Airy disk

The Airy disk is the bright central spot within a pattern of diffraction rings formed by an optical system when light from a point source, such as a star, is involved. This phenomenon was first explained by English astronomer George Biddell Airy in 1834.12

When a lens forms an image of a point source, it creates a small pattern of concentric rings around a central dot, known as the Airy disk. The size of this disk is a fundamental limit to the resolving power of optical instruments like telescopes and microscopes. The Rayleigh criterion, developed by Lord Rayleigh, states that two adjacent point sources can be distinguished if the central maximum of one's Airy disk falls on the first dark ring of the other's.23