Arago spot

An Arago spot is a small bright dot that appears in the center of a circular shadow when a flat object is placed in front of a light source. It happens because light travels in straight lines, but when it hits the object, it bends or diffracts around the edges. This bending causes the light to spread out in all directions, including back towards the center of the shadow. When the light waves from all points around the object overlap, they create a bright spot in the center of the shadow. It's named after a scientist named François Arago who discovered it in the early 19th century.