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    Re: Artificial horizon question
    From: J Parsons
    Date: 2009 Apr 20, 07:59 -0700

    Since the topic of artificial horizons has returned, let me bore you all with 
    a newbie's experience in learning to use one.
    
    Last night I made my first attempt at a star sight with the Davis artificial 
    horizon.  The pan was filled with mineral oil and sat on a table, uncovered.  
    I used no "house" as the weather was absolutely calm.  I found the star's 
    reflections were pretty faint (I am in a city) but could be picked up by 
    bringing my eye very close to the surface of the pool.  I then had to slowly 
    back away and simultaneously straighten up while keeping my eye on the 
    reflected image of the star in the pool until I was standing confortably, 
    some six or seven feet back from the table, and could still see the 
    reflection.  WIth the sextant set at zero I looked through the scope at the 
    star and brought the instrurment down while swinging the arm so as to keep 
    the star in the index mirror until I was again looking into the artificial 
    horizon.  
    
    Sirius and Arcturus were bright enough for this method, but Betelgeuse's 
    reflection just could not be seen once I began to back away from the table.  
    I remembered reading some postings in this list's archives about black glass 
    plates, etc., so I took the dark blue shade that comes with the Davis A.H. 
    and dropped it into the bottom of the pan of mineral oil.  It helped 
    somewhat, but not really enough.  I may go out looking for some black glass 
    this week.
    
    The biggest problem I had, and in fact always have with the A.H., is that I 
    can't seem to bring the two images very close together laterally, despite 
    adjusting the mirrors of my Davis Mark 15 beforehand. It is hard to tell 
    whether the images are level with one another when they are so separated.  
    The lateral space varies suddenly and without apparent reason; that is I 
    can't figure out what I am doing that causes them to converge and separate.  
    Moving my eye from side to side behind the telescope doesn't help; also the 
    images seem to move towards and away from one another as I move the index 
    arm, but not in a predictable manner.
    
    Can anyone suggest why I might be having this problem and what I could do about it?
    
    -John P.
    
    
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