Moiré patterns

Moiré patterns are secondary and visually evident superimposed patterns created when two identical (partly transparent) patterns on a flat or curved surface that  are displaced or shifted and overlaid from each other. 

Two intersecting circles produce a side ways ‘>’ and ‘<‘ shapes among other patterns.

These patterns are often also known as a type of image artefact in photography and naturally occurring interference patterns. 

Source adapted from: Moiré pattern. (2014, September 22). In Wikipedia, The Free Encyclopedia. Retrieved 09:00, September 28, 2014, from