Re: Expanded Nodi Shadow Experiment

[Gianni Ferrari]

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: Varese_Nodus.jpg>>

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