in the United States is the practice of setting the clock forward by one hour when there is longer daylight during the day, 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.
Samoa uses UTC+13:00 as standard time. It observed daylight saving time from 2010 to 2021, which it observed 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. Because it is located near the equator, Samoa traditionally did not observe daylight saving time. The introduction of daylight saving time was initially planned for 2009 but was postponed for one year in the aftermath of the 2009 Samoa tsunami.
Each state and territory of Australia determines whether or not to use daylight saving time (DST). However, during World War I and World War II all states and territories had daylight saving by federal law, under the defence power in section 51 of the constitution. In 1968, Tasmania was the first state since the war to adopt daylight saving. In 1971, New South Wales, Victoria, Queensland, South Australia, and the Australian Capital Territory also adopted daylight saving, while Western Australia and the Northern Territory did not. Queensland abandoned daylight saving in 1972. Queensland and Western Australia have observed daylight saving over the past 40 years from time to time on a trial basis.
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 of America participating, but much less so in South America.
As of 2018, daylight saving time (DST) is permanently observed in Morocco. Previously, time was advanced to UTC+01:00 at 02:00 on the last Sunday of March, and reverted to UTC±00:00, defined as Greenwich Mean Time locally, at 03:00 on the last Sunday of October. This practise was continued through October 2018, after which clocks were permanently advanced. An exception was made during the month of Ramadan during which clocks reverted to UTC+00:00.
As of 2017, daylight saving time is used in the following Asian countries:
The only African country and regions that use daylight saving time are:
The U.S. state of Idaho is covered by two time zones, as described below. All locations observe daylight saving time.
Permanent standard time refers to the year-round observation of standard time. Likewise, permanent daylight saving time refers to the year-round observation of daylight saving time (DST). Both permanent standard time and permanent DST eliminate the practice of biannual clock changes, specifically the advancement of clocks by one hour from standard time to DST in spring and the retraction of clocks by one hour from DST to standard time in fall. In the United States, Arizona, Hawaii, and all permanently inhabited territories observe permanent standard time. Observation of permanent DST is forbidden by the Uniform Time Act.
