Greenwich mean time zone

But what is GMT and why is it so important? Solar time varies throughout the year, as the time interval between the Sun crossing a set meridian line changes.

Toggle navigation GMT standard time. World Tinezone Map. GMT is a time zone officially used in some European and African countries. UTC is not a time zone , but a time standard that is the basis for civil time and time zones worldwide. This means that no country or territory officially uses UTC as a local time. Summer Time Is Daylight Saving Time Daylight saving time DST , also known as daylight savings time or daylight time United States and Canada , Summer Time , United Kingdom, European Union, and some others , Daylight saving time and summer time is the practice of advancing clocks typically by one hour during warmer months so that darkness falls at a later clock time. The typical implementation of DST is to set clocks forward by one hour in the spring " spring forward " and set clocks back by one hour in autumn " fall back " to return to standard time.

Greenwich mean time zone

At different times in the past, it has been calculated in different ways, including being calculated from noon ; [1] as a consequence, it cannot be used to specify a particular time unless a context is given. Because of Earth's uneven angular velocity in its elliptical orbit and its axial tilt , noon GMT is rarely the exact moment the Sun crosses the Greenwich Meridian [b] and reaches its highest point in the sky there. This event may occur up to 16 minutes before or after noon GMT, a discrepancy described by the equation of time. Noon GMT is the annual average the arithmetic 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, [d] while for almost everyone else it started at midnight. To avoid confusion, the name Universal Time was introduced in to denote GMT as counted from midnight. The term GMT should thus not be used for purposes that require precision. As the United Kingdom developed into an advanced maritime nation , British mariners kept at least one chronometer on GMT to calculate their longitude from the Greenwich meridian, which was considered to have longitude zero degrees, by a convention adopted in the International Meridian Conference of Synchronisation of the chronometer on GMT did not affect shipboard time, which was still solar time. But this practice, combined with mariners from other nations drawing from Nevil Maskelyne 's method of lunar distances based on observations at Greenwich, led to GMT being used worldwide as a standard time independent of location. Greenwich Mean Time was adopted across the island of Great Britain by the Railway Clearing House in and by almost all railway companies by the following year, from which the term railway time is derived. It was gradually adopted for other purposes, but a legal case in held " local mean time " to be the official time. For example, our polling booths were opened, say, at 8 13 and closed at 4 13 p. Universal Time UT , a term introduced in , initially represented mean time at Greenwich determined in the traditional way to accord with the originally defined universal day ; from 1 January as decided by the International Astronomical Union in Dublin in , at the initiative of William Markowitz this "raw" form of UT was re-labelled UT0 and effectively superseded by refined forms UT1 UT0 equalised for the effects of polar wandering [16] and UT2 UT1 further equalised for annual seasonal variations in Earth rotation rate. Indeed, even the Greenwich meridian itself is not quite what it used to be—defined by "the centre of the transit instrument at the Observatory at Greenwich".

Kenneth Seidelmann eds. Archived from the original on December 2, Saint Pierre and Miquelon.

A time zone is an area which observes a uniform standard time for legal , commercial and social purposes. Time zones tend to follow the boundaries between countries and their subdivisions instead of strictly following longitude , because it is convenient for areas in frequent communication to keep the same time. Time zones are defined as one or two offsets from Coordinated Universal Time UTC , and if two offsets are used the days when the offset changes. Some time zones switch between offsets throughout the year due to daylight saving time DST. Areas of extreme latitude are more likely to use DST. DST is usually used for about half of the year, typically by adding one hour to local time during spring and summer.

At different times in the past, it has been calculated in different ways, including being calculated from noon ; [1] as a consequence, it cannot be used to specify a particular time unless a context is given. Because of Earth's uneven angular velocity in its elliptical orbit and its axial tilt , noon GMT is rarely the exact moment the Sun crosses the Greenwich Meridian [b] and reaches its highest point in the sky there. This event may occur up to 16 minutes before or after noon GMT, a discrepancy described by the equation of time. Noon GMT is the annual average the arithmetic 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, [d] while for almost everyone else it started at midnight. To avoid confusion, the name Universal Time was introduced in to denote GMT as counted from midnight. The term GMT should thus not be used for purposes that require precision. As the United Kingdom developed into an advanced maritime nation , British mariners kept at least one chronometer on GMT to calculate their longitude from the Greenwich meridian, which was considered to have longitude zero degrees, by a convention adopted in the International Meridian Conference of Synchronisation of the chronometer on GMT did not affect shipboard time, which was still solar time. But this practice, combined with mariners from other nations drawing from Nevil Maskelyne 's method of lunar distances based on observations at Greenwich, led to GMT being used worldwide as a standard time independent of location.

Greenwich mean time zone

It is the main time zone in several countries , including the United Kingdom , the Republic of Ireland and Portugal. GMT was established in at the International Meridian Conference, [2] which met to establish a standardized system for measuring world longitude. This conference also decided that the time zone around the meridian, GMT, would be the time zone used for reference around the world. Other countries would define their time based on GMT. UTC was defined in as the new world reference for time. Other advantages of UTC are that calling the new standard Coordinated Universal Time avoids giving more importance to any one country, and that UTC does not adjust for Daylight Saving Time, which means the world always has a standard time. Contents move to sidebar hide. Page Talk. Read Change Change source View history.

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For example, the border between its Eastern and Central time zones ran through Detroit , Buffalo , Pittsburgh , Atlanta , and Charleston. June Area that observes a uniform standard time. National Aeronautics and Space Administration. It was the first clock ever to show Greenwich Mean Time directly to the public. Retrieved January 5, Oxford: Oxford University Press, By , the majority of countries had adopted hourly time zones, though some countries such as Iran , India , Myanmar and parts of Australia had time zones with a minute offset. Main article: List of time zone abbreviations. Modern DST was first proposed in and was in widespread use in as a wartime measure aimed at conserving coal. Archived PDF from the original on 4 February

At different times in the past, it has been calculated in different ways, including being calculated from noon ; [1] as a consequence, it cannot be used to specify a particular time unless a context is given.

The meridian line is marked by the cross-hairs in the Airy Transit Circle eyepiece. Visit Us. For example, if a New Yorker plans to meet someone in Los Angeles at 9 am, and makes a calendar entry at 9 am which the computer assumes is New York time , the calendar entry will be at 6 am if taking the computer's time zone. Archived from the original on October 5, The offset from UTC changes with daylight saving time , e. UCO Lick. The Times Digital Archive. New South Wales Government. Chronological dating Geologic time scale International Commission on Stratigraphy. Royal Observatory. The apparent position of the Sun in the sky, and thus solar time , varies by location due to the spherical shape of the Earth. This numeric representation of time zones is appended to local times in the same way that alphabetic time zone abbreviations or "Z", as above are appended. Retrieved August 22, For example, the border between its Eastern and Central time zones ran through Detroit , Buffalo , Pittsburgh , Atlanta , and Charleston. Government of Ireland.