Talk:Greenwich Mean Time

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Archive of Time Cube discussion

Contents

[edit] UTC

I'd like to know when the UTC took over from GMT because I have never seen UTC before coming to this site, hower GMT is still widly used all over The Net and in Newspapers and Television.

I don't know. I believe that these days civil time in the UK is UTC and in summer UTC+1, and we call them GMT and BST. Certainly the pips are synched to UTC. Morwen - Talk 19:27, 22 Jun 2004 (UTC)
Within the UK (and, I presume, UK-registered/based shipping?) GMT and BST are the only names used for time as measured in the UK. People outside the UK however, not wanting to appear UK-centric, seem to utilise the alternative expression of 'UTC'. They are, for most practical purposes, the same (I believe the leap-seconds and other adjustments may not always be exactly equivalent, but for most practical purposes they are). --VampWillow 22:54, 22 Jun 2004 (UTC)

What in the UK should you use to denote that the time you are specifying is local in the sense that something occurs at 10AM - 10AM GMT in the winter and 10AM BST in the summer? Clearly if I specify just 10AM then it could be just about any time. If I say 10AM GMT then this will be the wrong time all summer. --KayEss 06:04, 14 Sep 2004 (UTC)

[edit] UT1

UT1 is the same as GMT, isn't it? Currently UT1 redirects to Universal Time. —Ashley Y 13:40, 2005 Jan 24 (UTC)

Universal Time was invented as another name for GMT in 1928. UT was split into UT0, UT1, and UT2 in the 1960s. UTC was invented in 1972. But GMT has a much longer history than that. It began when the Royal Observatory was founded at Greenwich in 1675. For astronomers 00:00 GMT meant noon, but for civilians 00:00 GMT meant midnight, twelve hours earlier. As of 1 January 1925, the astronomical GMT day was shifted by twelve hours so that it also began at midnight. Thus GMT has not always been the same as UT1 by any stretch of the imagination. But UT1 has always been a type of Universal Time, thus the redirect is correct. — Joe Kress 08:02, Jan 25, 2005 (UTC)

[edit] Dublin-Mean Time

Could Dublin-Mean Time be included in this section or on a seperate page.It was 25 minutes behind of Greenwich according to The Irish Times Book Of The Century.I can't find my copy of the book but anyone with a copy could add the page if it is considered notable.--Fenian Swine 22:59, 22 August 2005 (UTC)

Hmm lots of cities had local times. Why add Dublin in particlular? Theresa Knott (a tenth stroke) 11:56, 25 August 2005 (UTC)
Is that apart from the fact that Dublin is the greatest city in the World.I was unaware of other local times.Why not add a page with the other local times.--Muc Fíníneach 15:01, 25 August 2005 (UTC)
You are free to create a page entitled "Dublin mean time" if you can make it larger than a stub (stubs serve no useful purpose). See Washington mean time and Washington meridian. — Joe Kress 17:08, August 25, 2005 (UTC)

[edit] The M means Mean?

I always thought it was Greenwich Meridian Time.

Everything I've read has GMT meaning Greenwich Mean Time, but some authors may have used GMT to mean Greenwich Meridian Time, which means almost the same thing. "Mean" indicates that the equation of time has been applied to the solar time at the Greenwich meridian. — Joe Kress 22:35, September 1, 2005 (UTC)

[edit] Zulu

The article stated: In the military, GMT is often referred to as "Zulu" time, ie 2000 Zulu would be 8:00pm in Greenwich. I have removed this. First of all, Zulu is another name for UTC, not GMT. Second of all, even if it were identical to GMT, then 2000 Zulu would 8:00pm in Greenwich only during winter, not during summer. --Netvor » user | talk | mail | work » 13:25, 15 March 2006 (UTC)

I think you're misunderstanding the meaning of GMT. Greenwich doesn't use GMT during the summer. GMT is an invariant time zone; the UK is on GMT for half the year and BST for the other half. 03:33, 20 September 2007 (UTC)03:33, 20 September 2007 (UTC) —Preceding unsigned comment added by 86.137.136.182 (talk)

[edit] Colored map slightly unclear

It is currently captioned: Dark colours indicate countries observing daylight saving. It's not clear which colors are dark. Are Russia and Eastern Europe "dark"? --Ds13 00:01, 5 May 2006 (UTC)

Yeah I noticed this too. I'm glad I'm not the only one. —Preceding unsigned comment added by 71.13.85.116 (talk) 03:38, 6 April 2008 (UTC)

[edit] 211's addition

211, you previously agreed at Talk:Greenwich Mean Time/Time Cube not to re-add this material. This behavior is inappropriate. You may not add any such material without first convincing the other editors on the talk page. — Knowledge Seeker দ 08:14, 30 September 2006 (UTC)

[edit] Merging?

Why don't we merge UTC, UT1 and GMT together in to 1 article named maybe, International Time, etc. --Jacklau96 01:11, 19 November 2006 (UTC)

Because they are different things? GMT has had a longer history than e.g. UTC. Also UTC strictly is not the same as GMT. In any case, International Time (without a qualifier such as "Atomic") is a non-existent: we have Universal Time instead. Tom Peters 14:11, 19 November 2006 (UTC)

[edit] Does anyone still use real GMT?

UTC is the international standard and it seems that even the broadcast time signal in the UK is UTC. The article does not make it clear whether there is someone still keeping a clock set at real GMT and whether anyone uses it and why. OK now re-read. GMT and everyone's time zones based on UT1 and there is a shift every so often by leap seconds to UTC & UT in step. JMcC 19:03, 27 November 2006 (UTC)

ZULU = GMT = UTC Greenwich Mean Time = Co-ordinated Universal Time (UTC) = "ZULU" a short form for the aforementioned. Originally referred to by all radio operators as Greenwich Mean Time or GMT... the term was "universalized" in the 70/80's to UTC, Co-ordinated Univeral Time. The term "ZULU" is the equivilant of the aforementioned, when referring to GMT or UTC.. i.e. "1436 ZULU" would be 14:36 UTC or 14:36 GMT; the purpose of which was and is simply to have a single, universal time standard by which people may set schedules worldwide... i.e. to someone in North America, 1436 ZULU is the same as to someone in Africa, or anywhere else in the world. Makes setting schedules amongst, for example, radio amateurs (shortware radio operators) easier. The use of "ZULU" was originally adopted by the military and, as previously indicated, was the equivilant of GMT (without DST applied). "ZUKU" was used instead of GMT because it was a word that is easily understood over less than ideal communications links. See WWV, WWVH time standards.

UTC is not offically recognised or even heard of by the vast majority of the britsih public so throughout most of Europe it is commonly assumed that GMT is used rather than UTC. UTC is percieved publically as just anothe USA invention to be awkward.--Lucy-marie 16:35, 26 May 2007 (UTC)

Well, not quite. UTC is officially recognised in the UK, but not used by the British public - clearly not the same things. This is why the BBC World Service gives the time in GMT and the Shipping Forecasts on Radio 4 also state "Issued at 23:15 GMT". The same is true for some other measurements (e.g., the international standard unit for measuring atmospheric pressure is the hectopascal, but in UK aviation the millibar is still quoted. They are, in fact, identical!) Emeraude 11:20, 27 May 2007 (UTC)

[edit] Map

Somebody needs to add the Serbian–Montenegrin border to the map. Tomasboij 10:56, 2 August 2007 (UTC)

I'm copying your complaint to Template talk:Time zones of Europe. — Joe Kress 01:54, 4 August 2007 (UTC)

[edit] Loftus

I'm moving the following statement (added to the article by an anonymous editor) to its talk page because its claim is tenuous at best.

GMT also changed many place names as often there were two of the same name, an example of this is there were two Lofthouse's so one had to be renamed Loftus to avoid confuson of travellers.

The name was indeed changed during the nineteenth century from Lofthouse to Loftus as implied by the history of Loftus. However, it had been known as North and South Loftus during that seventeenth century according to the same history. But the name change must have occurred after 1859 because Lofthouse appears on a paten given to the Church of St. Leonhard in 1859, eleven years after all British railways adopted GMT in 1848. — Joe Kress (talk) 21:14, 31 December 2007 (UTC)

And even if the claim were true, it would need some serious sourcing to explain what such name confusion could possibly have to do with time zones. –Henning Makholm 01:26, 1 January 2008 (UTC)

[edit] anomaly in time in Greenwich, UK?

The article/map seems to be telling me that the time in Greenwich, UK in the summer is not Greenwich Mean Time. Details:

1. The article's top-right time-zone map seems to be saying that the time in Greenwich in the summer is UTC plus one hour, because such town seems to be located within London, UK.

2. The article states that "UTC" is in common usage the same as "Greenwich Mean Time", i.e. "Greenwich Mean Time (GMT) is ... now often used to refer to Coordinated Universal Time (UTC) ... ."

3. So, restating "1" above, the time in Greenwich in the summer is GMT plus one hour??

I must be missing some idea. Sorry in advance if there's some relevant clue given in an existing Talk section. Thanks in advance for suggested answers or keys to the puzzle.

Bo99 (talk) 16:50, 23 February 2008 (UTC)

You are not missing anything. The time in Greenwich during the summer is not Greenwich Mean Time. British Summer Time is one hour ahead of Greenwich Mean Time during the summer. Greenwich Mean Time is the time in Greenwich only during the winter. GMT does not experience one hour shifts. The mean in Greenwich Mean Time indicates that it is the average time by the Sun at the Royal Observatory, Greenwich. — Joe Kress (talk) 21:08, 23 February 2008 (UTC)
Thanks very much. I sort of kind of understand, i think.
The fact that the time in Greenwich during the summer is not Greenwich Mean Time seems like an anomaly, or something not obvious to readers trying to use the article, or something useful to such readers. Do you or others think that such fact could go in the article?, perhaps at the start of the Anomaly section (before the political anomalies), or elsewhere in the article. If so, i could try to do the writing, though i know you would be a surer hand at it.
Bo99 (talk) 01:11, 24 February 2008 (UTC)
I think it worked out as it did for historical reasons. Mariners had come to rely on charts that marked longitude from Greenwich, and set their chronometers to Greenwich, long before summer time was thought of. These mariners had no interest in whether or not the British Isles observed summer time; most of them were elsewhere. So they ignored the adoption of summer time in the British Isles. --Gerry Ashton (talk) 02:13, 24 February 2008 (UTC)
I've clarified it at the end of the introductory paragraph. — Joe Kress (talk) 02:29, 24 February 2008 (UTC)
Thanks again. Bo99 (talk) 13:43, 24 February 2008 (UTC)

"In the community of Greenwich, GMT (in the form of UTC) is the official time only during winter (during summer the time in Greenwich is British Summer Time rather than GMT)."

This information is irrelevant in the context of the topic, and misleading inferring it's just local to the community of Greenwich, rather than the entire UK.
Please remove it entirely or contextualize correctly into the 'Time Zone' section of the page. 86.135.51.232 (talk) 15:16, 30 May 2008 (UTC)

[edit] The Change of 1925

The article now says "The old astronomical convention (before 1925) was to refer to noon as zero hours, whereas the civil convention during the same period was to refer to midnight as zero hours.". But did the change occur at the end of London Civil 1924-12-31 or 12 hours later at the end of Astronomical 1924-12-31 ? 82.163.24.100 (talk) 21:17, 6 April 2008 (UTC)

The former, at the end of civil GMT 1924-12-31 midnight, hence astronmical 1924-12-31 was only 12 hours long, beginning at noon and ending the following midnight, according to all astronomical almanacs of the year, such as the 1925 American Ephemeris and Nautical Almanac. — Joe Kress (talk) 03:09, 7 April 2008 (UTC)

[edit] Prime meridian

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

The above statement is incorrect, and is referring to the WGS/ITRF zero meridian derived from NAD27, (as used currently by GPS). If disputed please provide source.

The international prime meridian was set at the International Meridian Conference in Washington 1884, adopting the meridian passing through the centre of the transit instrument at the Observatory of Greenwich as the initial meridian for longitude.

Also the 5.31"E is a potentially misleading format, please use arcseconds or a full d.mm.ss format. 86.135.51.232 (talk) 15:10, 30 May 2008 (UTC)

I replaced the statement challenged by 86.135.51.232 with a quote from a reliable source. --Gerry Ashton (talk) 17:09, 30 May 2008 (UTC)
I left the spelling of center unchanged. Check Howse to see if he used the British spelling centre. — Joe Kress (talk) 19:13, 30 May 2008 (UTC)