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    Re: Reducing back sights
    From: Jim Thompson
    Date: 2004 Aug 11, 17:34 -0300

    Thanks George,
    
    My question is theoretical, since I have only tried a backsight with a
    sextant (not octant) once, for fun, and then did not really understand what
    to do with the observation.  Also I wanted to include more detail in my
    website at
    http://jimthompson.net/boating/CelestialNav/CelestNotes/SightReduction.htm#B
    ackSights , and a correspondent asked me via email to expand on the process.
    I was unable.
    
    I am interested in using a sextant for situation number 4: "At sea,He wishes
    to measure the altitude of a body above a horizon which is obscured by
    nearby land or by mist [or ships], though the horizon in the opposite
    direction is clear."
    
    Jim Thompson
    jim2{at}jimthompson.net
    www.jimthompson.net
    Outgoing mail scanned by Norton Antivirus
    -----------------------------------------
    
    > -----Original Message-----
    > From: George Huxtable
    
    > A further question now arises: what does Jim Thompson wish to use
    > an octant
    > backsight FOR? I can think of four applications.
    >
    > 4. At sea,He wishes to measure the altitude of a body above a
    > horizon which
    > is obscured by nearby land or by mist, though the horizon in the opposite
    > direction is clear.
    >
    > In cases 1, 2, and 3, dip doesn't enter the question at all,
    > because angles
    > aren't being measured from the horizon.
    >
    > Whatever purpose he wishes to use the back-sight quadrant for, Jim has to
    > decide just how he is going to determine its index correction, on land or
    > at sea. Only then can we say how the observation should be reduced.
    >
    > Over to you, Jim.
    
    
    

       
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