Talk:Coordinated Universal Time

GMT is avoided in careful writing?

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)

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)

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)

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)

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. . 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)

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.