The Alaska Time Zone observes standard time by subtracting nine hours from Coordinated Universal Time (UTC−9). During daylight saving time its time offset is only eight hours (UTC−8). The clock time in this zone is based on the mean solar time of the 135th meridian west of the Greenwich Observatory.
The zone includes nearly all of the U.S. state of Alaska and is one hour behind the Pacific Time Zone.
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.
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The Standard Time Act of 1918 authorized the Interstate Commerce Commission to define each time zone. The United States Standard Alaska Time was designated as UTC−10.[1] Some references prior to 1967 refer to this zone as Central Alaska Standard Time (CAT) [2] or as Alaska Standard Time (AST).[3] In 1966, the Uniform Time Act renamed this (UTC−10) zone to Alaska-Hawaii Standard Time[4] (AHST[5]), effective April 1, 1967.[6] This zone was renamed in 1983 [4] 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 (YST). However, the Yukon Territory switched to the Pacific Standard Time Zone in 1975 and the time zone was not used (except for Yakutat) until 1983 when the state of Alaska decided to move most of the state to UTC−9. Prior to that the Alaska Panhandle communities were in the Pacific Time Zone, while most of the interior was on UTC−10. Nome and the Aleutians previously observed Bering Standard Time or UTC−11.
The Alaska Time Zone is applied to the territory of the state of Alaska 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 (about 120° W) is used. For example, on June 12, the solar time 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, but the actual 'solar time' is 9:41 p.m. This is because at 150° W, 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, the sunrise is actually after "noon" clock time, at 12:02 p.m., about 4 hours before sunset at 3:56 p.m.
| Hours from GMT | Standard time | Daylight saving | |||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
| –10 | Hawaii-Aleutian | ||||||||||
| –9 | Alaska | Hawaii-Aleutian | |||||||||
| –8 | Pacific | Alaska | |||||||||
| –7 | Mountain | Pacific | |||||||||
| –6 | Central | Mountain | |||||||||
| –5 | Eastern | Central | |||||||||
| –4 | Atlantic | Eastern | |||||||||
| –3:30 | Newfoundland | ||||||||||
| –3 | Saint Pierre and Miquelon | Atlantic | |||||||||
| –2:30 | Newfoundland | ||||||||||
| –2 | Saint Pierre and Miquelon | ||||||||||
| See also: Time in Canada • Time in Mexico • Time in the United States | |||||||||||