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    Correction: Error in H.O. 229 Introduction/Explanation?
    From: Sean C
    Date: 2013 Apr 21, 08:02 -0700

    In an earlier message, I wrote:
    "Greg,
    [...]
    You continued:
    'When using the NGA 229 calculator the Z rules don't change when the altitude becomes negative (see attached pic 175).'

    This is also true. And, IMHO, in error. Which leads me to believe that whoever coded the calculator used the introduction as a guide."

    I would like to correct this particular statement. Upon first looking at Greg's screenshot of the NGA calculator, I did not notice that he had entered a North Latitude and Declination. Therefore, the result displayed is, in fact, correct. Further investigation on my part revealed that inputting a South Latitude and Declination, as is the case in the example from H.O. 229, also results in the correct azimuth of 134.4°.

    However, this does not change the fact that the introduction to H.O. 229 is in error. The author claims that a body with a Declination of 35°S at an LHA of 240°, when viewed from a location at 45°S, will have a true azimuth of 45.6°. This is simply wrong.

    I have attached three screenshots. One is of the NGA calculator with the correct values from the H.O. 229 example. The next is a screenshot from Stellarium, Showing Kaus Australis (with a Declination of S34°22.6', as close as I could reasonably find to 35°) as viewed from 45°00.0'S, 0°00.0'E with an LHA of 16h00m1s (~240°). The third is a detail of the information in the top left corner of the second shot. Here one can see the correct altitude/azimuth for this case of 6°10'16"/134°01'48".

    Apologies,
    Sean C.
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