Atlantic Standard Time Zone
The Atlantic Standard Time Zone (AST) is a geographic region that keeps time by subtracting four hours from Greenwich Mean Time (GMT), resulting in GMT-4 (UTC-4). The clock time in this zone is based on the mean solar time of the 60th degree meridian west of the Greenwich Observatory.
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 U.S. 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.