Re: Monsters from the id
John Cowan wrote: [If TAI - 33 s were taken as the new basis for civil timescales, then] It is UTC that would be eliminated as the basis for local time. It could be maintained for such other purposes as anyone might have. Yes, the IERS could maintain it as the timescale for a timezone whose local time approximates UT1 up to a second. Michael Deckers
Re: The real problem with leap seconds
Yes: there is an order on the set of values of timescales - it is a basic property of spacetime models that one can distinguish past and present, at least locally. Spacetime is a differentiable 4-dimensional manifold, its coordinate functions are usually two times differentiable or more. In particular, the set of values of timescales does indeed have a topology (which is Hausdorff). Sure - this is a reasonable definition of timescale, but I don't think it is wide enough to include UTC. As I understand it, and everyone will correct me if I'm wrong, UTC is not intended to be directly related to spacetime coordinates at all. UTC is (currently) an aproximation to the direction the earth is facing and is adjusted according to how long it takes the earth to end up facing the same direction again. All of this is completely independent from the choice of a particular calendar or of the time units to be used for expressing timescale values. I'd agree with this for TAI (including that it should be the integral of a nice 1-form), but I'm not so sure for UTC. If you subtract a time from a timescale value, you get another timescale value. If you mean to say that UTC takes its values in a different space than TAI then you cannot agree with UTC = TAI - DTAI, as in the official definition of UTC. And if you say that UTC - TAI can be discontinuous (as a function of whatever) with both UTC and TAI continuous then you must have a subtraction that is not continuous. Strange indeed. Where did I misinterpret your post? Yep - you've picked up my intent correctly. I'm saying that subtraction is a stange operator taking a UTC value and a TAI value and gives you something that's a real number. The reason that I came to this conclusion is because none of the documents I've read say that UTC can be expressed as a real number - they all suggest it is expressed as labelled seconds. (For example, see the way that Rec. 460-4 gives UTC values - I've never seen an official looking document that tries to write UTC as a real.) David.
Re: Monsters from the id
On Thu 2006/01/12 02:36:44 CDT, John Cowan wrote
in a message to: LEAPSECS@ROM.USNO.NAVY.MIL
We already have that repeated time sequence and gap in much of the world,
and live with it. These repetitions would be no better and no worse;
when a gap is present, the local sovereignty can omit the gap, but this
is not a necessary feature of the proposal.
At the start of daylight saving where I live the clocks are set forward
from 2am to 3am. Naively it looks like there is a gap. Likewise at the
end of daylight saving the hour from 2am to 3am appears to be repeated.
The apparent gaps and repeats are simply an artifact of what happens to
a clock display when you change it to read a different timescale.
Standard time Summer timeLegal time
--
2005/10/30 00:01:58 AEST (: ):
2005/10/30 00:01:59 AEST (2005/10/30 00:02:59 AEDT) AEST
2005/10/30 00:02:00 AEST - 2005/10/30 00:03:00 AEDT AEST/AEDT
(2005/10/30 00:02:01 AEST) 2005/10/30 00:03:01 AEDTAEDT
(: ) 2005/10/30 00:03:02 AEDTAEDT
(: ) ::
(: ) ::
(: ) 2006/04/02 00:02:58 AEDTAEDT
(2006/04/02 00:01:59 AEST) 2006/04/02 00:02:59 AEDTAEDT
2006/04/02 00:02:00 AEST - 2006/04/02 00:03:00 AEDT AEST/AEDT
2006/04/02 00:02:01 AEST (2006/04/02 00:03:01 AEDT) AEST
2006/04/02 00:02:02 AEST (: ):
:(: ):
It should be clear that the gaps and repeats are fictitious, especially
if you think of AEST and AEDT as existing beyond the times when they are
in legal use. Putting it in practical terms, suppose I have a traffic
accident at 0230 on 2006/04/02, what time will the police officer write
in his report? For most times of the year he can omit the timezone spec
because there is no legal ambiguity, but to do so for this specific hour
would be insufficient, he must specify AEDT or AEST.
The situation with the proposed leap hour is quite different. Given
that AEST is defined as UTC+1000, and AEDT as UTC+1100, would someone
care to speculate, in terms similar to the above, what will happen when
a leap hour is inserted?
Mark Calabretta
ATNF
Re: Monsters from the id
Rob Seaman scripsit: And the point I'm making is that you can't shift timezones at will to accomplish this without creating seams in legally realized time. We already have seams in legally recognized time. Just making the dark stay put would result in ambiguous timekeeping. Daylight saving time layered on solar locked standard time is a different thing from attempting to use an overtly similar mechanism to compensate for the misappropriate substitution of interval time for solar time. Stripped of the adjectives, why is it different? What starts out as gradual (also known as ignored completely) will end in the same familiar quadratic rush. Nothing about your notion mitigates this. In the end, it will be impossible to maintain the notion that a solar day is 24h of 60m of 60s each: we wind up, IIRC, with the solar day and lunar month both at about 47 current solar days. 1) provide a system for uniquely sequencing historical events Haven't got that now. 2) allow events in distant lands to be compared for simultaneity We have that now, but it takes a computer to keep track of all the details in the general case. 3) avoid disputes over contractual obligations That's done by specifying the legal time of a given place. If I agree to meet you under the Waverley at noon 13 March 2020, it's all about what the U.S. Congress says legal time in New York City is as of that date -- which is not predictable in advance. (You will also have a problem finding the Waverley, unless you are an old New Yorker.) 4) minimize the potential for political disagreements Good luck. 5) satisfy religious requirements Out of scope. 6) keep it dark near 00:00 and light near 12:00 Agreed. 7) support educational goals (Yes Virginia, the universe actually makes sense.) No problem. 8) allow coal miners to aspire to be amateur astronomers Eh? I am not recommending abolishing UT1, though it seems strange to me to measure angles in hours, minutes, and seconds instead of in radians like a proper SI-head. (Fourteen inches to the pound, oh Bog!) 9) permit the construction of sundials - public clocks with no moving parts Sundials don't show legal time or even a good approximation of it much of the time. 10) tie an individual's first breathe on her first day to her last breathe on her last day Where's the problem here? Any timescale can do that, even the Mayan Long Count. -- John Cowan [EMAIL PROTECTED] www.reutershealth.com www.ccil.org/~cowan The whole of Gaul is quartered into three halves. -- Julius Caesar
