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    Re: Index error by a star-star distance
    From: Bill B
    Date: 2008 Sep 22, 16:18 -0400

    Andres wrote:
    
    > I am writing an article about "Index error by a star-star distance".
    >
    > Unfortunately there is not much information about this subject, or I can't
    > found it. Anybody has any source of information; old books, papers, ... ?
    
    I have an Excel spreadsheet to calculate star-to-star distances.  It
    includes corrections for the observer's altitude above sea level, barometric
    pressure and temperature.
    
    Inputs are SHA (or GHA of planet), declination, and Hc of the bodies at a
    given time; plus altitude of observer, temperature and barometric pressure.
    
    I would be happy to send you a copy if you are interested.
    
    As to averaging, the SHA's of stars are a constant for all practical
    purposes over a 5 to 10 minute observation period, and the angular distance
    is not particularly sensitive to Hc changes.  If you pick a time and make
    observations plus/minus 5 minutes from that time any change in the angular
    distance would usually be far less than the ability of a man/sextant to
    measure it.
    
    If you program will run on a Mac OS, I would love to see it.
    
    Bill B
    
    
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