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    Re: Leap seconds
    From: Greg R_
    Date: 2008 Dec 30, 09:25 -0800

    --- 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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