Le 13/12/2016 à 14:02, Bald Eagle a écrit :
> I was exploring some unrelated things (as usual), and I found an interesting
> shadow clock that was easy to model
> 
>
https://www.dezeen.com/2015/10/23/breaded-escalope-touch-shadow-clock-vienna-design-week-2015/
> 
> And then I was noticing how the sun came into my apartment, and thinking back on
> a solar energy model I made a few years ago, and Ingo's sunpos.inc file, and I
> recalled that an ordinary watch can be used as a makeshift compass.
> 
> Orient the hour hand to point at the sun (accurately done with a blade of grass
> to cast a shadow across the hour hand) and then divide the angle between the
> hour hand and the 12:00 mark.  That's roughly South.
> 
> I wanted to see how it worked, and get an idea of how far off it would be.
> 
> So naturally I modeled it in POV-Ray   :)
> 
> Seems to work ok, and be off by +/- 30 degrees - dead on at noon.
> 

1. The hour should be corrected to be solar (ditch away summer time &
other delta: for instance at Paris, in winter, the hour is aligned with
Berlin, and about 1 hour wrong. It becomes 2 hours wrong in summer time)
(Paris is about 3° East, and does not justify a delta of 1 hour from
Greenwich : one hour is 15° of longitude)

2. It works only in North hemisphere (the further above the tropic, the
better (tropic is about latitude 28° ))
Between the north tropic and south tropic, you would have period of the
year with problems.
South of the south tropic, the clock is not turning in the right sense
to follow the sun (which is North at noon)

Post a reply to this message