Atlantic Standard Time (AST) is a time zone that is 4 hours behind Coordinated Universal Time (UTC-4). It is primarily observed in parts of the Caribbean and Canada, including provinces like Nova Scotia and New Brunswick. AST is used during the standard time period, which typically runs from the first Sunday in November to the second Sunday in March. During the rest of the year, many regions that observe AST switch to Atlantic Daylight Time (ADT), which is UTC-3. This change helps to make better use of daylight during the longer days of summer.