For ten points, name this "spot", which served as a proof for the wave nature of light.
This was first shown to exist experimentally by François Arago, for whom it is sometimes called. It served the exact inverse of the purpose that its usual namesake intended and was called a "strange result" by its theoretical discoverer, who showed it to be a direct mathematical consequence of Fresnel's wave theory of light. The existence of this is often demonstrated in modern contexts using a ball bearing and laser. For ten points, name this "spot", which served as a proof for the wave nature of light.
This was first shown to exist experimentally by François Arago, for whom it is sometimes called.
Poisson Bright Spot (accept Fresnel Bright Spot before it is mentioned)