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    Re: Lunar Distances with Alex's SNO-T
    From: Alexandre Eremenko
    Date: 2006 Dec 3, 19:11 -0500

    
    I made some further testing
    of this SNO-T sextant, following an advise of
    Frank (who tried it for several weeks).
    His advise was to slacken the
    pressure of
    the misterious adjusting screw on the drum
    (this tiny SNO-T screw was discussed several times
    on the old list). As a result, the worm can be rotated now
    with very light effort. The results seem to be satisfactory.
    (Previously, more than a year ago,
    I actually tightened this screw myself,
    thinking
    that I couldprevent or remove backlash this way).
    
    Nov 21 IC from Sun -0.4, 4SD exact
    
    Nov 22 IC from Sun -0.5, 4SD exact
    Using IC=-0.5:
    Deneb-Vega at 24d 3 observations, errors: 0.0, 0.2, 0.1
    Altair-Deneb at 38d 4 observations, errors: 0.3, 0.0, 0.0, 0.3
    
    Nov. 23 IC=-0.5 from Altair, 6 obs, sigma=0.2
    Using IC=-0.5:
    Deneb-Vega at 24d, 3 observations, errors: 0.1, 0.1, 0.0
    Altair-Deneb at 38d, 4 obs 0.0, 0.2, -0.2, 0.2
    
    Nov. 24 lunars:
    Sun-Moon at 46 degrees, errors: 0.3, 0.2, 0.2, -0.1, 0.2,
    Average error 0.16, sigma=0.15
    Sun-Moon at 47 degrees, errors: 0.1, 0.1, 0.2, 0.3, 0.1,
    Average error 0.16, sigma=0.09.
    
    Dec. 2 IC=-0.45 from Sun 4SD exact, 5 obs, sigma=0.15
    Using IC=-0.45
    Dec. 2 lunars:
    Moon-Altair at 99 degrees, errors: -0.1, 0.0, 0.4, -0.2, -0.1,
    average error 0.0, sigma=0.23.
    
    Alex.
    
    On Sat, 2 Dec 2006, Bill wrote:
    
    >
    >
    > Bill, you wrote:
    > > "Point being, I seriously doubt the lasers you refer to meet the standards  of
    > > both monochromatic and collimated light. "
    >
    > Frank replied:
    > > They're real lasers. They produce monochromatic, coherent light --no
    > > cheating on the terminology. All lasers have some beam spread, and you can
    > > counteract it, up to the diffraction limit, using a telescope...
    >
    > Ok. I'm buying into that.  Been shopping.  Found a straight-line laser for
    > $5 after rebate at Ace.  It's nice as the height in relation to the eyepiece
    > doesn't matter much, and very easy to center on eye-side scope lens, but it
    > does not produce the fine spike that a point source produces.
    >
    > Borrowed a friend's "Taiwan Tom" level laser complete with tripod and all
    > the niceties, but the off/on knob is on the front so one cannot center the
    > beam up with the scope.
    >
    > Finally, after realizing batteries for my aging Compaq pen/pointer gimme
    > would be $12 and considering that a poor investment as the dot is more of an
    > ellipse than a circle, I ferreted out a laser pointer/led light/pen at Wal
    > Mart for the princely sum of $2.88!  It works very well, with a fine
    > vertical diffraction line.
    >
    > Refining rigs to mount it now, as well as producing a circle to mount on the
    > eye end of the scope with a tiny hole to be sure I am shooting down the
    > center of the scope.  Centering the spot on the glass/mirror section of the
    > horizon mirror is simple trial and error and can be done satisfactorily by
    > eye.
    >
    > Using George's suggesting on how to determine the distance between the
    > horizon mirror and index mirror working points, I set up the rigs for trial
    > runs. The distance was only 40 ft, but the results were right on (probably
    > beginner�s luck.)
    >
    > Last sun IE check was 0.788' on the arc.  When matching the predetermined
    > mirror distance, the sextant reading was just a hair below 0.8' on the arc.
    >
    > I'm looking forward to more stringent tests as greater distances.
    >
    > Thanks for the idea Frank.
    >
    > Alex
    >
    > You ready to grab some sextants, a pair of FRS radios and go play?
    >
    > Bill
    >
    >
    > >
    >
    
    
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