Hi Bill the movie shows a property of some bifilar sundials: they may revolve.
The bifilar sundial of the movie has the dial in the meridian plane and it has a negative thread, that is a thread is in front of the dial, the other is behind. The two threads have the same distance from the dial, they are orthogonal and one of them is direct as the polar style. When a thread is negative the sundial is projective so the dial is transparent: the threads and the hour lines cast their shadows on a screen where it is possible to read the time watching the position of the knot (where the shadows of the threads cross themeselves,) on the shadows of the hour lines. The screen may have any orientation. This is the description of a generic bifilar sundial with a negative thread. Until it is fixed. The dial may revolve and also the threads. The angular speed of the dial must be twice the angular speed of the threads. In the movie the sun is fixed all the time (altitude 33°, azimuth 65°, at a latitude of 45° it means a sun declination of 7.73° at 15:20:22 local sun time) and the sundial shows always the same time demostrating its particular feature. In the last section of the movie, a screen rises to show how the projection doesn’t change from an horizontal plane to a vertical one. Some technical data: - a computer worked more than 20 days, not stop, to render 3240 frames of 600 x 450 pixels - the movie run 15 frames per second, so its length is 3 minutes and 36 seconds - the sun is fixed but the clouds run, it is an unintended effect - you may focus the gears to check the angular speeds or the shadows to check the time doesn’t change. - the sundial is schematic to show how the gears engaged themselves ciao Fabio Fabio Savian [email protected] Paderno Dugnano, Milano, Italy 45° 34' 10'' N, 9° 10' 9'' E, GMT+1 (DST +2) From: Bill Gottesman Sent: Wednesday, January 23, 2013 8:21 PM To: Fabio nonvedolora Cc: [email protected] Subject: Re: Hurray of Oz ! That is incredible Fabio. How did you figure this out? -Bill On Wed, Jan 23, 2013 at 10:07 AM, Fabio nonvedolora <[email protected]> wrote: Hi Kevin, the name is just right, I think to know what it was connected to: http://youtu.be/cwofR3J0Gh4 ciao Fabio Fabio Savian [email protected] Paderno Dugnano, Milano, Italy 45° 34' 10'' N, 9° 10' 9'' E, GMT+1 (DST +2) From: Kevin Karney Sent: Wednesday, January 23, 2013 1:50 PM To: Sundial list Sundial list Subject: Hurray of Oz ! A rare engine from Australia circa 1930 2hp Sundial type B engine …. Best wishes Kevin ------------------------------------------------------------------------------ --------------------------------------------------- https://lists.uni-koeln.de/mailman/listinfo/sundial --------------------------------------------------- https://lists.uni-koeln.de/mailman/listinfo/sundial
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