Many ‘mathematical phenomena’ find application and sometimesspectacular physical illustration in the physics of light. Conceptssuch as fractals, catastrophe theory, knots, infinity, zero, and evenwhen 1+1 fails to equal 2, are needed to understand rainbows, twinklingstarlight, sparkling seas, and simple experiments on interference,polarization and focusing, and oriental magic mirrors. The lecturewill be based on pictures (slides and demonstrations), and is nontechnicalyet intellectual.