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    Re: Sun SD, Sextant precision, SNO-T
    From: Lisa Fiene
    Date: 2004 Oct 11, 07:49 +1000

    Hi Alexandre,
    
    According to the Sun Ephemeris for 2004, the following is indicated:
    
    October 10th - 1922.1" (for diameter - just halve for SD) = 16'0175"
    
    See:  http://sunearth.gsfc.nasa.gov/eclipse/TYPE/sun2.html#su2004
    or
    http://www.cadastral.com/2004oct.htm
    
    Hope this helps,
    Lisa
    
    
    
    
    Alexandre Eremenko wrote:
    > Can anyone tell me more precise value of
    > the Sun radius on October 10?
    > (This quantity is called "semidiameter, or SD" in the
    > almanach. The almanach gives for October 10
    > the value of  16.0', but I noticed that it gives
    > 16.1' beginning from October 12, and the refraction table
    > implies the average value of 16.15 for October-March.
    > The "Astronomical Almanach" or maybe some software could probably
    > give it more precisely (I need one more digit).
    >
    > The reason I am asking: This morning I have fixed all
    > (hopefully!) problems with my inverting scope, and tried
    > to fing the index correction from Sun observations
    > (with a fixed scope and more experience than I had last time:-)
    > The results are the following:
    > (everything is in angular minutes. "UL" is the sextant reading
    > when the reflected image touches from above,
    > -LL is when it touches from below. "4SD" is the sum
    > of these readings, "-IC" is the difference divided by 2,
    > the negative of the Index Correction..
    >
    > 1. Rotating the drum in the decreasing direction:
    > UL  32.5,  32.3, 32.5, 32.4, 32.3,
    > LL  32.0,  32.1, 32.0, 32.1, 32.0,
    > 4SD 64.5,  64.4, 64.5, 64.5, 64.3, Almanac: 64.0
    > -IC 0.25,  0.1   0.25, 0.15, 0.15  Average: -0.2
    >
    > 2. Rotating the drum in the increasing direction:
    > LL  32.0,  32.0, 32.0, 32.1, 31.9,
    > UL  32.2,  32.5, 32.6, 32.5, 32.5,
    > 4SD 64.2,  64.5, 64.6, 64.6, 64.4 Almanac: 64.0
    > -IC 0.1,   0.25,  0.3,  0.2,  0.3 Average: -0.2
    >
    > These results indicate that my index correction is
    > something between -0.2' and -0.3' (Which is consistent
    > with my previous Sun observations, but NOT with the star
    > observation; star observation give consistently 0.0'.
    > Today will repeat star observations
    > with my newly fixed inverting scope.
    >
    > The problem with the Sun observations above
    > is that my measurements of
    > Sun's SD indicate
    > that it is closer to 16.1' rather than 16.0'.
    > This explains my question in the beginning. I have to multiply
    > the almanac value by 4. This increases the almanac rounding
    > error by the factor of 4.
    >
    > (The Russian manual says: if your measurement of 4SD is
    > within 0.4' from the almanac value, your measurement is OK.
    > Otherwise it should be repeated.
    > My measurement is on the boundary:-)
    >
    > (My apologies in advance to those list members who consider
    > all this activity "splitting of a hair":-)
    >
    > Alex.
    >
    >
    
    
    --
    Kind regards
    Lisa Fiene
    ***************************
    
    CopyCare Pacific Pty Ltd
    Lizard Tunes
    ABN 93 101 046 888
    PO Box 314 Ourimbah NSW 2258
    Australia
    Phone/Fax: (02) 43 627 583
    International: 61-2-43 627 583
    E-mail: lisa{at}copycarepacific.com
    Web: www.copycare.com/content/local/ccpaceng.asp
    
    
    

       
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