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    Re: venus
    From: Frank Reed CT
    Date: 2004 Oct 16, 17:26 EDT
    George H wrote:
    "The angle to be subtracted from TA to obtain OA is, in this routine-
    Arc-tan ( cos TA / ((23455 * D) - sin TA))
    The amount of this correction now corresponds very closely (with a change
    of sign) to the correction that's added to OA to obtain TA."

    Yes, except for the swapped sine and cosine which Herbert Prinz noted.

    The other way to get this parallax correction for the true altitude is to do the more familiar reverse calculation, h' = h + HP*cos(h), iteratively (twice, thrice). In other words, the true altitude plus parallax correction gets you close to the observed altitude. Then using that as input gets you as near as you would like to be to the correct parallax correction. That's the way my code did it and that's how it was done traditionally, but at some point (I believe it was months ago) I set the iteration count to 1 for testing and never set it back. That was the bug.

    Note that this did not affect any other calculations on my web site including almanac and lunar distance predictions.

    Frank R
    [ ] Mystic, Connecticut
    [X] Chicago, Illinois
       
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