Arago spot

Etymology
Named after Dominique-François-Jean Arago, who performed an experiment demonstrating the spot's existence.

Noun

 * 1)  A bright point that appears at the centre of a circular object's shadow due to Fresnel diffraction.
 * The Arago spot played an important role in the discovery of the wave nature of light and is a common way to demonstrate that light behaves as a wave.
 * The Arago spot played an important role in the discovery of the wave nature of light and is a common way to demonstrate that light behaves as a wave.