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    Re: Swinging the arc: two methods, one preferred
    From: Byron Franklin
    Date: 2011 Jan 6, 08:50 -0800

    The Vertical Sextant.
    This tip will enable even the inexperienced celestial navigator to plot
    celestial (pinwheels on the chart by using a simple sextant technique.
    In 1958, 1 was stationed on a Liberty ship of World War II vintage. For months
    at a time for five years, the ship was under way approximately 200 miles off
    the East Coast
    Using Loran ?A? and the sextant to maintain radar, air craft and missile
    tracking station. The duty was a pleasure for a celestial navigation nut like
    myself because in any month I observed, computed, plotted and evaluated an
    average of 20 morning and evening star fixes, plus countless sun lines.
    The best fixes were always when the horizon was fully lit, toward the day side
    of twilight. Once the stars became bright, the horizon would darken and
    become a thick band. The best plan was to sight while the stars were just
    showing, bring the star to the sharp horizon, swing the star (rock the
    sextant), and lay the star on the horizon. Many times, especially with a high
    star, the star would disappear on or near the well-lit horizon.
    The sky just above the horizon is lighter than the rest of the sky and the
    swinging takes away some of the concentration needed to stay locked onto the
    faint star or the pale disk of a planet. In order to sit that faint star on
    the distinct horizon, I experimented with bringing the faint star into the
    relatively darker water and rocking the sextant, watching the star enter and
    leave (in and out) the water.
    I found that I could quickly isolate the exact point under the star ?Vertical
    Sextant,? be it high or low. I could concentrate on putting the star on the
    horizon by halving the ?in and out? mentally and bringing the star above that
    point on the horizon and then coming down for the mark. It worked so well for
    me that I started using the same procedure for the sun and bright stars. Very
    accurate fixes were easy.
    I admit that my celestial fixes were not so accurate after a transfer to duty
    with less demanding celestial navigation practice. When I shifted back to
    ?Vertical Sextant? (in and out of the water), my fixes would improve and
    tighten with no random near misses. Give the technique a good try.
    Byron Franklin
    Newport, Rhode Island.


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