The Atlantic Standard Time Zone (AST) is a geographical region that keeps time by subtracting four hours from either Coordinated Universal Time (UTC) or Greenwich Mean Time (GMT), resulting in UTC-4 or GMT-4. The clock time in this zone is based on the mean solar time of the 60th meridian west of the Greenwich Observatory.
In Canada, the provinces of New Brunswick[1] and Nova Scotia[2] reckon time specifically as an offset of 4 hours from Greenwich Mean time (GMT-4). (UTC is regularly adjusted by means of leap seconds to keep it synchronized to within 1 second of GMT.) Prince Edward Island and small portions of Quebec (eastern Côte-Nord and the Magdalen Islands) are also part of the Atlantic Standard Time Zone. Officially, the entirety of Newfoundland and Labrador observes Newfoundland Standard Time,[3] but in practice most of Labrador uses the Atlantic Standard Time Zone.
For other parts of the world that keep time by subtracting four hours from UTC see UTC−04.
Those portions of the Atlantic Standard Time Zone that participate in daylight saving time do so as Atlantic Daylight Time (ADT), which has one hour added to make it only three hours behind GMT (UTC-3).
| 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 | |||||||||||
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