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--- On Tue, 12/30/08, George Huxtable  wrote:

> Geoffrey Kolbe's intervention has been particularly helpful in 
> clarifying matters.

Indeed. He says "not tightly coupled", and I say "disconnected". Your argument would be what exactly?

> Greg R has not since repeated that statement, but continues
> to defend it.

Why would I need to "repeat it" (ad infinitum...). Did it not register with you the first time I said it?

> It allows almanacs to be printed some years in advance of their 
> predictions, without needing to know whether, or when, leap-seconds 
> will need to be introduced in the interim.

Which was my original point (and I think you're agreeing with it here, though 
you're probably refusing to admit it) -  that whether or not we use 
leap-seconds is totally irrelevant as long as our timescale agrees with the 
one that's published in the almanacs.

--
GregR



--- On Tue, 12/30/08, George Huxtable  wrote:

> From: George Huxtable 
> Subject: [NavList 6851] Re: [NavList /] Re: Leap seconds
> To: NavList@fer3.com
> Date: Tuesday, December 30, 2008, 3:10 AM
> Greg R wrote-
> 
> "George
> 
> "I don't know if you're being pedantic here,
> or if we have an honest failure 
> to communicate (or maybe a little of both...). "
> 
> Yes, I am being pedantic. On a subject such as this, so
> easy to 
> misunderstand, we have to be precise about our words. Greg
> R and I are 
> completely failing to communicate properly. If we can't
> agree about this 
> initial matter, there's no point in further discussion,
> so let's have 
> another go. Geoffrey Kolbe's intervention has been
> particularly helpful in 
> clarifying matters.
> 
> The words in question came from a posting [6805] by Greg R,
> in which he 
> wrote- "Besides, the almanacs have been on UT since
> when - mid 70s? (and 
> thus pretty much "disconnected" from "sun
> time")."
> 
> Greg R has not since repeated that statement, but continues
> to defend it.
> 
> He continues, in [6849]-
> 
> "But I think we can both agree that the current
> timescale that most of us 
> navigators use (i.e. UT) is based on an atomic standard,
> right?"
> 
> No, we can't agree on that. Greg R's phraseing is
> woolly. What does he mean 
> by "based on"? Yes, the STARTING POINT is the
> counting of seconds, of Atomic 
> Time, unrelated to the rotation of the Earth. But then (and
> this is the 
> crucial bit) that count of seconds is SERIOUSLY MODIFIED,
> by the insertion 
> of an unpredictable leap-second here and there, to create
> UT which IS then 
> closely in step with the rotation of the Earth, within less
> than a second. 
> That's the time-scale that almanacs work to. It allows
> almanacs to be 
> printed some years in advance of their predictions, without
> needing to know 
> whether, or when, leap-seconds will need to be introduced
> in the interim.
> 
> George.
> 
> ===========================================
> 
> --- On Mon, 12/29/08, George Huxtable
>  wrote:
> 
> > From: George Huxtable 
> > Subject: [NavList 6848] Re: [NavList /] Re: Leap
> seconds
> > To: NavList@fer3.com
> > Date: Monday, December 29, 2008, 11:00 AM
> > Greg R wrote-
> >
> > ----- Original Message ----- 
> > From: "Greg R."
> 
> > To: 
> > Sent: Monday, December 29, 2008 12:09 AM
> > Subject: [NavList /] Re: Leap seconds. was: [6802]
> Longest
> > year since 1992
> >
> >
> >
> > You're still missing my point, which was (perhaps
> > obliquely) related to
> > whether we need leap seconds inserted into the UT
> scale or
> > not.
> >
> > What I'm trying to say (and I really don't
> know how
> > to re-word this to make
> > it any clearer) is that whatever time scale the
> navigation
> > community agrees
> > on (either with or without "leap seconds"),
> as
> > long as the time that we use
> > in the field (from a chronometer, radio time signal,
> > "atomic" watch,
> > whatever...) matches the time used in the various
> almanacs
> > it's *totally
> > irrelevant* whether or not that time matches the
> actual
> > "sun time" that's
> > been used for centuries.
> >
> > In other words, if the almanac shows a time of
> 16:00:00 for
> > noon at
> > Greenwich on a given day (granted that's a huge
> > difference from UT, but it
> > works for an example), as long as my local timepiece
> also
> > matches that time
> > scale I shouldn't have any problem working a sun
> sight
> > based on that (any
> > more that I would with a timepiece set to UT as is the
> > current practice).
> >
> > Granted it would be nice if our navigation timescale
> were
> > reasonably close
> > to "sun time", but as a practical matter
> whether
> > it does or not is really
> > irrelevant to solving the navigation problem.
> >
> > Make more sense now?
> >
> > =========================
> >
> > What I questioned was Greg R's statement in
> [6805], as
> > follows-
> >
> > "Besides, the almanacs have been on UT since when
> -
> > mid 70s? (and thus
> > pretty much "disconnected" from "sun
> > time"). "
> >
> > And I pointed out that the almanacs have remained
> closely
> > "connected" with
> > "sun time", precisely because of the
> insertions
> > of those leap seconds, by
> > which UT is made to correspond closely with the
> rotation of
> > the Earth..
> >
> > I wonder what it was that happened, in the mid 70s,
> > according to Greg R, to
> > bring that about the "disconnection" he
> refers
> > to? In one way or another,
> > the Nautical Almanac has followed mean Sun time at
> > Greenwich, within a
> > fraction of a second, since 1834, and continues to do
> so.
> >
> > Greg R  has complained that "I think you
> > misinterpreted what I was trying to
> > say", and now "You're still missing my
> > point".
> >
> > But he hasn't withdrawn those words that I quoted,
> and
> > questioned, above,
> > about the almanacs being "disconnected" from
> > "sun time". And I don't know
> > how to interpret those words any differently than the
> way I
> > did.
> >
> > If we can find a way to agree about this minor matter,
> > perhaps we can go on
> > to discuss leap seconds more fruitfully.
> >
> > George.
> >
> > contact George Huxtable, at  george@hux.me.uk
> > or at +44 1865 820222 (from UK, 01865 820222)
> > or at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13
> 5HX, UK.
> >
> >
> >
> >
> 
> 
> 
> 
> 
> 

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