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    Re: Angular Distance Between Stars By Camera and Sextant
    From: Marcel Tschudin
    Date: 2012 Sep 18, 22:15 +0300
    In the mean time I found an other possibility to verify Greg's Alioth-Alkaid observation. This time I used http://www.calsky.com by

    (1) Defining under "Intro" Greg's coordinates and
    (2) defining the user level as "Astronomer".
    (Do not forget to confirm these data at the bottom of the "Intro" page!)
    (3) Selecting then the "Deep-Sky" tab and afterwards the "Star Chart" tab.
    (4) Enter date and time.
    (5) Below are three parameter lists: Simulation, Telescope and Pointing. Enter under "Object Name" e.g. Alioth and then the enter-key. This provides you further below with a telescope view centered at Alioth.
    (6) Under the telescope view several observational data are listed, also the apparent R.A. and apparent Declination.

    Using these apparent coordinates from the two stars (multiplying R.A. with 15) one can again calculate their distance with e.g. Williams' Great Circle Calculator and obtains a distance of 627.7 moa. It appears that CalSky uses some standard values for P and T when calculating refraction. I could not find a possibility to adjust these values.

    At present we have the following situation:
    USNO's Almanac data converted and refraction added with Bill's Excel-sheet: D=627.7 moa
    Paul's calculation: D=627.3 moa
    Andrés program: D=627.7 moa
    CalSky (with standard P and T values for refraction): D=627.7 moa

    It looks like Paul's calculation may possibly contain a bug.

    From this comparison I would recommend that Windows-users perform such calculations with Andrés' program. Mac users could probably also use Andrés' program running it under a Windos VM. Mac users would otherwise probaly rather use the USNO Almanac with Bill's Excel sheet for adding refraction and calculating the distance.


    P.S: Brad, I try to answer your other mails later today or otherwise tomorrow.
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