Moiré Patterns
Morning GeoGebra sketch. Moiré Patterns inspired by this post via Curiosa Mathematica.
http://curiosamathematica.tumblr.com/post/98214338547/in-mathematics-physics-and-art-moire-patterns
More Moiré. http://en.wikipedia.org/wiki/Moir%C3%A9_pattern
More GeoGebra at bit.ly/mh-ggb