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    Re: Leap seconds
    From: George Huxtable
    Date: 2008 Dec 29, 19:00 -0000

    Greg R wrote-
    
    ----- Original Message -----
    From: "Greg R." 
    To: 
    Sent: Monday, December 29, 2008 12:09 AM
    Subject: [NavList 6847] 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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