The local time at Greenwich is considered yo be the international standards time give geographic reason
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Greenwich Mean Time (GMT) is the meansolar time at the Royal Observatory inGreenwich, London. GMT was formerly used as the international civil time standard, now superseded in that function by Coordinated Universal Time (UTC). Today GMT is considered equivalent to UTC for UK civil purposes (but this is not formalised) and for navigation is considered equivalent to UT1(the modern form of mean solar time at 0° longitude); these two meanings can differ by up to 0.9 s. Consequently, the term GMT should not be used for precise purposes.[1]
Because of Earth's uneven speed in its elliptical orbit and its axial tilt, noon (12:00:00) GMT is rarely the exact moment the suncrosses the Greenwich meridian and reaches its highest point in the sky there. This event may occur up to 16 minutes before or after noon GMT, a discrepancy calculated by theequation of time. Noon GMT is the annual average (i.e. "mean") moment of this event, which accounts for the word "mean" in "Greenwich Mean Time".
Originally, astronomers considered a GMT day to start at noon while for almost everyone else it started at midnight. To avoid confusion, the name Universal Time was introduced to denote GMT as counted from midnight.[2] Astronomers preferred the old convention to simplify their observational data, so that each night was logged under a single calendar date. Today Universal Time usually refers to UTC or UT1.[3]
The term "GMT" is especially used by bodies connected with the United Kingdom, such as the BBC World Service, the Royal Navy, theMet Office and others particularly in Arab countries, such as the Middle East Broadcasting Centre and OSN. It is a term commonly used in the United Kingdom and countries of the Commonwealth, including Australia, New Zealand, South Africa, India, Pakistan, Bangladesh and Malaysia; and in many other countries of the eastern hemisphere. In some countries (the United Kingdom for example) Greenwich Mean Time is the legal time in the winter and the population uses the term. See GMT in legislation, below, for further explanation.
Because of Earth's uneven speed in its elliptical orbit and its axial tilt, noon (12:00:00) GMT is rarely the exact moment the suncrosses the Greenwich meridian and reaches its highest point in the sky there. This event may occur up to 16 minutes before or after noon GMT, a discrepancy calculated by theequation of time. Noon GMT is the annual average (i.e. "mean") moment of this event, which accounts for the word "mean" in "Greenwich Mean Time".
Originally, astronomers considered a GMT day to start at noon while for almost everyone else it started at midnight. To avoid confusion, the name Universal Time was introduced to denote GMT as counted from midnight.[2] Astronomers preferred the old convention to simplify their observational data, so that each night was logged under a single calendar date. Today Universal Time usually refers to UTC or UT1.[3]
The term "GMT" is especially used by bodies connected with the United Kingdom, such as the BBC World Service, the Royal Navy, theMet Office and others particularly in Arab countries, such as the Middle East Broadcasting Centre and OSN. It is a term commonly used in the United Kingdom and countries of the Commonwealth, including Australia, New Zealand, South Africa, India, Pakistan, Bangladesh and Malaysia; and in many other countries of the eastern hemisphere. In some countries (the United Kingdom for example) Greenwich Mean Time is the legal time in the winter and the population uses the term. See GMT in legislation, below, for further explanation.
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(1) The International standard time has been decided according to 0° longitude.
(2) 0° longitude passes through Greenwich, England.
(3) For an international co-ordination, it is essential to bring compatibility between the standard time of various countries in the world. For this purpose, the local time at Greenwich is considered to be the International standard time.
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