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    Re: Index Error - Real vs. Artificial Horizon
    From: Brad Morris
    Date: 2013 Mar 1, 10:38 -0500

    Hi David

    I do hope that you are not suggesting that we check the index error by over lapping star images!  Stars do not present themselves as points or even have crisp edges. 

    Far better to use the sun, whose parallax is negligible for our purposes.  The Sun provides crisp edges and the apparent diameter is well known.


    On Mar 1, 2013 10:31 AM, "David Fleming" <d.l.fleming.1---.com> wrote:


    You are not over thinking the problem of parallax and an artificial horizon mirror.

    Your observation of parallax when checking index correction by looking at nearby objects is useful. Best to check parallax with a star, you get a point image to overlap.

    The artificial horizon does mean you are looking at an object from two different points even more widely seperated than the horizon mirror and the index mirror and so the parallax problem is worse. If you tried to measure index error by focusing on an airplane thru AH you would see you have a good
    method of measuring the distance to the airplane.

    However when you observe only celestial objects they will be too far to observe parallax.
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