- published: 14 Jul 2012
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The Eastern Time Zone contains 17 states in the eastern part of the Continental United States and is shared by parts of Canada and three countries in South America. These places use Eastern Standard Time (EST) when observing standard time (autumn/winter) - which is 5 hours behind Coordinated Universal Time (UTC−05) - and Eastern Daylight Time (EDT) when observing daylight saving time (spring/summer) - which is 4 hours behind (UTC−04). On the second Sunday in March, at 2:00 am EST, clocks are advanced to 3:00 am EDT leaving a one hour gap. On the first Sunday in November, at 2:00 am EDT, clocks are moved back to 1:00 am EST.
The 1966 Uniform Time Act in the United States meant that EDT was instituted on the last Sunday in April, starting in 1966. EST would be re-instituted on the last Sunday in October. The act was amended to make the first Sunday in April the beginning of EDT as of 1987. The Energy Policy Act of 2005 extended daylight saving time in the United States beginning in 2007, so that the local time changes at 2:00 am EST to 3:00 am EDT on the second Sunday in March and returns at 2:00 am EDT to 1:00 am EST on the first Sunday in November. In Canada, the time changes as it does in the United States.
Standard time is the result of synchronizing clocks in different geographical locations within a time zone to the same time rather than using the local meridian as in local mean time or solar time. Historically, this helped in the process of weather forecasting and train travel. The concept became established in the late 19th century. The time so set has come to be defined in terms of offsets from Universal Time. Where daylight saving time is used, the term standard time typically refers to the time without daylight saving time.
The adoption of Standard Time, because of the inseparable correspondence between time and longitude, solidified the concepts of halving the globe into an eastern and western hemisphere, with one Prime Meridian (as well its opposite International Dateline) replacing the various Prime Meridians that were in use.
A standardized time system was first used by British railways on December 11, 1847, when they switched from local mean time to Greenwich Mean Time (GMT). It was also given the name Railway time reflecting the important role the railway companies played in bringing it about. The vast majority of Great Britain's public clocks were being synchronised using GMT by 1855.