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    Re: First sights
    From: Gary LaPook
    Date: 2007 Jan 22, 15:38 -0800

    Gary LaPook wrote:
    
    You can also take sights using an artificial horizon.
    To make one of these simply put water in a saucer (or,
    much better if you can get it, use murcury) and the
    surface of the liquid will be perfectly horizontal.
    Measure the altitude of the star using its reflection
    in the saucer as the reference point instead of the
    horizon. Due to the geometry of the situation (angle
    of incidence equals angle of reflection) you end up
    measuring exactly twice the altitude. Then simply
    apply the index correction and divide the remainder by
    2, then apply refraction but not dip corrections. You
    need a still night so that the wind doesn't ripple the
    surface of the water. I have been using a small bottle
    of murcury for over forty years for this and because
    of its reflective quality I can take second magnitude
    stars such as polaris, with water you can shoot first
    magnitude stars easily. If shooting the sun make sure
    you use both sets of shades and line up the lower limb
    with its reflection in the liquid which will be the
    top of the sun's reflection.
    
    I remember one night in 1990 we were anchored in a
    long fjord on the east coast of Tahaa (an island about
    20 nm east of Bora Bora) and it was so still that I
    could see the stars reflected in the ocean around the
    boat. I got out my Tamaya and took a round of sight
    and got a fix that crossed on our anchorage.
    
    
    --- Gary  wrote:
    
    >
    > Thanks to everyone for the great information.  Took
    > my new sextant to
    > the lake sat morning and took some sights before the
    > clouds rolled in
    > and the snow descended.  after using HO 299 for the
    > calculations I
    > ended up between 2 - 5 miles from where the GPS said
    > I was standing on
    > the shore.  Had to use dip short calculations as the
    > lake was 1.2 miles
    > wide in the direction of the sights.  Overall it was
    > great fun to
    > reduce the sun and see what things looked like in
    > the sextant.  I still
    > need to understand the filters better, as well as
    > need LOTS more
    > practice.  My 15 yr old daughter who was recording
    > info for me enjoyed
    > taking some sights as well.  Actually she turned out
    > to be the closest
    > once all the calculations were done.
    >
    >
    >
    >
    >
    
    
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