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    Re: Altitudes, close to 90
    From: Frank Reed CT
    Date: 2004 Dec 1, 15:27 EST
    Bill wrote:
    "This thread has been a bit difficult for me to follow.  Would you please be
    more specific regarding the error(s) you perceive on page 106?"
    Sure. Bauer writes:
    "Swinging an arc is also called rocking the sextant and simply means rotating the instrument from side to side around the line of sight to the horizon."
    And that's not right, but it's a very common error. When this is done correctly, the axis of rotation is about the line of sight to the object in the sky. If the object is nearly straight up, that means you have to rotate the instrument around a nearly vertical axis.
    Two pages later, Bauer has two paragraphs that begin "One more wrinkle.." (I don't have time to copy them here right now but if it would help someone following the discussion, let me know and I will make the effort). His comments there make it clear that he is doing this wrong. If you're observing the Sun, at any altitude, and you "swing the arc", the Sun should remain visible right in the middle of the field of view throughout the process. You sweep back and forth keeping the Sun in view and line it up exactly at the low point of the arc.
    Frank R
    [ ] Mystic, Connecticut
    [X] Chicago, Illinois
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