Re: The opportunity of leap seconds
On Sun, 8 Jan 2006, Tom Van Baak wrote: Peter, So where do these modern telescope get UT1? Do you or The last time I was involved personally was during my time as a support astronomer at the Isaac Newton Group on La Palma in the early nineties. We had a radio receiver which required upcoming leapseconds to be entered manually ahead of time. This provided a one second per second UTC interrupt to the telescope control computers. The TCS computers were programmed with an upcoming leapsecond, and with the corresponding jump in DUT1. To compute fractions of a UTC second, the computer adds its own clock to the one-second interrupt count, which gives high precision. The whole system gives UT1 to high precision throughout a leapsecond event and beyond. Pete.
Re: The opportunity of leap seconds
On Sat, 7 Jan 2006, Poul-Henning Kamp wrote: What Astronomers use UTC for, in your own many times repeated words, is a convenient approximation of UT1, and consequently it follows that if instead of an approximation astronomers used the Real Thing, leap seconds could harmlessly be removed from UTC. Too simple; many old telescopes, with equatorial mounts, such as the historic telescopes at the Institute of Astronomy where I work, do indeed use UTC as a UT1 approximation. The time error involved in this is a small offset in one axis which you calibrate out on a clock star. Research-quality telescopes, in particular all the ones built in the last few decades on alt-azimuth mounts, do of course use UT1; a 0.9s error would be a complex ~10 arcsec error in both axes and give a quite useless pointing performance. However, UTC is often used as a UT1 delivery system; because it's an international standard, and is widely available, and DUT1 is guarenteed to be less than 0.9s, it's a natural choice for supplier of time. Interestingly, because control algorithms tend to be rigorous, a large DUT1 probably would be ok in itself (there would be a cost involved in checking that this would be so) but certainly in the case of a couple of telescope control systems of which I have the required knowledge, the DUT1 input method does a 0.9 second range check. Peter.
Re: The opportunity of leap seconds
On Sun 2006-01-08T12:41:21 +0100, Poul-Henning Kamp hath writ: It sounds to me like BIPM ought to make an Internet service available which will deliver UT1 to astronomers in a timely fashion ? That would have to be the IERS. Something as simple as finger [EMAIL PROTECTED] Or even just a more stringent formatting of the bulletins on the ftp site could do it as well. I do not believe that any of the IERS bureaus have internet connections and servers which are anywhere near robust and redundant enough to make that a reliable service. There is a lot that could and should be done. The USNO branch of the IERS issues two files with predictions about earth orientation every Thursday. It is not widely known that last July on the Thursday following the Daniel Gambis announcement one of those files acknowledged the leap second we just experienced, and the other did not. This was fixed with a new release which happened by Friday. (Despite some NTP servers which reportedly still have not acknowledged the leap second, I think the overall indications are that the NTP network did better than 50 %.) The existing IERS system is dysfunctional. -- Steve Allen [EMAIL PROTECTED]WGS-84 (GPS) UCO/Lick ObservatoryNatural Sciences II, Room 165Lat +36.99858 University of CaliforniaVoice: +1 831 459 3046 Lng -122.06014 Santa Cruz, CA 95064http://www.ucolick.org/~sla/ Hgt +250 m
Re: The opportunity of leap seconds
On Jan 8, 2006, at 4:41 AM, Poul-Henning Kamp wrote: It sounds to me like BIPM ought to make an Internet service available which will deliver UT1 to astronomers in a timely fashion ? Not sure BIPM is necessarily the appropriate agent, but otherwise agree 100%. Perhaps we should seek other areas of agreement rather than continually focusing on issues in hot debate. Both this and the extended leap second scheduling represent improvements to infrastructure that would also support market-based decision making about civil time issues in general. The current timekeeping landscape is simply too sparse to create significant emergent behavior.
Re: The opportunity of leap seconds
In message [EMAIL PROTECTED], Steve Allen writes: Something as simple as finger [EMAIL PROTECTED] Or even just a more stringent formatting of the bulletins on the ftp site could do it as well. I do not believe that any of the IERS bureaus have internet connections and servers which are anywhere near robust and redundant enough to make that a reliable service. There is a lot that could and should be done. I'm certainly starting to get the impression that a modernization project to move the time-lords a few decades forward would not be out of order. (Despite some NTP servers which reportedly still have not acknowledged the leap second, I think the overall indications are that the NTP network did better than 50 %.) My estimate is 50-70% of the pool.ntp.org servers did something close enough to the right thing. -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 [EMAIL PROTECTED] | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence.
Re: The opportunity of leap seconds
In message [EMAIL PROTECTED], Peter Bunclark writes: On Sun, 8 Jan 2006, Poul-Henning Kamp wrote: finger [EMAIL PROTECTED] You mean [EMAIL PROTECTED] That would be quiet useful. Otherwise let's not bother with NTP protocol, just [EMAIL PROTECTED] I don't really care what the service is called, but I agree that it should be simple :-) -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 [EMAIL PROTECTED] | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence.
Re: The opportunity of leap seconds
Research-quality telescopes, in particular all the ones built in the last few decades on alt-azimuth mounts, do of course use UT1; a 0.9s error would be a complex ~10 arcsec error in both axes and give a quite useless pointing performance. However, UTC is often used as a UT1 delivery system; because it's an international standard, and is widely available, and DUT1 is guarenteed to be less than 0.9s, it's a natural choice for supplier of time. Interestingly, because control algorithms tend to be rigorous, a large DUT1 probably would be ok in itself (there would be a cost involved in checking that this would be so) but certainly in the case of a couple of telescope control systems of which I have the required knowledge, the DUT1 input method does a 0.9 second range check. Peter. Peter, So where do these modern telescope get UT1? Do you or any other astronomers on the list know if they pick off bits from WWV (or equivalent SW or LF broadcast)? Or is there a nice thumbwheel switch in a control room that someone gets to advance anytime they get an IERS Bulletin by FAX or email? Or is it a software interface to the IERS website? I guess in all the years this list has operated, and with all the detailed anecdotes about leap seconds I've never heard details of how an observatory anywhere actually obtains, and uses, DUT1; and to what level of precision. /tvb
Re: The opportunity of leap seconds
In message [EMAIL PROTECTED], Rob Seaman writes: Astronomers use UT1. Astronomers use UTC. Astronomers are among the biggest users of TAI and GPS and likely any other timescale you care to name. And they certainly have a lot of trouble seeing the rest of the world in for the brightness of their own majesty. The only timescale I am interested in here is UTC, and astronomers are not even close to registering as a marginal group in the user communities of UTC. What Astronomers use UTC for, in your own many times repeated words, is a convenient approximation of UT1, and consequently it follows that if instead of an approximation astronomers used the Real Thing, leap seconds could harmlessly be removed from UTC. By your logic, the U.S. Surgeon General should be a chiropractor. Once the US government tries to shoulder their national deficit that would undoubtedly be a good idea. [various ramblings] Canoli = common basis for diverse time usage worldwide Eclair = baseline representation of Earth orientation Unless we *completely* change our notion of Canoli, Canoli is tightly constrained to follow Eclair simply by the fact that today and tomorrow and the million days that follow are all required to be dark at night and light in the day. Wrong on all points. Light of day and darkness of night already is, and for all relevant future can be, assured by governmental adjustments of the two functions government control in the formula: Civil Time(time) = UTC(time) + TimeZoneOffset(country, subdivision, time) + SeasonalOffset(country, subdivision, time) [various ramblings] -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 [EMAIL PROTECTED] | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence.
Re: The opportunity of leap seconds
Rob Seaman scripsit: Unless we *completely* change our notion of Canoli, Canoli is tightly constrained to follow Eclair simply by the fact that today and tomorrow and the million days that follow are all required to be dark at night and light in the day. I think you are getting carried away by your own rhetoric here. It will be dark at night and light in the daytime even if we smash every clock on Earth (not a bad idea, I think sometimes). What you surely mean is that it should be locally dark when local clocks say and thereabouts, and consequently light when they say 1200 and thereabouts. There is much room for adjustment around the midpoints, however. Whether we choose to bleed off the daily accumulating milliseconds one second or 3600 at a time, bleed them we must...and even people who loathe the very notion of leap seconds admit this. NO, I DON'T ADMIT THAT. On the contrary, I deny it, flatly, roundly, and absolutely. (The craven ITU proposal is obligated to pay lip service to leap hours, though what they really are saying is let's close our eyes and wish it away.) Time to move on. The leap-hour proposal can be read as either (a) a serious proposal to inject an hour into UTC at some future date, or (b) a cynical proposal to abandon leap seconds and not replace them. I think (a) is just as foolish as leap seconds, if not more so. As for (b), it may be the best political approximation to what I really want, which is (c): abandon leap seconds altogether. But then, soon enough, it won't be dark at ! Yes it will, just not in the skies over Greenwich. Practical difficulties can be overcome by making secular changes to the offsets between LCT and UTC, just as is done today when such problems arise. (In the next two years, the U.S., to name just one country, will make two secular changes to its LCT offsets.) The computerniks of the world already know how to handle such things, so future migrations will not be a problem. And people who want, for their legitimate purposes, to have access to UT1 will have to get it some other way. -- It was impossible to inveigle John Cowan [EMAIL PROTECTED] Georg Wilhelm Friedrich Hegel http://www.ccil.org/~cowan Into offering the slightest apology http://www.reutershealth.com For his Phenomenology. --W. H. Auden, from People (1953)
Re: The opportunity of leap seconds
Poul-Henning Kamp scripsit: By your logic, the U.S. Surgeon General should be a chiropractor. Once the US government tries to shoulder their national deficit that would undoubtedly be a good idea. Chiropractors are by no means cheaper to hire than other doctors. Nor are their treatments necessarily the worse because their theory is crappy. Light of day and darkness of night already is, and for all relevant future can be, assured by governmental adjustments of the two functions government control in the formula: Civil Time(time) = UTC(time) + TimeZoneOffset(country, subdivision, time) + SeasonalOffset(country, subdivision, time) Indeed. I did a quick look once at the number of secular changes to the TimeZoneOffset function since the adoption of standard time in the various countries; I may have posted the results here. If not, I'll try to dig them up. -- John Cowan [EMAIL PROTECTED] www.reutershealth.com www.ccil.org/~cowan There was an old manSaid with a laugh, I From Peru, whose lim'ricks all Cut them in half, the pay is Look'd like haiku. He Much better for two. --Emmet O'Brien
Re: The opportunity of leap seconds
On Jan 7, 2006, at 11:37 AM, John Cowan wrote:Whether we choose to bleed off the daily accumulating milliseconds one second or 3600 at a time, bleed them we must...and even people who loathe the very notion of leap seconds admit this. NO, I DON'T ADMIT THAT. On the contrary, I deny it, flatly, roundly, and absolutely.Alternately, you could read what I said. I wasn't claiming all such people would admit it (though, of course, they should). I was pointing out that the ITU already felt obligated to admit it.We've long since devolved into a Monty Python sketch: Owner: Well, o'course it was nailed there! If I hadn't nailed that bird down, it would have nuzzled up to those bars, bent 'em apart with its beak, and VOOM! Feeweeweewee! Mr. Praline: "VOOM"?!? Mate, this bird wouldn't "voom" if you put four million volts through it! 'E's bleedin' demised! Owner: No no! 'E's pining! Mr. Praline: 'E's not pinin'! 'E's passed on! This parrot is no more! He has ceased to be! 'E's expired and gone to meet 'is maker! 'E's a stiff! Bereft of life, 'e rests in peace! If you hadn't nailed 'im to the perch 'e'd be pushing up the daisies! 'Is metabolic processes are now 'istory! 'E's off the twig! 'E's kicked the bucket, 'e's shuffled off 'is mortal coil, run down the curtain and joined the bleedin' choir invisibile!! THIS IS AN EX-PARROT!The leap-hour proposal can be read as either (a) a serious proposal to inject an hour into UTC at some future date, or (b) a cynical proposal to abandon leap seconds and not replace them.I think (a) is just as foolish as leap seconds, if not more so.Glad to hear you say it.The computerniks of the world already know how to handle such things, so future migrations will not be a problem.Thanks! I needed a good chuckle :-)
