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    Re: Angular Distance Between Stars By Camera and Sextant
    From: Marcel Tschudin
    Date: 2012 Sep 18, 01:43 +0300
    Finally I managed to recalculate Greg's Alioth-Alkaid-observation. I see now that the USNO Almanac data may lead in this case to confusion. Refraction here is mentioned with a negative sign which gives for this particular case the wrong impression to be subtracted from Hc. I guess however that these almanac data are normally used for comparing a sextant measurement with Hc. In order to obtain Hc from the sextant measurement refraction has indeed to be subtracted from it. However, for calculating the OBSERVED distance refraction has to be ADDED to Hc of the almanac.

    Using the attached USNO almanac data for the time of the observation UT 3:05:00 (instead of UT 2:45:00) one obtains with the attached great circle calculation a Distance=627.6 moa compared to 628.0 moa as measured in photo (and using the calibration obtained from HS measurements).

    Marcel


    On Sun, Sep 16, 2012 at 7:37 AM, Greg Rudzinski <gregrudzinski@yahoo.com> wrote:
    .....

    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'

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