Re: [LEAPSECS] future access to solar time?
The Astronomical Almanac (2019) says ∆UT = UT1 - UTC DUT1 = predicted value of ∆UT, rounded to 0.1 s, given in some radio time signals (Unfortunately, this scan cuts off part of the leftmost characters. But you can deduce them, except perhaps Ee and Eo: equation of the equinoxes and equation of the origins.) https://archive.org/details/binder1_202003/page/n121/mode/2up?view=theater IERS Bulletins A and B say "UT1-UTC" instead of ∆UT. I think that's a good idea. It prevents confusion about the sign. The current version of Bulletin A estimates UT1 will lose about 0.1 s with respect to atomic time during the next year. https://www.iers.org/IERS/EN/Publications/Bulletins/bulletins.html ___ LEAPSECS mailing list LEAPSECS@leapsecond.com https://pairlist6.pair.net/mailman/listinfo/leapsecs
Re: [LEAPSECS] future access to solar time?
Interesting!
Another example of “polysemy”
(http://hanksville.org/futureofutc/aas223/presentations/2-1-ISOterminologyAAS.pdf)
in timekeeping.
In addition to changes in funding (be careful what you ask for, precision time
community), best practices (and worse practices) should get a good workout as
this foundational standard is redefined.
Rob
On 11/21/22, 8:30 AM, "LEAPSECS" wrote:
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 2022-11-21 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?
Interesting. 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”. To the UTC decision-makers does “operability” mean legal constraints or does it mean physical reality / technical infrastructure? (“UTC no longer depends on UT1, so why should we pay for it?”) For UTC/GPS context, Stephen Malys had a talk at the Exton meeting in 2011: http://hanksville.org/futureofutc/2011/preprints/32_AAS_11-675_Malys.pdf, but I don’t see the question of high precision requirements addressed directly (and much may have changed in 11 years). Which is to ask, I suppose, will redefining UTC imply that activities like VLBI will need to seek different funding streams? Rob Seaman Lunar and Planetary Laboratory University of Arizona On 11/21/22, 6:37 AM, "LEAPSECS" wrote: 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 ___ LEAPSECS mailing list LEAPSECS@leapsecond.com https://pairlist6.pair.net/mailman/listinfo/leapsecs
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] future access to solar time?
Tony Finch said: > Well, no, not for more than half the year. I happen to be close to the > Greenwich meridian so my clocks currently show something close to mean > solar time (about 30 seconds fast, I think?) but that isn't true for most > people. Indeed. I live 1 minute 37 seconds east of the prime meridian - I'm probably closest to it of anyone on this list. > The clock on the wall tells the time for social > purposes, not for the position of the sun in the sky. Right. And that's without the equation of time coming into the, um, equation. -- Clive D.W. Feather | If you lie to the compiler, Email: cl...@davros.org | it will get its revenge. Web: http://www.davros.org | - Henry Spencer Mobile: +44 7973 377646 ___ LEAPSECS mailing list LEAPSECS@leapsecond.com https://pairlist6.pair.net/mailman/listinfo/leapsecs
Re: [LEAPSECS] future access to solar time?
Hi Tony, The time zone system and daylight-saving time are layered on UTC. My clock shows Mountain Standard Time year-round. Other people’s show other local times and 10-15% of these change by an hour twice a year. These small complications will not be made simpler by attempting to remove the concept of mean solar time from the system. Those who want to dispute this might ask themselves why they bother, considering the lab-coated acolytes of atomic time have already voted to redefine UTC. Similarly, complications like the equation of time and its graphical representation as the analemma don’t change the (current) fundamental traceability back to mean solar time. See innumerable discussions on this list or at meetings like Exton or Charlottesville. We are ultimately not talking about the “leap second” we are talking about the definition of the word “day”. Many astronomical systems do care at the level of the current UTC approximation. Some care at much higher precision. So, what alternative standards and infrastructure will be available in the future? Time to move on… Rob On 11/20/22, 10:31 AM, "LEAPSECS" wrote: External Email Seaman, Robert Lewis - (rseaman) wrote: > > Getting the solar time currently means looking at your watch or the > upper right-hand corner of the monitor. Well, no, not for more than half the year. I happen to be close to the Greenwich meridian so my clocks currently show something close to mean solar time (about 30 seconds fast, I think?) but that isn't true for most people. I assumed from your complaint about losing access to solar time that you cared about roughly-second or subsecond precision, because if your precision requirements are "look at the clock on the wall" your complaint does not make sense. The clock on the wall tells the time for social purposes, not for the position of the sun in the sky. -- Tony Finchhttps://dotat.at/ Isle of Man: West 5 or 6, backing south 3 or 4, then southeast 6 or 7 later. Mainly moderate, becoming slight for a time. Showers, rain later. Mainly good, becoming moderate or poor later. ___ LEAPSECS mailing list LEAPSECS@leapsecond.com https://pairlist6.pair.net/mailman/listinfo/leapsecs ___ LEAPSECS mailing list LEAPSECS@leapsecond.com https://pairlist6.pair.net/mailman/listinfo/leapsecs
Re: [LEAPSECS] future access to solar time?
Seaman, Robert Lewis - (rseaman) wrote: > > Getting the solar time currently means looking at your watch or the > upper right-hand corner of the monitor. Well, no, not for more than half the year. I happen to be close to the Greenwich meridian so my clocks currently show something close to mean solar time (about 30 seconds fast, I think?) but that isn't true for most people. I assumed from your complaint about losing access to solar time that you cared about roughly-second or subsecond precision, because if your precision requirements are "look at the clock on the wall" your complaint does not make sense. The clock on the wall tells the time for social purposes, not for the position of the sun in the sky. -- Tony Finchhttps://dotat.at/ Isle of Man: West 5 or 6, backing south 3 or 4, then southeast 6 or 7 later. Mainly moderate, becoming slight for a time. Showers, rain later. Mainly good, becoming moderate or poor later. ___ LEAPSECS mailing list LEAPSECS@leapsecond.com https://pairlist6.pair.net/mailman/listinfo/leapsecs
Re: [LEAPSECS] future access to solar time?
As important as UT1 is in astrology, look to South Asia/East Asia for a solution to this problem. It is also important in the determination of Jewish and Islamic prayer times. Many existing apps that provide these services rely on UTC as a rough representation of UT1, but if UTC drifts from UT1 by more than 1 second, they will develop new ways to handle that difference. I expect there will be a proliferation of updated apps, some of which are tied to various national observatories, that will compete in the offering of some form of UT1 or DUT1 that could then be related to UTC on local systems. But given the importance of UT1 to many people, I will be curious to see if some nations set up their own time synchronization protocols to disseminate UT1. Between China and India, there's a large enough market for this. Cheers, Kevin -- "Time is the measure of a wobbly world, and things slipping away." Rabanus Maurus, 9th century. Kevin K. Birth Department of Anthropology Queens College, CUNY Flushing, NY 11367 From: LEAPSECS On Behalf Of Seaman, Robert Lewis - (rseaman) Sent: Sunday, November 20, 2022 10:55 AM To: Leap Second Discussion List Subject: Re: [LEAPSECS] future access to solar time? Hi Tony, Getting the solar time currently means looking at your watch or the upper right-hand corner of the monitor. Would anybody else's summary of the notion of "easy access" include phrases like: "8.23 bits two's complement fixed point" or "NMEA sentences that contain anything like UT1 or DUT1 or delta-T"? I have been presuming tenth-second DUT1 values are slated for demolition with leap seconds. Can anybody confirm differently? I applaud the goal of ensuring understanding and usage of whatever infrastructure will exist. Few systems currently use DUT1. One of the issues is that many more will need to start. UT1 itself is only known retroactively. If your use of the word "stunt" wasn't a typo, it seems to me that NIST rather needs robust and easy-to-use infrastructure. I was never able to get reliable access to the UT1 NTP server, and generally, our group doesn't build reliance on third-party NTP pools into our operational systems. We should all welcome GNSS support for access to UT1 (or a coherent variation known in advance), but as you suggest this will require new infrastructure and standards. Perhaps I'm off the mark, but that most definitely doesn't imply anybody else has yet found the mark themselves. Rob Seaman, Robert Lewis - (rseaman) mailto:rsea...@arizona.edu>> wrote: > The plan, rather, is to cease easy access to solar time. The resolution says the GCPM : encourages the BIPM to work with relevant organizations to identify the : need for updates in the different services that disseminate the value of : the difference (UT1-UTC) and to ensure the correct understanding and use : of the new maximum value. So I think your summary is a bit off the mark. I guess the ITU is going to revise TF.460 to allow larger values of DUT1 in time signals, and MSF etc. will accommodate the change too. (Do any of the national broadcast signals actually follow the ITU spec?) GPS L5 signals provide UT1 as an 8.23 bits two's complement fixed point difference from GPS time. This is enough to cope with the changes in the CGPM resolution. See IS-GPS-705 p. 87 at https://www.gps.gov/technical/icwg/<https://nam02.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.gps.gov%2Ftechnical%2Ficwg%2F=05%7C01%7Ckevin.birth%40qc.cuny.edu%7C0032e12a552a4f38e1e908dacb0f94e9%7C6f60f0b35f064e099715989dba8cc7d8%7C0%7C0%7C638045565490819930%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C=UkI6Nr1O%2FtHAf4Hx3f32qFwzA58K6r%2B3TrK8MQL%2BCvc%3D=0> I have not been able to find any specs for NMEA sentences that contain anything like UT1 or DUT1 or delta-T, but I expect they will be created before too long, as more GPS receivers support L5 signals. And there are other sources of UT1 like NIST's stunt NTP servers. -- Tony Finch mailto:d...@dotat.at>> https://dotat.at/<https://nam02.safelinks.protection.outlook.com/?url=https%3A%2F%2Fdotat.at%2F=05%7C01%7Ckevin.birth%40qc.cuny.edu%7C0032e12a552a4f38e1e908dacb0f94e9%7C6f60f0b35f064e099715989dba8cc7d8%7C0%7C0%7C638045565490819930%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C=rW6Z4%2F9joFauwpFzsMmi24ULV3S8HcfEKkSC%2FAffO98%3D=0> ___ LEAPSECS mailing list LEAPSECS@leapsecond.com https://pairlist6.pair.net/mailman/listinfo/leapsecs
Re: [LEAPSECS] future access to solar time?
Hi Tony, Getting the solar time currently means looking at your watch or the upper right-hand corner of the monitor. Would anybody else’s summary of the notion of “easy access” include phrases like: “8.23 bits two’s complement fixed point” or “NMEA sentences that contain anything like UT1 or DUT1 or delta-T”? I have been presuming tenth-second DUT1 values are slated for demolition with leap seconds. Can anybody confirm differently? I applaud the goal of ensuring understanding and usage of whatever infrastructure will exist. Few systems currently use DUT1. One of the issues is that many more will need to start. UT1 itself is only known retroactively. If your use of the word “stunt” wasn’t a typo, it seems to me that NIST rather needs robust and easy-to-use infrastructure. I was never able to get reliable access to the UT1 NTP server, and generally, our group doesn’t build reliance on third-party NTP pools into our operational systems. We should all welcome GNSS support for access to UT1 (or a coherent variation known in advance), but as you suggest this will require new infrastructure and standards. Perhaps I’m off the mark, but that most definitely doesn’t imply anybody else has yet found the mark themselves. Rob Seaman, Robert Lewis - (rseaman) wrote: > The plan, rather, is to cease easy access to solar time. The resolution says the GCPM : encourages the BIPM to work with relevant organizations to identify the : need for updates in the different services that disseminate the value of : the difference (UT1-UTC) and to ensure the correct understanding and use : of the new maximum value. So I think your summary is a bit off the mark. I guess the ITU is going to revise TF.460 to allow larger values of DUT1 in time signals, and MSF etc. will accommodate the change too. (Do any of the national broadcast signals actually follow the ITU spec?) GPS L5 signals provide UT1 as an 8.23 bits two's complement fixed point difference from GPS time. This is enough to cope with the changes in the CGPM resolution. See IS-GPS-705 p. 87 at https://www.gps.gov/technical/icwg/ I have not been able to find any specs for NMEA sentences that contain anything like UT1 or DUT1 or delta-T, but I expect they will be created before too long, as more GPS receivers support L5 signals. And there are other sources of UT1 like NIST's stunt NTP servers. -- Tony Finchhttps://dotat.at/ ___ LEAPSECS mailing list LEAPSECS@leapsecond.com https://pairlist6.pair.net/mailman/listinfo/leapsecs
Re: [LEAPSECS] future access to solar time?
Seaman, Robert Lewis - (rseaman) wrote: > > The plan, rather, is to cease easy access to solar time. The resolution says the GCPM : encourages the BIPM to work with relevant organizations to identify the : need for updates in the different services that disseminate the value of : the difference (UT1-UTC) and to ensure the correct understanding and use : of the new maximum value. So I think your summary is a bit off the mark. I guess the ITU is going to revise TF.460 to allow larger values of DUT1 in time signals, and MSF etc. will accommodate the change too. (Do any of the national broadcast signals actually follow the ITU spec?) GPS L5 signals provide UT1 as an 8.23 bits two's complement fixed point difference from GPS time. This is enough to cope with the changes in the CGPM resolution. See IS-GPS-705 p. 87 at https://www.gps.gov/technical/icwg/ I have not been able to find any specs for NMEA sentences that contain anything like UT1 or DUT1 or delta-T, but I expect they will be created before too long, as more GPS receivers support L5 signals. And there are other sources of UT1 like NIST's stunt NTP servers. -- Tony Finchhttps://dotat.at/ East Sole, Lundy, Fastnet: Westerly backing southerly, 5 to 7, then becoming cyclonic 7 to severe gale 9 later, perhaps storm 10 later. Rough or very rough, becoming very rough or high later. Rain or showers. Good, occasionally poor. ___ LEAPSECS mailing list LEAPSECS@leapsecond.com https://pairlist6.pair.net/mailman/listinfo/leapsecs
[LEAPSECS] future access to solar time?
Whatever they do to poor old UTC and by extension to the concept of Universal Time as the modern realization of Greenwich Mean Time, atomic time and solar time will continue to be separate kinds of time scales, both of which are necessary for diverse engineering requirements for civil timekeeping, as well as for technical applications. “Ceasing leap seconds” is an incoherently stated goal since there already are timescales without leaps. The plan, rather, is to cease easy access to solar time. The past 20 years have seen a concerted effort to avoid the 2003 Torino consensus to define a new leap-less time scale. We now have a few years before Universal Time becomes Universal-except-for-solar Time. Could we perhaps spend the time more productively and design a new solar time scale, with-or-without leaps? UT1 as it currently exists is not sufficient. Flat files on 19th-century servers are not sufficient. Arnold Rots supplied an excellent diagram of timescales in the solar system for a session we held at the 2014 meeting of the American Astronomical Society: http://hanksville.org/futureofutc/aas223/ None of this complexity goes away by waving a wand to vanish leap seconds. Rather, the green box between UTC and UT1 gets much more complicated, including some fictional future leap-minute or repeated redefinitions of worldwide time zones or some fantasy of the whole world moving to a single time zone. What are the overall engineering requirements for the multi-timescale system-of-systems? What are the best practices for evaluating possible timekeeping infrastructure and standards in a world that freezes UTC at a static offset from TAI? The concept of operations isn’t limited to how our gill-equipped, web-fingered descendants will implement a leap-hour long after we’re all dead. Maybe they’ll switch to tide-based clocks. The question is how do we optimize access to the diversity of time scales starting now? Rob Seaman Lunar and Planetary Laboratory University of Arizona ___ LEAPSECS mailing list LEAPSECS@leapsecond.com https://pairlist6.pair.net/mailman/listinfo/leapsecs
