Alaska Time Zone
Encyclopedia
Standard time
Standard time is the result of synchronizing clocks in different geographical locations within a time zone to the same time rather than using the local meridian as in local mean time or solar time. Historically, this helped in the process of weather forecasting and train travel. The concept...
by subtracting nine hours from Coordinated Universal Time
Coordinated Universal Time
Coordinated Universal Time is the primary time standard by which the world regulates clocks and time. It is one of several closely related successors to Greenwich Mean Time. Computer servers, online services and other entities that rely on having a universally accepted time use UTC for that purpose...
(UTC−9). During daylight saving time
Daylight saving time
Daylight saving time —also summer time in several countries including in British English and European official terminology —is the practice of temporarily advancing clocks during the summertime so that afternoons have more daylight and mornings have less...
its time offset
Time offset
The UTC offset is the time offset from Coordinated Universal Time . It is mostly given as hour or hour and minute. Many time zones employ two time offsets, one for standard time and one for daylight saving time...
is only eight hours (UTC−8). The clock time in this zone is based on the mean solar time of the 135th meridian west
135th meridian west
The meridian 135° west of Greenwich is a line of longitude that extends from the North Pole across the Arctic Ocean, North America, the Pacific Ocean, the Southern Ocean, and Antarctica to the South Pole....
of the Greenwich Observatory.
The zone includes nearly all of the U.S. state of Alaska
Alaska
Alaska is the largest state in the United States by area. It is situated in the northwest extremity of the North American continent, with Canada to the east, the Arctic Ocean to the north, and the Pacific Ocean to the west and south, with Russia further west across the Bering Strait...
and is one hour behind the Pacific Time Zone
Pacific Time Zone
The Pacific Time Zone observes standard time by subtracting eight hours from Coordinated Universal Time . The clock time in this zone is based on the mean solar time of the 120th meridian west of the Greenwich Observatory. During daylight saving time, its time offset is UTC-7.In the United States...
.
- standard time: Alaska Standard Time (AKST)
- daylight saving time: Alaska Daylight Time (AKDT)
The western Aleutian Islands observe Hawaii-Aleutian Time, one hour behind the remainder of the state.
Effective 2007, the local time changes from AKST to AKDT at 02:00 LST to 03:00 LDT on the second Sunday in March and returns at 02:00 LDT to 01:00 LST on the first Sunday in November.
History
The Standard Time ActStandard Time Act
The Standard Time Act, , also known as the Calder Act, was the first United States federal law implementing standard time and Daylight saving time in the United States. It authorized the Interstate Commerce Commission to define each time zone....
of 1918 authorized the Interstate Commerce Commission
Interstate Commerce Commission
The Interstate Commerce Commission was a regulatory body in the United States created by the Interstate Commerce Act of 1887. The agency's original purpose was to regulate railroads to ensure fair rates, to eliminate rate discrimination, and to regulate other aspects of common carriers, including...
to define each time zone. The United States Standard Alaska Time was designated as UTC−10. Some references prior to 1967 refer to this zone as Central Alaska Standard Time (CAT) or as Alaska Standard Time (AST). In 1966, the Uniform Time Act
Uniform Time Act
The Uniform Time Act of 1966, , was a United States federal law 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 is...
renamed this (UTC−10) zone to Alaska-Hawaii Standard Time (AHST), effective April 1, 1967. This zone was renamed in 1983 to Hawaii-Aleutian Standard Time (HAST) when most of Alaska was moved out of the zone.
The Alaska Time Zone (UTC−9) is what was previously known as the Yukon Standard Time Zone
Yukon Standard Time Zone
The Yukon Standard Time Zone was a geographic region that kept standard time by subtracting nine hours from Coordinated Universal Time resulting in UTC−9 after 1971, or from Greenwich Mean Time before 1972....
(YST). However, the Yukon Territory
Yukon
Yukon is the westernmost and smallest of Canada's three federal territories. It was named after the Yukon River. The word Yukon means "Great River" in Gwich’in....
switched to the Pacific Standard Time Zone in 1975 and the time zone was not used (except for Yakutat
Yakutat City and Borough, Alaska
Yakutat City and Borough is a unified city-borough in the U.S. state of Alaska. As of the 2010 census, the population was 4035. The name is Tlingit, Yaakwdáat, meaning "the place where canoes rest", but it originally derives from an Eyak name diyaʼqudaʼt and was influenced by the Tlingit word...
) until 1983 when the state of Alaska decided to move most of the state to UTC−9. Prior to that the Alaska Panhandle
Alaska Panhandle
Southeast Alaska, sometimes referred to as the Alaska Panhandle, is the southeastern portion of the U.S. state of Alaska, which lies west of the northern half of the Canadian province of British Columbia. The majority of Southeast Alaska's area is part of the Tongass National Forest, the United...
communities were in the Pacific Time Zone
Pacific Time Zone
The Pacific Time Zone observes standard time by subtracting eight hours from Coordinated Universal Time . The clock time in this zone is based on the mean solar time of the 120th meridian west of the Greenwich Observatory. During daylight saving time, its time offset is UTC-7.In the United States...
, while most of the interior was on UTC−10. Nome
Nome, Alaska
Nome is a city in the Nome Census Area in the Unorganized Borough of the U.S. state of Alaska, located on the southern Seward Peninsula coast on Norton Sound of the Bering Sea. According to the 2010 Census, the city population was 3,598. Nome was incorporated on April 9, 1901, and was once the...
and the Aleutians previously observed Bering Standard Time or UTC−11.
Anomalies
The Alaska Time Zone is applied to the territory of the state of AlaskaAlaska
Alaska is the largest state in the United States by area. It is situated in the northwest extremity of the North American continent, with Canada to the east, the Arctic Ocean to the north, and the Pacific Ocean to the west and south, with Russia further west across the Bering Strait...
to the east of 169°30′ W. Given that the UTC−9 time corresponds to the solar time at 9 × 15° = 135° W (roughly, Juneau), the westernmost locales where Alaska time gets applied are off by 169°30′ − 135° = 34°30′ from their solar time. This means that when a clock correctly set to Alaskan time, at a location just east of 169°30′ W, shows noon, the solar time is actually around 9:42 a.m. When UTC−8 is applied in the summer, this effect becomes even more apparent, since the solar time at Fresno, California
Fresno, California
Fresno is a city in central California, United States, the county seat of Fresno County. As of the 2010 census, the city's population was 510,365, making it the fifth largest city in California, the largest inland city in California, and the 34th largest in the nation...
(about 120° W
120th meridian west
The meridian 120° west of Greenwich is a line of longitude that extends from the North Pole across the Arctic Ocean, North America, the Pacific Ocean, the Southern Ocean, and Antarctica to the South Pole....
) is used. For example, on June 12, the solar time
Solar time
Solar time is a reckoning of the passage of time based on the Sun's position in the sky. The fundamental unit of solar time is the day. Two types of solar time are apparent solar time and mean solar time .-Introduction:...
at the extreme westerly points of the Alaskan time zone will actually be only 8:42 a.m. Very few people however, notice this as these locations are virtually uninhabited, and for the very few people who do live there, the long days in the summer and short days in the winter make the sunrise and sunset times less important than areas closer to the equator. By contrast, in Juneau, which is much closer to the 135° west meridian, mean solar noon occurs around 11:57 a.m., very close to clock noon.
In Anchorage, visitors from more southerly latitudes are often surprised to see the sun set at 11:41 p.m. on the summer solstice
Solstice
A solstice is an astronomical event that happens twice each year when the Sun's apparent position in the sky, as viewed from Earth, reaches its northernmost or southernmost extremes...
, but the actual 'solar time' is 9:41 p.m. This is because at 150° W
150th meridian west
The meridian 150° west of Greenwich is a line of longitude that extends from the North Pole across the Arctic Ocean, North America, the Pacific Ocean, the Southern Ocean, and Antarctica to the South Pole....
, Anchorage is a full solar hour behind the legal time zone and observes daylight saving time as well. Some local residents refer to this phenomenon as "double daylight time". In Fairbanks, the same circumstances cause sunset to occur at 12:47 a.m. on the next calendar day. In the winter, even without daylight saving time, another anomaly is that on the winter solstice in Nome
Nome, Alaska
Nome is a city in the Nome Census Area in the Unorganized Borough of the U.S. state of Alaska, located on the southern Seward Peninsula coast on Norton Sound of the Bering Sea. According to the 2010 Census, the city population was 3,598. Nome was incorporated on April 9, 1901, and was once the...
, the sunrise is actually after "noon" clock time, at 12:02 p.m., about 4 hours before sunset at 3:56 p.m.