Refraction is the change in direction of a wave as it travels from one medium to another. For instance, when light travels from air to glass or water waves travel from deep to shallow water.

A ray diagram showing refraction at the boundary between air and glass Refraction can cause optical illusions as the light waves appear to come from a different position to their actual source.

A theoretical astrophysicist from the University of Kansas may have solved a nearly two-decade-old mystery over the origins ...