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    Re: Instrument Error
    From: Bill B
    Date: 2005 Apr 24, 17:42 -0500

    Fred
    
    I am envious of your standard deviations, especially with the larger angles.
    To date every Sun/moon I have shot had the Sun to the west of the moon
    (April 13, 2005 and on), and I prefer separating, so did try some
    set-and-leave shots for separation.
    
    What I find interesting is despite different methodologies, scopes,
    instruments and locations we both wind up over shooting the target
    consistently (and it would appear we both saw the same Sun and moon in April
    ;-)
    
    What time(s) of day did you make your April 05 observations?  As I noted
    before, while my STDEV's of error were horrible, the observations I made
    when the Sun and moon had Hc's over 40d turned out remarkably well, with
    mean errors in the 0.25' to 0.5' range.  The "easy" shots with the moon high
    in the sky and the Sun in the 15d-25d range all had sub 0.2' STDEV error
    means, but error means were in the 0.5' to 1.0' range.  Admitted the
    instrument in in the hands of a novice, and I don't have enough data points
    to justify a firm conclusion, but it appears the lower the Sun gets the more
    I overshoot.  There is not enough flattening of the Sun by refraction to
    account for the trend.  If you are using Franks calculator, I recall he did
    have a correction for Sun/noon flattening, then disabled it.  I do not know
    if he has plugged it back in.  Either way flattening could only account for
    0.1' or so.
    
    If memory serves, Alex had run test using the Sun for IE with both his
    Galilean and inverting scopes, and saw little or no significant difference.
    
    Still stumped
    
    Bill
    
    
    > I mentioned that my sun-moon lunars were markedly inferior to other
    > lunars.  Here are some data on that.  For a while, I thought I was
    > failing to converge the objects in the center of the glass, so I bought
    > a Russian 7x (6x ?) inverting scope with wires in the field of view, so
    > that I could center the objects (and get greater magnification than
    > offered by my 4x star scope).  This didn't seem to help, as indicated
    > below.  In general, the sun lunars show a gap of about 1.2' to 1.4' of
    > arc, while the star and planet lunars show no gap.  The one difference
    > that remains to be explored is that the sun lunars have much larger
    > distances than the star lunars, so that arc eccentricities or failure
    > to maintain the sextant in the plane of observation may be occurring.
    >
    > I haven't used the inverting scope very much yet, so I'm far from
    > proficient with it.  But the bias appears to persist with it, and
    > appears to be .
    >
    > Date    Telescope       Objects Mean(clrd
    > D)      N(delarc')      Mean(delarc')   StdDev(delarc')
    > 09/22/2004      4xGalilean      Moon,Antares    38      2       0.1     0.38
    > 04/18/2005      7xinverting     Moon,Jupiter    58      7       0.5     0.21
    > 04/20/2005      4xGalilean      Moon,Jupiter    21      6       -0.1    0.28
    > 10/06/2004      4xGalilean      Moon,Venus      49      7       -0.2    0.26
    > 10/07/2004      4xGalilean      Moon,Venus      38      6       -1.1    0.23
    > 09/20/2004      4xGalilean      Moon,Sun        80      6       1.2     0.37
    > 09/21/2004      4xGalilean      Moon,Sun        92      6       1.3     0.49
    > 10/05/2004      4xGalilean      Moon,Sun        97      6       1.4     0.15
    > 10/06/2004      4xGalilean      Moon,Sun        87      8       1.2     0.34
    > 10/08/2004      4xGalilean      Moon,Sun        66      10      0.7     0.38
    > 11/07/2004      4xGalilean      Moon,Sun        62      6       1.7     1.28
    > 04/16/2005      7xinverting     Moon,Sun        93      6       1.4     0.15
    > 04/17/2005      7xinverting     Moon,Sun        103     8       1.2     0.24
    
    
    

       
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