Airy disk

The Airy disk is a pattern of light observed when a point source of light, such as a distant star, is imaged through a circular aperture, such as a lens or an optical telescope. It occurs due to the diffraction of light, which causes waves to spread out when passing through the aperture. The Airy disk is characterized by a central bright spot, known as the Airy central maximum, surrounded by a series of concentric dark and bright rings.