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, greenwich mean time zone. But each day measured by a clock has the same length, equal to the average mean length of a solar day.

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.

Greenwich mean time zone

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. When DST is in effect, approximately during spring and summer, their UTC offset is increased by one hour except for Lord Howe Island , where it is increased by 30 minutes. 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 variation corresponds to four minutes of time for every degree of longitude , so for example when it is solar noon in London , it is about 10 minutes before solar noon in Bristol , which is about 2. The Royal Observatory, Greenwich , founded in , established Greenwich Mean Time GMT , the mean solar time at that location, as an aid to mariners to determine longitude at sea, providing a standard reference time while each location in England kept a different time. In the 19th century, as transportation and telecommunications improved, it became increasingly inconvenient for each location to observe its own solar time.

Calendar systems nowadays usually tie their time stamps to UTC, and show them differently on computers that are in different time zones. Archived PDF from the original on September 4, Archived from the original on 5 July

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.

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.

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.

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Category Commons. Australia - Daylight saving starts each year at am on the first Sunday in October, and ends at am on the first Sunday in April. Until the midth century, almost every town kept its own local time, defined by the Sun. A Lead to the World". United States : Alaska most. Keep track of time with our famous Shepherd Gate clock replica for your wall. For other uses, see GMT disambiguation. Archived from the original on 14 June Australia : Eucla. Historical Dictionary of British Radio.

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.

Canadian statute "Interpretation Act ". Contents move to sidebar hide. March 23, FreeBSD British mariners started keeping at least one chronometer set to GMT. By , time signals were also sent from the clock to Harvard University in Cambridge, Massachusetts via the new transatlantic submarine cable. Retrieved 7 June Area that observes a uniform standard time. In terms of the distribution of accurate time into everyday life, it is one of the most important clocks ever made. Bibcode : Metro.. The apparent position of the Sun in the sky, and thus solar time , varies by location due to the spherical shape of the Earth.