The Eastern Time Zone extends through the United States and Canada, and Eastern Daylight Time (EDT) and Eastern Standard Time (EDT) vary because of the effects of daylight-saving time. As of 2007, daylight-saving time starts on the second Sunday of March and ends on the first Sunday of November.
A time zone is a region where the time of the day is the same. Time-zone regions are based on longitude-line boundaries, but were modified to fit the geopolitical canvas of the region. For example, time zone lines can be modified, so a country has only one time zone instead of two or made to follow political subdivision lines in the case of federal countries.
EDT is Greenwich time minus four hours while EST is Greenwich time minus five hours. EDT is used during the summer, and EST is used during the winter. Daylight-saving time was instituted to allow greater daylight time for human activity during the winter.
The eastern boundary of the Eastern time zone in regard to the United States is in the Atlantic Ocean and the western boundary extends from Michigan to Florida, crossing portions of Michigan, Indiana, Kentucky, Tennessee and Florida and including the state line of Georgia. All of the Eastern time zones have adopted daylight savings time.
The Eastern time zone in Canada includes the Nunavut territory and Ontario and Quebec provinces. In the Nunavut territory, the Eastern time zone starts in the Atlantic ocean and encompasses the whole territory with the exception of Kugluktuk and Cambridge Bay that both use Central Time and Southampton Island that uses EST all year long. The Eastern time zones also includes Ontario from the Atlantic Ocean to Highway 90 West and Quebec from the Atlantic Ocean to Highway 63.