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    Re: Navigation without Leap Seconds
    From: Fred Hebard
    Date: 2008 Apr 15, 08:38 -0400

    Completely unrelated, but stemming from the same article.
    The author states that height can only be known to some few cm or
    whatever because of variations in gravity, if I remember correctly.
    It would seem that this is due to our tradition of assuming we are on
    the surface of a spheroid or ellipsoid when doing navigation.
    Confining ourselves to a surface makes the trig easier, but couldn't
    one position oneself with greater accuracy (with feet firmly planted
    on earth, not on a boat) using only stars or stars plus the sun,
    ignoring the earth's horizon, by measuring star-star distances?  Make
    it a true 3-D problem.  Or would uncertainties in the positions of
    stars still hamper ones efforts, especially uncertainty in their
    distance from us?
    Fred Hebard
    On Apr 14, 2008, at 9:50 PM, frankreed@HistoricalAtlas.net wrote:
    > The fascinating article which Fred Hebard linked:
    >  http://www.physicstoday.org/vol-59/iss-3/p10.html
    > includes a detailed discussion about the problems of gravitational
    > time
    > dilation and extremely accurate clocks. That's the main topic, and
    > it's
    > great stuff.
    > The article also mentions leap seconds and navigation:
    > "Celestial navigators --that vanishing breed-- also like leap
    > seconds. The
    > Global Positioning System, however, cannot tolerate time jumps and
    > employs a
    > time scale that avoids leap seconds."
    > So here's my question: what's the best way of doing celestial
    > navigation if
    > leap seconds are dropped from official time-keeping? I don't think
    > it should
    > be all that difficult to work around, but I'm not sure what the best
    > approach would be. Assume we get to a point where the cumulative time
    > difference is, let's say, 60 seconds (that shouldn't happen for
    > decades, so
    > this is just for the sake of argument). Should we treat the
    > difference as a
    > 60 second clock correction before working the sights? Or should it
    > be a 15
    > minute of arc longitude correction after working the sights? Or
    > something
    > else entirely??
    >  -FER
    > Celestial Navigation Weekend, June 6-8, 2008 at Mystic Seaport Museum:
    > www.fer3.com/Mystic2008
    > >
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