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    Re: instances of the use of "horizon grazing" technique
    From: George Huxtable
    Date: 2009 Oct 23, 17:32 +0100

    Apache Runner is right to be sceptical about all these concepts, though I'm
    saying that without having read the particular work he refers to, by Leif
    Karlsen.
    
    But do "horizon-grazing stars" exist, in reality? Can any star be seen, as
    it just grazes the horizon? Maybe Venus or Jupiter, at rising or setting,
    but I'm somewhat doubtful about that. Stars tend to disappear, within a few
    degrees of the horizon, because of the enormous attenuation of light by the
    hundreds of miles of atmosphere that their light has to pass through.
    
    So, for any proponent of "horizon-grazing stars", I have a few questions.
    
    If a star was seen actually at the horizon, I would expect its light to
    flicker sharply on and off, for a few seconds, as the point-source was first
    occulted, then not, by moving waves at the horizon, and heaving of the
    observer. Has anyone, on the list, ever observed this, anywhere in the
    World? I haven't, but then my experience is in the famously murky
    environment of UK waters.
    
    Has anyone observed even Venus or Jupiter as they actually rise and set, at
    the horizon?
    
    If, to handle horizon-grazing stars, the observer has to apply an
    extinction-angle, above the horizon, at which such stars will vanish, can
    anyone suggest what value should be used, how it would vary with the star's
    magnitude and the clarity of the air? And what would be the expected
    accuracy of the result?
    
    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.
    ----- Original Message -----
    From: "Apache Runner" 
    To: 
    Sent: Friday, October 23, 2009 4:35 PM
    Subject: [NavList 10254] Re: instances of the use of "horizon grazing"
    technique
    
    
    | I've read Karlsen's book.   It's quite entertaining, and I was interested
    to
    | see that he spent a fair amount of time testing out the use of calcite as
    a
    | way of measuring the polarization state of the sky.
    |
    | He does discuss at length both the concept of the Viking sun compass and
    the
    | sun stone.  As this list is quite familiar, these two items are
    | controversial topics, as neither are fully accepted.   My main
    | disappointment with Leif's book is that he doesn't do a critical
    evaluation
    | of these, although I was impressed with the lengths he went to evaluate
    the
    | efficacy of Icelandic spar.
    |
    | The issue for me is that, because he bought the sun stone, and sun compass
    | concepts wholly, that it made me more skeptical of other techniques he
    | discusses.
    |
    | My question really goes to whether there is some documented proof of
    horizon
    | grazing stars.
    |
    | Another associated technique that survival books teach is latitude by
    length
    | of day.    Although it seems to be possible in practice, I'm unaware of
    | people actually employing this, although I am aware of people using
    | sunrise/sunset timing for navigation.
    |
    |
    | John H.
    |
    | |
    |
    
    
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