Hello Gianni,
Thanks for showing this application, and also for
your contributions to this fascinating thread.
Are there pictures anywhere on the internet which
show the overall installation? It's not
completely clear to me just where the nodus is
located, relative to the analemma.
Best wishes,
Mac Oglesby
After a lots of theory
. a practical object :- )
I send attached the image of the nodus used by
the Italian dialist Roberto Baggio in a meridian
line built in 2003, in a square of the town of
Varese (northern Italy)
The nodus is put at a height of 4 m and it is
made with a square plate of brass (side=25
cm) containing a great hole (diameter 14 cm )
and a central disk with the diameter = 4.5 cm,
fixed with metallic threads.
On the 4 points the letters N,E,S,O are cut out (O=Ovest = West).
The analemma is long 10.6 m and is made with 750
marble tesserae of 3x3 cm .
From the summer solstice to the equinoxes the
central disk gives a distinctly visible shadow:
the ratio (distance nodus-image / disk-diameter)
= 410/4 <108
From the equinoxes to the winter solstice the
image of the outer circle disappears (fully in
penumbra) because the shadow of the disk widens
and that of the inside ring approaches the
center. In these seasons as nodus the shadow of
the whole plate is used . Its center is easily
located using the symmetry of the structure.
Gianni Ferrari
Attachment converted: Macintosh HD:Varese_Nodus.jpg (JPEG/«IC») (00275479)
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