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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

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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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