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    Re: Buying a sextant- a cautionary tale.
    From: Alexandre Eremenko
    Date: 2006 Apr 30, 18:15 -0400

    The math behind the proposed method is the SAME
    as with the Sun. Think of the Sun as two stars,
    32' apart. One at the upper limb another at the lower limb.
    You can read these 32' in two ways: on the arc and off the arc.
    (I assume for simplicity in this example that the IC is actually zero).
    You can do the same with two stars at small distance if the
    "off" part of your arc permits. The "off part" of my arc is
    5 degrees. So I can practice this method on any pair of stars
    whose distance is less than 5 degrees.
    I always assume that the IC is small, say less than a minute
    in all these examples.
    On Sun, 30 Apr 2006, Bill wrote:
    > Alex wrote
    > > I use two pairs, one is Castor-Pollux, 4d30'.3 apart, another
    > > delta-zeta Orion, 2d44'.2 apart. I use essentially the same method as
    > > with the Sun: bring the pair together once on the arc, another time
    > > off the arc. The average gives me (the negative of) IC,
    > > and the difference twice the distance for control. My sextant permits
    > > to measure up to -5d (off the arc).
    > I am not clear about your method.  Are you superimposing the point sources
    > in a clockwise and anti-clockwise direction, or trying to achieve tangency
    > (either in one direction or two directions of drum turns)?  Either way,
    > unless your IE is way of, I don't see how you can wind up off the arc with
    > star-to-star angular differences in the 3d to 4d range.
    > Bill

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