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    Re: Davis MK III Index Error
    From: Brad Morris
    Date: 2015 May 11, 18:54 -0400


    *any* celestial object can be used for this.

    The moon, the stars, a comet, a planet, etc.  I like the sun and the moon because the superimposition of images permits the edges to be closely examined.

    Your cloud may be closer than you think!  As Frank points out, that will lead to error.  Will it do in a pinch?  But of course!  As will a fence, distant lamp post, etc.  Just be aware that you will inject a small error. 

    The object?  To get the ray of light from the index mirror to be parallel to the ray of light thru the horizon mirror when the index arm reads zero.  The more distant the object observed, the more parallel the rays.  Naturally, at some point the parallelism (or minor lack thereof) does not affect your celestial measurements, as it is too small to care about.


    On May 11, 2015 6:47 PM, "Herman Dekker" <NoReply_Dekker@fer3.com> wrote:

    Hello Brad, with the Davis MKIII it is not possible to look direct to the sun. The horizon shades are too light, I used last night Venus, that works, but is not useable if I want to use the sun. So perhaps high cloud with sharp edge. Hopefully not to many clouds that hide the sun.


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