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    Re: Sun squash- was Green Flash and Longitude
    From: Frank Swift
    Date: 2006 Jan 19, 17:51 -0800

    For those of us lucky enough to be on the west coast, the January
    edition of "Latitude 38" in the column "Max Ebb: photo finish", p.p.
    158 - 161 is of interest.
    The gist of the article was that on a race to Mexico the Navigator
    forgot his sextant.  He determined his position using photoshop and a
    digital camera.
    He measured the number of pixels that told him the angle.  He knew the
    focal length of the lens, the size of the sensor in the camera and the
    number of pixels across the image.
    Using photoshop he determined the sun to be 303 pixels wide at the zoom
    He then checked the Nautical Almanac data:  Semi-diameter of the sun is
    16.3 minutes at that time of year which came out to 0.176 minutes per
    He then measured the distance from the top edge of the sun to the
    horizon; checked the line length and divided by 60 and he got the
    "observed altitude" of the sun's upper limb in degrees.
    He then checked the clock time of the camera with the GPS time for the
    chronometer correction and used the PC-Nav DOS program from Davis and
    cranked out the program.
    He got the longitude position that was within 0.4 miles.
    Frank Swift
    KG6WZA                         S/V "Is A Bella"
    ~ _) ~ The world is not interested in how many storms you survived,
                            only that the ship arrived. ~ _) ~
      ~ ~ (\_ ~ (\_ ~ (\_~ ~ ~ ~ ~ ~ ~ ~ (\_ ~ (\_ ~ (\_~ ~

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