historic sub-second time offsets
From their inception the International Time Bureau (BIH) produced records of the deviations between various time sources. I have a sampling of those BIH publications from 1960 in images here https://plus.google.com/photos/112320138481375234766/albums/6078225731350227...
1960 is after the availability of cesium atomic chronometers and during the era when Heure Definitive was UT2. These pages include part of the initial attempt to "coordinate" radio broadcasts between the US NBS station WWV and the UK NPL station MSF. They include time offset plots for various observatories for the entire year of 1960, and a couple of pages of the radio broadcast offsets for the end of the year. Also note that these data were not published until as much as a year after the measurements, and only then could one know what time it should have been.
From the turn of the 20th century it was agreed that everyone would use the same the technical basis for determining civil time, but the quality of time available in any particular place depended on available resources and training, so the implementation was imperfect. In many countries the observatory time was the legal time, and the broadcast time signals were, practically, the official time. Plowing through these historic records of time offsets only makes sense for projects such as re-reducing occultation data.
The tz database has always eschewed sub-second offsets. The data on these pages show part of why that is a good thing. -- Steve Allen <sla@ucolick.org> WGS-84 (GPS) UCO/Lick Observatory--ISB Natural Sciences II, Room 165 Lat +36.99855 1156 High Street Voice: +1 831 459 3046 Lng -122.06015 Santa Cruz, CA 95064 http://www.ucolick.org/~sla/ Hgt +250 m
On 11/05/2014 07:47 AM, Steve Allen wrote:
1960 is after the availability of cesium atomic chronometers and during the era when Heure Definitive was UT2.
Was heure définitive really UT2? My French is pretty weak, but page 253 of your source has a table entitled "Temps Universel 2 - Heure Définitive", which makes it appear to be listing the difference between UT2 and heure définitive. Also, I just now looked at a seemingly-authoritative paper on this (see citation below), and its pages 177-8 seem to say that heure définitive was closer to what is now called UT1. It's funny: just today I was wading through the HTML5 spec, which says: "Times in dates before the formation of UTC in the mid twentieth century must be expressed and interpreted in terms of UT1." <http://www.w3.org/TR/html5/infrastructure.html#global-dates-and-times> I'm not brave enough to put anything that specific into the tz documentation. I suspect that nobody putting an accurate circa-1957 time stamp into an HTML5 document has ever consulted a UT2−UT1 difference table in order to conform to the HTML5 standard. And I'm a bit puzzled as to why the HTML5 committee was so specific about which UT variant to use before UTC was introduced. Should we write to the HTML5 committee and say that they got their pre-UTC timescales slightly wrong and they shouldn't have tried to be that precise anyway? Or would that be too brave in the opposite direction? (When was UT1 introduced anyway? :-) My source: Guinot B. History of the Bureau International de l'Heure. Polar Motion: Historical and Scientific Problems, ASP Conference Series, Vol. 208, also IAU Colloquium #178. 2000. pp 175-84. http://adsabs.harvard.edu/full/2000ASPC..208..175G
On Nov 5, 2014, at 2:15 PM, Paul Eggert <eggert@CS.UCLA.EDU> wrote:
On 11/05/2014 07:47 AM, Steve Allen wrote:
1960 is after the availability of cesium atomic chronometers and during the era when Heure Definitive was UT2.
Was heure définitive really UT2? My French is pretty weak, but page 253 of your source has a table entitled "Temps Universel 2 - Heure Définitive", which makes it appear to be listing the difference between UT2 and heure définitive.
No, I think that’s a dash in that table heading, not a minus sign. In other words, the two phrases are synonyms. That is supported by the text on slide 5 (page 258), just below the middle, which says “Les heures définitives (TU2)...”. paul
On Wed 2014-11-05T11:15:47 -0800, Paul Eggert hath writ:
Was heure definitive really UT2?
UT2 became the goal for broadcasts and the reports starting at the beginning of 1956. The distinction between UT0, UT1, and UT2 were described, and the use of UT2 was prescribed at the 1956 August General Assembly of the IAU in Dublin. In August there were no names for the three flavors of UT. I think it is probably Guinot who has written that he supposes the names of the time scales were worked out during the next few months in correspondence between IAU Comm 31 president Markowitz and Stoyko at BIH.
My French is pretty weak, but page 253 of your source has a table entitled "Temps Universel 2 - Heure Definitive", which makes it appear to be listing the difference between UT2 and heure definitive.
In the title it is in fact a hyphen, not a minus sign. The tabulated numbers are for TU(i) or TU2(i), where (i) is a particular station. The difference between that and Heure Demi-Definitive was published bi-monthly with whatever data had been provided to BIH. For the final Heure Definitive the differences were published annually after gathering data from every possible contributor. BIH was perennially under-staffed, under-funded, months to a year arrears in publishing, and during that era all of those calculations and plots were being done by hand. When the algorithms changed the new schemes were published in Bulletin Horaire, but the notations require very close attention to be sure what they thought they were doing. It was a very fiddly process with unique parameters for each data source, and the algorithms are described with terminology that is no longer in use. The bi-monthly series of Bulletin Horaire for 1955 Nov/Dec have tables with the heading (and I am not making a typo here) Temps Uniersvel - Heure Demi-Definitive That issue gives an indication of their strained proofreading resources; it arrived only 6 months in arrears.
Also, I just now looked at a seemingly-authoritative paper on this (see citation below), and its pages 177-8 seem to say that heure definitive was closer to what is now called UT1.
I have not dug through enough volumes to find the incept date for that particular change, but that was true during roughly the 1940s through 1955 as the systematic offsets between what eventually became called UT0 and UT1 had become recognized.
It's funny: just today I was wading through the HTML5 spec, which says:
"Times in dates before the formation of UTC in the mid twentieth century must be expressed and interpreted in terms of UT1." <http://www.w3.org/TR/html5/infrastructure.html#global-dates-and-times>
As stated that is close enough to correct. Go farther back and the times are now better described as UT0, but the measurement errors of the technologies contributing to the numbers which were available to the general public get as big as the difference between UT1 and UT0. The point is that neither the HTML5 spec nor the the tz database should be burdened with the chaos of the way time and time signals were handled differently from one location (or one decade) to another prior to 1972. There was a common goal, that goal was based on what we know as Universal Time, and the details only dare be incorporated into the most specialized purposes. -- Steve Allen <sla@ucolick.org> WGS-84 (GPS) UCO/Lick Observatory--ISB Natural Sciences II, Room 165 Lat +36.99855 1156 High Street Voice: +1 831 459 3046 Lng -122.06015 Santa Cruz, CA 95064 http://www.ucolick.org/~sla/ Hgt +250 m
On 11/05/2014 12:30 PM, Steve Allen wrote:
BIH was perennially under-staffed, under-funded, months to a year arrears in publishing
I can certainly identify with that! Thanks for the info. So, it appears that HTML5 authors and readers are not supposed to use definitive circa-1960 civil time stamps. They are supposed to use astronomical time stamps instead. Astronomers rule! This can't be what was intended. I have submitted a bug report against the HTML5 spec about this, here: https://www.w3.org/Bugs/Public/show_bug.cgi?id=27253
The tz database has always eschewed sub-second offsets.
This was a result of the early work being focused on supporting non-sub-second functions such as "localtime;" absence of sub-second timestamps in early versions of UNIX also played a role. We might expect TZDBv6 to have sub-second offsets, as well as Julian calendar support, Persian calendar support, and noon typing (solar, local mean, civil:-) @dashdashado On Wed, Nov 5, 2014 at 10:47 AM, Steve Allen <sla@ucolick.org> wrote:
From their inception the International Time Bureau (BIH) produced records of the deviations between various time sources. I have a sampling of those BIH publications from 1960 in images here
https://plus.google.com/photos/112320138481375234766/albums/6078225731350227...
1960 is after the availability of cesium atomic chronometers and during the era when Heure Definitive was UT2. These pages include part of the initial attempt to "coordinate" radio broadcasts between the US NBS station WWV and the UK NPL station MSF. They include time offset plots for various observatories for the entire year of 1960, and a couple of pages of the radio broadcast offsets for the end of the year. Also note that these data were not published until as much as a year after the measurements, and only then could one know what time it should have been.
From the turn of the 20th century it was agreed that everyone would use the same the technical basis for determining civil time, but the quality of time available in any particular place depended on available resources and training, so the implementation was imperfect. In many countries the observatory time was the legal time, and the broadcast time signals were, practically, the official time. Plowing through these historic records of time offsets only makes sense for projects such as re-reducing occultation data.
The tz database has always eschewed sub-second offsets. The data on these pages show part of why that is a good thing.
-- Steve Allen <sla@ucolick.org> WGS-84 (GPS) UCO/Lick Observatory--ISB Natural Sciences II, Room 165 Lat +36.99855 1156 High Street Voice: +1 831 459 3046 Lng -122.06015 Santa Cruz, CA 95064 http://www.ucolick.org/~sla/ Hgt +250 m
participants (4)
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Arthur David Olson -
Paul Eggert -
Paul_Koning＠dell.com -
Steve Allen