Arago's (Poisson's) spot is observed by shining a laser beam at a small spherical object, such as a ball bearing. Despite the object creating a shadow, a bright spot appears at the center of the shadow on the screen, due to constructive interference of light waves diffracted around the object. This phenomenon, predicted by Poisson and experimentally confirmed by Arago, demonstrates the wave nature of light and the principles of diffraction and interference.