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    Re: Index Error - Real vs. Artificial Horizon
    From: Norm Goldblatt
    Date: 2013 Mar 1, 12:07 -0800

    Interesting point about aligning two stars as opposed to using the limb of the Sun- Stars present themselves as Airy Discs whose angular size is approx 2.44 wavelength/Diameter of objective, as mentioned in an earlier post. The limb of the sun will also image, not to a sharp edge, but it will have a 'chamfer' on it whose radius is similar in size. So, really, the ability to align to Sun is easier only because it's an extended arc, and we mentally extrapolate to where crosshairs or adjacent reference objects will touch or become tangent. This ability is called vernier acuity, also discussed on this board nd it enables us to align two parallel straight lines to an angle far tighter than even our visual native resolution.

    This, from someone who has YET to take a fix on anything. All talk, no action. Forgive. Corrections graciously accepted.

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