A

David

Darling

caustic curve

caustics

A caustic curve is the envelope of rays of light reflected (or refracted) by a given curve from a given point source of light. A catacaustic results from reflection, a diacaustic from refraction.

 

Among the caustic curves of a circle are limaçon, if the light source is nearby, a nephroid, if the source if at infinity, and a cardioid, if the source is on the circle.