Re: [LEAPSECS] prep for WRC 23
On 2023-12-22 22:35, Seaman, Robert Lewis - (rseaman) wrote: E pur si muove Natura non facit saltus -- why should UTC? UTC may no longer serve as a kind of solar time (after 2026 or 2035, or somebody said 2040 the other day), but civil time will continue to have engineering requirements tracing to both solar and atomic time scales. As far as required by local civil time scales, continuous UTC can stand for solar time (UT1 up to 15 min) for several centuries. Current positioning applications on the surface of the Earth cannot be performed without knowledge of UT1 up several milliseconds. These applications work in wrist watches today and they do not need nor exploit the leap seconds of UTC. What type of engineering requirements can be satisfied with the current UTC with leap seconds that fail when UTC becomes continuous? The Russians have required more time for updates in satellite software, they have not said that it cannot be done. Michael Deckers. ___ LEAPSECS mailing list LEAPSECS@leapsecond.com https://pairlist6.pair.net/mailman/listinfo/leapsecs
Re: [LEAPSECS] prep for WRC 23
On 2023-12-21 18:22, Poul-Henning Kamp wrote: My Tl;dr version of the resolution is: . Please keep DUT1 less than 100 seconds. I do not read that from the text. The original [page 399] says: " recognizing . k) that the maximum value for the difference between UT1 and UTC should be no less than 100 seconds, taking into account the constraints of the technological systems expected to be used to disseminate this value, " This seems to say that on the contrary, at least 3 decimal digits will be needed for the integral part of the approximation of |UT1 - UTC| in time signals that include an estimate of UT1 - UTC after 2035. Anyway, I do not think that the CIPM will recommend a maximal value of 100 s for |UT1 - UTC| because there is a slim chance that this will not be enough until 2135. On the other hand, ITU-R might come up with a scheme where the approximation of (UT1 - UTC) is only given modulo 100 s in radio signals, so that 2 digits would suffice for the integral part. Michael Deckers. ___ LEAPSECS mailing list LEAPSECS@leapsecond.com https://pairlist6.pair.net/mailman/listinfo/leapsecs
Re: [LEAPSECS] prep for WRC 23
On 2023-11-26 06:59, Steve Allen wrote: This week began the meeting of ITU-R WRC 23. ..and it ended on 2023-12-15. The ITU-R news channel [https://www.itu.int/en/mediacentre/Pages/PR-2023-12-15-WRC23-closing-ceremony.aspx] mentions a "key outcome"of WRC23: " ∙ Endorsement of the decision by the International Bureau of Weights and Measures (BIPM) to adopt Coordinated Universal Time (UTC) as the de facto time standard by 2035, with the possibility to extend the deadline to 2040 in cases where existing equipment cannot be replaced earlier. " It is unclear what this is intended to mean: endorsement of the CGPM (not BIPM) decision implies that UTC will be continuous (not "de facto standard") from 2035 onward, so what "deadline" may still be shifted to 2040? ITU-R continue their (and CCIR's) tradition of murky statements about UTC. Michael Deckers. ___ LEAPSECS mailing list LEAPSECS@leapsecond.com https://pairlist6.pair.net/mailman/listinfo/leapsecs
Re: [LEAPSECS] prep for WRC 23
On 2023-11-26 06:59, Steve Allen wrote: This week began the meeting of ITU-R WRC 23. After closure of work related to resolution 655 of WRC 2015 at the World Radio Conference 2023 in Dubai, the BIPM has added the web page [https://www.bipm.org/en/-/2023-12-12-wrc-dubai] One particular technical aspect is mentioned on this page: some lead time is required to adapt the (few) radio time signals that disseminate the approximation DUT1 of UT1 - UTC to the larger range of |UT1 - UTC| that will be allowed after 2035. This is worded quite implicitly, so that one cannot be sure ∙ whether there will still be an official approximation of of UT1 - UTC after 2035, similar to the one currently produced by the IERS with Bulletin D; ∙ if, yes, what the resolution and the range of that approximation would be. The CIPM will certainly try to avoid to introduce an official approximation of UT1 - UTC with a resolution of whole seconds and whose values change only at the end of a UTC month. Michael Deckers. ___ LEAPSECS mailing list LEAPSECS@leapsecond.com https://pairlist6.pair.net/mailman/listinfo/leapsecs
Re: [LEAPSECS] prep for WRC 23
On 2023-11-26 17:38, Michael Deckers wrote: online at [https://www.itu.int/oth/R0A0807/en] when he meant: nline at [https://www.itu.int/pub/publications.aspx?lang=en=R-REP-TF.2511-2022] Michael Deckers. ___ LEAPSECS mailing list LEAPSECS@leapsecond.com https://pairlist6.pair.net/mailman/listinfo/leapsecs
Re: [LEAPSECS] prep for WRC 23
On 2023-11-26 06:59, Steve Allen wrote: This week began the meeting of ITU-R WRC 23. One preparation for this meeting was a document issued early this year The future of Coordinated Universal Time https://www.itu.int/en/itunews/Documents/2023/2023-02/2023_ITUNews02-en.pdf This looks at the use of time in several arenas, many of which would like UTC to stop having leap seconds. The result of resolution 655 of WRC 2015 is ITU-R document TF 2511-0, online at [https://www.itu.int/oth/R0A0807/en]. It gives an overview of how users of UTC are affected by the current (discontinuous) form of UTC and by the proposed continuous form; it was written before the CGPM decision of 2022 on the change in UTC. Many also allow that keeping agreement with the earth in the long run is necessary, and that they have no idea how to do that. A working group of the CCTF has since been charged with developing (among other, more important things) a proposal for measures to constrain |UT1 - UTC| after the new bound is reached. Since such measures would only apply in over 100 years, when the requirements for a reference time scale cannot reliably be predicted, anything beyond a necessarily incomplete list of possibilities (a discontinuous step, change in the rate d(UTC)/d(TT), using predictions of UT1 - UTC, etc) would be wasted effort. Michael Deckers. ___ LEAPSECS mailing list LEAPSECS@leapsecond.com https://pairlist6.pair.net/mailman/listinfo/leapsecs
Re: [LEAPSECS] negative leap second milestone
On 2023-08-26 17:58, John Sauter via LEAPSECS wrote: According to the IERS, today, for the first time since the establishment of the modern definition of UTC in 1973, the quantity UT1-UTC crosses zero while increasing. If this continues we will have a negative leap second, probably some time in the 2030s. https://datacenter.iers.org/data/html/bulletina-xxxvi-034.html I do not think that a negative leap second is coming up so soon with the latest predictions of the IERS. At the currently predicted LOD of -0.08 ms/d, it takes 24 years for UT1 - UTC to increase from 0.0 s to 0.7 s; and by then, leap seconds will have been "suspended". Michael Deckers. ___ LEAPSECS mailing list LEAPSECS@leapsecond.com https://pairlist6.pair.net/mailman/listinfo/leapsecs
Re: [LEAPSECS] speeding up again?
On 2023-06-20 12:21, Michael Deckers via LEAPSECS referenced: [https://link.springer.com/chapter/10.1007/1345_2022_167] which was already cited by Richard Langley on 2023-06-17. Sorry for the duplication. MD. ___ LEAPSECS mailing list LEAPSECS@leapsecond.com https://pairlist6.pair.net/mailman/listinfo/leapsecs
Re: [LEAPSECS] speeding up again?
On 2023-06-16 01:48, Tom Van Baak wrote about the relationship of LOD with El Niño: Attached is an LOD plot I made a while ago. A random web google link says "The five strongest El Niño events since 1950 were in the winters of 1957-58, 1965-66, 1972-73, 1982-83 and 1997-98". To my eyeball I just don't see that in the historical LOD plot. The relationship between LOD and the El Niño events is not so easy to spot, see eg [https://link.springer.com/chapter/10.1007/1345_2022_167] Michael Deckers. ___ LEAPSECS mailing list LEAPSECS@leapsecond.com https://pairlist6.pair.net/mailman/listinfo/leapsecs
Re: [LEAPSECS] speeding up again?
On 2023-06-16 13:46, jimlux wrote: 10 terasquare meters You mean 10 square megameters = 10 Mm²; SI suffixes apply to named units, not to its powers. Michael Deckers. ___ LEAPSECS mailing list LEAPSECS@leapsecond.com https://pairlist6.pair.net/mailman/listinfo/leapsecs
Re: [LEAPSECS] Inside GNSS published an update of my CGSIC talk
On 2023-03-20 19:36, Michael Deckers wrote: This seems to be lenient enough to allow for not scheduling a negative leap second even in the case that the difference (UT1 - UTC) should go a bit below -1 s before 2035. when he meant "a bit above +1 s" MD. ___ LEAPSECS mailing list LEAPSECS@leapsecond.com https://pairlist6.pair.net/mailman/listinfo/leapsecs
Re: [LEAPSECS] Inside GNSS published an update of my CGSIC talk
On 2023-03-20 07:54, Jürgen Appel via LEAPSECS wrote: In your Conclusion, you say "the CGPM resolution also stipulates that no change to current practices can occur before 2035." This is not how I read read the CGPM document on the BIPM website: "The General Conference on Weights and Measures (CGPM), at its 27th meeting [...] decides that the maximum value for the difference (UT1-UTC) will be increased in, or before, 2035," So in case the negative leap seconds become a real threat, according to my interpretation is is an option to increase the tolerance value earlier than 2035 to avoid trying out negative leap seconds a last and first time. Can someone confirm my view? You read correctly, the French (official) version has ..."décide que la valeur maximale pour la différence (UT1 - UTC) sera augmentée au plus tard en 2035," which means "in 2035 at the latest". Note also that the definition of UTC as approved by the CGPM never mentions _any_ explict bound for |UT1 - UTC|; it only says that (TAI - UTC) is an integral multiple of 1 s as determined by the IERS. It is the IERS who state that "Coordinated Universal Time (UTC) a measure of time that conforms, within approximately 1 s, to the mean diurnal motion of the Sun and serves as the basis of all civil timekeeping." quoting the IAU "Nomenclature for Fundamental Astronomy (NFA)" found at http://syrte.obspm.fr/iauWGnfa/NFA Glossary.html. This seems to be lenient enough to allow for not scheduling a negative leap second even in the case that the difference (UT1 - UTC) should go a bit below -1 s before 2035. Michael Deckers. ___ LEAPSECS mailing list LEAPSECS@leapsecond.com https://pairlist6.pair.net/mailman/listinfo/leapsecs
Re: [LEAPSECS] King Charles
On 2022-12-04 17:01, Steve Allen wrote: On Sun 2022-12-04T16:30:01+ Tony Finch hath writ: So if you agree with Donald Sadler, has already GMT concluded. I do agree, and I also disagree, for Sadler was in large part responsible for another tacit change to GMT. Like others engaged in the present redefinitions, given his job Sadler could not have dared to describe the consequences of that in plain language. The upcoming redefinition of UTC may well be seen as the logical consequence of its tremendous success as a reference time scale: billions of devices need an easily accessible continuous time scale with constant rate for sequencing events and for the computation of time derivatives. And the secular deviation of UT from UTC in the future might be one of the consequences that you think D H Sadler did not dare to describe in plain language. Michael Deckers. ___ LEAPSECS mailing list LEAPSECS@leapsecond.com https://pairlist6.pair.net/mailman/listinfo/leapsecs
Re: [LEAPSECS] future access to solar time?
On 2022-11-21 14:19, Seaman, Robert Lewis - (rseaman) wrote:
In a post-leap-second world, precision values for dUT1 either become more
critical or less. Or rather, they become no-less important scientifically but
perhaps negligible politically. For
example,https://www.sciencedirect.com/science/article/pii/S0273117719302388
says “Global Navigation Satellite Systems (GNSS) are dependent on VLBI as they
need dUT1 to maintain its operability”.
I am not sure if we mean the same thing by "dUT1". I used
it in the sense:
dUT1 is an additonal correction to UTC so that
UTC + DUT1 + dUT1
is a better approximation of UT1 than just
UTC + DUT1
and takes its values in the set {0, ±20, ±40, ±60, ±80} ms.
dUT1 in this sense is used only by some Russian time signals,
and its value is not defined by the IERS. Moreover, since the
amplitude of UT1 - UT2 is about 34 ms, dUT1 must be adjusted
for annual variations of UT1 - UTC.
I have seen the term "dUT1" to be used for ΔUT1 = UT1 - UTC
(and that is how I read it in the paper you quoted), and
also for the rate d(UT1) -- but these are different beasts.
Michael Deckers.
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Re: [LEAPSECS] future access to solar time?
On 2022-11-20 15:15, Tony Finch asked: (Do any of the national broadcast signals actually follow the ITU spec?) Lists of UTC time signals with details about the coding are in the Annual reports of the BIPM time department, at [https://www.bipm.org/en/time-ftp/annual-reports]. A few of them transmit DUT1 (and even dUT1). Michael Deckers. ___ LEAPSECS mailing list LEAPSECS@leapsecond.com https://pairlist6.pair.net/mailman/listinfo/leapsecs
Re: [LEAPSECS] Alanna Mitchell in NYT
On 2022-11-14 19:48, Steve Allen wrote: The NYT article ends with Arias ruminating about how someday there will have to be a leap minute or leap hour. Of course, nobody will propose leap minutes or leap hours in UTC after 2135 just to decrease the difference UTC - UT1. The reason why the CIPM (for now) sticks to the requirement that |UTC - UT1| be bounded is most probably the argument brought forward by some people from ISO who say that, without explicit bound on |UTC - UT1|, UTC had to change its name so that "polysemy" is avoided. Michael Deckers. ___ LEAPSECS mailing list LEAPSECS@leapsecond.com https://pairlist6.pair.net/mailman/listinfo/leapsecs
Re: [LEAPSECS] fb/meta join the leap second haters
On 2022-07-26 05:08, Steve Allen wrote: The CNET article includes a quote from correspondence which repeats a trick that has been performed since the 1960s, that being to produce a significant underestimate of the difference between solar and atomic time by saying that the absence of leap seconds will not be noticed for 2000 years. The CGPM resolution to be adopted in November, online at [https://www.bipm.org/documents/20126/66742098/Draft-Resolutions-2022.pdf/2e8e53df-7a14-3fc8-8a04-42dd47df1a04] only requires continuity of UTC - TAI for 100 years. Michael Deckers. ___ LEAPSECS mailing list LEAPSECS@leapsecond.com https://pairlist6.pair.net/mailman/listinfo/leapsecs
[LEAPSECS] IERS Bulletin D141
Another first has happened: Bulletin D141 at [https://datacenter.iers.org/data/latestVersion/17_BULLETIN_D17.txt] specifies that DUT1 jumps from -0.2 s to -0.1 s on 2021-07-21T00Z. This is the first time ever (since 1972) that the approximation UTC + DUT1 of UT1 makes a jump upwards (is advanced). Michael Deckers. ___ LEAPSECS mailing list LEAPSECS@leapsecond.com https://pairlist6.pair.net/mailman/listinfo/leapsecs
Re: [LEAPSECS] DUT1 about to backtrack
On 2021-01-08 19:57, John Sauter via LEAPSECS wrote: I attach a plot of historical values of DUT1 based on the old issues of Bulletin A kept on the IERS' web site. I think the graph of DUT1 is not quite correct, for instance: On 2009-01-01, there was a switch of DUT1 from -0.6 s to +0.4 s due to a leap second (Bulletin C36) On 2009-03-12, there was a switch of DUT1 from +0.4 s to +0.3 s (Bulletin D102) Your graph only has one switch, on 2009-01-01 from -0.6 s to +0.3 s Michael Deckers. ___ LEAPSECS mailing list LEAPSECS@leapsecond.com https://pairlist6.pair.net/mailman/listinfo/leapsecs
[LEAPSECS] LOD reaches 0 s/d
The latest Bulletin A [https://datacenter.iers.org/data/latestVersion/6_BULLETIN_A_V2013_016.txt] predicts that d(UT2)/d(TAI) = 1 after 2021-11-13, ie the rates of UTT2 and TAI are expected to agree for the next year. This has never happened since 1961. We may not need to abolish leap seconds for quite a while. Michael Deckers. ___ LEAPSECS mailing list LEAPSECS@leapsecond.com https://pairlist6.pair.net/mailman/listinfo/leapsecs
Re: [LEAPSECS] long interval predicted
On 2020-08-08 10:46, John Sauter via LEAPSECS wrote: UT2 captures the seasonal change in the length of day, so it can be ignored for long-term estimates. The important number, therefore, is -0.00010, which I will call the UT1 slope. Perhaps "slope of UT2 - UTC (as predicted by the IERS)" would be a better name, as the formula of Bulletin A implies (by taking the derivative after adding the implied units): d(UT2)/d(UTC) = 1 - 0.10 ms/d. But anyway, UT2 still contains known short period (<= 35 d) fluctuations, and currently, the combined amplitude of these fluctuations exceeds by far the indicated secular trend of UT2 during their periods. Another observation, namely the increase in the uncertainty of UT1 - TAI as given in the long term EOP parameters (published by the IERS in [https://datacenter.iers.org/data/latestVersion/38_EOP_C01.1900-NOW_V2013_0138.txt]) from 4 µs to 30 µs since J2020.40 = 2020-05-26.6 may be a related effect. Michael Deckers. ___ LEAPSECS mailing list LEAPSECS@leapsecond.com https://pairlist6.pair.net/mailman/listinfo/leapsecs
Re: [LEAPSECS] Bulletin C number 60
On 2020-07-07 22:37, Steve Allen wrote: The earth has accelerated so that it is spinning as fast as it was during World War 2, and before that, the 1890s. Yes, Bulletin A vol 33 no 027 predicts that 2020 will be the first year since 1972 without change of DUT1 (= UT1 - UTC up to 0.1 s). And its prediction for the (seasonally smoothed) length of day after 2021.5 is d(UTC)/d(UT2) ~= 1 + 0.13 ms/d. Michael Deckers. ___ LEAPSECS mailing list LEAPSECS@leapsecond.com https://pairlist6.pair.net/mailman/listinfo/leapsecs
Re: [LEAPSECS] Leap seconds have a larger context than POSIX
On 2020-02-04 21:16, Steve Allen wrote:
The first time that the 4th meeting of the CCDS happened was in 1966,
but that meeting is not found in any official record. The meeting
ended with a vote to recommend that the CGPM should adopt an SI second
based on cesium, but the circumstances of that vote were deemed so
abusive that the entire meeting was nullified. That did not stop the
rush for an atomic second. During the next year subsets of the CCDS
members gathered for discussions at other meetings. When the second
4th meeting of the CCDS was held in 1967 they did recommend the cesium
second to the CGPM.
From the standpoint of a physicist, the 1960 definition of the SI second
(based on ET and Newcomb's tables for the Sun) was extremely
impractical.
With the wide availability of Cs clocks, the atomic second was much
easier and more precisely reproducible than the SI second, so a
redefinition of the second (or at least a practical unit, as with
the recently abolished practical volt and ohm) was urgent.
On the other hand, you are certainly right that the actions of the
CCDS in 1967 appear strange: they propose to redefine the SI second,
and then go on to propose that the BIH, IAU, IUGG, URSI, and CCIR
study the problems arising from the new definition ("étudier les
problèmes soulevés par l'application des décisions prises
concernants la nouvelle définition de l'unité du temps").
Apparently, it did not even occur to them that this is bad
engineering.
The proposal of the IAU GA13 in 1967 to introduce an (unsteered)
international atomic time scale would have allowed to study the
possible problems of a redefinition of the SI second before
applying it.
Folks at the PTB took a different aim by introducing draft legislation
that the German government passed in 1969. The law made it illegal
for the German government to broadcast anything other than SI seconds,
and it would become effective in 1970. This seems to have pulled the
trigger on the CCIR process, for without some kind of quick action a
major nation would be broadcasting time signals using a different
scale than other nations.
The law on legal units in West Germany, from 1969-07-02, lists under
the title "tasks of the Physikalisch-Technische Bundesanstalt"
that the PTB has to publicize the procedures by which units without
material prototype are realized, including the units of time and
time scales, as well as the temperature unit and temperature scales.
(" hat die Verfahren bekanntzumachen, nach denen nicht verkörperte
Einheiten, einschließlich der Zeiteinheiten und der Zeitskalen
sowie der Temperatureinheit und Temperaturskalen, dargestellt
werden,")
This can be taken to imply the task to disseminate a standard
frequency (which they already did). But in my opinion it does not
imply that UTC must have the same rate as the atomic time scales
at the time -- the law even allows for several time scales.
I'll try to find out how the PTB was involved in this legislation
as far as time in concerned. In Germany, federal law can only
be proposed by members of parliament, and by federal and state
governments; but the PTB was certainly heard during the legislative
process.
In my home state of California the process that led to UTC with leap
seconds would have been illegal under the Brown Act that requires
public access to meetings. But in the full context that is not the
most criminal aspect of the process that led to the 1970 CCIR
decision.
Yes, and the ITU-R deliberations before the WRC in 2015 were not
transparent either. Nevertheless, past decisions of the CCIR and
the IAU have become accessible nowadays.
Let's hope that the CIPM treats any future discussions about
a redefinition of UTC in an open manner, and that it adheres
to rational design and decision processes. The recent revision
of the SI has been largely transparent and guided by good practices.
Michael Deckers.
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Re: [LEAPSECS] Leap seconds have a larger context than POSIX
On 2020-02-04 13:44, Tony Finch wrote: The IERS Bulletins C state a value of UTC-TAI "until further notice". However the machine-readable files from IERS and NIST give an expiry date of a few days less than 6 months after the announced (lack of) leap second, or a bit more than 11 months after the latest Bulletin C. Is this expiry date reliable or just advisory? History suggests it's reliable, but the standards do not. It's unclear to me what governs the frequency of announcements or their validity period, i.e. where are current practices documented? what is the process for changing them? how will we know if a change is planned? and so on. This is all about how much we can assume that the IERS will continue to operate leap seconds as they have for nearly 50 years, or whether they will make use of the much weaker guarantees given by TF.460, or (wishful thinking) whether they can schedule leap seconds further in the future. The IERS (and BIH) policy to use only the primary choices for the insertions of leap seconds is only guaranteed in the text of Bulletin C -- if LOD increases sufficiently, that text will have to change. There is a similar situation for Bulletins D -- each of them announces when the next one is expected to be issued. But even nowadays these predictions of UT1 - UTC are not very reliable, and they often err on the "wrong" side (DUT1 changes earlier than predicted). For instance, Bulletins D139, D134, and D129 each came earlier than predicted by the preceding Bulletin D; Bulletin D129 (of 2016-04-15) was even significantly earlier (45 d) than predicted by Bulletin D128 (of 2016-02-19). Michael Deckers. ___ LEAPSECS mailing list LEAPSECS@leapsecond.com https://pairlist6.pair.net/mailman/listinfo/leapsecs
Re: [LEAPSECS] Leap seconds have a larger context than POSIX
On 2020-02-02 22:30, Steve Allen wrote: On Sun 2020-02-02T17:59:20+ Michael Deckers hath writ: The maximum deviation |UTC - UT1| <= 0.9 s as stipulated in 1974 by CCIR Rec. 460-1 has never been violated until now. That violates the agreement that the difference between UTC and UT1 would be encoded as part of the time broadcasts. Actually, the difference |UTC - UT1| has always been < 0.8 s except around 1973-01-01. And DUT1 has assumed the value 0.8 s only once, for a few days on and after 1994-07-01, as specified in Bulletin D46 (online at [https://datacenter.iers.org/data/17/bulletind-046.txt]). That Bulletin is remarkable in several respects: it describes two switches of DUT1, not just one, and it was issued on 1994-06-21, only 10 days before the first switch (rather than a month before it, as was requested -- from the BIH -- in CCIR Rec 460-4 of 1986). In one case it was broken specifically because a high official at CCIR conceded to a high official from USSR and directed the BIH to violate the wording of the existing agreement. Do you mean the only violation of applicable CCIR rules, the introduction of a leap second into UTC at 1973-01-01? Right. Sadler covers this in his memoir and in several contemporary publications. Delving into this reveals more of the fear in the process. Several memoirs show that the principals involved with the creation of UTC with leaps were very concerned that the change of broadcast time signals might cause havoc with ships using celestial navigation. Reading through those shows palpable relief when they managed to evoke from the Maritime Safety Committee of the IMCO a statement that Rec. 460 would not cause difficulties with navigation predicated on the expectation that governments whose radio broadcasts used new UTC would issue notices about the change of their broadcasts. That meant that the Time Lords did not have their arses on the line if a ships might collide as a result of the new system. With the maximum difference of 0.7 s that could be encoded in the radio broadcasts not being able to handle the 0.9 s difference that put their arses back on the line. Other concern was expressed that exceeding the 0.7 limit might be blamed on the BIH and might trigger governmental review of the operation and funding of the BIH. At that time about 80% of the funds for BIH were coming from Observatoire de Paris as slush from their allotment from the French government. That was hardly an "international" arrangement, but BIH had only just been handed the responsibility for maintaining TAI specifically because any other arrangement would have required effectively duplicating the expertise and hardware of the BIH and finding a way to fund that. Prompting governments or journalists to open an investigation into the process of writing an international "technical" specification that was violated in less than two years was not a welcome notion. Very interesting, thanks for these details! Concerning the technical expertise of the CCIR with time scales: one of the early proposals of the CCIR has been a "stepped atomic time" with steps of 1 s and maximal difference of 0.5 s from UT2 (as mentioned in the 1970 report of commission 31 available via your web site on [https://ui.adsabs.harvard.edu/link_gateway/1970IAUTA..14..343Z/ADS_PDF]) -- apparently they had not consulted any astronomer, even though they used to "request" many actions from the BIH in their specifications of time scales. The 1970 report also contains the proposal that the CIPM should be responsible for the definition of UTC, and 49 years later, the CGPM in 2019 seems to have taken on that task with the resolution [https://www.bipm.org/en/CGPM/db/26/2/] which notably has no requirement that |UTC - UT1| be bounded. Michael Deckers. ___ LEAPSECS mailing list LEAPSECS@leapsecond.com https://pairlist6.pair.net/mailman/listinfo/leapsecs
Re: [LEAPSECS] Leap seconds have a larger context than POSIX
On 2020-02-01 23:59, Steve Allen wrote: In every instance where a document specified a maximum deviation that agreement was later violated. The maximum deviation |UTC - UT1| <= 0.9 s as stipulated in 1974 by CCIR Rec. 460-1 has never been violated until now. In one case it was broken specifically because a high official at CCIR conceded to a high official from USSR and directed the BIH to violate fthe wording of the existing agreement. Do you mean the only violation of applicable CCIR rules, the introduction of a leap second into UTC at 1973-01-01? If so -- this was the choice of using either the date 1973-01-01 for the insertion of the leap second, or a later date before 1973-07-01. This is evident because at the time, the mean excess length of day LOD = d(TAI - UT1)/d(UT1) was observed to be >= 3 ms/d, which is more than 0.5 s per 6 months. Hence the choice was to either stick with the bound 0.7 s for |UT1 - UTC| as required by CCIR Report 517 of 1971, or else stick with the primary choices for the possible dates of the insertion of leap seconds. Apparently, the "high official from USSR" must have preferred the latter. Michael Deckers. ___ LEAPSECS mailing list LEAPSECS@leapsecond.com https://pairlist6.pair.net/mailman/listinfo/leapsecs
Re: [LEAPSECS] complete history of UT2
On 2019-06-05 05:28, Steve Allen wrote: I have plowed through enough of Bulletin Horaire to find the complete history of UT2. https://www.ucolick.org/~sla/leapsecs/seasonal.html Missing from the earlier version of the plots on this web page was the story of how exactly the BIH performed the transition between the first version of UT2-UT1 and the second version. Naively the change of the expression requires a jump of 6 ms at the beginning of 1962, but that is not what the BIH dictated. Look at the middle plot and see how the year started along one curve and finished along the other. Thanks! That clarifies that the 5 ms step down in UTC at 1961-01-01 has nothing to do with the change in the formula for UT2 as a function of UT1. Nowadays, the role of UT2 is reduced: it is given in Bulletin A as a linear function of UTC, as a means to extend the prediction of UT1 as given in the Bulletins. Michael Deckers. ___ LEAPSECS mailing list LEAPSECS@leapsecond.com https://pairlist6.pair.net/mailman/listinfo/leapsecs
Re: [LEAPSECS] DCF77 and the inception of leap seconds
On 2019-02-01 17:56, Steve Allen wrote: The PTB-controlled broadcasts were pure SI seconds thus making those broadcasts a form of Stepped Atomic Time which was approved as experimental by CCIR Rec 374-1 in 1966. The DCF77 service started on 1959-01-01 and sent astronomically determined signals for UT2 or UTC until 1970-04-01 when the signals of DHI stopped. The PTB used Cs clocks since 1962, and the PTB time signals in DCF77 used steps but never used an offset in rate. See Andreas Bauch, Peter Hetzel, Dirk Piester: "Zeit- und Frequenzverbreitung mit DCF77: 1959 – 2009 und darüber hinaus". in: PTB Mitteiliungen, 2009 Heft 3. 2009-09 Braunschweig. online at [https://www.ptb.de/cms/fileadmin/internet/publikationen /ptb_mitteilungen/mitt2009/Heft3/PTB-Mitteilungen_2009_Heft_3.pdf] Michael Deckers. ___ LEAPSECS mailing list LEAPSECS@leapsecond.com https://pairlist6.pair.net/mailman/listinfo/leapsecs
Re: [LEAPSECS] the epoch of TAI, with no more doubt
On 2019-01-22 05:17, Steve Allen wrote: Curiously there is not a big jump in the value of UT2 - A3 at that same date which would have been caused by changing from the old expression for UT2 - UT1 to the new expression. I surmise that this means Stoyko and Guinot did correct the old values of UT2 for the change in that formula. In [https://www.ucolick.org/~sla/leapsecs/taiepoch.html], the table F on page 74 in fact does not show a step in ΔA3 = UT2 - A3 between the lines for 1961 January 00 and January 05 (which is why you could interpolate linearly to obtain UT2 - A3 = -1.4123 s for 1961-01-01). And the column "WWV3" equally shows no step at 1961-01-01, and since it is probably meant to be "BIH integrated atomic time - time signaled by WWV3" (where the latter should include the step down by 5 ms), the point of tabulation "Janvier 0" may actually be the instant when UT2 was 1960 Dec 31 - 5 ms. So yes, the entry may have been "corrected". Anyway, a jump down by 5 ms occurred in (what was later baptized) UTC on 1961-01-01 (see [Explanatory Supplement 1992, p 87]). I always thought that this was done to adapt to the jump in UT2 caused by the change in the formula for UT2 - UT1, but from the graphs in [https://www.ucolick.org/~sla/leapsecs/seasonal.html] (thanks!) I have to conclude that UT2 must have made an upward jump by about 5 ms, while the step by 5 ms in UTC at 1961-01-01 definitely was a downward jump (it is also included as such in the SOFA function iauDat()). Did I make a sign error? Michael Deckers. ___ LEAPSECS mailing list LEAPSECS@leapsecond.com https://pairlist6.pair.net/mailman/listinfo/leapsecs
Re: [LEAPSECS] the epoch of TAI, with no more doubt
On 2019-01-21 00:42, Steve Allen wrote: Of course there was a time step. The BIH had to deal with totally hetergeneous data from an ever changing set of contributors. Almost every year for the BIH there was a systematic offset from the times of other years. But until the cesium standard there really is little worth in the absolute values; the importance of the numbers in Bulletin Horaire liese in seeing and understanding the differences between contemporary time services. For the internally used and tabulated time scales, yes, there may be steps, as convenient. But steps in a time scale used to dissmeinate time signals with their own steps and rate offsets are highly inconvenient. I was of the incorrect opinion that the BIH integrated atomic time scale was aligned with the coordinated atomic time scales used by the RGO, NBS, USNO etc since 1960-01-01; but it was not, and only joined on 1961-01-01. Thanks for the corretion! A3 begins 1961-01-01. It does not exist before then. Not even when Guinot re-interpolated all the atomic time scales in Bulletin Horaire ser J no 7 did he extend A3 before then. He introduced his final reconstruction of the old atomic data with It is therefore possible to construct, starting from an arbitrary common origin, scales of Atomic Time ... By that 1966 publication Guinot had ceased to mention 1961-01-01, but linear interpolation of his new A3 tabulation has the value -1.4123 s on 1961-01-01T20, the same as had been used by Anna Stoyko when she re-set all of the BIH atomic time scales. You are of course right; instead of "A3" I should have said "the integrated atomic time scale produced by the BIH for 1957..1960 and which agrees with UT2 at J1958.0", as described on pages 99..101 in [https://www.bipm.org/utils/common/pdf/CC/CCTF/CCDS2.pdf]. From the steps in the WWV time signals as documented in the Explanatory Supplement 1992, p 86..87, I compute a decrease of 1.465 056 s in the WWV time signals against the underlying Cs atomic scale, while this scale ranged over the interval from J1958.0 until 1961-01-01, and this applies to all continuous time scales with the same rate. So, when A3 - UT2 at 1961-01-01 was set to 1.4123 s by the BIH, this must amount to a step of about -53 ms at 1961-01-01 in the BIH integrated atomic time scales before and after 1961-01-01. (And there was no step in UT2 on 1961-01-01.) If this step was done to align A3 with the coordinated times already in use, I am surprised that such a large deviation between integrated atomic clocks could accrue over three years -- A and N Stoyko estimated the deviation after 3 years to be 10 ms in the paper quoted above. Regardless of this difference, there is a thing common to all integrated atomic time scales that suggests that they all are intended to have J1958.0 as their origin: their difference to ET (and later to TT and TDB). In fact, TT - TAI remains very close to 32.148 s, which in turn is close to the value ET - UT2 when UT2 was J1958.0 (but ET - UT2 differs by about 0.5 s for the neighboring years). A step of 0.05 s does not change this property. Guinot also indicates that he retained the jump of 1.6 ms on 1962-01-01 in his new tabulation of A3. These various tabulations deserve to be plotted and examined closely for a step, especially because 1962-01-01 was also the date of the final change in the expression for the seasonal variation of UT2 - UT1. https://www.ucolick.org/~sla/leapsecs/seasonal.html That change should introduce a step of about 6 ms, and this subject is not mentioned in any of the BIH writeups. Do you happen to know in which tabulation the jump by 1.6 ms occurs? A3 minus which other time scale? The 1962 change in the UT2 formula did not apply to prior years; a step in UT2 may have influenced the disseminated time signals which followed UT2, and the step causes jumps in some differences such as A3 - UT2, but it does not not cause a step in UT1 or in any (integrated) atomic time scale. Michael Deckers. ___ LEAPSECS mailing list LEAPSECS@leapsecond.com https://pairlist6.pair.net/mailman/listinfo/leapsecs
Re: [LEAPSECS] the epoch of TAI, with no more doubt
On 2019-01-20 17:19, Steve Allen wrote:
Those pages are a response to Recommendation 2 from the second CCDS
meeting held 1961-04-11/1961-04-12. At the CCDS meeting BIH presented
an initial effort to integrate and compare all the cesium standards
for which data were available, and BIH was the only place with the
timing data from all the labs. The BIPM has now scanned and published
the proceedings from all the CCDS meetings, so anybody can look at this.
During those CCDS proceedings is the discussion on what value to give
to an atomic time scale:
The president [Danjon] insists on the need to define a zero, even
arbitrary, for the time scale; it is necessary to date terrestrial
and astronomical events in a certain calendar.
Thanks for the pointer!
Yes, Danjon wants a zero epoch defined, but Markowitz opines that
this is of interest only ("uniquement") for the IAU who should
decide upon it.
The table with the inception of A9 in my web page from Bulletin
Horaire ser 5 no 13 was created scant months after the original
table in ser G no 8. The intro to the A9 table discusses the
difference between the "5 anciens" standards and the 4 new ones.
The intro explicitly states that the BIH is choosing to reset their
value of all these atomic time scales at 1961-01-01T20:00:00 UT2.
But this seems to state something about the inputs for the data
reduction by the BIH. It does not say that the integrated atomic
time scale of the BIH, the BIH output, has had a step at the time,
or a step in rate, or does it?
I understand that the BIH had to adapt every once in a while the
constants for integrating the atomic time scales from their
intermittent comparisons (because of the addition of new clocks,
and because of the increasing accuracy). But I would assume that
the goal in such adaptations must have been to keep the phase and
rate of A3 without any noticeable steps over such a change.
Guinot knew this, in part because after Anna Stoyko decided to create
A3 and sync it with A9 Guinot later re-interpolated A3. More
unquestionably, in Bulletin Horaire ser J no 1 p 3 Guinot wrote
that the origin of A3 and all other BIH TAi values was 1961 Jan 1
and he referred to Bulletin Horaire ser 5 no 13.
Guinot must have known, but in 2004 he said (together with Arias)
that the origin was J1958.0. Couldn't that mean that the change on
1961-01-01 was designed to have no effect on A3 as published by
the BIH?
Michael Deckers.
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Re: [LEAPSECS] the epoch of TAI, with no more doubt
On 2019-01-20 00:50, Steve Allen wrote: I took a closer read and cross reference of the relevant issues of Bulletin Horaire and finalized my web page. The epoch at which TAI was set is definitely 1961-01-01T20:00:00 UT2 Arias and Guinot say in "Coordinated Universal Time UTC: Historical Background And Perspectives", online at [https://syrte.obspm.fr/journees2004/PDF/Arias2.pdf]: "In 1961, the BIH assigned a common origin to these time scales [atomic time A1 of USNO for other integrated atomic times] by coincidence with UT2 on the 1st of January 1958 (Stoyko, 1961). The same origin was used for the BIH mean atomic time." The reference is to: "Stoyko A., 1961, Bulletin Horaire du BIH, Série G, 241-245." That is probably a source you may have access to. The quote implies that the BIH scale A3 (precursor of TAI) was taken to agree with UT2 at J1958.0, but of course this does not rule out that the two time scales also agreed at some later instant. Apparently, the origin J1958.0 was taken retrospectively, and did not just appply to the BIH atomic scales. Since atomic scales had an uncertainty of a few ms per year at the time, it should be possible to verify whether they all agreed at J1958.0 or at 1960-01-01T20 -- it is unlikely that they all ever agreed on more than one instant. Michael Deckers. ___ LEAPSECS mailing list LEAPSECS@leapsecond.com https://pairlist6.pair.net/mailman/listinfo/leapsecs
Re: [LEAPSECS] leapseconds, converting between GPS time (week, second) and UTC
On 2019-01-18 17:11, Michael H Deckers wrote: .. insert a step of 0.2 s in their time signal about every 71 days. when he meant "about every 77 days". Michael Deckers. ___ LEAPSECS mailing list LEAPSECS@leapsecond.com https://pairlist6.pair.net/mailman/listinfo/leapsecs
Re: [LEAPSECS] the inception of leap seconds
On 2018-08-15 11:49, Zefram wrote: Time Service Announcement 14 #8 (1971-10-08) discusses the irregular leap (still called a "step") at the end of 1971, but weirdly gives a different size for that step from that which is implied by tai-utc.dat. The announcement states a step size of 107600 us, but the expressions in tai-utc.dat imply a step size of exactly 107758 us. The announcement is The 107758 us computed from tai-utc.dat is in microseconds of TAI, and the leap is only a few nanoseconds shorter in UTC. I cannot explain the -107.6 ms jump of the Announcement; but the 1992 "Explanatory Supplement to the Astronomical Almanac" contains jumps of WWV on p 86..87 that are not in tai-utc.dat. Anyway, I also think that the jump of UTC(USNO) did not happen when TAI was 1972-01-01 + 10 s, as implied by the Announcement, but a bit earlier. See below. . The announcement is ambiguous as to whether this step size is specified in microseconds of UTC or of TAI, apparently ignoring the UTC frequency offset for this purpose, though the offset isn't anywhere near big enough to account for the discrepancy. While UTC is defined to be a piecewise linear function of TAI, the practice was (and still is) to specify TAI - UTC (and thus TAI) as a piecewise linear function of UTC. The "steps" specified in Bulletin C are steps in TAI - UTC, hence also of TAI, as a function of UTC -- which probably is what you mean by "microseconds of TAI". Time Service Announcement 14 #8 of 1971-10-08 is no exception: it gives TAI - 10 s - UTC(old) as maintained by the USNO as a function of UTC(old), where UTC(old) is the unique linear extension of UTC as defined directly before 1972-01-01. Thus, the member 2 592 (MJD - 41 317) has to be read as 2 592·(UTC(old) - 1972-01-01)/(1 d). The inverse relation to UTC as a function of TAI is not a function: UTC assumes some values twice, for different values of TAI (when UTC makes a jump down); and UTC did not assume some values (when UTC made a jump up, as it last did around 1968-02-01). So TAI is a sometimes two-valued (positive leaps) and sometimes undefined (negative leaps) "function" of UTC, and it is not always clear where it differs from the function TAI of UTC that is officially specified. The discontinuity of UTC near 1972-01-01 is an exception because the jump up of TAI - UTC from 9.892 242 s to 10 s was accompanied by a jump in the (piecewise constant) rate d(TAI)/d(UTC) from 1 + 2.592 ms/d down to 1 (the only case where both TAI - UTC and d(TAI - UTC) have been discontinuous). Here we do know that a jump of UTC from 1972-01-01 to 1972-01-01 - 0.107 758 s must have happened when TAI was 1972-01-01 + 9.892 242 s. At any other value of TAI between 1972-01-01 + 9.892 242 s and 1972-01-01 + 10 s, the jump in phase would have been by a different amount, and not by an integral multiple of 1 µs. HTH Michael Deckers. ___ LEAPSECS mailing list LEAPSECS@leapsecond.com https://pairlist6.pair.net/mailman/listinfo/leapsecs
Re: [LEAPSECS] Windows Server 2019
On 2018-07-20 18:05, Stephen Scott wrote: While there is no perfect answer, it seems that Microsoft Azure servers got it right for the last one, incorporating the leap second just before midnight local time. No, they didn't. A leap second describes a discontinuity in the function TAI - UTC. For the last leap second, the value TAI - UTC was 37 s since TAI was 2017-01-01T00:00:37, and for some time before that, it was 36 s until TAI reached 2017-01-01T00:00:36. The standards do _not_ say when exactly TAI - UTC switched from 36 s to 37 s, but it must have been between the TAI values 2017-01-01T00:00:36 and 2017-01-01T00:00:37, inclusive, as can be inferred (perhaps with some good will) from IERS Bulletin C52 of 2016-07-06 (the official specification of this leap second). The time interval between these TAI values (excluding the TAI value 2017-01-01T00:00:37) is called a positive leap second; the corresponding UTC values are denoted (in ISO 8601 format) with second values >= 60 (as specified in ITU-R TF.460-6 of 2002). This is true everywhere near the surface of the Earth, even for Kiritimati. So Kiritimati had its last leap second when every other location on the Earth had it, that is, when TAI went from 2017-01-01T00:00:36 to just before 2017-01-01T00:00:37, and UTC went from 2016-12-31-23:59:60Z to just before 2017-01-01T00:00:00Z; so that local time went from 2017-01-01T13:59:60+14 to just before 2017-01-01T14:00:00+14 during that leap second. HTH. Michael Deckers. ___ LEAPSECS mailing list LEAPSECS@leapsecond.com https://pairlist6.pair.net/mailman/listinfo/leapsecs
Re: [LEAPSECS] Windows Server 2019
On 2018-07-21 01:08, Steve Allen wrote: At that same meeting IAU Comm 31 was led to yield that they had no influence over the leap seconds that the CCIR had instituted, and IAU Comm 31 was pressed to produce a statement declaring that leap seconds were "the optimum solution." http://adsabs.harvard.edu/abs/1971IAUTB..14..198W Thanks for that document! I note the typo on page 198 where it says under the heading "9. Designation of the epoch of steps in UTC": "9.1. If UTC is to be advanced, then second 00 will follow 23h 59m 58s of the previous day." "9.2. If UTC is to be retarded, then the second of the previous day 23h 59m 58s will be followed by the next second 0h 00m 00s of the first day of the month." And the text "9.4. The time of an event given in the old scale, before the leap second, will be given as a data in the previous month, exceeding 24h if necessary. The time of an event given in the scale after the step will be given as a data in the new month, with a negative time, if necessary." gives not only the leap second notation long before CCIR codified it in 1978, but also shows an alternative notation. All of the above strike me as "something is seriously wrong here." Looking deeper into the history and memoirs by folks who were involved it becomes clear that the inception of leap seconds was the culmination of a 20 year game of international regulatory and scientific agency pinball. After the CCIR introduced them that game continued for another 10 years as other agencies and governments were led to approve the notion of UTC with leap seconds using words like "parfaitment recommandable". I do not see what you mean here. Before 1972, the BIH (under control of the IAU) had defined UTC. The document (above) you quoted contains the approval by IAU Commissions 4 and 31 to the leap second scheme as proposed by the CCIR. The introduction of leap seconds happened with the support of the BIH, and all the discrepancies among disseminated radio time scales vanished on 1972-01-01. Not much gaming. The recommendation of the 15th CGPM in 1975 that "this usage [of UTC] can be strongly endorsed" does not appear to me to have been forced upon the CGPM. The resolution does not even call UTC a time scale, it merely states what was obvious at the time: • that the system called “Coordinated Universal Time” (UTC) is widely used, • that it is broadcast in most radio transmissions of time signals, • that this wide diffusion makes available to the users not only frequency standards but also International Atomic Time and an approximation to Universal Time (or, if one prefers, mean solar time), • that this Coordinated Universal Time provides the basis of civil time, the use of which is legal in most countries. Compare this with the proposed resolution B of the 26th CGPM in 2018 November which declares that: • UTC produced by the BIPM, based on TAI, is the only recommended time scale for international reference and the basis of civil time in most countries, This latter resolution can in fact be seen as the BIPM claiming the defining authority for UTC from ITU-R, by making it clear that the realization of UTC (except for the encoding of time signals) is already completely controlled by data from Bulletin T of the BIPM. If I were looking for a competition between standardizing bodies, I would rather point to this resolution. I have found nothing that directly explains why it was repeatedly deemed impossible for any of these agencies to explain and recommend the existence of two kinds of time scales, but it seems clear that the legal considerations led toward the notion of a compromise. I do not think that there was any disagreement around 1970 about the need for multiple time scales, neither among astronomers (who used many more time scales than just two) nor among radio people (who would at least distinguish TAI, UT0, UT1, UT2 and UTC). The CCIR wanted to select a reference time scale to be disseminated world-wide in order to achieve global synchronization in phase and frequency. Disseminating two different reference time scales for that purpose does not make sense: a single globally available reference time scale allows for the dissemination and comparison of the readings of any number of time scales across the globe (up to the uncertainty of the rate of the reference time scale and only as far as these time scales use the same concept of synchronicity near the surface of the Earth). So we have betrayal, eroded trust, and reduced usefulness because some folks wanted to take what looked like a politically expedient shortcut which was full of unexplained
Re: [LEAPSECS] final report of the UK leap seconds dialog
On 2015-02-05 11:16, Peter Vince wrote: Yes, I took part in the initial meeting of professionals (so-called stakeholders), where the issues were indeed thoroughly discussed, and well understood (apart from some unfortunate absences - no-one from the military was there, for example). But on the video on the linked page below, nine members of the public gave their views, one of them said If it's not broke, don't fix it, and two others said they didn't understand what the fuss was all about - it's been working OK for the last 25 times. (And none of the nine people were in favour of changing the system.) I would sympathise with both those views, but they seem ill-informed: I believe this discussion has come about exactly because it *is* broken, and *hasn't* been working perfectly for the last 25 times. None of the people interviewed had even heard of leap-seconds - clearly the stories about the long delays at Sydney(?) last time because of the Quantas problem were too far away to register with them. That's all fine, *we* were busy managing the problem so the rest of the world didn't have to worry - as it should be. But as I said before, I am disappointed that those members of the public were left with the impression that there is nothing wrong, and we timekeepers just want to change things for the sake of it. But where is the detailed list of the problems with the current version of UTC, where is the analysis of this list, and the exploration of the solution space? Take for example the bad predictability of the current UTC, brought up repeatedly by Warner Losh. This could perhaps be alleviated by a long term specification of future leap seconds -- but this is apparently not even discussed by the ITU experts for Study Question ITU-R 236/7. It is exactly this lack of due engineering process that leads to the if it ain't broke position. And if the WRC votes for abandoning leap seconds, we would not know whether the IERS will continue to publish DUT1, or whether the BIPM will revoke TAI. I do not find it the least bit surprising that most average citizens oppose such a change. Michael Deckers. ___ LEAPSECS mailing list LEAPSECS@leapsecond.com https://pairlist6.pair.net/mailman/listinfo/leapsecs
Re: [LEAPSECS] [QUAR] Bulletin C and all that
On 2015-01-26 20:05, Brooks Harris wrote: As a practical matter of modern timekeeping the UTC timescale started at 1972-01-01T00:00:00Z (UTC). NTP, POSIX, 1588/PTP and others refer to epochs and timescales they call UTC that occur earlier than 1972-01-01, so this confuses matters. But those epochs exist on Gregorian calendar timescale that is proleptic to the UTC origin, not on the modern UTC timescale proper. We've got to get past this confusion. A calendar provides a method for denoting datetime values. A time scale is a coordinate function within coordinate systems for physical (astronomical) models that assigns datetime values to each point in its domain of definition. Hence a calendar should not be confused with a time scale, even if the calendar is used exclusively for the notation of the values of a single time scale (which is not the case for the Gregorian calendar). Values of the time scale later called UTC by the BIH can be exactly related to TAI since 1961, see [hpiers.obspm.fr/iers/bul/bulc/UTC-TAI.history]. Steve Allen's Time Scales page points out - Time Scales http://www.ucolick.org/~sla/leapsecs/timescales.html Nothing resembling the name UTC was used prior to 1960, so any claim that UTC can be used before then is inappropriate. The name UTC did not appear in any official context until 1974, so any claim that UTC was used prior to 1974 is almost certainly a reinterpretation of history which does not correspond to anything in contemporary documents. The history is tangled, but none of it matters except to historians. I think that 1974 is just a typo for 1964; I do not see any error in the history. Michael Deckers. ___ LEAPSECS mailing list LEAPSECS@leapsecond.com https://pairlist6.pair.net/mailman/listinfo/leapsecs
Re: [LEAPSECS] Bulletin C and all that
On 2015-01-25 14:58, Rob Seaman wrote: Please let me know about typos, suggestions, etc. Needless to say this remains a prototype. ... MM before after encoded crc IP Decodedflags -- 1972 1 9 10 f8000a00 f5 248.0.10.245- OK 1972 1 10 1 (1, 0) It would be incorrect to consider the discontinuity of the difference TAI - UTC at the epoch when TAI was 1972-01-01T00:00:10 as a leap second; the difference increased by about 0.108 s, not by 1 s. Hence, a timestamp such as 1971-12-31T23:59:60.2Z should not be made acceptable. The first leap second occurred when UTC reached 1972-07-01; the information about a leap second says something about TAI - UTC both before and after the date referenced. At 1972-01-01, however, the information can only say something about TAI - UTC for TAI on or after 1972-01-01T00:00:10, but nothing (correct) for smaller values of TAI. Michael Deckers. ___ LEAPSECS mailing list LEAPSECS@leapsecond.com https://pairlist6.pair.net/mailman/listinfo/leapsecs
Re: [LEAPSECS] the big artillery
On 2014-11-06 13:10, Steffen Nurpmeso wrote in defense of the description by the German metrology laboratory in [https://www.ptb.de/cms/en/fachabteilungen /abt4/fb-44/ag-441/coordinated-universal-time-utc.html]: Hm, indeed a sloppy translation of the original German text Die Einführung der Zeitskala UTC geht auf Vorschläge des CCIR (Comité Consultatif International des Radiocommunications) zurück which is more like Introduction of the time scale UTC originates in suggestions made by... But the German text is equally wrong. The CCIR was tasked to find a common time scale for radio dissemination, but they did not suggest the underlying concepts of UTC. The concepts were developed about 1960 within the RGO, NPL, USNO and the BIH, at a time when time determination meant the reduction of UT0 to UT1, and a common reference time scale with rate close to UT2 was an enormous help. But of course passion can't be replaced by anything else. Maybe money? I do not see which point you want to make here. Michael Deckers. ___ LEAPSECS mailing list LEAPSECS@leapsecond.com https://pairlist6.pair.net/mailman/listinfo/leapsecs
Re: [LEAPSECS] the big artillery
On 2014-11-04 22:26, Steve Allen quoted Bernard Guinot about the unit for the difference TAI - UT1: Guinot explained this using the term graduation second in section 2.2 of 1995 Metrologia 31 431 http://iopscience.iop.org/0026-1394/31/6/002 He points out that the way the IAU has written the definitions of the time scales uses a subtly ambiguous notation. He writes The numerical value of UT1(IERS)-TAI does not of course, express a duration. In this context, the s only conveys the information that the readings of the two time scales are expressed in graduation seconds. Guinot comes back to this question, and revises his position, in [Guinot 2011, section 7.a, p 4139], where he exposes the underlying fundamental question: how can the set of spacelike and timelike coordinates be given consistent dimensions (invariant under the Minkowski group). He writes: (a) Unit of relativistic coordinates Some authors consider the relativistic coordinates as dimensionless, others give a special name to their unit, such as the ‘TCB second’ or a global name such as ‘graduation unit’. I was myself in favour of the latter name. However, after long discussions with eminent metrologists, Quinn and de Boer, I agreed that it was simpler to name ‘second’ the graduation unit. Thus, more generally, all quantities having the dimension of time have the second (without any qualifier) as their unit, even if they have different natures, such as time interval and reading of a time scale. If the logic of this point of view seems rather obscure, then it is possible to consider it as a convention which has the merit of being in agreement with the quantity calculus. It also agrees with the metrological rule that the unit does not define a quantity. While I can only agree with Guinot's position, I am not sure whether space coordinates and relativistic change of coordinates can be modeled neatly in that way. Amazing that simple questions about time scales can lead to such really fundamental conceptual issues! Reference: [Guinot 2011] Bernard Guinot: Time scales in the context of general relativity. in: Philosophical Transactions of the Royal Society A. vol 369 p 4131..4142. 2011-09-19. online at: [rsta.royalsocietypublishing.org/content/369/1953/4131.full.pdf] Michael Deckers. ___ LEAPSECS mailing list LEAPSECS@leapsecond.com https://pairlist6.pair.net/mailman/listinfo/leapsecs
Re: [LEAPSECS] the big artillery
On 2014-11-04 22:26, Steve Allen wrote: Guinot explained this using the term graduation second in section 2.2 of 1995 Metrologia 31 431 http://iopscience.iop.org/0026-1394/31/6/002 He points out that the way the IAU has written the definitions of the time scales uses a subtly ambiguous notation. He writes The numerical value of UT1(IERS)-TAI does not of course, express a duration. In this context, the s only conveys the information that the readings of the two time scales are expressed in graduation seconds. Thank you for that information! Yes, not every quantity with dimension time is a duration, let alone a duration of proper time. The difference between clock readings need not relate to proper time, and not even to the same time scale. A few operations with durations of differing time scales are considered to result in durations (eg, a weighted average of durations measured in different time scales), but most can not. And a sedimentation rate (a quotient velocity/acceleration) can not be considered as a duration, nor as the result of any other operation with time scales. Nevertheless, all these quantities have the dimension of time and can therefore be expressed with the SI unit for time, even though the SI second is (currently) defined as a duration of proper time. This is essential for the meaningful operations that one wants to perform with these quantities (differences of clock readings, averages of durations), but it also makes many meaningless operations possible (such as subtracting a sedimentation rate from a clock reading). Michael Deckers. ___ LEAPSECS mailing list LEAPSECS@leapsecond.com https://pairlist6.pair.net/mailman/listinfo/leapsecs
Re: [LEAPSECS] the big artillery
On 2014-11-05 11:28, Steffen Nurpmeso wrote: Oh, the German Physikalisch-Technische Bundesanstalt (PTB) also has a general -- at least -- overview of the set of problems. (English: [1] and all around that; oops, not everything is translated, what a shame! I hope it's not due to lack of resources, which seems to become notorious in Germany [for things that really matter at least].) .. [1] https://www.ptb.de/cms/en/fachabteilungen/abt4/fb-44/ag-441/realisation-of-the-si-second.html Rest under https://www.ptb.de/cms/en/fachabteilungen/abt4/fb-44/ag-441/realisation-of-legal-time-in-germany/ The very beginning of the last reference is misleading and wrong: Properties of UTC The time scale UTC (Coordinated Universal Time) owes its existence to the CCIR (International Consultative Committee of Radiocommunications) of the ITU (International Telecommunications Union) which proposed to broadcast time signals worldwide in a coordinated way, i.e. by reference to a common time scale. The concept for UTC was devised by people from the BIH and some other metrology institutes, not by the CCIR; and the CCIR has never produced a time scale. It is unfortunate that most sources about time and time scales are full of inaccuracies and errors like these, perpetuated through hundreds of papers and books. Steve Allen's page [http://www.ucolick.org/~sla/leapsecs/timescales.html] gives a carefully researched, reliable account of the history of UTC and other time scales, based on the primary sources. It is the result of an enormous labor in extracting the facts from a mixture with myth and hearsay. Michael Deckers. ___ LEAPSECS mailing list LEAPSECS@leapsecond.com https://pairlist6.pair.net/mailman/listinfo/leapsecs
Re: [LEAPSECS] the big artillery
On 2014-11-05 16:27, Zefram wrote: ... UTC is always an integral number of seconds offset from TAI, and so by construction UTC(NPL) is always an integral number of seconds offset from TAI(NPL). Hence each of the marks also occurs at the top of a second of TAI(NPL). The symbol TAI(k) is defined in RECOMMENDATION ITU-R TF.536-2: Time-scale notations of 2003 with the text: TAI(k): Time-scale realized by the institute “k” and defined by the relation TAI(k) = UTC(k) + DTAI, where DTAI is the number of integral seconds specified by the International Earth Rotation Service (IERS) as being the difference between UTC and TAI; I do not know whether that notation has ever been put to serious use outside this recommendation. The contributions by the various metrology institutes to TAI are independent from the UTC(k) and are denoted by TA(k) in Circular T by the BIPM. The recommendation explains it as: TA(k): Atomic Time-scale, as realized by the institute “k”; Michael Deckers. ___ LEAPSECS mailing list LEAPSECS@leapsecond.com https://pairlist6.pair.net/mailman/listinfo/leapsecs
Re: [LEAPSECS] the big artillery
On 2014-11-04 12:34, Zefram wrote: UT1 always ticks a second for that ERA increase, but Warner's point is that the second of UT1 isn't an *SI* second. The time taken for that ERA increase, and hence the duration of a UT1 second, very rarely exactly matches an SI second. The second of UT1 is an angular unit, defined as 1/86400 circle (= 15 arcseconds), not a unit of physical time. Then which unit would that be? When the IERS compute a difference TAI - UT1, how do they do it? Do they convert the UT1 reading in any way before they subtract? Or, if they don't, what is the unit of the difference, SI seconds or second of UT1? The IERS Conventions certainly do not mention any of this. How could they if the units would really differ? Of course, due to the history, we alias angular seconds to physical seconds all over the place, especially in the mathematical expressions that we use to describe relationships between time scales. Usually we gloss over that by just calling them both second. But if you're going to specify which type of second you mean, better pick the right one for the time scale. I am puzzled by the fact that some people do not seem to accept with time what they easily accept with other quantities. For instance in geodesy, normal height is expressed in meters (or feet) even though it is actually a difference in geopotential observed by leveling. The expression in meters is derived from some conventional normal gravity potential model; comparison with orthonormal height thus gives an intuitive notion of its deviation from the real gravity field. But nobody calls for different units for orthometric and normal heights, on the grounds that a meter of normal height would not be an SI meter of real length while a meter of orthometric height would be. On the contrary, everybody agrees that normal and orthometric height must use the same unit so as to make them comparable. (And, as with time scales, there is a bunch of other important notions of height to which they need to be compared!) The mean solar day on the rotating surface of the Earth is given by the comparison of UT1 with TAI (or TT). Its value, d(TAI)/d(UT1)·(86 400 SI seconds) would be a bad unit of time because it varies remarkably with time. And the mean solar day in a geocentric inertial system (as used in satellite dynamics) is a different value altogether, namely d(TCG)/d(UT1)·(86 400 SI seconds) at the geocenter. Neither quantity is used as a unit to express UT1; instead, both are derived from expressions of UT1, TAI, and TCG in SI units. Michael Deckers. ___ LEAPSECS mailing list LEAPSECS@leapsecond.com https://pairlist6.pair.net/mailman/listinfo/leapsecs
Re: [LEAPSECS] the big artillery
On 2014-11-01 23:31, Steve Allen wrote:
In the appropriate contexts there are days of Terrestrial Time,
International Atomic Time, Barycentric Coordinate Time, Geocentric
Coordinate time, GPS system time, BeiDou system time, etc. Each of
those days is 86400 SI seconds in its own reference frame.
In other contexts there are days of Universal Time, Sidereal Time,
Ephemeris Time. Each of those days is 86400 of its own kind of
seconds.
I disagree. One wants to compare all these time scales with
each other, and comparison requires expression in the
/same/ unit, not in different units.
For instance, the differential rate d(TAI - UT1)/d(UT1) is
published as LOD by the IERS as a dimensionless number
with unit ms/d. To compute this, one must be able to
subtract the reading of UT1 from that of TAI, and to
compute the difference numerically one has to convert to
equal units. The rate is computed correctly /only/ if
one assumes that a second of TAI equals a second of UT1.
I agree that it can still make sense to use different
symbols for the same unit (such as s{TAI} and s{UT1});
it is similarly common practice to distinguish masses
of carbon dioxide from masses of carbon by different
unit symbols g{CO₂} and g{C} for the same unit gram.
Nevertheless, the BIPM seem to advise against such use
[SI brochure 2006, section 5.3.2, p 132]:
Units are never qualified by further information
about the nature of the quantity; any extra
information on the nature of the quantity should
be attached to the quantity symbol and not to the
unit symbol.
Reference:
[SI brochure 2006]:
http://www.bipm.org/utils/common/pdf/si_brochure_8_en.pdf
Michael Deckers.
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Re: [LEAPSECS] the big artillery
On 2014-11-02 19:04, Warner Losh wrote: On Nov 2, 2014, at 11:21 AM, Michael Deckers via LEAPSECS leapsecs@leapsecond.com wrote: For instance, the differential rate d(TAI - UT1)/d(UT1) is published as LOD by the IERS as a dimensionless number with unit ms/d. To compute this, one must be able to subtract the reading of UT1 from that of TAI, and to compute the difference numerically one has to convert to equal units. The rate is computed correctly /only/ if one assumes that a second of TAI equals a second of UT1. This isn’t entirely true. You have to compute the length of the different time scales to the same seconds. You can compute the difference by comparing the clock readings at a fixed point in time after interpolation to a common grid. This will give you the difference in terms of the units of the common grid. If you select UT1 as the common grid, then you can also get a rate to come up with the unit less number. Thanks for your reply. If I understand you right you are saying that comparisons require the same time unit being used in the expression of the time scale values. I agree. But I must confess that I do not understand your use of grid. Time scales are quantities whose values can always be expressed as a sum fundamental epoch + a time value, the latter expressed in a common time unit. The difference between the values (= phases) of two time scales at the same point in spacetime thus is just the sum of the difference of their fundamental epochs plus the difference of their time values (both differences are again time values). And if I compare the rates of the two time scales, then the fundamental epochs used to express the values of either become irrelevant because they are fixed for each time scale. I am not sure which common grid is needed here. You can also compute the frequency ticking of each time scale in terms of one or the other (or a third independent one) to compute the frequency error of one or both of the time scales. Once you have a frequency error (or difference), conversion of units is trivial. This is more likely how the LOD drift number is computed. It’s how you compare different atomic clocks to say this one is slow, that one is fast and assign a frequency error to each one (and a similar construct to assign the phase error of the PPS each one is producing). ... Yes, measuring the differential quotient d(TAI)/d(UT1) and measuring the drift rate LOD = d(TAI - UT1)/d(UT1) = d(TAI)/d(UT1) - 1 are obviously equivalent. .. There are a variety of ways to measure these differences (though UT1 something has to involve astronomy since it is an observational time base) and compute these numbers. Well, most time scales are observed, directly or indirectly -- just the relationships TCB - TDB and TCG - TT are fixed, and UTC and the many civil time scales are determined by fiat. Also, UT1 were ticking in SI seconds, there would be no rate difference. :) No. The unit used to express the values of a time scale does not determine the rate of the time scale. UT1 is a timescale that ticks 1 SI second when the Earth Rotation Angle increases by exactly (2·π rad)/86 636.546 949 141 027 072, and TCB ticks 1 SI second when proper time at the barycenter of the solar system increases by 1 SI second. Each of these time scales is defined or extended to the geoid where their rates differ from that of TAI. Michael Deckers. ___ LEAPSECS mailing list LEAPSECS@leapsecond.com https://pairlist6.pair.net/mailman/listinfo/leapsecs
