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    Re: Problem with a sextant
    From: Alexandre Eremenko
    Date: 2006 Apr 25, 11:18 -0400

    Here are my yesterday results
    using close pairs of stars.
    To pre-compute the distances, the Astronomical
    Almanac was used. It is available on line.
    
    April 23. Index from Sun: -0.35 (6 observations, sigma=0.1')
    April 24. Index from stars: -0.2 (12 observations.
    6 clockwise and 6 counterclock, sigma=0.1')
    
    The following observations are given WITHOUT applying any IC,
    just the numbers I read on the sextant, averaged:
    
    April 24. Epsilon Orion to Zeta Orion, computed dist 1d 21'4.
    Observed 1d 21'.8 (3 observations, sigma=0.2') Error -0.4'
    
    Epsilon Orion to Delta Orion, computed 1d 23'.2
    Observed 1d 23'.8 (5 observations, sigma=0.3') Error -0.6'
    
    Delta Orion to Zeta Orion, computed 2d 44'.2
    Observed 2d 44'.6 (7 observations, sigma=0.2') Error -0.4'
    
    Castor-Pollux, computed 4d 30'3
    Observed 4d 31.0, Error -0.7'.
    
    Here are the 5 observations of Castor-Pollux:
    4d 31'.2, 4d 31'1, 4d.31'.0, 4d 31'.1, 4d 30'.9.
    The series seems very good.
    
    Now, if I use IC=-0.7, ALL my star distances taken
    ikn the last two weeks will be within 0.3' of the true
    results, which is the best one can probably hope.
    (sigma is 0.2 in those observations and error ranges
    from 0.6 to 1.0)
    
    It looks like some smooth transition happens
    from IC=-0.2 determined by the usual method to
    -0.7 for Castor-Pollux distance and then eventually
    to -1.0.
    
    Two control observations
    Procyon-Capella at approx 51 degrees, error -0'.8
    Betelgeuse-Alioth at approx 91 degrees, error -1'.0
    show that at large distances nothing changed
    in these two days.
    
    (Two days ago I took many star distances (10 pairs of stars,
    5-7 times each) uniformly spread over the arc
    from 9 degrees to 104 degrees, with average
    error -0'.8 and sigma =0.22 over the whole scale!)
    
    All this, of course seem to contradict Freibergers
    factory testing, but the sextant has been in a small
    boat since.
    
    On the other hand, even before Freibergers testing
    I ALWAYS had overshots since I bought this sextant,
    I mean in my two thick notebooks of observations
    it is hard to find a single UNDERSHOT by more than 0.2
    (Freibergers testing showed that the arc is
    almost perfect).
    
    Alex.
    
    
    

       
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