Talk:Coordinated Universal Time

GMT is avoided in careful writing?

Really, in the Summer, the UTC time is one hour less that the GMT time. So its ok... 207.6.122.86 (talk) 00:21, 16 March 2011 (UTC)

I don't agree with this statement "GMT is avoided in careful writing" in the introduction. It does not have a citation. On the Wikipedia page "Citing Wikipedia, "The Harvard Journal of Law and Technology has adopted the following format for citations to articles in Wikipedia:"

[Signal] Wikipedia, [article], http://en.wikipedia/wiki/[article] [(optional other parenthetical)] (as of [date], [time] GMT). Here is an example: See Wikipedia, Bluebook, http://en.wikipedia/wiki/Bluebook (describing history and application of the Bluebook) (as of Mar. 21, 2006, 20:50 GMT).

They seem to be partial to GMT. Nly8nchz (talk) 08:04, 20 December 2008 (UTC)

Perhaps it would be better to that that GMT is avoided in technical contexts. Martin Hogbin (talk) 09:32, 20 December 2008 (UTC)

Perhaps it would. As I understand it the Greenwich Meridian is no longer prime but has moved 90 feet or so in order that the 90 degree line should pass through Chicago observatory. Thus it would be wrong either to refer to GMT or the "Greenwich" meridian except in an historical context. —Preceding unsigned comment added by Drg40 (talk • contribs) 09:05, 29 March 2010 (UTC)

Like most things, the real answer is more complicated than that, see Prime meridian. The term GMT is is everyday use in some parts of the world but is best avoided in technical use, as the article currently states. I think this is a reasonable description of the current state of affairs. Martin Hogbin (talk) 10:48, 29 March 2010 (UTC)

Hilarious!! The fact is no one uses UTC in any practical sense (except scientists astrologers etc) UTCis for practical use merely GMT by another name--and very confusing at that-there is of course no such thing as universal time -it has to be measured from somewhere and whether the greenwich meridian is now 100m off centre etc that is where time starts from.Knowing you are gmt plus 5 etc immediately fixes your place on the earth relative to greenwich london.The human brain demands such reference points to work properly. Even when forced to use zulu for example the individual is still mentally thinking of greenwich and not an abstract meaningless number... —Preceding unsigned comment added by 89.132.130.90 (talk) 20:06, 31 October 2010 (UTC)

The second and third sentences currently give indistinguishable definitions of GMT and UT, and maybe they should be merged. The difference is that it encourages the use of UT ("if high precision is not required the general term Universal Time (UT) (without a suffix) may be used") but discourages "GMT" ("generally avoided in technical contexts"). The reference cited doesn't support that. The rationale given -- that it might mean either UT1 or UTC -- would seem to apply equally to UT. How about one sentence describing these synonyms, and if necessary, a second explaining any subtle difference that makes "UT" preferable? 71.139.177.112 (talk) 00:57, 16 February 2009 (UTC)

I think the rational is that while GMT might be used by someone who has not kept up with the terminology, or who is deliberatly "dumbing-down" a text for consumption by the general public, UT is a deliberate indication that for the purposes at hand, the small differences in the various flavors of UT do not matter. I'm not sure if that rational actually works, but I think that is what the passage is trying to get across. --Gerry Ashton (talk) 01:08, 16 February 2009 (UTC)

Its fascinating seeing the desperate way some people here make attempts to discredit the use of GMT Of course there are some scientific differences that are important if you are involved in space flight etc but really for most people GMT is so much more understanable that there is no way it is ever going to not be used. For example I always wonder how someone explains to an intelligent child what UTC is . When the child asks Why does it say New York is UTC - 5 ? Minus five from WHERE..I dont understand?. The parent (yes even American!) then has to say well er actually it means New York time is 5 hours behind the time in London actually the time at a place in London called Greenwich and if a time is say in advance of London Greenwich time then it will say Plus then a number. Of course the child or adult will naturally say why dont they just call it Greenwich Time since its really based on the time at Greenwich? The answer to that is that the Americans get upset about people saying the the worlds time comes from Greenwich in London so thats why the have invented UTC. Thats the truth if we are really honest. The fact is that throughout the world GMT is going very strong for the obvious reasons Ive mentioned. Incidentally at the 1884 washington conference on time I believe it was decided that the new year begins at the stroke of midnight GMT (when Big Ben strikes 12..Big Ben in London is coordinated with Greenwich which is several seconds away. This means that all the emphasis on New Years celebrations elsewhere is misplaced When New York celebrates New Year the New Year is already five hours old!

Really, in the Summer, the UTC time is one hour less that the GMT time. So its ok... 207.6.122.86 (talk) 00:21, 16 March 2011 (UTC)

New comments go at the end of the thread, so I've moved 207.6.122.86's comment. This illustrates what a horrible term GMT is. All the scientific bodies have abandoned it, and if you ask one of them what it means, they'll refuse to answer and tell you to stop using it. The UK considers it to be their legal time, but won't pass a definitive piece of legislation telling exactly how it's defined. The general news media is hopeless on scientific and technical matters, so you can't pay any attention to those folks. What a mess. Jc3s5h (talk) 00:30, 16 March 2011 (UTC)

So are we not right to stick to my suggestion and the current wording that GMT is best avoided in technical contexts. The term is widely used in the UK but it is ill-defined. Anyone who wants to be precise uses UTC but GMT is used in everyday speech. Gerry Ashton expresses it well, GMT is used by people who do not care that much about fractions of a second and correct terminology for precise timekeeping. Martin Hogbin (talk) 18:30, 16 March 2011 (UTC)

I agree and furthermore right at the top of this article it is not correct to say "UTC is synonymous with GMT" because UTC has no British Summer Time offset. Too many people confuse UTC with GMT in GUIs and region configuration screens, even some popular OS builds I've seen! The article on GMT in Wikipedia states this clearly right at the beginning. So I feel it is incorrect that this UTC article suggests the opposite; that they are "synonymous" in the first paragraph. I suggest this statement is removed and information added about this common mistake near the top. Right now this is just adding to confusion. Codechief (talk) 20:03, 9 April 2014 (UTC)

User:Codechief, do you contend that GMT advances in (northern hemisphere) spring and falls back in autumn? If so, I have seen many uses of GMT that never observe any daylight saving adjustment. If you can provide a reliable source that GMT includes a daylight saving adjustment, we might be able to edit several articles to state that GMT is hopelessly confused and therefore totally useless. Jc3s5h (talk) 20:22, 9 April 2014 (UTC)

Just to confirm, GMT is never used to refer to daylight savings time, which is called BST in the UK. Martin Hogbin (talk) 10:00, 10 April 2014 (UTC)

Most Recent Leap Second

The most recent Leap Second just occurred Dec 31, 2008. Should this be in the article (or is it and I missed it)? Pointless trivia that should not be included: 2008 was adjusted to be 366.000012 days long.wcf Facts are stubborn. Comments? 21:36, 11 January 2009 (UTC)

The most recent Leap Second just occurred June 30, 2012. Georges Theodosiou email: chretienorthodox@hotmail.fr

page clock

on some refreshes this does not work and shows some random time (it does have some preference for 10:50) and why is the date in YYYY-MM-DD ? Machete97 (talk) 11:21, 3 February 2009 (UTC)

For me it shows in 12 hour form without AM/PM. At the moment it reads 07:01 when it should be 7:01PM or 19:01 80.47.218.9 (talk) 19:05, 19 October 2013 (UTC)

Just tried it myself. When I loaded the page, it gave me an 07:09, when it was 07:19 UTC. When I clicked the refresh, the correct time came up. That may be a cache dependent issue.Wzrd1 (talk) 20:29, 19 October 2013 (UTC)

dubious fact

Just to note that I've tried to clear up some loose/inaccurate language which seemed to be all that made the tagged 'fact' 'dubious' (see 1st para under 'History', about Greenwich and meridian conference). Terry0051 (talk) 01:13, 26 February 2009 (UTC)

Bogus example

I can't find any guarantee that the magic word CURRENTTIME, used below, is UTC. It seems likely that it would depend on the server's locale. As the locale is not necessarily UTC, and this example does not illustrate another part of the UTC standard, I have taken it off the article:

Gyro Copter (talk) 14:54, 25 March 2009 (UTC)

• I just checked, according to [1], the time generated is determined by the user preferences, defaulting to UTC. This cannot be trusted to always give UTC (presumably some users change their preferences). Gyro Copter (talk) 14:58, 25 March 2009 (UTC)

• This was a useful utility. Could it be restored with a disclaimer that the time is dependent upon the user's preferences being accurately referenced to UTC? AusJeb (talk) 21:54, 28 April 2009 (UTC) (Well assuming my preferences are correct, and really assuming that any of this is correct, because ultimately, isn't this an arbitrary reference to an arbitrary reference used to mark the passage of time)

• I oppose presenting potentially false information, even with a disclaimer. --Jc3s5h (talk) 22:08, 28 April 2009 (UTC)

Describe UCT

The article doesn't mention the abbreviation UCT. It's a common (mis?)abbreviation used when discussing time zones. Searching for UCT time zone on Wikipedia or Google both refer to this page, I think the page should describe, or at least mention it.

Chei (talk) 15:38, 9 April 2009 (UTC)

Daylight saving time

I am not sure if it is mentioned, I may have missed it - but :

Is time zone, as the basic one, a subject of changing with Daylight Saving Time, or is it (like I prefer to believe) locked to Standard time / winter time ? --TorSch (talk) (of Wikipedia.no) 12:14, 19 July 2009 (UTC)

I'm not sure I understand the question. If you mean does UTC "spring ahead and fall back" as with daylight savings time, no, UTC is never affected by daylight savings time in any way, shape, or form. --Jc3s5h (talk) 17:55, 19 July 2009 (UTC)

OK, then it was like I believed it was. Maybe the line you wrote above, UTC is never affected by daylight savings time in any way, should be found in the article text, to make sure there will never be any doubt? TorSch (talk) (of Wikipedia.no) 18:52, 21 July 2009 (UTC)

Aren't the acronym for most time zones changes when they are taken to their spring time, such as by replacing one of their letters with the letter D? Doesn't that suggests that all time zones never affected by daylight savings time in any way? anonymous 1:48, 8 Feb 2015 (UTC) — Preceding unsigned comment added by 217.132.101.41 (talk)

If you look at Time in the United States you will see that time zones and daylight saving time are specified in different parts of the law. I've read that it's even more complicated in the European Union; there is EU legislation that controls the dates when the daylight saving change is made, but the time zone and amount of the change is controlled by laws in each member nation. So I think it's useful to keep the idea of time zone separate from the idea of daylight saving time. Jc3s5h (talk) 02:01, 8 February 2015 (UTC)

The claim in the article still need to be referenced.....

even the info is within the article such as from the table of Compromise abbreviation--222.64.25.204 (talk) 22:35, 28 July 2009 (UTC)

The claims you wanted supported are indeed supported, either by a citation at the end of the paragraph, or earlier in the article. --Jc3s5h (talk) 00:19, 29 July 2009 (UTC)

Pre-1960 Standards

"WWV time signal's frequency was set to a simple offset from the TAI frequency: initially an offset of 1.0 × 10-8, so that WWV ticked exactly one second for every 1.00000001 s of TAI."

I'm not sure that is accurate. First, there was nothing simple about what WWV did in the late 1950s. 20 millisecond jumps were added, and the clock rate was changed daily to match USNO's measurements of universal time. I'v seen it quoted that they used an offset of 100 parts per 1.0E-10, but I find no evidence of that in their publications. The frequency offsets fluctuated around 0.0, and in 1959 they rose to around 25 - 35 parts per 1.0E-10. In 1959, the british MSF service used a frequency offset of 170.

Perhaps an average shift of 100 for the US frequency standard comes from combining the 25-35 shifts in 1959 with the switch from UT Hz to ET Hz cesium frequency standard (9,192,631,838 Hz 9,192,631,770 Hz), which amounts to about 74 parts in 1.0E-10. But I'm not at all sure I am comparing the right things (USFS, WWV, UT vs. ET, etc).

Maybe someone can provide a reference that clarifies this? DonPMitchell (talk) 18:09, 7 August 2009 (UTC)

OK, I see the -100.0E-10 offset implicit in a graph in a January, 1960 IRE paper from the NBS. (National Standard of Time and Frequency in the United State, Proc. IRE, January 1960, p 106). That frequency offset reflects the hypothetical UT oscillator around 1956. DonPMitchell (talk) 20:40, 7 August 2009 (UTC)

[From Terry0051] Does this help? --- The paper "Time Scales" by Louis Essen in 1968 (Metrologia, vol.4, pp.161-165) says on p.162 that Essen and Parry measured the UT2 mean solar second of their time at 9,192,631,830 cycles (taking a year for the calibration), and then (in collaboration with Markowitz and Hall --- who tracked ET using a moon camera at the USNO) measured the ET second over three years at 9,192,631,770. Terry0051 (talk) 10:05, 8 August 2009 (UTC)

Thanks, yes I've read that paper. I'm not sure that is why they were running their frequency standard at 100.0E-10 below the ET rate. It may have just been done to help them track the UT rate with fewer corrections. The British standards lab was running 170.0E-10 below ET than, probably for the same reason. These frequency shifts are explicitly talked about in reports from the 1960s, but not mentioned in the monthly bulletins in the 1950s. DonPMitchell (talk) 23:51, 8 August 2009 (UTC)

Dubious history

The history section seems to need a bit of clearing up. There is a statement UTC was officially initiated at the start of 1961 (but the name Coordinated Universal Time was not adopted by the International Astronomical Union until 1967). This is said to be supported by Nelson & McCarthy 1995, 15. But nothing of 1995 by Nelson & McCarthy is cited, either in the 'bibliography' or in the misnamed 'notes' (which actually are inline citations to references, or anyhow references with at most a few traces of notes about them).

On the other hand, a source that is cited, Nelson, McCarthy et al 2001 (Metrologia 2001, vol.38, pp.509-529) positively says on page 509 "Since 1972, when UTC was introduced, there have been twenty-two leap seconds, all of which have been positive."

(Any clear-up action needs to be done bearing in mind that epoch dates in matters of astronomy and time-scales have sometimes been assigned retrospectively. I don't know if that happened here, it might be a possibility, I haven't had time yet to look at the details.)

Terry0051 (talk) 23:32, 7 August 2009 (UTC)

Sorry, I wrote the date of the reference wrong. The other source by Nelson and McCarthy (with no et al.) states "Name Coordinated Universal Time (UTC) adopted by IAU in 1967". --Jc3s5h (talk) 23:58, 7 August 2009 (UTC)

Also, Nelson, McCarthy et al. in 2001 wrote "The name 'Coordinated Universal Time (UTC)' was approved by a resolution of IAU Commissions 4 and 31 at the 13th General Assembly in 1967". (Page 515.) --Jc3s5h (talk) 00:12, 8 August 2009 (UTC)

Thanks for that. But it does still leave some weirdness, because the two articles (with overlapping authorship) seem to flat-out contradict each other. On WP:RS grounds, maybe the peer-reviewed article in Metrologia saying "1972" should be preferred over the non-reviewed presentation saying "1961", but I wouldn't want to be too picky about that, because I strongly suspect you are right.

What one needs, I guess, in a situation like this, is additional sources (and after all, working scientists are often not too worried about historical matters anyway).

At least part of the answer seems to be in the paper on "Time Scales" by Louis Essen in Metrologia vol.4 (1968). Essen states on page 162 "UTC. This scale is now used by many time services ..." (and he then describes its features, substantially different from what they are now, involving frequency offsets and step adjustments of 0.1 second at a time.) Essen's article was received May 1968, thus completely disproving the "1972 start" statement by Nelson and McCarthy in Metrologia (2001).

What seems to have happened is that 1972 marked, not the beginning of UTC, but the beginning of a substantially different basis of UTC, with steps of a whole second and use of a constant frequency without offsets. I think there are references from about the time of transition that talk in terms of the "new UTC", so that may be some explanation of why Nelson and McCarthy could say it started in 1972. I'll see if I can dig these out when I get a chance.

Terry0051 (talk) 09:44, 8 August 2009 (UTC)

Nelson et al (Metrologia 2001) gives a detailed history of the evolution of coordinated universal time: Broadcasting a UT-like time signal, governed by atomic clocks was first done in the US and UK in the late 1950s. On Jan 1, 1960, those two countries began to coordinate their broadcasts and frequency offsets and time steps, and other countries soon joined. Nelson calls this the "Original UTC system" A UTC standard was adopted by CCIR (Redommendation 374) in 1963, using 100 ms time step adjustments. Nelson calls that the "Revised UTC System". The name "Coordinated Universal Time (UTC)" was approved by the IAU in 1967. These early forms used frequency shifts and time step adjustments to map atomic time to universal time, but frequency shifts were unpopular for technical reasons involving the equipment that generates pulse trains. In Jan 1, 1972, a new UTC system began using a constant frequency the same as TAI and 1 second adjustments. Nelson calls this the "Present UTC system". DonPMitchell (talk) 01:21, 9 August 2009 (UTC)

1961 was when Britain and America turned over the coordination of UT time signals to BIH. So you could argue that begins the offical international system. The 1960 standards was just an arrangement controlled by USNO and RGO and other labs in the US and UK. DonPMitchell (talk) 01:24, 9 August 2009 (UTC)

No form of the term "UTC" exists in CCIR Recommendations prior to 460-1 in 1974. UTC could not have been standardized by the CCIR in 1961 because their Plenary Assemblies were in 1959 (for Rec. 319) and 1963 (for Rec. 374). The earliest documented occurrence of "UTC" or "TUC" is in the first BIH Bulletin Horaire of year 1964.Steven L Allen (talk) 21:56, 7 November 2011 (UTC) CCIR Rec. 374 from 1963 does not use the term UTC, but rather UT2. Nothing in the IAU proceedings from 1967 can be construed as approving of the name UTC, but merely as recognizing that the time service bureaus used the term UTC as the name of the time scale they were constructing in order to satisfy the CCIR Recs that specified broadcasts to track UT2. The first IAU approval of UTC was in 1973.Steven L Allen (talk) 23:54, 9 November 2011 (UTC)

I have placed Citation needed for the claim of a 1961 origin in the CCIR. The CCIR (then) and the ITU-R (now) exist to hold meetings, produce documents at those meetings, and produce documents about those meetings. If there is no document from the CCIR/ITU-R then there was no "official" action.Steven L Allen (talk) 07:27, 5 January 2013 (UTC)

Use of UTC vs. use of name "UTC"

I undid a recent revision because it claims that "formally:, UTC replaced GMT as the basis of civil time, "although informally, GMT continues to be widely used."

This is not correct. Outside of astronomical observatories and a few other special situations, almost all clocks are set to UTC, or UTC adjusted by a time zone offset and possibly daylight savings time. (That is, almost all clocks are set as best the person doing the setting is able, and if one traces the setting path from one clock to another, one will almost always come to a clock that is based on UTC.) So UTC is almost always used. The formality or informality lies in what it is called. If the time scale is offset by a time zone or daylight savings time, neither of the names "UTC" or "GMT" are applicable. If actually referring to the UTC scale, it is formally named "UTC" but often the informal name "GMT" is used instead.

Of course "GMT" is also the name of a time scale based on the mean solar time at the Royal Observatory, Greenwich, but no scientific body maintains a time scale named "GMT" so there is no rigorous definition for the term. Jc3s5h (talk) 18:11, 26 August 2010 (UTC)

I will look at the passage to see if it can be improved.Jc3s5h (talk) 18:11, 26 August 2010 (UTC)

I recently learned that the Danish national metrology agency interprets Danish law, which bases the legal time of Denmark on the Greenwich meridian, so strictly as to exclude UTC, because UTC is not GMT.[2] Also, The Nautical Almanac published jointly by the Nautical Almanac Offices of the US and UK still defines UT as GMT, explicitly stating that it differs from UTC by up to 0.9 seconds.

"The time argument on the daily pages of this Almanac is 12^h + Greenwich Hour Angle of the mean sun and is here denoted by UT, although it is also known as GMT. This scale may differ from the broadcast time signals (UTC) by an amount which, if ignored, will introduce an error of up to 0'.2 in longitude determined from astronomical observations. (The difference arises because the time argument depends on the variable rate of rotation of the Earth while broadcast time signals are now based on an atomic time-scale.) Step adjustments of exactly one second are made to the time signals as required (normally at 24^h on December 31 and June 30) so that the difference between the time signals and UT, as used in this Almanac, may not exceed 0^s.9." The Nautical Almanac, 1989–2011, page 254.

— Joe Kress (talk) 08:56, 29 August 2010 (UTC)

I think the article was meant to mean '"although informally, the term GMT continues to be widely used." Would changing the text to that solve the problem? Martin Hogbin (talk) 17:58, 29 August 2010 (UTC)

Before I reverted the change the paragraph in question read:

Time zones around the world can be expressed as positive or negative offsets from UTC as in this list; formally, UTC replaced GMT as the basis for the main reference time scale or civil time in various regions on 1 January 1972, although informally, GMT continues to be widely used. [References removed]

I think the paragraph above the one that was changed adequately covers the informal nature of "GMT". The paragraph in question is about time zones. Except in the British Isles during winter, neither "GMT" nor "UTC" are used in time zone names. The zone time is almost always an integer number of half hours different from UTC; that is the sense in which zone time is based on UTC. Since neither of the terms "UTC" or "GMT" are used when presenting zone time to the public, there is no reason to discuss casual use of "GMT" in this paragraph. Jc3s5h (talk) 19:20, 29 August 2010 (UTC)

I agree, a section on time zones is not the right place to mention GMT. The subject is discussed above. Martin Hogbin (talk) 00:00, 30 August 2010 (UTC)

Necessity of making the opening comprehensible to non-scientists

Without in any way losing the absolute scientific description of UTC - there is a need that the opening be understandable by ordinary people arriving at this page seeking to know what UTC is. If the opening line is a purely scientific definition - with no regard for the lay-person - then the article fails in the purpose of elucidating readers. As long as the scientific information is prominent - then the simplified descriptive is a benefit to the article and the purpose of Wikipedia. Davidpatrick (talk) 11:09, 1 November 2010 (UTC)

Coordinated

Should "coordinated" be spelt "co-ordinated"?Osborne 14:38, 17 November 2010 (UTC)

It should be spelt "Coordinated" because it is part of the proper name of a time scale.[3]

Jc3s5h (talk) 16:14, 17 November 2010 (UTC)

UTC is 5 hours ahead of local time on the east coast of the United States during winter, but 4 hours ahead during summer

This implies that UTC changes. —Preceding unsigned comment added by 81.140.57.113 (talk) 12:11, 15 December 2010 (UTC)

The paragraph begins "UTC does not change with a change of seasons...." I'm sorry, but sometimes a sentence cannot be properly understood without reading the whole paragraph. If, in light of the whole paragraph, you still think the paragraph implies it is UTC and not civil time that is being adjusted, please explain your reasoning. Jc3s5h (talk) 13:30, 15 December 2010 (UTC)

Citation format

This article uses a mixture of different citation formats. The first inline citation I find uses the {{Cite xxx}} family of templates. Thus, I intend to

• change all citations in "References" to that family of templates
• change any full citations in "Notes" to short citations and move the full citation to "References"

Are there any comments or objections? Jc3s5h (talk) 15:17, 3 July 2011 (UTC)

I have substantially completed this change, although I have to investigate a couple of cases where clicking on the short footnote does not leap to the full citation; the {{Svn}} template is used for the footnotes. Jc3s5h (talk) 15:16, 18 July 2011 (UTC)

Too many solar time articles

Please see Wikipedia talk:WikiProject Time#Too many solar time articles Jc3s5h (talk) 17:38, 2 August 2011 (UTC)

Universel Temps Coordonné?

The sources supporting the claim that "Universel Temps Coordonné" is unofficial French for Coordinated Universal Time are weak. The first is an online forum, the other is some instructions for an online chat service. Both appear to have been written by people fluent in English, and no evidence is presented that the authors are knowledgeable about actual French usage. Jc3s5h (talk) 04:18, 5 August 2011 (UTC)

There has been some discussion on this topic in the past, but if the references are weak I suggest you remove the offending statement. Martin Hogbin (talk) 08:50, 5 August 2011 (UTC)

Now, this has been changed to Temps Universel Coordonné. But how is this shortened to UTC?? —Kri (talk) 14:49, 24 April 2014 (UTC)

This is explained in the "Abbreviation" section of the article. Jc3s5h (talk) 16:10, 24 April 2014 (UTC)

Legal time

Question, should we add a list of countries/regions/etc. where UTC is in law described as the basis for time-keeping? I would find this to be highly interesting. Also considering that the European Union Commission's directive 2000/84/EG (http://eur-lex.europa.eu/LexUriServ/LexUriServ.do?uri=CELEX:32000L0084:EN:HTML) states that EU summertime uses GMT. But a later directive UTC (http://eur-lex.europa.eu/LexUriServ/LexUriServ.do?uri=OJ:C:2011:083:0006:01:en:HTML). Another issue regarding EU law is that different translations uses different terms (e.g. GMT, UTC and even others). Wronguy (talk) 17:57, October 5 2011 (UTC)

It would be interesting, but difficult. The European Union illustrates some of the problems, where it isn't very clear to a non-lawyer when individual country laws would control and when EU laws would control. Jc3s5h (talk) 19:53, 5 October 2011 (UTC)

GA Review

This review is transcluded from Talk:Coordinated Universal Time/GA1. The edit link for this section can be used to add comments to the review.

Reviewer: Looie496 (talk) 17:01, 15 October 2011 (UTC)

I will review. Pyrotec (talk) 19:57, 9 August 2011 (UTC)

Sorry for the delay. I will review from today.

Initial comments

On the basis of a very quick read, perhaps the article will make GA-status time round. However the WP:Lead appears to be quite poor and the Uses section is somewhat under-referenced.

I'm now going to work my way through the article starting at the Uses section and considering the WP:Lead last. This is likely to take at least one day, possibly more. Pyrotec (talk) 20:05, 30 August 2011 (UTC)

• Uses -

• The first two paragraphs are unreferenced.
• The claim in the third paragraph, i.e. "International broadcasters such as the BBC World Service also use UTC ..." is unreferenced.
• The claim in the fourth paragraph about Zulu time is unreferenced.
• The claim in the final paragraph about the international space station is unreferenced.
• Most of these paragraphs are short, very short, sometimes a single sentence, so they should be merged.

• The first paragraph is probably OK as it stands. The second paragraph is a single sentence about about global commerce: I see no reason why it can be merged with the fifth paragraph which is about global transportation.

• Definition and relationship to other standards -

• This has much more in-line citations but also suffers from mostly single sentence paragraphs, one two-sentence paragraph and a three-sentence paragraph. The first three paragraphs could be merged into one.
• There is no need to wikilink both occurrences of Universal Time is a single section, this is WP:Overlinking.

Pyrotec (talk) 18:00, 4 September 2011 (UTC)

• Notation -

• Looks OK. I'll accept Notation as a section title, but is it really notation that is being discussed (its more like abbreviations)?

• Mechanism -

• Poor grammar: I'm not convinced that the second paragraph is a paragraph, i.e. "Thus, in the UTC time scale, the second and all smaller time units (millisecond, microsecond etc.) are of constant duration, but the minute and all larger time units (hour, day, week etc.) are of variable duration." It seems to a single sentence that has escaped from the first paragraph.
• The second proper paragraph, i.e. the 86,400 second-day paragraph is unreferenced. I'm happy to accept that 24 hr x 60 min x 60 sec = 86,400 seconds, but all the claims and statements about 59 second and 61 second minutes need a citation, i.e. compliance with WP:Verifiability.

....Stopping for now. To be continued. Pyrotec (talk) 18:54, 4 September 2011 (UTC)

• • Time zones -

• Looking at my old school atlas, Reykjavik is listed as 21° 53' W so it is not obvious that "is always on UTC time and does not use daylight saving". There are two claims here that need a citation (possibly only one citation is needed).

• • Daylight saving -

• The given example about East Coast time needs a citation.

• History -

• The first, fourth, fifth and sixth paragraphs are unreferenced.

• Rationale -

• This is mostly unreferenced, but as it is mostly explanation, and the one statement is referenced, I'll accept this as it is.

• Future -

• There is a {{who}} flag that needs to be addressed.
• The penultimate paragraph states: "....An ITU study group was to have voted on this possibility during 2008, possibly leading to official approval by the World Radiocommunication Conference in 2012 and the subsequent cessation of leap seconds.", as we are now 75% of the way through 2011 I would have expected an update as to whether the 2008 vote took place, and whether approval next year (in 2012) is possible?

• WP:Lead -

• This part of the article has to functions: to introduce the topic cover by the article and summarise the main points. What we have is four paragraphs: one comprised of two sentences and three paragraphs of one sentence. Perhaps they are bullet points with out the points.
• For a short article such as this, I would have expected one or two (proper) paragraphs introducing the topic (yes it possibly does) and summarising the main points. Its not really my job to state what the main points are: perhaps they are all covered, in which case perhaps a more detail is needed e.g. Atomic time has a link, but no mention of a Caesium clock, GMT is mentioned by not Zulu time.

At this point, I would regard the article as non-compliant in respect of prose/grammar and WP:Verifiability. The article is well referenced in parts and some of the existing references might provide adequate verification for the statements discussed above that are not currently verifiable. I'm therefore going to put this review On Hold to allow corrective actions to take place. None have taken place in the last five days. I've been distracted elsewhere on wikipedia, so I know that distractions do occur. Pyrotec (talk) 19:23, 9 September 2011 (UTC)

I believe I have addressed this to some degree, although I'm sure some editors will feel the writing can be further improved. Jc3s5h (talk) 16:56, 21 September 2011 (UTC)

Status check

This review seems to be inactive at the moment, and it's been open for two months. Do we have a decision? Do you need some help? WhatamIdoing (talk) 15:17, 11 October 2011 (UTC)

I observe that Pyrotec has not made any Wikipedia contributions since 15 September. Jc3s5h (talk) 16:34, 11 October 2011 (UTC)

It appears that s/he announced a wikibreak on the user page. No e-mail, either. What would you like to do? WhatamIdoing (talk) 22:00, 13 October 2011 (UTC)

I think it would be best to have another editor do the review. Pyrotec has made a real contribution by finding a number of issues, and it couldn't hurt to have someone else look at it from a different point of view. Jc3s5h (talk) 22:32, 13 October 2011 (UTC)

Picking up review

I'm not quite sure what has been going on here, but I'll pick up this review. Contrary to the previous reviewer, the first thing I would like to address is the lead, which is seriously lacking. I would like to see the lead give brief answers to these questions:

• How is UTC information provided to clients?
• Where is the clock located?
• How are UTC times determined? The lead currently says that UTC is based on TAI, but the reader should not need to go to the TAI article for a basic answer.
• How precisely are UTC times specified?
• What is the rationale for deciding when to add a leap second? In other words, who makes this decision and what is the basis for the decision?
• In what way does UTC differ conceptually from TAI and UT1?
• Where did the acronym UTC come from?
• Who decided to make UTC a standard, and when did this happen?
• Will UTC be the standard forever?

Most or all of this information is in the article, of course, but it should all be addressed in the lead. Looie496 (talk) 17:01, 15 October 2011 (UTC)

That's too much for the lead, in my view. Some of these questions cannot possibly be answered (will UTC be the standard forever?). Others have multiple interpretations and answers (How is UTC information provided to clients?) Some can't really be answered in their present form (where is the clock located?) Let me give some off-the-cuff answers to show the complexity:

1. How is UTC information provided to clients? Pure UTC with no source designated is not provided in real time; instead, a list of how far off each of 68 laboratories were is issued retrospectively in Circular T.
2. Where is the clock located? There is no one clock that provides UTC. There are quite a few laboratories around the world that are included in the computation of UTC (listed in Circular T), and there are many more clocks that provide approximations of UTC.
3. How are UTC times determined? The lead currently says that UTC is based on TAI, but the reader should not need to go to the TAI article for a basic answer. The requirement is to provide leap seconds to keep |UT1 - UTC| < 0.9 s.
4. How precisely are UTC times specified? UTC is computed, not specified. The largest difference between the retrospectively computed UTC and a time laboratory in the latest Bulletin C that I can pick out by eye is for Budapest, -56436.6 ns.
5. What is the rationale for deciding when to add a leap second? In other :words, who makes this decision and what is the basis for the decision? The criterion is stated in the answer to question 3. The decision appears to be made by the International Earth Rotation AND Reference Systems Service and is contained in Bulletin C.
6. In what way does UTC differ conceptually from TAI and UT1? It is a compromise between them, having seconds of uniform length (as measured by atomic clocks) like TAI, but, because of leap seconds, staying close to mean solar time (as implemented by UT1).
7. Where did the acronym UTC come from? It was chosen by the CCIR (now named ITU-R) in 1967, according to McCarthy and Seidelmann. That organization also stated the names were Coordinated Universal Time in English and Temps Universel Coordonné in French. (2009, p. 227)
8. Who decided to make UTC a standard, and when did this happen? See previous answer. Also, various other organizations and governments have explicitly or implicitly endorsed UTC.
9. Will UTC be the standard forever? There is a big fight about this going on in the precision time community.

Do you think the following draft might serve as a starting point for creating a more informative lead?:

Coordinated Universal Time (abbreviated UTC) is the primary time standard by which the world regulates clocks and time. Computer servers, online services and other entities that rely on having a universally accepted time use UTC for that purpose. If only limited precision is needed, clients can obtain the current UTC time from a number of official internet UTC servers . For nanosecond precision, clients can obtain the time from radio or satellite signals. Time zones around the world are expressed as positive or negative offsets from UTC, as in this list.

Coordinated Universal Time is closely related to International Atomic Time (TAI), a time standard calculated using a weighted average of signals from over 200 atomic clocks located in over 70 national laboratories around the world. The only difference between the two is that UTC is occasionally adjusted by adding a leap second in order to keep it within one second of Universal Time, which is defined by the Earth's rotation. In the 49 years up to 2010, a total of 24 leap seconds have been added.

The UTC standard was officially initiated in 1961 by the International Radio Consultative Committee, at the request of five national laboratories. The system was changed several times over the following years, until it reached its final form until 1972. A number of proposals have been made to replace it with a new system, but no consensus has yet been reached to do so.

Looie496 (talk) 22:21, 15 October 2011 (UTC)

That looks promising. I intend to break it down into a list of claims, and see what claims are presented as introductory information in the current article and one or two books I have. Then I'll suggest additions or deletions. Jc3s5h (talk) 22:28, 15 October 2011 (UTC)

That isn't quite the right way to think about it. In a Wikipedia article, lots of readers only look at the lead, so it should give them as comprehensive a picture as it can without going into too much detail. In books and printed articles the introduction serves a different purpose -- a Wikipedia lead is more like the abstract of a paper than the introduction of a paper. Looie496 (talk) 22:43, 15 October 2011 (UTC)

Can I suggest, 'Coordinated Universal Time is based on International Atomic Time' because that is the way things work. The actual clocks determine TIA and UTC is calculated from this. Martin Hogbin (talk) 11:59, 16 October 2011 (UTC)

I will put a draft lead section derived from Looie496's version below. Jc3s5h (talk) 15:21, 16 October 2011 (UTC)

Proposed lead section

Coordinated Universal Time (abbreviated UTC) is the primary time standard by which the world regulates clocks and time. It is one of several closely related successors to Greenwich Mean Time. Computer servers, online services and other entities that rely on having a universally accepted time use UTC for that purpose. If only limited precision is needed, clients can obtain the current UTC time from a number of official internet UTC servers . For sub-microsecond precision, clients can obtain the time from satellite signals. Time zones around the world are expressed as positive or negative offsets from UTC, as in this list.

Coordinated Universal Time is based on International Atomic Time (TAI), a time standard calculated using a weighted average of signals from atomic clocks located in nearly 70 national laboratories around the world.(International Bureau of Weights and Measures 2011) The only difference between the two is that UTC is occasionally adjusted by adding a leap second in order to keep it within one second of UT1, which is defined by the Earth's rotation. In the 50 years up to and including 2011, a total of 34 leap seconds have been added.

The UTC standard was officially standardized in 1961 by the International Radio Consultative Committee, after having been initiated by several national time laboratories. The system was changed several times over the following years, until leap seconds were adopted in 1972. A number of proposals have been made to replace it with a new system, which would eliminate leap seconds, but no consensus has yet been reached to do so.

• International Bureau of Weights and Measures (10 October 2011). "Circular T". {{cite web}}: Invalid |ref=harv (help)

Jc3s5h (talk) 15:21, 16 October 2011 (UTC)

As I see it, my role here is to make suggestions, and perhaps to copy-edit, but not to add substantive content to the article, because if I did I would not be a neutral reviewer. So you should edit the article in any way you think is appropriate, and if I think there is a problem with it I'll say so. In this particular case, the version above looks fine to me. Looie496 (talk) 15:31, 16 October 2011 (UTC)

I have made changes substantially as I described above; I hope the review process can continue. Jc3s5h (talk) 12:33, 22 October 2011 (UTC)

Picking up review again, sorry for delay

• Uses: Is the bit about amateur radio important enough for this article? If so, a ref should be added to support the statement.

I think the use by amateur radio operators is relevant because they illustrate that UTC is used by a widely-distributed group of people with a wide range of educational background; not just by physicists, astronomers, and telecommunications engineers. It will also raise in readers mind the possibility that any geographically dispersed group might use UTC for scheduling. I added a citation, and reworded the article to mention scheduling, rather than logging. A general readership would be rightly uninterested in amateur radio logs. Jc3s5h (talk) 17:03, 24 October 2011 (UTC)

• Mechanism: I think this section should probably mention that the schedule of addition of leap seconds can't be predicted because of tectonic events that cause small but significant changes in the earth's rate of rotation.
• "UTC is derived from International Atomic Time..." This paragraph is very hard to understand. Can I suggest that you leave out the material about what happened before 1972, and simply describe how it works now? I don't think that alone will solve the problem, but at least it should help.
• "As with TAI, UTC is only known with the highest precision in retrospect." I don't understand what this sentence means.
• "Because of time dilation,..." This paragraph doesn't seem to belong in this section, since it describes how UTC is conveyed, not how it is calculated.
• Daylight savings: This doesn't really justify a separate section -- I think it could just be a paragraph added to the previous section.
• History "The signal frequency was changed less often." I don't understand this sentence.
• "In 1958, data was published linking the frequency for the caesium transition, newly established, with the ephemeris second." You should either explain what this means and why it is relevant, or delete it.

• It will take a little time to look into all these points, but I can answer one right off. "As with TAI, UTC is only known with the highest precision in retrospect" means that there are many atomic clocks being compared; each is an approximation to TAI or UTC. These comparisons are carried out by the International Bureau of Weights and Measures and published in Circular T, which is issued at one month intervals. So if one wanted the most accurate value of UTC possible, one would obtain the best real-time transmission from a time laboratory as is availible in one's locality, and record events according to that time scale. Then one would wait about a month and adjust the value by the amount in Circular T to get the best possible estimate of the time of the event.

For example, if the best time source available to someone was UTC(MKEH) in Budapest, and on that time scale an event occurred at 00:00:00.000 000 000 0 on Sept 30, 2011, one would see that UTC was 56436.6 ns slower than UTC(MKEH), so a better estimate of the time of the event would be 00:00:00.000 056 436 6 Jc3s5h (talk) 20:10, 28 October 2011 (UTC)

• I think "Daylight saving" should remain as a separate section, because it is one of the key points a person learning to convert between zone time and UTC must keep in mind. Jc3s5h (talk) 15:30, 29 October 2011 (UTC)

• A colloquium on the future of UTC was held, and the presentations have just become available. I intend to consider these papers before making further edits. Jc3s5h (talk) 19:50, 3 November 2011 (UTC)

Closing review

Due to the lack of progress I am going to fail this GA review. I think the article still needs significant work -- feel free to renominate it when it is ready. Looie496 (talk) 18:33, 14 November 2011 (UTC)

Citation in paren. seems wrong

It's a small thing but I've traced it as far as I can, have gotten in trouble before on sci. notations.

In the Rationale section, 2nd & 3rd paragraphs, there are two McCarthy/Seidelmann cites, 1st p. 54, 2nd p. 230. For some reason the 2nd shows up all in paren.; looked off to me.

I got that the 1st used {sfn...}, the second {harv...} formats; and here; but, sorry, have to leave it at that. Hopefully helpful somehow; or please explain for the uninf'd -- I'll check back. Thanks. Swliv (talk) 12:01, 11 April 2012 (UTC)

The sfn template has built-in <ref> elements, but if the citation is too complicated for that template, one must use the more flexible harvnb template. That one is like sfn in that there are no parentheses around it (or as the brits like to say, no brackets). But by accident the harv template was used, which does have parentheses. I fixed it. Jc3s5h (talk) 13:33, 11 April 2012 (UTC)

I can't imagine understanding it right now; maybe someday; maybe some other nimbler brain will learn from you; and it's fixed meantime; best Wiki tradition! Thank you. And someday I will learn what those brits call a "[". Swliv (talk) 01:34, 13 April 2012 (UTC)

Abbreviation?

"UTC" is not an abbreviation; it's technically an initialism. The word 'initialism' isn't used by many people though... would correcting this only serve to confuse visitors?

As per Abbreviation, "In strict analysis, abbreviations should not be confused with contractions or acronyms (including initialisms), with which they share some semantic and phonetic functions, though all three are connoted by the term "abbreviation" in loose parlance."

Jediknightbob (talk) 02:09, 14 October 2013 (UTC)

I believe that the term initialism would confuse many readers, as it is a rarely used term, especially by the lay public.Wzrd1 (talk) 02:28, 14 October 2013 (UTC)

Why not just call it an acronym? Although, technically, an acronym is also a type of abbreviation ;) Wolfbeast (talk) 10:53, 25 April 2014 (UTC)

I understand that when spoken, the letters of an acronym are considered to form a word; the individual letters are not spoken one at a time. Since UTC is spoken yew tee cee, it is not an acronym. Jc3s5h (talk) 12:51, 25 April 2014 (UTC)

Wikipedia use

I always understood that WP and the Wikimedia Foundation strongly prefer the use of UTC over GMT in their own applications. Yet, here's an error message I got today:

• If you report this error to the Wikimedia System Administrators, please include the details below.
• ....
• ....
• Error: 503, Service Unavailable at Sun, 23 Feb 2014 19:24:17 GMT. (my bolding).

What gives? -- Jack of Oz ^{[pleasantries]} 22:58, 23 February 2014 (UTC)

Suggestion: split out the explanation of variable earth time

I'd suggest that the entire explanation of the earth's rotation and how it impacts measured/agreed upon time in detail be split out into a separate Wikipedia article. It has nothing to do with UTC as a time zone/definition concept and makes this article too complicated to read for people looking for a definition and explanation of UTC. Wolfbeast (talk) 10:49, 25 April 2014 (UTC)

Variable earth rotation is the reason UTC must exist; if earth rotation were not variable, UTC, TT, UT1, and TAI would all collapse into a single time scale. Since it is the fundamantal reason UTC exists, it must not be omitted. Jc3s5h (talk) 12:54, 25 April 2014 (UTC)

Out of date?

" In the 41 years up to and including 2012, a total of 25 leap seconds have been added; the most recent was added on 30 June 2012." Is this still up to date, and if not can someone who knows where to find the info update it please? Richard75 (talk) 16:04, 11 June 2014 (UTC)

It's still up-to-date. I put the current offset in a separate section and referred to it from the lead so that when it changes it won't be necessary to update several parts of the article. I also provided the source. Jc3s5h (talk) 16:42, 11 June 2014 (UTC)

Good idea. Martin Hogbin (talk) 09:30, 8 February 2015 (UTC)

parsed to idiocy

on seeing an eclipse expressed in UTC I came here to discover what that even means and scanning the article I can NOT tell what freaking time is meant ... and so you have written this and parsed meaning to idiocy so that you can NOT tell what time is meant by expressions in UTC ...it appears to mean about Greenwich time corrected by approx. an hour ....re write all of this article into English thanks 47.18.43.166 (talk) 17:08, 19 March 2015 (UTC)real time sr

I'm trying to address this but I'm running into headwinds. This is all non - controversial. It is well - known that many countries use daylight saving time and the 0.9 second offset referred to in the lead is discussed in more detail later. As for the change in nomenclature, I'll add a reference.

References

Information introduced to lead

These changes introduce incorrect information.

• "Coordinated Universal Time (Template:Lang-fr), abbreviated as UTC, is the primary civil time standard by which the world regulates clocks and time. It is always, within 0.9 seconds, mean solar time at 0° longitude;"

No. As the cited author Bernard Guinot writes in the abstract of his paper, "The International Conference held in 1884 at Washington defined a universal time as the mean solar time at the Greenwich meridian (GMT). Now, the Universal Time, version UT1, is strictly defined as proportional to the angle of rotation of the Earth in space. In this evolution, the departure of UT1 from GMT does not exceed one or two seconds." The 0.9 potential difference between UT1 and UTC is in addition to the one or two seconds stated by Guinot.

The change to the article also stated "Greenwich Mean Time corresponds to UT1" which is clearly contrary to what Guinot stated.

Dennis McCarthy also indicates there are at least two possible modern meanings for GMT:

The nomenclature ‘GMT’ continues to cause confusion to this day because of its use in the United Kingdom as the name attached to the civil time and its common navigational usage to mean UT1, discussed below. With all of these identities it is not advisable to use the term GMT as a timescale for precise purposes without carefully defining its meaning. ["Evolution of timescales from astronomy to physical metrology" in Metrologica 48 (2011) p. S134].

Jc3s5h (talk) 17:28, 16 April 2015 (UTC)

What is the "angle of rotation of the Earth in space?" Is this an hour angle or something different? 156.61.250.250 (talk) 18:19, 16 April 2015 (UTC)

Universal Time article says "all of these versions of UT are based on Earth's rotation relative to distant celestial objects". It's always been this way. The sidereal time is calculated and then an adjustment made (knowing delta T) to get UT. 156.61.250.250 (talk) 18:44, 16 April 2015 (UTC)

In the context of the current definition of UT1 , the angle of rotation of the Earth in space is the Earth Rotation Angle. The glossary of the Astronomical Almanac defines that as:

Earth Rotation Angle (ERA):

the angle, θ, measured along the equator of the Celestial Intermediate Pole (CIP) between the direction of the Celestial Intermediate Origin (CIO) and the Terrestrial Intermediate Origin (TIO). It is a linear function of UT1; its time derivative is the Earth's angular velocity.

This introduces some other new 21st century nomenclature. The Celestial Intermediate Origin replaces the March equinox (in the sense of a direction in space, not as an event). It is part of a system (ICRF) that uses Very-long-baseline interferometry to measure radio sources outside the Milky Way galaxy. Because they are so far away, they seem to be motionless, so make a better reference framework than the bright stars that used to be used. The ICRF is designed to be aligned, as best they could, to the north pole and March Equinox at a certain point in time, J2000.0, in January 2000. The Terrestrial Intermediate Origin is 0° longitude in the International Terrestrial Reference Frame (ITRF), which replaces the meridian through the Airy transit circle which was used back when Greenwich Mean Time was first introduced. Zero degrees longitude in the ITRF system is very close to the system used by GPS receivers, and is around 100 meters away from the Airy transit circle.

So if we use the nomenclature informally, the angle of rotation of the Earth in space is the angle between the 0° meridian and where where the March equinox used to be in January 2000.

Also note that calculating UT1 is not quite as simple as converting the earth rotation angle from degrees to hours; it also has to be multiplied by a constant to allow for the average position of the Sun. Without the multiplication, Earth Rotation Angle is very similar to sidereal time. Jc3s5h (talk) 18:52, 16 April 2015 (UTC)

156.61.250.205 wrote "The sidereal time is calculated and then an adjustment made (knowing delta T) to get UT." Not anymore. The Earth Rotation Angle is calculated and multiplied by a constant to get UT1. The difference is that the Earth Rotation Angle is referenced to radio sources outside the Milky Way, and those radio sources have virtually no change in direction over long periods of time. Sidereal time is referenced to the equator and the March equinox, which is subject to precession and other changes. Jc3s5h (talk) 18:57, 16 April 2015 (UTC)

There's nothing new here. The Terrestrial Intermediate Origin is just a fancy name for what used to be called the ephemeris meridian. There was always a constant added to allow for the sun to move from the ephemeris meridian to the Greenwich meridian. The Earth Rotation Angle is also referenced to the March equinox, under its fancy name of Celestial Intermediate Origin.

According to the Astronomical Almanac:

UT universal time; counted from 0h at midnight: unit is mean solar day

prior to 1925 [Greenwich Mean Time] was reckoned, for astronomical purposes, from Greenwich mean noon (12h UT).

universal time (UT): a measure of time that conforms, within a close approximation, to the mean diurnal motion of the Sun and serves as the basis of all civil time - keeping. UT is formally defined by a mathematical formula as a function of sidereal time. Thus UT is determined from observations of the diurnal motions of the stars. The time - scale determined directly from such observations is designated UT0; it is slightly dependent on the place of observation. UT1 is derived by removing from UT0 the effect of the variation of the observer's meridian due to polar motion. When the designation UT is used in this volume, UT1 is implied.

Dennis McCarthy confirms this. There are inaccuracies within the tables - for example a decrement of 1.34 seconds in delta T has been applied to reconcile the moon's computed position to observation. None of this warrants an observation that GMT has differed from UT1 by two seconds. Guinot does not say this has ever happened. Unless there is within his paper a statement that an event has been timed by both GMT and UT1 and a discrepancy has been observed we can go with the Astronomical Almanac and McCarthy. 156.61.250.250 (talk) 08:45, 17 April 2015 (UTC)

Since I provided above a link to the latest edition of the glossary of the Astronomical Almanac, and since the purported quote from 156.61.250.250 contains a significantly different definition of Universal Time, I consider this to be a deliberate false statement and trolling. 156.61.250.250 this is your last warning! Any editing of the article based on this outdated information will cause me to seek dispute resolution from administrators.

The current definition of Universal Time in the Astronomical Almanac Online is

Universal Time (UT):

a generic reference to one of several time scales that approximate the mean diurnal motion of the Sun; loosely, mean solar time on the Greenwich meridian (previously referred to as Greenwich Mean Time). In current usage, UT refers either to a time scale called UT1 or to Coordinated Universal Time (UTC); in this volume, UT always refers to UT1. UT1 is formally defined by a mathematical expression that relates it to sidereal time. Thus, UT1 is observationally determined by the apparent diurnal motions of celestial bodies, and is affected by irregularities in the Earth's rate of rotation. UTC is an atomic time scale but is maintained within 0s.9 of UT1 by the introduction of 1-second steps when necessary. (See leap second.) [Hyperlink of leap second as in original text.]

Jc3s5h (talk) 12:39, 17 April 2015 (UTC), missing word added 14:55 UT.

I'm not sure what a "significantly definition of Universal Time" is, but I'm on my way to check out the latest edition of the Astronomical Almanac. 156.61.250.250 (talk) 12:50, 17 April 2015 (UTC)

I quoted the definition

UT [stated to be UT1] is formally defined by a mathematical formula as a function of sidereal time.

That means the same thing as

UT1 is formally defined by a mathematical expression that relates it to sidereal time.

You said (18:57, 16 April) that it was no longer related to sidereal time. I consider this to be a deliberate false statement and trolling. Jc3s5h this is your last warning!

We know the relationship with sidereal time has not changed because there have been no discontinuities in UT1 since inception. 156.61.250.250 (talk) 14:16, 17 April 2015 (UTC)

Significant differences between purported quote of Astronomical almanac provided by 156.61.250.250 (without giving the year page) and the current definition:

• The old "Thus UT is determined from observations of the diurnal motions of the stars" versus the new "Thus, UT1 is observationally determined by the apparent diurnal motions of celestial bodies..."; the most important celestial bodies currently used are extra-galactic radio sources, which are not necessarily stars.
• The old version makes no mention of UTC; the new version says UTC is one of the forms of time that falls under the UT umbrella.
• The old definition says "UT is formally defined by a mathematical formula as a function of sidereal time." The new definition says UT is "a generic reference to one of several time scales that approximate the mean diurnal motion of the Sun; loosely, mean solar time on the Greenwich meridian (previously referred to as Greenwich Mean Time)." The definition avoids saying that Greenwich Mean Time corresponds to any particular current time scale. The glossary does not contain a definition of Greenwich Mean Time.

• The new and old version generally agree that "UT1 is formally defined by a mathematical expression that relates it to sidereal time." However, the Explanatory Supplement to the Astronomical Almanac (Urban & Seidelmann, University Science Books, p. 233) states "The IAU (2003c) redefined UT1 with respect to the Earth Rotation Angle (ERA or Ω) beginning on 2003 January 1 as" and goes on to give the same defining equation that appears in the article. The same book, on page 81, does give expressions for the ratio between mean sidereal time and UT1 (and the inverse), but does not describe these as a definition.

Essentially the same information appears on page 15 of McCarthy and Seidelmann (2009, full bibliography entry in the article) with the additional information "The new equation is a linear relationship between the Earth Rotation Angle (Ω) and UT1, which continues the phase and rate of UT1" [Emphasis added]. So 156.61.250.250's claim "We know the relationship with sidereal time has not changed because there have been no discontinuities in UT1 since inception" is not correct; the constant terms in new definitions of UT1 were chosen to provide continuity with the previous definition. McCarthy and Seidelmann also, on the same page 15, describe a change in definition in 1984. Jc3s5h (talk) 15:40, 17 April 2015 (UTC)

You're really grasping at straws now. I confirmed when I examined the latest Astronomical Almanac that the information I gave you (apart from the modification in the definition of Universal Time, which is another way of saying the same thing) has not changed. Whether you're measuring the diurnal motion of "the stars" or "celestial bodies" they both reflect the rotation of the Earth, so the change in terminology doesn't affect it. You then claim that "the constant terms in new definitions of UT1 were chosen to provide continuity with the previous definition". That's exactly what I said, although I phrased it " ... the relationship with sidereal time has not changed". The claim "The definition avoids saying that Greenwich Mean Time corresponds to any particular current time scale" is correct but irrelevant. Since the astronomers do not use the term "Greenwich Mean Time" why should they waste ink and paper by making the obvious remark that Greenwich Mean Time is a current time scale? Since they do not use the term "Greenwich Mean Time" in the tables it's obvious that they will not define it in the glossary. You removed two perfectly good references from reliable sources and replaced them with nothing. The purpose of giving expressions for the relationship between mean sidereal time and UT1 is to define it. Again, making the obvious point that this is a definition is wasting ink and paper. 156.61.250.250 (talk) 18:31, 17 April 2015 (UTC)

The lead already says, ' Leap seconds are inserted as necessary to keep UTC within 0.9 second of universal time, UT1', so I do not see the need to add more detail about this subject to it. Better to find a way to address the complaint of one reader who was unable to understand what UTC was all about. The lead should give a clear overview of the subject, not discuss intricate detail; that should be done in the body of the article.

I don't much like the phrase "Leap seconds are inserted as necessary to keep UTC within 0.9 second of universal time, UT1" [emphasis added, the emphasized text was added by User:BillFlis at 10:20, 22 April 2014 UT]. The problem is that the emphasized phrase implies that UT1 is only one variety of UT; the phrase implies that UT1 is the one and only version of UT. But at the same time, we really don't want to get too much detail in the lead. Any suggestions on a simple, short way to rephrase this without making people think there is only one flavor of UT? Jc3s5h (talk) 22:09, 17 April 2015 (UTC)

Dispute accuracy of article

The claim in the lead of this article, introduced by User:156.61.250.250‎, that GMT corresponds to UT1, is not true.

As Bernard Guinot writes in the abstract of his paper, "The International Conference held in 1884 at Washington defined a universal time as the mean solar time at the Greenwich meridian (GMT). Now, the Universal Time, version UT1, is strictly defined as proportional to the angle of rotation of the Earth in space. In this evolution, the departure of UT1 from GMT does not exceed one or two seconds." Clearly there cannot be a departure between two time scales if they are the same. Jc3s5h (talk) 20:02, 18 April 2015 (UTC)

References

• Guinot, Bernard (August 2011). "Solar time, legal time, time in use". Metrologica. 48 (4): S181–185. Bibcode:2011Metro..48S.181G. doi:10.1088/0026-1394/48/4/S08. {{cite journal}}: Invalid |ref=harv (help)

You're citing the abstract of the paper, not the paper itself? Unless you remedy that I'll remove the tag. The only circumstance in which Guinot would be relevant would be if he had experimentally timed an event by both GMT and UTC1 and found a discrepancy. 156.61.250.250 (talk) 12:12, 19 April 2015 (UTC)

Answered at Talk:Greenwich Mean Time.

It does seem to me that GMT is no longer precisely defined. Is ther a current source that gives a precise definition of GMT, as the term is used today? Martin Hogbin (talk) 17:09, 19 April 2015 (UTC)

The main discussion has developed at Talk:Greenwich Mean Time. I suggest you move your question there. Jc3s5h (talk)

Edit by Fgnievinski

I think this edit by User:Fgnievinski would have been better if that editor had started with the lead as it was in this version from 27 April. The version I suggest does not contain the unqualified claim that "Greenwich Mean Time corresponds to UT1" which has been disproved with numerous reliable sources at Talk:Greenwich Mean Time#Dispute accuracy of History section. The version I suggest is also shorter and simpler, in the hopes of satisfying the complaint of User: 47.18.43.166 in the "#parsed to idiocy" section above.

Also, I don't agree with Fgnievinski's edit summary "UTC is not UT". An article in Metrologica (2011, v. 48 pp. S186–S194) by Seidelmann and Seago (beginning on p. S189) argues that so long as UTC retains leap seconds it is a version of universal time, but if leap seconds are discontinued (has been proposed) it will no longer be a form of universal time and the new version should be given a different name that does not contain the phrase "universal time". Jc3s5h (talk) 16:26, 21 May 2015 (UTC)

• The rationale was as follows. UTC is TAI kept within 0.9 s of UT. If leap seconds are dropped, it's TAI (modulo a constant). The lede to UTC was talking about all the flavors of UTx too soon. First define UTC, then fill in the details. Fgnievinski (talk) 22:59, 21 May 2015 (UTC)

I'm fine with the lead until we get to this part: "It is realized as an atomic timescale that has occasional leap seconds to remain synchronized (0.9 s tolerance) with the rotation of the Earth, as given measured by the (non-coordinated) Universal Time scale (UT)." The first problem is that the 0.9 s tolerance only applies to |UTC-UT1|. There is no such guarantee for |UTC-UT0|, |UTC-UT2|, or any other version of UT someone decides to measure (because UT is a generic term that applies just as much to the UT I measure in my back yard as any version measured by the IERS). The second problem is that UTC is widely considered to be a version of UT, and so we're saying we insert leap seconds to keep UTC synchronized with itself. I'd be happy if we changed it as follows:

It is realized as an atomic timescale that has occasional leap seconds to remain synchronized (0.9 s tolerance) with UT1, a timescale directly related to the rotation of the Earth., as given measured by the (non-coordinated) Universal Time scale (UT). In its turn, UT has been split into three closely related versions, UT0, UT1, and UT2, which all tick the same to within fifty milliseconds. Greenwich Mean Time (GMT) corresponds to UT1.

Agreed. Fgnievinski (talk) 08:23, 22 May 2015 (UTC)

We could then also delete this:Leap seconds are inserted as necessary to keep UTC within 0.9 second of universal time, UT1.^[6] Jc3s5h (talk) 00:54, 22 May 2015 (UTC)

Disagreed. Fgnievinski (talk) 08:23, 22 May 2015 (UTC)

India is not correctly showed in the World MAP

Hello,

 I am an Indian National. I was reading the page when I found that in the MAP India is not shown properly. I request Wikipedia to correct the MAP ASAP. This is not acceptable at any cost, as an Indian national I don't appreciate this type of offense spatially from Wikipedia.

Regards. — Preceding unsigned comment added by Saishdhuri (talk • contribs) 11:15, 28 August 2015 (UTC)

The map is located at [4]. I suggest you use the talk page there to request a correction. It would also be helpful if you could provide a reliable source that gives the correct information. Jc3s5h (talk) 13:18, 28 August 2015 (UTC)

What is the authoritative definition of UTC?

Hello.

I have searched for a document which is the official definition of UTC but I have not found anything satisfactory. The article mentions the International Telecommunications Union Recommendation TF.460-6. I have consulted that document, and it only includes a very rough description of UTC; it does not looks like an authoritative definition. This document leaves almost all important technical details. It states that UTC is defined through TAI as a time scale based on the geoid, but does not states which geoid (There are several definitions). It does not states at all how UTC is realized. It does not mentions that it is realized as an average of national metrology institutes nor what algorithm is used to compute that average, nor the protocols that national metrology institutes are expected to follow regarding the realization of UTC and TAI. It does not states the procedures used to determine leap second insertion. Where can I find all of this information?.

Maybe most of these details are found in the TAI documentation. I searched for the TAI documentation but did not find anything relevant. I searched too in the BIPM site. It contains information about UTC and TAI, but it contains mostly the database of the offsets that relate those timescales (UTC and TAI) to the realizations in national metrology institutes, but that is not the information I am looking for.

I think that this information should be in the article. I would appreciate if somebody can give me a pointer regarding where to find that information or expand the article to include it. Thanks. Mario Castelán Castro (talk) 17:26, 5 September 2015 (UTC).

It is not necessary to specify which geoid is used for TAI because, conceptually, there is only one geoid, 'the equipotential surface that would coincide with the mean ocean surface of the Earth if the oceans and atmosphere were in equilibrium, at rest relative to the rotating Earth'. The various geoids that you refer to are the different mathematical models used to represent the actual geoid, which is a property of the Earth itself. Martin Hogbin (talk) 18:32, 28 November 2015 (UTC)

Let's stop knocking Greenwich Mean Time

I endorse what 176.63 says, but there's actually more to it. Occam's razor, the simplest system is always the best. In Greenwich time, the seconds are all the same length and the clock keeps pace with the sun. UTC is so complicated that no clock is capable of displaying it. This information is contained in a discussion I noticed at the Science reference desk. I've copied the thread below and highlighted the relevant passage:

No, you have misunderstood. The 4 minutes per day add up to one full revolution per year, which is accounted for by the revolution of the earth round the sun. A day is the average time taken from one noon to the next (see Equation of time for why this isn't constant), and the only correction necessary is the occasional leap-second. The leap year is to keep the seasons from drifting from their usual dates (see Gregorian Calendar). Dbfirs 08:14, 16 December 2015 (UTC)

Some of Dbfirs' disingenuities have been corrected in "Sunrise and sunset" above. A day is the average time taken from one noon to the next as he says but this average is the "mean solar day" and no further correction is required for "leap seconds". Joe Public (i.e. the person to whom this resource is directed) does not use leap seconds. The only people who use leap seconds are scientists who need units of measurement which are not constantly changing in length, and have therefore devised an artificial "SI second" which is the length of the mean solar second as it was back in 1820. 89.240.30.73 (talk) 10:17, 16 December 2015 (UTC)

Hold the insults! I was simplifying to help the OP, but here in the UK, we use the SI second. It is broadcast by the Greenwich Time Signal, and an extra "pip" signifies the leap second for rare minutes that have 61 seconds. Many other countries use the same system. Dbfirs 19:30, 16 December 2015 (UTC)

[Discussion on the length of the sidereal day]

To clear up a possible misconception, the use of leap seconds to convert the grand total of atomic seconds accumulated since the system was devised about 1960 to the familiar hours, minutes and seconds recorded by our clocks is nothing to do with the occasional 29 February which adjusts for the difference between a fixed 365 - day year and the actual time between successive equinoxes. That four minutes per day you have to allow for if you are using the stars to tell the time when the sun is below the horizon actually amounts to two hours per day (24 hours over a year), which is why if you are using the star charts printed in newspapers to do some stargazing you have to correct to allow for the fact that the stars rise two hours earlier each month. 86.151.51.24 (talk) 16:43, 16 December 2015 (UTC)

A day is actually 24 hours and 1 millisecond near this decade and since OP wanted the "non-fictional day" then it has to be said. This is not unit-mixing, noone uses the 1/86400th of a real solar day second anymore. The 24 hour day isn't any more "real" than the 365 day year. If we kept using the fictional units then the seasons would be 1 month wrong in only a century and change and the time would be 8 hours off about 3 or 4 millenia ago or a similar distance in the future. A 24 hour day is clearly close enough most of the time, though. Sagittarian Milky Way (talk) 17:15, 16 December 2015 (UTC)

It seems clear 86 is using some weird definition of a second to be 1/86400 of a solar day. (I.E. The length of a second varies.) While 86 is free to use whatever weird definitions they want to, they shouldn't confuse the issue by pretending their definition is normal. It's not. The second which most people i.e. "Joe Public" use, including the UK government and people (and not just the BBC) is the SI one. On other words, this definition is not some weird definition that ony scientists use, it's the definition that nearly everyone uses. It is for example what nearly all modern clock (with the except of sundials) etc aim for. While I believe it's fairly unlikely a clock you're using has the precision that it makes a difference (although I'm not an expert on how long the length of a solar day varies), this doesn't mean such confusion is acceptable. Nil Einne (talk) 19:46, 16 December 2015 (UTC)

I don't think Nil Einne lives in Britain. There was a discussion a few days ago about what all those books are on the table of the House of Commons. They are law books. If you look up Halsbury's Laws or Halsbury's Statutes (which is basically what the clerks do) title "Time" you will see that this country has been on Greenwich Mean Time since about 1880. Now a mean time scale doesn't have a place for leap seconds, so there aren't any (don't need 'em). Everybody uses Greenwich Mean Time because that's the law of the land. Saying they use leap seconds implies that once every eighteen months or thereabouts the whole population rushes about adjusting its timepieces by one second and if you actually live in this country you will see that they don't. There is a mechanism for disseminating time which does involve leap seconds - the Greenwich Time Signal - but if you asked the BBC if they disseminate the legal time they will say "no, we don't." If you ask them why they don't disseminate the legal time they will say "just after we insert a leap second the time we disseminate is a fraction of a second behind the legal time, and just before we insert a leap second the time we disseminate is a fraction of a second ahead of the legal time. Clocks are made to run to mean solar time and the legal time is in line with what is displayed by clocks."

Some people are making a big issue of this and saying that there is a huge discrepancy between BBC time and legal time but this is simply not the case. Every century the number of days in a year reduces by about 1/2 - second. There are roughly 30,000,000 seconds in a year so after 100 years the length of the second increases by a factor of 1 in sixty million. After one year the second has grown by just one part in 600,000,000,000. Why are we getting het up about this? 86.151.51.24 (talk) 21:43, 16 December 2015 (UTC)

I agree that leap seconds are not a big issue since the discrepancy between UTC and UT1 is always less than one second. I disagree that clocks are made to run to mean solar time. They are synchronised to UTC. Perhaps you are thinking of sun dials? By the way, UTC is not just BBC time, it is understood world-wide, and often (incorrectly in your view) called GMT. UTC "is the primary time standard by which the world regulates clocks and time". I agree that GMT is taken to be UT1 for navigational purposes, but GMT is often considered identical to UTC for civil purposes, despite what old laws said. Why are we arguing over a fraction of a second? Dbfirs 23:01, 16 December 2015 (UTC)

I don't get this. If there is an EC directive relating to "apples" and a shop sells "apples", people coming in wanting to buy will ask for "apples". Nobody is going to call them pears. Mean time (without leap seconds) is as different from atomic time (with leap seconds) as apples are from pears. I note the weasel words creeping in:

"old laws".

The law against killing dates back to Biblical times. It doesn't matter how old it is - if you break it you go to jail.

"Nearly all modern clock".

How is my bedside quartz alarm clock going to assimilate a leap second? Or my wind - up alarm clock, come to that. Or my Apple watch, mobile phone or computer? Computers aren't programmed to accept a leap second. If you want them to do so you have to patch them, but nobody bothers. People adjust their clocks and watches primarily from their mobile phones, or a timecheck from a radio announcer, or a platform clock or (in London) the clock on a bus. If you look at these platform clocks you will see that the seconds displays are not synchronised, so the suggestion that they are influenced by leap seconds is ludicrous.

As for

UTC"is the primary standard by which the world regulates clocks and time"

that unsourced claim was removed from the article with the following result:

• Another editor edit - warred it back in (with no source)
• The Arbitration Committee protected the article for a very long time.

So what price "Wikipedia:The free encyclopaedia that anyone can edit" and "all contributions must be sourced"? 81.151.101.74 (talk) 14:09, 17 December 2015 (UTC)

... Do you really have only old wind-up clocks and non-radio quartz clocks in your house? Most modern mobile phones have a GPS receiver and so pick up GPS time. They then make the correction to UTC by subtracting 17 seconds. That's a fourth source of UTC to add to my three above. Fifthly, my computer seems to pick up UTC by automatically synchronising with an Internet Time server. It's only eight years old, so I suppose this is "modern". It seems to me that UTC is becoming more common on modern equipment. Dbfirs 16:07, 17 December 2015 (UTC)

It doesn't matter what the exposure to UTC is. Digital radio is new but receivers are incapable of receiving an accurate time signal. Your argument is based on the sole premise that modern clocks are manufactured to keep atomic time as opposed to mean solar time. Given that the common quartz unit is accurate to ten seconds a month, what's the basis of that claim? The typical non - mechanical clock/watch does not contain a radio receiver. Do you know how much more expensive a radio - controlled clock is compared to one with a standard motor? The typical non - battery timepiece has an electric motor which drives the hands according to the frequency of the current passing through it. Such a clock is incapable of adjusting for leap seconds. That is why the master clocks of the electricity companies show mean time, not atomic time.

Adjusting GPS time to UTC is a joke. The time between leap seconds is so long that the processors overflow and produce spurious readings. The companies that provide time signals to internet - connected devices do not send leap seconds because the devices cannot handle them. The reality is that most, if not all the timepieces in homes and offices show GMT/BST and when leap seconds come along no effort is made to adjust them. 81.151.101.74 (talk) 17:01, 17 December 2015 (UTC)

On that last point, that's only because your average person doesn't care about a second here or there. But if the leap seconds were to accumulate to 60 and thus into the next minute, rest assured that plenty of us would adjust our clocks so as to not miss the bus or the start of our favourite TV program. Akld guy (talk) 18:32, 17 December 2015 (UTC)

You seem to misunderstand how these things are done. Mains synchronous electric clocks are not accurately adjusted to any particular time because the frequency varies according to load. The distribution companies do try to keep the average frequency to 50 Hz (in the UK) so that a synchronous electric clock matches their reference clock as closely as possible (usually within 30 seconds). The reference clock is most probably a radio clock (UTC) rather than a quartz oscillator clock that is adjusted to UT1, since this is much simpler than trying to adjust the oscillator to an exact fraction of a day. Do you really have no modern timepieces in your home? The companies that provide time signals to the internet send the time (UTC), with SI seconds, and include leap seconds when necessary. Radio clocks have come down in price remarkably over the past few years. Mobile phones with GPS receive GPS time which uses the SI second. It is possible that there is a delay (seconds, hours, days, or until the next software update?) before a leap-second is implemented since the adjustment is within the phone. I agree that if shops and offices use older timepieces, then they probably don't adjust them to the second, but if leap seconds become more common (as Akld guy says above), then they will eventually need to be adjusted by hand to take account of these seconds, or the regulator adjusted to the new UT1 if exact time is important. Dbfirs 20:47, 17 December 2015 (UTC)

So the mobile phones don't show UTC because you need a gizmo within the phone to do it, which may work but probably won't. And anyway, they don't show UTC because the display does not include seconds. So there's no exposure to UTC as opposed to GMT/BST. Same remark applies to radio - controlled clocks, which don't display seconds either. So far, the exposure of the general population to UTC is zero. Now let's consider the Greenwich Time Signal. UTC is an Alice - in - Wonderland type system in which you can ask the March Hare the time, he can pull out his pocketwatch and look at it and he won't be able to tell you. This is because there is no clock in existence that shows UTC. The times shown by all the clocks are analysed and, several months later, somebody makes an arbitrary decision as to what the time actually was. Compare this fiasco with the eminently sensible system set up by our legislators which is well supported:

• Platform clocks provide GMT/BST to the exact second. No messing with leap seconds - if you watch them at the time a leap second is supposed to be inserted nothing happens. So Dbfirs and Akld guy have it the wrong way round. Trains are sent off according to the time on the platform clock. If you let the leaps accumulate to sixty and then move your watch back you will miss your train.

• Electric clocks. The inaccuracy of the correction system (adjusting the oscillations) does not permit the clock to distinguish between GMT/BST and UTC.

• A countrywide network of public clocks set to GMT/BST.

For example:

• Big Ben. Seen and heard over a wide area of Central London and regularly broadcast by the BBC.

• Local chiming clocks. Example: the clock on top of Lambeth Town Hall, seen and heard across the town centre. Also by millions as they transit between the overground station and Brixton tube (subway) station, which is where the underground system begins.

• In the financial district: The clocks in the plaza outside Canary Wharf station have a sweep second hand. You can bet your bottom dollar that this doesn't suddenly jerk when a leap second is added.

• The clocks on London buses. The main display doesn't show seconds but the display on the closed circuit television screen immediately beneath it does.

If all else fails, Britons can use the common sense for which they are renowned. Listening to the Greenwich Time signal and making a split - second adjustment to compensate for the time since the last leap second gives the legal time.

All these issues are notable. We now have a new Arbitration Committee, one that shows signs of having some sense. Someone should contact them and ask them to look at the matter again. 86.151.51.8 (talk) 13:19, 18 December 2015 (UTC)

The ultimate base source is GMT. It has just been confirmed that at least for the next eight years UTC will be fudged to be as close as possible to invariant GMT. Of course, it's not invariant in the true sense of the word, but having varied by a mere one part in three million over the past two thousand years that's as near as makes no difference. 213.107.94.232 (talk) 21:01, 20 December 2015 (UTC)

213.107.94.232, I am proud to be British and happen to live yards from the Greenwich meridian and I am a memeber of the British Sundial Society but you are wrong and seem to misunderstand what UTC is and why GMT now has no clearly defined scientific meaning. The time used throught the world, including the UK, and as propagated by the BBC time pips (note that on all digital chanels these are delayed a couple of seconds due to the decoding delay, but AM and FM are OK) and by the British national high-accuracy timekeeping service Time from NPL, and all other UK accurate timekeeping services is UTC, including the leap seconds. The astronomical time at Greenwhich is never propaged to the public as 'the time'.

It is true that, in the UK and some other coutries, GMT is used losely as a synonym for UTC but there is no longer any genarlly accepted, precise, and clearly defined meaning to the term GMT. Although international politics has played some part in world timekeeping (the name UTC for example) the reason that the original GMT is no longer used is that it no longer precise and accurate enough for many modern timekeeping purposes. Astronomical times, based on the Greenwhich meridian, are still used for some scientific purposes but the time used by nearly everyone for all normal purposes is UTC.

I have to say that I do not know whether British law still refers to GMT and whether the precise meaning of this has tested in the courts but I would guess that if it were the meaning given today to GMT in English law would be UTC. Martin Hogbin (talk) 11:54, 4 January 2016 (UTC)

Sundials are of interest to amateur astronomers. Professional astronomers are meticulous in their definitions and measurements (William Herschel was sacked by Nevil Maskelyne, the Astronomer Royal, because he thought his reactions were too slow). Ninety years ago, when Greenwich Mean Time started to be measured from midnight instead of noon, the name Universal Time was introduced to avoid confusion. The tick rate was exactly the same, and the term Greenwich Mean Time was retained in communications to the general public to avoid confusion. Nothing has changed. Specifically, Greenwich Mean Time remains astronomical time based on the Greenwich meridian, which astronomers refer to as "UT1" amongst themselves. This is a very precise timescale derived from astronomical observations.

I can confirm that British law still refers to "Greenwich mean time" and there is no reason to suppose that judges would quibble with the astronomers' definition of it.

As I highlight above, the general public will never have access to UTC. It also has very limited access to the approximation to it which is the Greenwich Time signal broadcast by the BBC. Radio controlled clocks do not show seconds and the government has signalled that it wants to switch off the AM/FM radio signal. When this happens the public will have no access to UTC time signals. 188.222.58.239 (talk) 12:23, 4 January 2016 (UTC)

Many radio controlled clocks, including my own watch, have second hands and therefore show UTC, which is propagated to a high precision by the Time from NPL service. UTC is also easily obtained from internet time servers and can also easily be obtained from GPS time, which is very accurate and freely available. These are the sources, along with BBC time signals, that are used to set public clocks. How do you think that they are set? UTC is also used by stock and currency exchanges worldwide, including the UK.

UT1 is indeed a well-defined and accurate time but is UT1 made available and used by the public?

How do you think that GMT is defined? How would I find out what the time is in GMT? Martin Hogbin (talk) 15:38, 4 January 2016 (UTC)

If even the metrology laboratories don't know what the UTC time is until they are informed several months later it's a sure bet that the general public doesn't know either. Most of the general public get their time by looking at their quartz/wind-up clocks or watches which tick mean solar seconds, or listening out for the chimes of public clocks (such as Big Ben) which also run to mean solar time. They are incapable of recognising leap seconds. If they're not checking their watches they'll probably catch a time check from a radio announcer or be viewing the time displays on mobile phones, which don't include seconds. Radio - controlled clocks and watches with second hands do not show UTC - they show a guesstimate of it. Internet time servers do not show even an approximation to UTC because they also are incapable of handling a leap - second - Google, for example, uses a "leap smear". GPS time is atomic time with an offset, so suffers from the same limitations as UTC. GMT is not so much defined as measured, using the positions of celestial objects. 188.222.58.239 (talk) 16:51, 4 January 2016 (UTC)

Unfortunately I, along with most other people, do not have the means to accurately measure the position of celestial objects and I have no way of knowing UT1.

UTC is what is transmitted by Britain's national standards laboratory, the NPL. The accuracy of a clock set by this depends on the clock itself and the way that it uses the time signal. The clock has no possible way of knowing what UT1 is.

The most accurate time that most people can get is GPS time, which aways differs fron UTC by a well known number of whole seconds.

You have still not answered my question. How do I get UT1? Martin Hogbin (talk) 17:08, 4 January 2016 (UTC)

There is an acronym in computing, GIGO, which means "garbage in, garbage out". The accuracy of a clock is dependent on the actions of the person setting it, or in the case of the radio - controlled clock its interpretation of the time signal. The person who regulates the time signal has no way of knowing what the UTC is until several months later, and therefore the radio - controlled clock does not disseminate UTC. A quartz/windup clock or watch will, within the limits of its accuracy, tell mean solar time (Greenwich Mean Time). Astronomers disseminate the offset between GMT and UTC. Hope this answers your query. 188.222.58.239 (talk) 17:37, 4 January 2016 (UTC)

You seem to be referring to the nanosecond scale corrections retrospctively made to UTC by 'circular T' and trying compare these to the timekeeping errors of a typical clock or watch. The timekeeping errors of a high quality clock or watch will be vastly greater.

No, you have not answered my questions. Please tell me:

Where can I find a definition of GMT that meets current timekeeping standards, that is to say defined within a few tens of nanoseconds?

How can I as get the precise value (to sub-microsecond precision) of whatever you claim GMT to mean?

As I have already pointed out, a GPS receiver will get you (if you can subtract whole numbers) UTC to well under a microsecond. So if you cannot tell me how to do this with GMT there is no real contest and no point continuing this discussion. Martin Hogbin (talk) 18:01, 5 January 2016 (UTC)

"Current timekeeping standards". Why would the man in the street want to know "the time" (whether GMT/BST or UTC) to nanosecond accuracy? Granted that the Greenwich Time Signal gives the time to nanosecond accuracy, that accuracy is lost when the user sets a quartz/windup watch by hand. As said watch keeps GMT/BST, for all practical purposes the Greenwich Time Signal gives mean solar time (GMT/BST). As said watch is only accurate to ten seconds a month the nanoseconds difference between GMT/BST and UTC is of no practical importance. You can determine the local mean solar time by looking at a sundial and applying the equation of time. If you apply a longitude offset you have GMT/BST. It won't be very accurate, but astronomers use the same principles to establish GMT with perfect accuracy. If you yourself want GMT/BST accurate to nanoseconds you can either listen to Big Ben or make use of the astronomers' equivalent of 'circular T' which gives, to nanoseconds, the offset between GMT/BST and UTC. There is a legal maxim, lex non curat de minimis. A Bill was introduced into Parliament to ditch GMT/BST in favour of UTC. It failed. If you feel strongly about the matter you would be better off lobbying your Member of Parliament than discussing it with anonymous Wikipedia editors. 188.222.58.239 (talk) 19:32, 5 January 2016 (UTC)

I am finding it increasingly difficult to determine the point that you are making. You seem to be muddling up several things. You mentioned that UTC is only known months after the event. Yes, that is true if you are interested in nanosecond accuracy but it seems that is not if interest to you. Anyone can easily get UTC to a sub microsecond accuracy at any time.

In practice all clocks and watches will be set to UTC simply because all the time signals that the setter might use such as the BBC time pips, the time from the BT telephone service, Time from NPL, or GPS (with a well-known subtraction) time will all be UTC. As explained above, the seconds on any clock will be SI seconds because all time and frequency devices used to calibrate clock and the crystals and other components will be traceable to a national standards, which will use the SI second. Do you dispute any of this? If so, what?

Of course the time actually shown on a clock will be how-good-the-clock-is-and-how-and-when-it-was-set time but the intention will allways be to set it to UTC because that is the time you get from the available services, and it will always be designed to tick in SI seconds because that is what the standards are based on.

Regarding the bill that you mentioned can you give me details please, I would like to check it out. Martin Hogbin (talk) 17:14, 6 January 2016 (UTC)

There are no sources for any of this. It is pure speculation. You cannot build into a quartz/windup clock or watch the ability to handle leap seconds. For accuracy, therefore, it is better to design it to run on mean solar time. If you can provide a source for your claim, fine. In the meantime, I'll work up a text which will include some of the information which Mario Castelan Castro asked to be added. For a discussion of the legislative aspect see Talk:Greenwich Mean Time#House of Lords debate. 188.222.58.239 (talk) 15:28, 7 January 2016 (UTC)

I see no sign of the bill being thrown out but it was very limited in scope anyway, as it says 'Most statutes do not specify a timescale, but one exception is the Summer Time Act 1972'.

I do not need sources, this is the talk page, however everything I say is well known. If you want to discuss this subject any more I suggest we do it in user space, mine or yours. Martin Hogbin (talk) 18:52, 7 January 2016 (UTC)

The sole purpose of the talk page is to discuss improvements to the article. For that reason all claims you make have to be sourced, and those sources have to be somewhere editors can evaluate them. So discussing this on user talk pages is not a good idea. Your proposition is that there was a change in manufacturing methods of quartz/windup clocks and watches to accommodate them to UTC. Bearing in mind that leap seconds are added at irregular intervals and the only method of adjusting an alarm clock is the lever on the back which makes it run faster or slower how was this change effected? In the case of pendulum clocks, how much was lopped off the length of the pendulum when this alleged change was made?

As for the fate of the various bills introduced into Parliament in an attempt to foist UTC on the British public, you will find links at Talk:Greenwich Mean Time#Dispute acccuracy of History section. 188.222.58.239 (talk) 19:51, 7 January 2016 (UTC)