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    Re: Fix by equal altitude sights around local apparent noon
    From: Geoffrey Kolbe
    Date: 2009 Oct 14, 21:35 +0100

    George Huxtable wrote of the precision astrolabe [NavList 10131]
    
    >  How much greater than 60�, then, was the
    >recommendation, which would determine the time-lapse between the two events,
    >and also affect the achievable precision?
    >
    >George.
    
    A very good question George, and I am afraid I do 
    not have an answer. If, as the body transits the 
    meridian, the transit altitude of the body is 
    very close to 60�, then the altitude is varying 
    very slowly through the sensitive angle and there 
    is a lack of precision in deciding exactly when 
    the two images coincide. So it is difficult to 
    get an accurate longitude. If the transit 
    altitude is a lot higher than 60�, the body moves 
    relatively quickly in altitude through 60� - both 
    applying and separating from its transit across 
    the meridian - giving good precision for those 
    times. But then, as the bodies are increasingly 
    observed towards the East and the West at large 
    azimuth differences, latitude becomes difficult 
    to measure accurately. In practice, a number of 
    stars of differing declinations would be 
    observed, consistent with the star's transit altitude being greater than 60�.
    
    Geoffrey.
    
    
    
    
    
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