|Alaska Time Zone|
|01:26, 15 November 2019 AKST|
|Observance of DST|
|DST is observed throughout this time zone.|
The Alaska Time Zone observes standard time by subtracting nine hours from Coordinated Universal Time (UTC-09:00). During daylight saving time its time offset is eight hours (UTC-08:00). The clock time in this zone is based on mean solar time at the 135th meridian west of the Greenwich Observatory.
Effective from 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.
Two time zones have been referred to as the "Alaska Time Zone": a zone based on UTC-10:00 that covered much of Central Alaska in the early 20th century, and a zone based on UTC-09:00 zone that has covered all of the state except the Aleutian Islands since 1983.
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-10:00. 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 renamed the UTC-10:00 zone to Alaska-Hawaii Standard Time (AHST), effective April 1, 1967. This zone was renamed in 1983 to Hawaii-Aleutian Standard Time when the majority of Alaska was moved out of the zone.
Prior to 1983, the current Alaska Time Zone (UTC-09:00) was known as the Yukon Time Zone, observing Yukon Standard Time (YST). This time zone included Canada's Yukon Territory and a small portion of Alaska including Yakutat. The Alaska Panhandle communities were in the Pacific Time Zone, while most of the interior was on UTC-10:00.Nome and the Aleutians previously observed Bering Standard Time or UTC-11:00. In 1975, the Yukon Territory switched to Pacific Standard Time, leaving Yakutat the only land area in the zone.
With the reorganization of Alaska's time zones in 1983 to place the entire state in either a zone based on UTC-09:00 or UTC-10:00, the Yukon Time Zone based on UTC-09:00 was renamed the Alaska Time Zone.
The Alaska Time Zone applies to the territory of the state of Alaska east of 169°30? W. Given that the UTC-09:00 time corresponds to the solar time at 9 × 15° = 135° W (roughly, Juneau), the westernmost locales of the Alaska Time Zone are off by up to 169°30? - 135° = 34°30? from local solar time. This means that when a clock correctly set to Alaska time, at a location just east of 169°30? W, shows noon, local solar time is around 9:42 a.m. When UTC-08:00 is applied in the summer (because of daylight saving time), this effect becomes even more apparent. For example, on June 12 at noon AKDT, the solar time at the extreme westerly points of the Alaskan time zone will be only 8:42 a.m. Very few people notice this, however, 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 while the 'solar time' is 9:41 p.m. This is because at 150° W, Anchorage is one solar hour ahead of 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. the next calendar day and the solar sunset is at 10:47 p.m. Even without daylight saving time, another anomaly is that on the winter solstice in Nome, the sunrise is after "noon" clock time, at 12:02 p.m., about 4 hours before sunset at 3:56 p.m.
The territory of the state of Alaska spans almost as much longitude as the contiguous United States (57.5° vs. 57.6°) so the use of two time zones will inevitably lead to some distortions. Alaska would "naturally" fall into four time zones, but political and logistical considerations have led to the use of two, leading to the distortions mentioned above.