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    Star finder, 2102-D, further modification
    From: Gary LaPook
    Date: 2010 Nov 08, 19:41 -0800

    
    
    Last year I wrote explaining some modifications to the 2102-D that I had made 
    in the past. I have now looked
    at these modifications again and have found an easier way to draw in the 
    ecliptic. My previous post had this method
    for drawing in the ecliptic.
    
    
    "At this point to use the modified 2102-D I still needed to know the time in order to set it so I decided
    to add some more scales to eliminate having to refer to the Almanac. To accomplish this I first added
    the ecliptic which was simple to do. I had the position of the sun for the
    first and the fifteenth of each
    month, the previously computed positions along the ecliptic, and the declination for the sun for the
    same dates. I plotted these points and then fared a curve through them by hand, see image 148."
    
    See: http://fer3.com/arc/imgx/IMG_0148.JPG
    
    and:
    
    http://www.fer3.com/arc/m2.aspx?i=107982&y=200904
    
    ---------------------------------------------------------
    
    I didn't realize at the time (many years ago) I made these modifications that the ecliptic, due to the
    projection used for the star base, would plot as a circle which makes it much easier to place on the
    star base. The radius of the ecliptic is 90° on the declination/latitude scale 
    and the center is placed on the
    arctic circle at its intersection with the right ascension of the the sun at 
    the time of the winter solstice
    which is 270° on the star base. To determine where to place the center of the 
    ecliptic I placed a straightedge
    from 90°   to 270°  and drew a line extending from about 70°
       north to about 30° south. I placed the red disk over it and marked 23.5°
       south. I then set the drawing compass to extend from the pole to the 
    equator and swung an arc from 23.5°
       south so that it placed a mark on the line at 66.5° north. Then I used this 
    mark as the center to draw the ecliptic,
       see the attached photos.
    
    Also see:
    
       http://www.fer3.com/arc/m2.aspx?i=107986&y=200904
    
    gl
    
    
    
    
    
    
    
    

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