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As the BBC World Service is broadcast to all time zones, the announcers use the term «Greenwich Mean Time» consistently throughout the year. Historically, GMT has been used with two different conventions for numbering hours. The long-standing astronomical convention, dating from the work of Ptolemy, was to refer to noon as zero hours (see Julian day). This contrasted with the civil convention of referring to midnight as zero hours dating from the Roman Empire.

Its time was sent by telegraph wires to London, Edinburgh, Glasgow, Dublin, Belfast and many other cities. By 1866, time signals were also sent from the clock to Harvard University in Cambridge, Massachusetts via the new transatlantic submarine cable. This meant there was no standard timings for when the day would begin and end, or what length an hour might be.

GMT and the quest for longitude

The latter convention was adopted on and after 1 January 1925 for astronomical purposes, resulting in a discontinuity of 12 hours, or half a day. The instant that was designated as «December 31.5 GMT» in 1924 almanacs became «January 1.0 GMT» in 1925 almanacs. Here he had the best pendulum clocks installed and set them to the local time.

The Shepherd gate clock can be seen at the gates to the Royal Observatory. It was the first clock ever to show Greenwich Mean Time directly to the public. It is a ‘slave’ clock, connected to the Shepherd master clock which was installed at the Royal Observatory in 1852. During the experiment of 1968 to 1971, when the British Isles did not revert to Greenwich Mean Time during the winter, the all-year British Summer Time was called British Standard Time (BST).

1. In terms of the distribution of accurate time into everyday life, it is one of the most important clocks ever made.
2. It continues to show Greenwich Mean Time and is not adjusted for British Summer Time.
3. The long-standing astronomical convention, dating from the work of Ptolemy, was to refer to noon as zero hours (see Julian day).
4. Universal Time remains in general use in a modified form as Coordinated Universal Time (UTC), which serves to accommodate the timekeeping differences that arise between atomic time (derived from atomic clocks) and solar time.
5. During Daylight Saving Time the correct time zone is British Summer Time (BST).

The meridian at this longitude is called the prime meridian or Greenwich meridian. Greenwich Mean Time (GMT) has been used to clearly designate epoch by avoiding confusing references to local time systems (zones). Greenwich Mean Time (GMT) is often interchanged or confused with Coordinated Universal Time (UTC).

The clock was changed in the 20th century to indicate Greenwich Mean Time, in which the counting of the 24 hours of each day starts at midnight. It continues to show Greenwich Mean Time and is not adjusted for British Summer Time. Indeed, even the Greenwich meridian itself is not https://www.topforexnews.org/ quite what it used to be—defined by «the centre of the transit instrument at the Observatory at Greenwich». Nevertheless, the line in the old observatory’s courtyard today differs no more than a few metres from that imaginary line which is now the prime meridian of the world.

Discover gifts from the home of time

BBC radio stations broadcast the «six pips» of the Greenwich Time Signal. It is named from its original generation at the Royal Greenwich Observatory. If announced (such as near the start of summer time or of winter time), announcers on domestic channels declare the time as GMT or BST as appropriate.

The overseas territories and crown dependencies of the UK bring the total to 9 time zones. This meant they could calculate their longitude from the Greenwich meridian (longitude 0° by convention). However, some of the countries that use GMT switch to different time zones during their DST period. 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. However, the 1850s and 1860s saw the expansion of the railway and communications networks. These were tables of ‘lunar distance’ data based on observations at Greenwich and using GMT as the time standard.

How did Greenwich Mean Time begin?

This was Greenwich Mean Time, or the average time when the Sun crossed the meridian at Greenwich. At first though, Greenwich time was only really important to astronomers. Greenwich Mean Time is defined in law as standard time in the following countries and areas, which also advance their clocks one hour (GMT+1) in summer. By the mid-1850s, almost all public clocks in Britain were set to Greenwich Mean Time and it finally became Britain’s legal standard time in 1880. Greenwich Mean Time (GMT), the name for mean solar time of the longitude (0°) of the Royal Greenwich Observatory in England.

GMT was also crucial to the other great solution to the ‘longitude problem’, represented by John Harrison’s famous timekeepers. In 1767 Maskelyne introduced the Nautical Almanac as part of the great 18th century quest to determine longitude. Greenwich Mean Time is the yearly average (or ‘mean’) of the time each day when the Sun crosses the Prime Meridian at the Royal Observatory Greenwich. For example, the United Kingdom is not on GMT all year, it uses British Summer Time (BST), which is one hour ahead of GMT, during the summer months.

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. Most time zones were based upon GMT, as an offset of a number of hours (and possibly half or quarter hours) «ahead of GMT» or «behind GMT». Historically, astronomers used Greenwich Mean Astronomical Time (GMAT), in which the astronomical day began at noon at longitude (0°), in accord with scientific tradition.

Elsewhere on timeanddate.com

Until the mid-19th century, almost every town kept its own local time, defined by the Sun. There were no national or international conventions which set how time should https://www.forexbox.info/ be measured. The United Kingdom was one of the first countries to use a standard time for the whole country, instead of each place keeping its own local mean time.

In 1925 GMT was adopted by astronomers so that the astronomical day began at midnight, the same time as the civil day. Some confusion in terminology resulted, though, and in 1928 the International Astronomical Union changed the designation of the standard time of the Greenwich meridian to Universal Time. Universal https://www.currency-trading.org/ Time remains in general use in a modified form as Coordinated Universal Time (UTC), which serves to accommodate the timekeeping differences that arise between atomic time (derived from atomic clocks) and solar time. The term Greenwich Mean Time is still used to represent the civil time in Britain.