Atlantic Standard Time Zone

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AST is UTC-4

The Atlantic Standard Time Zone (AST) is a geographic 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 degree 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 with 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 practise Labrador uses the Atlantic Standard Time Zone.

Other parts of the world that keep time by subtracting four hours from UTC include Bermuda, in the North Atlantic; many Caribbean islands, including Puerto Rico, the US Virgin Islands; and several South American countries, such as Paraguay, Chile, Bolivia, and parts of Brazil. Venezuela used AST until December 9, 2007, when it switched to UTC-4:30.

AST is known (where applicable) as Atlantic Daylight Time (ADT) during daylight saving time, and has one hour added to make it three hours behind GMT (UTC-3).

[edit] Major metropolitan areas

v • d • e Time zones in North America
Time Zone	UTC-10	UTC-9	UTC-8	UTC-7	UTC-6	UTC-5	UTC-4	UTC-3:30	UTC-3	UTC-2:30	UTC-2
Name	Hawaii-Aleutian Standard	Alaska Standard	Pacific Standard	Mountain Standard	Central Standard	Eastern Standard	Atlantic Standard	Newfoundland Standard	Saint Pierre and Miquelon Standard	Newfoundland Daylight	Saint Pierre and Miquelon Daylight
Name	Hawaii-Aleutian Standard	Hawaii-Aleutian Daylight	Alaska Daylight	Pacific Daylight	Mountain Daylight	Central Daylight	Eastern Daylight	Newfoundland Standard	Atlantic Daylight	Newfoundland Daylight	Saint Pierre and Miquelon Daylight

[edit] Sources

v • d • e Time offsets from Coordinated Universal Time (UTC)

−12 • −11 • −10 • −9:30 • −9 • −8 • −7 • −6 • −5 • −4:30 • −4 • −3:30 • −3 • −2:30 • −2 • −1 • −0:44 • −0:25 • UTC (0) • +0:20 • +0:30 • +1 • +2 • +3 • +3:30 • +4 • +4:30 • +4:51 • +5 • +5:30 • +5:40 • +5:45 • +6 • +6:30 • +7 • +7:20 • +7:30 • +8 • +8:30 • +8:45 • +9 • +9:30 • +10 • +10:30 • +11 • +11:30 • +12 • +12:45 • +13 • +13:45 • +14

Daylight saving time (DST): * in Northern Hemisphere ** in Southern Hemisphere