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), Alaskan Standard Time (AKST), Hawaii-Aleutian Standard Time (HST), Samoa standard time (UTC-11) and Chamorro Standard Time (UTC+10). The United States uses nine standard time zones. A new federal law took effect in March 2007 which extends Daylight Saving Time by four weeks. Eastern Standard Time (EST) becomes Eastern Daylight Time (EDT), and so forth. The names in each time zone change along with Daylight Saving Time. On the first Sunday in November areas on Daylight Saving Time return to Standard Time at 2:00 a.m. local time on the second Sunday in March. In the United States Daylight Saving Time begins at 2:00 a.m. Virgin Islands and American Samoa do not observe Daylight Saving Time. In places not observing Daylight Saving Time the local UTC or GMT offset will remain the same year round. As a result, their UTC or GMT offset would change from UTC -5h or GMT - 5h to UTC -4h or GMT - 4h. In areas of the United States that observe Daylight Saving Time local residents will move their clocks ahead one hour when Daylight Saving Time begins. Coordinated Universal Time is also known Zulu Time or Z time. The usage of UTC and GMT is based upon a twenty four hour clock, similar to military time, and is based upon the 0 degrees longitude meridian, referred to as the Greenwich meridian in Greenwich, England.Ĭoordinated Universal Time is based on cesium-beam atomic clocks, with leap seconds added to match earth-motion time, where as Greenwich Mean Time is based upon the Earth's rotation and celestial measurements. UTC+5h or GMT +5h would refer to that time zone being five hours ahead of UTC of GMT and so forth for the other time zones. In this example the (-5h) refers to that time zone being five hours behind UTC or GMT and so forth for the other time zones. You will often see time zones represented similar to UTC - 5h or GMT - 5h. Coordinated Universal Time replaced the use of Greenwich Mean Time (GMT) in 1972. Today, Greenwich Mean Time (GMT) is only the name of a time zone that is used by a few countries in Africa and Western Europe, including the UK during winter and all year in Iceland.Coordinated Universal Time (UTC) is used as the official world reference for time. Since then, GMT is no longer a time standard. Until 1972, Greenwich Mean Time (also known as Zulu time) was the same as Universal Time (UT). UTC was adjusted several times until 1972, when leap seconds were introduced to keep UTC in line with the Earth's rotation, which is not entirely even, and less exact than atomic clocks. The name Coordinated Universal Time was officially adopted in 1967. In 1960, the International Radio Consultative Committee formalized the concept of UTC, and it was put into practice the year after. The transit circle is a part of the telescope's mechanics and it is still cited as the prime meridian's original reference (0° longitude). The reference line or starting point, the Prime Meridian, was determined to be the transit circle at the Royal Observatory in Greenwich, London. This is the basis for the 24-hour time zone system we know today.Īt the time, Greenwich Mean Time (GMT) was chosen as the world’s time standard. Universal Time (UT) was created at the International Meridian Conference in 1884. It is used to compare the pace provided by TAI with the actual length of a day on Earth. Universal Time (UT1): Also known as astronomical time or solar time, it refers to the Earth's rotation.International Atomic Time (TAI): A time scale that combines the output of some 400 highly precise atomic clocks worldwide, and provides the exact speed for our clocks to tick.Two components are used to determine UTC: The world's timing centers have agreed to keep their time scales closely synchronized - or coordinated - therefore the name Coordinated Universal Time. UTC is the time standard commonly used across the world. ©/stocknshares A Standard, Not a Time Zone The Greenwich Meridian in London, England. Business Date to Date (exclude holidays).
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