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    Re: Angular Distance Between Stars By Camera and Sextant
    From: Greg Rudzinski
    Date: 2012 Sep 16, 18:24 -0700

    Brad,

    If you look at the rules for table 15-2 then the correction is always positive and added to the sextant distance which is what I did.

    Greg Rudzinski


    [NavList] Re: Angular Distance Between Stars By Camera and Sextant
    From: Brad Morris
    Date: 16 Sep 2012 20:31
    For the Alioth Alkaid pair

    I get refraction corrections for each object at
    1 minute 35 seconds
    1 minute 19 seconds

    Corner Cosines
    0.61255
    -0.52942

    Which has the affect of a delta refraction correction of
    18.75 seconds
    This agrees closely with your +0.3 minute correction.

    ADDING the refraction correction to the true distance, I get an observed distance of
    10 Degrees 28 minutes 1 second

    Please note that this differs from your method whereby you added the delta refraction correction to the observed distance and compared that to the true distance.

    If I add the refraction correction to each true altitude, and compute the spherical distance I get the same result (10 28 1).

    We obviously both can't be correct with such an apparent divergence in procedure. I expect to be proven in error shortly! Hopefully an independent colleague will weigh in.

    Best Regards
    Brad

    On Sep 16, 2012 12:59 AM, "Greg Rudzinski" <gregrudzinski---com> wrote:
    >
    > This evenings star pair observations included Vega Deneb (by sextant) and Alioth Alkaid (by sextant and camera). This time the on-line William's GC calculator was used properly to calculate true star pair distance. The Vega Deneb pair was corrected for refraction using the approximation method of 0.1' per 5* of angular distance. The Alioth Alkaid pair was corrected for refraction using the table provided by Mike Burkes (attached).
    >
    > Vega Deneb Hc 85*65*
    > 23* 50.1' observed distance by sextant
    > +0.5' refraction correction (approximation 0.1' per 5*)
    > 23* 50.6' true distance
    > 23* 50.8' true calculated distance by William's on-line calculator
    > Low 0.2'
    >
    > Alioth Alkaid Hc 31*37*
    > 10* 27.1' observed distance by sextant
    > +0.3' refraction correction by table
    > 10* 27.4' true distance
    > 10* 27.6' true calculated distance by William's on-line calculator
    > Low 0.2'
    >
    > Alioth Alkaid
    > 10* 28.0' observed distance by camera
    > +0.3' refraction correction by table
    > 10* 28.3' true distance
    > 10* 27.6' true calculated distance by William's on-line calculator
    > Hi 0.7'
    >
    > The camera image was disappointing showing 4' wide stars. Settings were ISO 1600, f 2, 1/8 sec, infinite focus using a fixed prime 50 mm lens. Sextant results were good.
    >
    > Greg Rudzinski
    >
    >
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