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.

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.

Greenwich mean time zone

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. As a result, there is one hour day in late winter or early spring and one hour day in the autumn. Daylight saving time DST in the world United States and Canada - daylight saving time starts on the second Sunday in March and ends on the first Sunday in November, with the time changes taking place at am local time. With a mnemonic word play referring to seasons, clocks "spring forward, fall back" - that is, in springtime the clocks are moved forward from a. The Uniform Time Act of established the system of uniform daylight saving time throughout the US. Russia - Observed DST in —, some areas , and —

In the 19th century, as transportation and telecommunications improved, it became increasingly inconvenient for each location to observe its own solar time. Reprinted in Time-reckoning for the twentieth century at the Internet Archive.

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.

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. Tools Tools.

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

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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. This contrasted with the civil convention of referring to midnight as zero hours dating from the Roman Empire. The Interpretation Act , section 9, provides that whenever an expression of time occurs in any Act, the time referred to shall unless otherwise specifically stated be held to be Greenwich mean time. Archived from the original on October 28, Retrieved February 13, Archived from the original on 5 July Tools Tools. Retrieved February 12, Cocos Keeling Islands Myanmar. For the global time standard, see Universal Time. Kenneth Archived from the original on December 2,

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.

The meridian line is marked by the cross-hairs in the Airy Transit Circle eyepiece. As the reference for GMT, the Prime Meridian at Greenwich therefore became the centre of world time and the basis for the global system of time zones. For more time zone lists, see Lists of time zones. It officially became 'Railway Time'. Times, London, England, 14 May By , time signals were also sent from the clock to Harvard University in Cambridge, Massachusetts via the new transatlantic submarine cable. However, in practice each ship may choose what time to observe at each location. Clipperton Island Pitcairn Islands. Some junctions served by several railroads had a clock for each railroad, each showing a different time. Since the s, a nautical standard time system has been in operation for ships on the high seas. 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 The offset from UTC changes with daylight saving time , e.