[LEAPSECS] Nit-pick: SI second
That may all be true. But is the SI second a unit of measurement? yes, one that can be reproduced a priori anywhere in the universe that someone has a cesium atom. Doesn't it depend upon gravity (aka sea level)? Is that standardized? -- These are my opinions, not necessarily my employer's. I hate spam. ___ LEAPSECS mailing list LEAPSECS@leapsecond.com http://six.pairlist.net/mailman/listinfo/leapsecs
Re: [LEAPSECS] Nit-pick: SI second
On Mon, 7 Feb 2011, Hal Murray wrote: Doesn't it depend upon gravity (aka sea level)? Is that standardized? Yes. The SI second is defined independent of any reference frame. The TAI second is the SI second as realised on the geoid. There are other timescales that are based on SI seconds in particular reference frames, most notably TCG and TCB. Tony. -- f.anthony.n.finch d...@dotat.at http://dotat.at/ HUMBER THAMES DOVER WIGHT PORTLAND: NORTH BACKING WEST OR NORTHWEST, 5 TO 7, DECREASING 4 OR 5, OCCASIONALLY 6 LATER IN HUMBER AND THAMES. MODERATE OR ROUGH. RAIN THEN FAIR. GOOD. ___ LEAPSECS mailing list LEAPSECS@leapsecond.com http://six.pairlist.net/mailman/listinfo/leapsecs
Re: [LEAPSECS] Mean ... Orbits
On Fri, 4 Feb 2011, Steve Allen wrote: But cesium chronometers became available at the very same IAU meeting which defined UT2, and by the time cesium had been calibrated with ET and UT2 it was already evident that cesium revealed the earth, and thus UT2, was badly irregular. I thought that this had been established before WWII, by highly stable quartz clocks. So the time bureaus recognized that it was impractical to follow the CCIR recommendation, that broadcast signals wanted to be as regular as possible, and much more regular than UT2. So for the sake of broadcasts the time bureaus created a cesium-regulated time scale aimed at roughly following UT2. I got the impression that the key problem in the 1950s was that it required lengthy observations to derive time and frequency corrections. They had switched from using solar transitions to lunar occlusions because the stability of the orbit of the moon is much greater than the rotation of the earth. But this was not good enough for real-time broadcasts of stable time and frequency references. Hence the rapid switch to atomic clock references when they became available. Tony. -- f.anthony.n.finch d...@dotat.at http://dotat.at/ HUMBER THAMES DOVER WIGHT PORTLAND: NORTH BACKING WEST OR NORTHWEST, 5 TO 7, DECREASING 4 OR 5, OCCASIONALLY 6 LATER IN HUMBER AND THAMES. MODERATE OR ROUGH. RAIN THEN FAIR. GOOD. ___ LEAPSECS mailing list LEAPSECS@leapsecond.com http://six.pairlist.net/mailman/listinfo/leapsecs
Re: [LEAPSECS] LEAPSECS Digest, Vol 51, Issue 22
On Mon 2011-02-07T12:21:08 -0500, Finkleman, Dave hath writ: Neiher Gravity nor the Geoid are standardized. The SI definition for TAI says rotating geoid. Resolution B1.9 (Re-definition of Terrestrial Time TT) from the XXIVth IAU GA recognizes both that the geoid changes and that it is hard to specify the geoid, therefore the rate of TT was changed from the rotating geoid to a constant potential offset from the coordinate time of the geocenter. Bernard Guinot has stated his belief that TAI is supposed to be a realization of TT, therefore the CCTF should incorporate the IAU definition for TT into TAI, but that has not happened. I suspect that CCTF has not acted because as a practical matter it would make no difference. Until there is an ensemble of cesium chronometers not on the surface of the earth there is no easy way to measure the potential depth to 1e-10, so the corrections currently being used to compensate for the NIST and PTB chronometers being about a mile high are as good as things can get. If it turns out that an actual measurement finds the potential of the geoid to differ then that would require a notable rate change in TAI. So the fact is that we should all be preparing our children for the day when the rates of TT and TAI differ. Alternatively, the IAU might redefine TT again. It's hard to say which would cause less grief. -- Steve Allen s...@ucolick.orgWGS-84 (GPS) UCO/Lick ObservatoryNatural Sciences II, Room 165Lat +36.99855 University of CaliforniaVoice: +1 831 459 3046 Lng -122.06015 Santa Cruz, CA 95064http://www.ucolick.org/~sla/ Hgt +250 m ___ LEAPSECS mailing list LEAPSECS@leapsecond.com http://six.pairlist.net/mailman/listinfo/leapsecs
Re: [LEAPSECS] LEAPSECS Digest, Vol 51, Issue 22
On 7 Feb 2011, at 17:21, Finkleman, Dave wrote: I finally get a chance to look like I might know something. Neiher Gravity nor the Geoid are standardized. Witness that maps from some countries do not employ WGS-84. United Kingdom uses OSGB36 rather than WGS84, and a different Elipsoid too (Airy 1830) which is a better fit locally. ian ___ LEAPSECS mailing list LEAPSECS@leapsecond.com http://six.pairlist.net/mailman/listinfo/leapsecs
Re: [LEAPSECS] Nit-pick: SI second
Doesn't it depend upon gravity (aka sea level)? Is that standardized? Hal, Yes and no. The SI second is defined in the local reference frame. So your cesium clock at sea level ticks SI seconds for you there. Your cesium clock on a mountain ticks SI seconds for you there. The fact that the two clocks will disagree when compared with each other is true; but both clocks are still ticking SI seconds in their own frames. Now to make a time-scale out of these identical but differing SI seconds does require some statement of common elevation. So this is why reported clock data is all adjusted to sea level in the computation of TAI (and hence UTC). /tvb ___ LEAPSECS mailing list LEAPSECS@leapsecond.com http://six.pairlist.net/mailman/listinfo/leapsecs
Re: [LEAPSECS] LEAPSECS Digest, Vol 51, Issue 22
On Mon, 7 Feb 2011, Steve Allen wrote: Until there is an ensemble of cesium chronometers not on the surface of the earth there is no easy way to measure the potential depth to 1e-10, so the corrections currently being used to compensate for the NIST and PTB chronometers being about a mile high are as good as things can get. The PTB campus is at about 75m above sea level. Also, doesn't the GPS count as an ensemble of atomic clocks? Tony. -- f.anthony.n.finch d...@dotat.at http://dotat.at/ HUMBER THAMES DOVER WIGHT PORTLAND: NORTH BACKING WEST OR NORTHWEST, 5 TO 7, DECREASING 4 OR 5, OCCASIONALLY 6 LATER IN HUMBER AND THAMES. MODERATE OR ROUGH. RAIN THEN FAIR. GOOD. ___ LEAPSECS mailing list LEAPSECS@leapsecond.com http://six.pairlist.net/mailman/listinfo/leapsecs
Re: [LEAPSECS] Nit-pick: SI second
On 02/07/2011 10:58, Tom Van Baak wrote: Now to make a time-scale out of these identical but differing SI seconds does require some statement of common elevation. So this is why reported clock data is all adjusted to sea level in the computation of TAI (and hence UTC). It is also why TAI's rate was adjusted in the 1990's to compensate for the red-shifted data that had been collected at NIST in Boulder, since it sits at about 5400' (1700m) above sea level (as well as other facilities not at sea level). Warner ___ LEAPSECS mailing list LEAPSECS@leapsecond.com http://six.pairlist.net/mailman/listinfo/leapsecs
Re: [LEAPSECS] LEAPSECS Digest, Vol 51, Issue 23
This discussion exposes the fact that we don't all have to work in the same reference frame or time system - as long as we understand what we are using and make it clear to users. Orbit data transfer standards developed by CCSDS and others require sufficient metadata that users can reproduce your results with the same outcome and transform your data into the time system and reference frame they wish to use. Metadata also includes characteristics of the geopotential model. There is no point in propagating to high order and degree initial information that was created at low order or degree, for example. Unfortunately, some operators don't know what is inside the black box. We accommodate this by requiring the fields but not the real content. If geopotential info fields are filled with default characters, we know that this idiot doesn't even know what he did and discount his input. Lying is another story. However, there are institutional sanctions for providing false information. Like, you get cut off from everyone else's data. These lessons came hard. For example, lack of gravitational metadata led to low perigee events in Superbird 6, a Comsat. The launch provider included lunar gravitation and the on-orbit operator did not. The handover state provided by the launch agency did not lead to the desired final orbit for the operator. With regard to what is significant and what is not. If someone raised the issue, then it must be significant to him. If the others don't care or it doesn't matter to them, it won't matter if they have the additional information or greater precision. I've said this before, We don't create standards for people who don't need them. We create standards for those who do need them. The don't cares usually don't get a vote. GRACE mission data is available in near real time for those who worry about Earth tides and millimeters of ocean height! (The units are cm/sec^2, which are now called Gals -- for Galileo.) Dave Finkleman Senior Scientist Center for Space Standards and Innovation Analytical Graphics, Inc. 7150 Campus Drive Colorado Springs, CO 80920 Phone: 719-510-8282 or 719-321-4780 Fax: 719-573-9079 Discover CSSI data downloads, technical webinars, publications, and outreach events at www.CenterForSpace.com. ___ LEAPSECS mailing list LEAPSECS@leapsecond.com http://six.pairlist.net/mailman/listinfo/leapsecs
Re: [LEAPSECS] LEAPSECS Digest, Vol 51, Issue 23
On Mon, 7 Feb 2011, Finkleman, Dave wrote: This discussion exposes the fact that we don't all have to work in the same reference frame or time system - as long as we understand what we are using and make it clear to users. Though the whole point of universal time is that it's the default timscale for civil use and only specialists should need anything else. Tony. -- f.anthony.n.finch d...@dotat.at http://dotat.at/ HUMBER THAMES DOVER WIGHT PORTLAND: NORTH BACKING WEST OR NORTHWEST, 5 TO 7, DECREASING 4 OR 5, OCCASIONALLY 6 LATER IN HUMBER AND THAMES. MODERATE OR ROUGH. RAIN THEN FAIR. GOOD. ___ LEAPSECS mailing list LEAPSECS@leapsecond.com http://six.pairlist.net/mailman/listinfo/leapsecs
Re: [LEAPSECS] LEAPSECS Digest, Vol 51, Issue 22
Those wishing to bone up on geodesy and coordinate systems, especially those used in the U.K., may wish to read: http://www.ordnancesurvey.co.uk/oswebsite/gps/docs/A_Guide_to_Coordinate_Systems_in_Great_Britain.pdf -- Richard Quoting Ian Batten i...@batten.eu.org: On 7 Feb 2011, at 17:21, Finkleman, Dave wrote: I finally get a chance to look like I might know something. Neiher Gravity nor the Geoid are standardized. Witness that maps from some countries do not employ WGS-84. United Kingdom uses OSGB36 rather than WGS84, and a different Elipsoid too (Airy 1830) which is a better fit locally. ian ___ LEAPSECS mailing list LEAPSECS@leapsecond.com http://six.pairlist.net/mailman/listinfo/leapsecs === Richard B. LangleyE-mail: l...@unb.ca Geodetic Research Laboratory Web: http://www.unb.ca/GGE/ Dept. of Geodesy and Geomatics EngineeringPhone:+1 506 453-5142 University of New Brunswick Fax: +1 506 453-4943 Fredericton, N.B., Canada E3B 5A3 Fredericton? Where's that? See: http://www.city.fredericton.nb.ca/ === ___ LEAPSECS mailing list LEAPSECS@leapsecond.com http://six.pairlist.net/mailman/listinfo/leapsecs
Re: [LEAPSECS] LEAPSECS Digest, Vol 51, Issue 22
GPS Time actually come from a paper clock composed of all satellite and ground station clocks: http://tycho.usno.navy.mil/gpstt.html. -- Richard Quoting Tony Finch d...@dotat.at: On Mon, 7 Feb 2011, Steve Allen wrote: Until there is an ensemble of cesium chronometers not on the surface of the earth there is no easy way to measure the potential depth to 1e-10, so the corrections currently being used to compensate for the NIST and PTB chronometers being about a mile high are as good as things can get. The PTB campus is at about 75m above sea level. Also, doesn't the GPS count as an ensemble of atomic clocks? Tony. -- f.anthony.n.finch d...@dotat.at http://dotat.at/ HUMBER THAMES DOVER WIGHT PORTLAND: NORTH BACKING WEST OR NORTHWEST, 5 TO 7, DECREASING 4 OR 5, OCCASIONALLY 6 LATER IN HUMBER AND THAMES. MODERATE OR ROUGH. RAIN THEN FAIR. GOOD. ___ LEAPSECS mailing list LEAPSECS@leapsecond.com http://six.pairlist.net/mailman/listinfo/leapsecs === Richard B. LangleyE-mail: l...@unb.ca Geodetic Research Laboratory Web: http://www.unb.ca/GGE/ Dept. of Geodesy and Geomatics EngineeringPhone:+1 506 453-5142 University of New Brunswick Fax: +1 506 453-4943 Fredericton, N.B., Canada E3B 5A3 Fredericton? Where's that? See: http://www.city.fredericton.nb.ca/ === ___ LEAPSECS mailing list LEAPSECS@leapsecond.com http://six.pairlist.net/mailman/listinfo/leapsecs
Re: [LEAPSECS] LEAPSECS Digest, Vol 51, Issue 23
On 2/7/2011 2:49 PM, Tony Finch wrote: On Mon, 7 Feb 2011, Finkleman, Dave wrote: This discussion exposes the fact that we don't all have to work in the same reference frame or time system - as long as we understand what we are using and make it clear to users. Though the whole point of universal time is that it's the default timscale for civil use and only specialists should need anything else. Tony. Many units are derived from the second. While I might be interested in reporting the time of day of an event in UTC, I will make virtually all other measurements, such as current, force, mass, and length, in units derived from the SI second as it exists in my reference frame. If I carry out a precision realization of any of the other units, the SI second in my reference frame will follow, even if I don't have an atomic clock. Gerry Ashton ___ LEAPSECS mailing list LEAPSECS@leapsecond.com http://six.pairlist.net/mailman/listinfo/leapsecs
Re: [LEAPSECS] LEAPSECS Digest, Vol 51, Issue 23
Tony Finch wrote: the whole point of universal time is that it's the default timscale for civil use and only specialists should need anything else. Stephen should add this to the consensus building list. ___ LEAPSECS mailing list LEAPSECS@leapsecond.com http://six.pairlist.net/mailman/listinfo/leapsecs
[LEAPSECS] The comedy of the commons
On Feb 7, 2011, at 12:37 PM, Finkleman, Dave wrote: Unfortunately, some operators don't know what is inside the black box. We accommodate this by requiring the fields but not the real content. If geopotential info fields are filled with default characters, we know that this idiot doesn't even know what he did and discount his input. Idiot may or may not be accurate, but it doesn't seem the key engineering point. Plenty of people are ignorant of the appropriate values to place in a geopotential info field, including probably 98% of the readers of this list and certainly including me. For an operator of any system to be ignorant of key control parameters, however, is simply unacceptable. The question is why they remain ignorant - and why they don't recognize it - and why others don't find out until problems result. Possibilities to look at are training, user interfaces, discordant standards, etc., and quite likely interactions between multiples of these. These lessons came hard. For example, lack of gravitational metadata led to low perigee events in Superbird 6, a Comsat. The launch provider included lunar gravitation and the on-orbit operator did not. The handover state provided by the launch agency did not lead to the desired final orbit for the operator. Whatever the handover state, should it not have been vetted in advance? Surely launch sequence workflows are simulated in advance of lighting the big candle? It can't be a novel experience for launch providers and on-orbit operators to be working from different versions of the script. Aren't there tools for reconciling differences before tons of expensive equipment are burning up over Fiji? We don't create standards for people who don't need them. We create standards for those who do need them. The don't cares usually don't get a vote. There is a difference between needing and caring. Very few care about leap seconds. Very few know about leap seconds. The final statement of this syllogism might be modified to: The don't needs don't get a vote. ...but even this isn't quite right. Technical issues, including most standards issues, don't really devolve to voting as an ideal decision-making process. We can likely all agree on wording like: Standards are for those who need them. The question is what process - in the inevitable presence of ignorant stakeholders as well as the remarkable lack of foresight and planning shown repeatedly by humans - is what process should be followed to figure out who needs what. That party A may not need something party B does, does not mean that party A has no interest in seeing that party B gets what they need. (Yet another variation of the tragedy of the commons.) Rob ___ LEAPSECS mailing list LEAPSECS@leapsecond.com http://six.pairlist.net/mailman/listinfo/leapsecs
Re: [LEAPSECS] Nit-pick: SI second
On 02/07/2011 12:10, Tom Van Baak wrote: It is also why TAI's rate was adjusted in the 1990's to compensate for the red-shifted data that had been collected at NIST in Boulder, since it sits at about 5400' (1700m) above sea level (as well as other facilities not at sea level). Warner Are you sure you aren't confusing red shift (which has been a known factor since the 60's) with blackbody shift (which only arose in the 90's as clocks hit the 1e-15 level)? I may well be confused between the two... Warner ___ LEAPSECS mailing list LEAPSECS@leapsecond.com http://six.pairlist.net/mailman/listinfo/leapsecs
Re: [LEAPSECS] Nit-pick: SI second
On Mon 2011-02-07T14:39:10 -0700, Warner Losh hath writ: Are you sure you aren't confusing red shift (which has been a known factor since the 60's) with blackbody shift (which only arose in the 90's as clocks hit the 1e-15 level)? I may well be confused between the two... Astronomically-speaking neither one has a relevant effect. The IAU did not object when BIH/BIPM changed the rate of TAI by 1e-12 on 1977-01-01. Whereas the SI second was based on the ephemeris second, and the ephemeris second was originally specified to 1e-12, the effect of the rate change amounts to 0.25 s over the entirety of written human history. No astronomical observation was ever likely to distinguish the change. -- Steve Allen s...@ucolick.orgWGS-84 (GPS) UCO/Lick ObservatoryNatural Sciences II, Room 165Lat +36.99855 University of CaliforniaVoice: +1 831 459 3046 Lng -122.06015 Santa Cruz, CA 95064http://www.ucolick.org/~sla/ Hgt +250 m ___ LEAPSECS mailing list LEAPSECS@leapsecond.com http://six.pairlist.net/mailman/listinfo/leapsecs
Re: [LEAPSECS] LEAPSECS Digest, Vol 51, Issue 23
On 02/07/2011 14:03, Rob Seaman wrote: Tony Finch wrote: the whole point of universal time is that it's the default timscale for civil use and only specialists should need anything else. Stephen should add this to the consensus building list. Yes. Along with the point that civil time keepers use whatever they are told to use... (eg, the shift from UT1 to UTC and China's very wide timezone). Warner ___ LEAPSECS mailing list LEAPSECS@leapsecond.com http://six.pairlist.net/mailman/listinfo/leapsecs
[LEAPSECS] Consensus has value
Warner Losh wrote: On 02/07/2011 14:03, Rob Seaman wrote: Tony Finch wrote: the whole point of universal time is that it's the default timscale for civil use and only specialists should need anything else. Stephen should add this to the consensus building list. Yes. Along with the point that civil time keepers use whatever they are told to use... (eg, the shift from UT1 to UTC and China's very wide timezone). Again - the point is to build consensus, not to divide and conquer. An assertion that civil time keepers use whatever they are told to use is not something I would back when engineering a system, no matter what my opinion on other issues. It is a complex value judgement and likely irrelevant (and probably wrong on its face in this instance). Perhaps you can reword it? As far as eg examples, these also seem orthogonal to the consensus building exercise. Examples are great, but have to be interpreted. I don't know that I understand what you are trying to imply by the shift from UT1 to UTC. Whatever it is, I suspect it is on shaky ground historically. And while we've discussed timezones any number of times over the years, we've often disagreed on the interpretation of the issues involved. (Note I'm forgoing my usual explication of my own position here - I think the consensus exercise is of value.) It appears that Warner does agree with Tony and me that: [T]he whole point of universal time is that it's the default timscale for civil use and only specialists should need anything else. Perhaps this can be split in two: Universal Time is the default timescale for civil use. Specialists may need other timescales. That we each may have different ideas about the meaning of such assertions is not pertinent to building a consensus on the ideas we do share. Rob ___ LEAPSECS mailing list LEAPSECS@leapsecond.com http://six.pairlist.net/mailman/listinfo/leapsecs
Re: [LEAPSECS] LEAPSECS Digest, Vol 51, Issue 24
Addressing all comments at once: 1. I had a similar exchange with Yuri Davydov, then Deputy Director of ROSKOSMOS, the Russian Space Agency. His response to operators not understanding their own operation was, Get smarter operators! He is correct. Some day, when I have been retired from the Air Force a bit longer, I will better qualify that exchange. I retired in 1993. It has not been long enough. 2. Whoever observed that ALL pertinent exchanges between collaborators should be vetted in advance is right on the mark. When time and intellect allow, there should always be well coordinated Interface Control Documents (ICD). The standard message formats are very clearly qualified to be guides for such negotiation. However, they are an expedient for communication among those who do almost never work with each other -- for example, when two satellites that are uncoordinated come too close to each other. If you visit the SOCRATES page on our website (http://www.centerforspace.com) you will see that this happens hundreds of times each day. (It's under Tools.) Dave Finkleman Senior Scientist Center for Space Standards and Innovation Analytical Graphics, Inc. 7150 Campus Drive Colorado Springs, CO 80920 Phone: 719-510-8282 or 719-321-4780 Fax: 719-573-9079 Discover CSSI data downloads, technical webinars, publications, and outreach events at www.CenterForSpace.com. ___ LEAPSECS mailing list LEAPSECS@leapsecond.com http://six.pairlist.net/mailman/listinfo/leapsecs
Re: [LEAPSECS] LEAPSECS Digest, Vol 51, Issue 24
On Mon 2011-02-07T19:07:17 -0500, Finkleman, Dave hath writ: When time and intellect allow, there should always be well coordinated Interface Control Documents (ICD). Who's volunteering to persuade all local governments to conform to an ICD for communicating a change in daylight/summer time to the tz mailing list and to advise them on the expected lead time required for changes to zoneinfo files to be propagated to all affected operating systems? -- Steve Allen s...@ucolick.orgWGS-84 (GPS) UCO/Lick ObservatoryNatural Sciences II, Room 165Lat +36.99855 University of CaliforniaVoice: +1 831 459 3046 Lng -122.06015 Santa Cruz, CA 95064http://www.ucolick.org/~sla/ Hgt +250 m ___ LEAPSECS mailing list LEAPSECS@leapsecond.com http://six.pairlist.net/mailman/listinfo/leapsecs
Re: [LEAPSECS] Consensus has value
Warner Losh wrote: Might be a better way to put it. Civilian time users just need to agree on what time it is amongst the various parties. Everything else is a second order effect. We seem to be debating again, rather than seeking assertions of consensus :-) Parties are not necessarily human. This appears to be the essence of the Chicken Little The computers are falling! argument. In particular, parties may sometimes (my position) include Mother Earth (or at least, Mother Nature's sons). Also, second order effects are not always negligible. Which is to say that I don't believe we've reached consensus on this phrasing. My statement wasn't so much to say that we can dictate and the civilian users will follow but rather once a time convention becomes established, civilian users tend to not worry too much about the details and accept whatever greater authorities tell them the time is. They call the time hotline and/or lookup time via ntp rather than building their own sundial, surveying it and using it to get second-accurate time. ...speaking of second order effects :-) There are numerous issues relating to the ease or difficulty of (initially) instituting this or that policy. These are orthogonal to the long term wisdom of any particular policy. The official time is becoming UTC. It used to be UT1, or rather a more strict mean solar time than UTC strictly speaking is (as it is just an approximation of mean solar time). We'll leave aside the fact that this transition is occurring as a tactic to redefine civil timekeeping :-) I have no problem with the notion of approximation. Simply ceasing leap seconds would cause UTC to drift secularly from Universal Time (strict or otherwise) - it would no longer be such an approximation. Whatever it is, I suspect it is on shaky ground historically. I don't see how. You asserted it used to be UT1. Rather, the definition of UT1 was some complex part of the UTC saga itself. For instance, UT1 is only known after the fact. Civil time used to be (substitute your preferred verb here) Greenwich Mean Time. I just point out that timezones and DST suggest that a strict, to the second, synchronization with local sun time is unnecessary. I'll refrain from my usual response that this confuses secular with periodic effects. Mean time is not averaged apparent time, etc and so forth. UTC is the basis of the common worldwide civil timekeeping system upon which the timezones are layered. UTC is itself layered on TAI. The ITU is seeking to remove a layer from the middle of the cake - and, in effect, claims this won't even disturb the icing (fondant for Charm City fans). My point here is that Universal time is used because it was widely available, not necessarily because of any other intrinsic property of Universal time. Ubiquity is indeed a key requirement. It would be unwise to assume that all the characteristics of UT1 are required in any successor. ...and it would be unwise to assume that redefining the meaning of the word day is a trivial change. Avoiding unwarranted assumptions is the point of building consensus before taking action. That's why I said above that tweaks to the system that are somehow promulgated or become defacto standards are adopted when they are easy. This is an excellent argument for change based on evolving the current standard rather than replacing one standard (UTC) with another (TAI) that addresses a different set of requirements. It isn't that change is being considered - the astronomers here have supported the possibility of various (prudent) changes). It is that a dramatic change to the entire dual architecture of (civil) timekeeping is being unilaterally pursued. You can see it in UTC even: everybody does the easy parts, many botch leap seconds and hope that ntpd and/or manual intervention will paper-over any mistakes. Folks on both sides have used these observations to support their positions. Some of these changes are minor and matter not at all, while other changes matter a lot (eg, changing the rate that TT ticks by 1e-15 didn't matter, while changing GMT from starting at noon to starting at midnight matter so much that a new name for the new GMT was invented). The ITU has been free at any point to define a new timescale with a new name. Rob ___ LEAPSECS mailing list LEAPSECS@leapsecond.com http://six.pairlist.net/mailman/listinfo/leapsecs
[LEAPSECS] Correspondence of solar to civil time
Recently my mom was visiting me in Florida from New York, and when I was taking her to the airport, she noticed the time was about 4:45 PM, and that it was broad daylight outside, and remarked that at this time in New York it would be dark already. This is an example of how people do make note of the correspondence of civil time to solar time in their particular locality at a particular time of year, and notice when the current correspondence differs from what they're used to. And the famous song that Christina Aguilera flubbed the lyrics to at the Super Bowl refers to the dawn's early light and the twilight's last gleaming, not to atomic time! -- == Dan == Dan's Mail Format Site: http://mailformat.dan.info/ Dan's Web Tips: http://webtips.dan.info/ Dan's Domain Site: http://domains.dan.info/ ___ LEAPSECS mailing list LEAPSECS@leapsecond.com http://six.pairlist.net/mailman/listinfo/leapsecs
Re: [LEAPSECS] LEAPSECS Digest, Vol 51, Issue 24
In message 3b33e89c51d2de44be2f0c757c656c880a1c4...@mail02.stk.com, Finklema n, Dave writes: come too close to each other. If you visit the SOCRATES page on our website (http://www.centerforspace.com) you will see that this happens hundreds of times each day. (It's under Tools.) Nice tool, but it looks slightly silly to predict near hits for space-crafts which are docked to each other, in particular when it takes up 7 of 10 slots on your list... -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 p...@freebsd.org | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence. ___ LEAPSECS mailing list LEAPSECS@leapsecond.com http://six.pairlist.net/mailman/listinfo/leapsecs
