what do u mean GMT?

Answer 1

GMT means "Greenwich Mean Time" (GMT) is a term originally referring to mean solar time at the Royal Observatory, Greenwich in England. It is now often used to refer to Coordinated Universal Time (UTC) when this is viewed as a time zone, although strictly UTC is an atomic time scale which only approximates GMT in the old sense. It is also used to refer to Universal Time (UT), which is the astronomical concept that directly replaced the original GMT.

Noon Greenwich Mean Time is not necessarily the moment when the Sun crosses the Greenwich meridian (and reaches its highest point in the sky in Greenwich) because of Earth's uneven speed in its elliptic orbit and its axial tilt. This event may be up to 16 minutes away from noon GMT (this discrepancy is known as the equation of time). The fictitious mean sun is the annual average of this nonuniform motion of the true Sun, necessitating the inclusion of mean in Greenwich Mean Time.

Historically the term "GMT" has been used with two different conventions for numbering hours. The old astronomical convention (before 1925) was to refer to noon as zero hours, whereas the civil and more modern convention is to refer to midnight as zero hours. The more specific terms "UT" and "UTC" do not suffer this ambiguity, always referring to midnight as zero hours.

History

As the United Kingdom grew into an advanced maritime nation, British mariners kept their timepieces on GMT in order to calculate their longitude "from the Greenwich meridian", which was by convention considered to have longitude zero degrees. This did not affect shipboard time itself, which was still solar time. This combined with mariners from other nations drawing from Nevil Maskelyne's method of lunar distances based on observations at Greenwich, eventually led to GMT being used world-wide as a reference time independent of location. Most time zones were based upon this reference as a number of hours and half-hours "ahead of GMT" or "behind GMT".

Greenwich Mean Time was adopted across the island of Great Britain by the Railway Clearing House in 1847, and by almost all railway companies by the following year. It was gradually adopted for other purposes, but a legal case in 1858 held "local mean time" to be the official time. This changed in 1880, when GMT was legally adopted throughout Great Britain. GMT was adopted on the Isle of Man in 1883, Jersey in 1898 and Guernsey in 1913. Ireland adopted Greenwich Mean Time in 1916, supplanting Dublin Mean Time.[1]

Hourly time signals from Greenwich Observatory were first broadcast on 5 February 1924.

The daily rotation of the Earth is somewhat irregular (see ΔT) and is slowing down slightly. Atomic clocks constitute a much more stable timebase. On 1 January 1972, GMT was replaced as the international time reference by Coordinated Universal Time, maintained by an ensemble of atomic clocks around the world. UT1, introduced earlier, represents "earth rotation time". Leap seconds are added to or subtracted from UTC to keep it within 0.9 seconds of UT1.

The international prime meridian is no longer precisely the Greenwich meridian, but remains close to it (5.31"E).

Answer 2

GMT is Greenwich Mean Time

Greenwich, England has been the home of GMT since 1884. GMT is sometimes called Greenwich Meridian Time because it is measured from Greenwich Meridian Line at the Royal Observatory in Greenwich. It is the place where from all time zones are measured.

The Greenwich Meridian (Prime Meridian or Longitude Zero degrees) marks the starting point of every time zone in the World. GMT is Greenwich Mean (or Meridian) Time is the mean (average) time that the earth takes to rotate from noon-to-noon.

Answer 3

It is a world standard time, also known as Universal Coordinated Time, or Zulu Time. That way, airlines, military operations and train companies - as well as any other entity that operates across time zones, has one time to reference. Here in Hawaii, it is Z-10, so if it is 1130 GMT, it is 1:30 in the morning. As other posters said, it is the time in Greenwich, England ...except when they observe British Summer Time, in which case GMT is one hour behind the actual clock in Greenwich. The reason Greenwich was selected is because it is the British city through which the 0 Longitude Meridian runs.

Answer 4

Greenwich Mean Time - GMT is a mathematical mean, defined in terms of the solar second, measured at the former location of the Royal Observatory in England, located on the Prime Meridian (zero degrees longitude).

Answer 5

GMT - Greenwich Mean Time----its a Time zone abbreviation. Standard time is calculated base on that clock.

Answer 6

Its the Greenwhich Mean time. Its the international Date Line. Acutally when a person crosses this Longitude from east to west he enters the previous day and vice versa.

Answer 7

Greenwhich Mean Time. The universal time zone. Cuts through England

Answer 8

Greenwich Mean Time....its a point of reference for time...

Answer 9

GREENWHICH MEAN TIME if its in geography. or else in telescope field Giant Magellan Telescope

Answer 10

Good Morning Toots...
Just to be different !!!