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    Re: Hello (+ a few questions)
    From: Dan Hogan
    Date: 1999 Feb 08, 15:25 EST

    Welcome to the list. I hope you join in on the navigation problems.
    This is the list for Non-electronic navigation so you have come to the
    right place.
    > I have two questions which I hope someone on this list can help me with.
    > 1) I am trying to locate an obscure reference cited in Bowditch?s
    > _American Practical Navigator: An Epitome of Navigation_ (p. 423, 1958
    > edition; vol. II, p. 546, 1977/81 edition) to a study performed by the
    > Carnegie Institute of Washington on the application of the standard
    > formula for the correction for dip:
    >   dip (minutes of arc) = 0.97 sqrt(h[ft])
    Well, I don't know much about the history of dip. There is some history
    on dip in."A History of Nautical Astronomy, by Charles H. Cotter, 1968
    Hollis & Carter Ltd, ISBN 470-00460-4.
    The current U.S. constant, as published in "Pub No. 9, The American
    Practical Navigator, Bowditch, 1995, DMAH", is D = 0.97' x SQRT Height
    of eye in feet.
    > The constant 0.97 in the above relation depends on the local atmospheric
    > conditions and the quoted value applies to average weather conditions. The
    > studies by the Carnegie Institute appear to have been made to verify how
    > well this relation stands up to varying weather conditions and how large
    > the deviations can be in extreme cases.
    > I would be most grateful if someone on this list can provide me with a
    > more complete reference to this study.
    > 2) My second question is of a more cartographical nature. After
    > inspecting several 20th-century atlases I noticed that in each source the
    > International Date Line (IDL) is drawn along a slightly path and that no
    > two atlases agree completely. Is there such a thing as an Internationally
    > agreed Date Line? If so, who decides on these matters? And what do
    > countries who straddle the IDL have to say in this matter?
    > As everyone probably already knows the issue has become more complicated
    > since 1995 when the island Republic of Kiribati decided to shift the IDL,
    > which bisected the country, to follow its eastern boundaries. Which leads
    > to another question again: what are the internationally recognized borders
    > of Kiribati? Again different recent atlases represent them slightly
    > differently.
    The nautical international date line is the 180 degree longitude line.
    Everything else is political and is subject to change at the whim of
    the affected governing body. Not meant as a smart remark , just the way
    it works.
    > I measured a set of approximate co-ordinates for the corner points
    > defining the eastern boundary of Kiribati from the _National Geographic
    > Atlas of the World_ (6th ed., 1992). Rounded to the nearest degree, I
    > found the following latitudes and longitudes (positive in eastern
    > direction):
    >   {+2,180},
    >   {0,-179},
    >   {0,-165},
    >   {-3,-165},
    >   {-3,-160},
    >   {+2,-160},
    >   {+2,-162},
    >   {+5,-162},
    >   {+5,-154},
    >   {-8,-151},
    >   {-12,-151},
    >   {-12,-157},
    >   {-9,-157},
    >   {-9,-178}
    > Does anyone on this list know how to obtain more accurate figures?
    Since all the political international date line is good for (IMHO) is
    local time, I think one would have to contact the government of
    Kiribati. Hopefully one of the experts on the list can supply you
    better information.
    Dan Hogan WA6PBY
    Catalina 27 "GACHA"
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