Airy disk

The Airy disk is a pattern of light that occurs when a lens or mirror focuses light from a point source, like a distant star. Instead of producing a single sharp dot of light, it creates a small, circular spot surrounded by a series of faint rings. This phenomenon happens due to the wave nature of light and the way optics work. The size of the Airy disk is influenced by the aperture of the lens or mirror; larger apertures create smaller disks, which helps in distinguishing closely spaced objects, like stars in astrophotography or fine details in microscopy.