A pattern of illumination caused by diffraction at the edge of a circular aperture, consisting of a central core of light surrounded by concentric rings of gradually decreasing intensity.
The circular diffraction image inside the first minimum of the point spread function.
The bright central part of the image of a star. It is surrounded by diffraction rings and its size is determined by the aperture of the telescope. About 85% of the light from the star should fall into the Airy disc.