[Radiance-general] Re: Solar Footprint&In-Reply-To=s1826993.056@wmtao.com

[Carsten Bauer]

Mark de la Fuente wrote:
> Very cool picture.  What I was trying to point out is that my sun 
> positions are not lining up the way I think they should.  Instead of 

The effect is a result of a) the earth orbit around the sun being an 
ellipse and b) the inclination of the earth's rotation axis v.s the 
orbit plane. The elliptic orbit results in a periodically varying speed 
of the earth along it's path around the sun, which changes the length of 
the solar day, i.e the time from one culmination to another. Overlayed 
on this is b), the fact that the sun doesn't move along the projected 
earth equator ('ecliptic') in the sky, but changes it's height during a 
year.

People in the stone age didn' t have this problem, they still could live 
with that (roughly) +/- 15 min time difference (max. amplitude for mean 
latitudes around 50°, compared to a mean solar time of exact 24 hours) 
during a years period. They didn't have to bother about computers and 
Radiance parameters also...

-cb