Time Zone Essay

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Running head: World Time Scale Time Zone Theresa Hinton University of Phoenix January 21, 2012 Introduction Many cities around the world historically kept their own time by using some type of instrument to monitor the sun’s high point at noon. The earliest time measuring devices used either the sun’s shadow or the rate in which water runs out of a vessel. The pendulum clock was developed during the 17th century – these clocks were sufficiently accurate to be used at sea to determine longitude and for scientific time measurement in the 18th century. (timeanddate,2010) Explanation of Time Zone A standard time zone generally refers to any of the 24 regions of the earth’s surface, divided by longitude, in which standard time is kept. However, the number of standard time zones is questionable and discussed among various sources, particularly with regard to the International Date Line. (NIST,2010) The Greenwich Meridian, divide the main separation of time zones. Each time zone is 15 degrees of longitude in width, with local differences, and views a clock time one hour earlier than the zone immediately to the east. (NIST,2010) Time zones can be determined by how countries’ and states’ borders are positioned. Individual zone boundaries are not straight because they are adjusted for the convenience and wishes of local populations. Furthermore, some geographically large countries, such as India and China, use only one time zone but other large countries, such as Russia and the United States, have more than one time zone. The United States uses nine standard time zones. From east to west they are Atlantic Standard Time (AST), Eastern Standard Time (EST), Central Standard Time (CST), Mountain Standard Time (MST), Pacific Standard Time (PST),

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