Solar Footprint&[email protected]

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...