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    Re: Angular Distance Between Stars
    From: Sean C
    Date: 2012 Sep 14, 23:39 -0700

    I use the following formula for lunars which can also be used for stars:

    arccos[sin(Dec1)*sin(Dec2)+cos(Dec1)*cos(Dec2)*cos(GHA2-GHA1)]

    It's from Frank's "Easy Lunars" page. There are formulas there for refraction as well:

    "For star-star sights, the equation [is]

    corrected_dist = observed_dist + dh1*A + dh2*B

    where dh1 and dh2 are the altitude corrections and A and B are the percentages or "corner cosines" for the arc in question."

    http://www.historicalatlas.com/lunars/easylun.html
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