Airy disk
The central spot in the diffraction pattern of the image of a star at the focus of a telescope, named after George Airy. It is surrounded by several fine diffraction rings like the rings around the bull's-eye of a target.
Airy Disk
(top): The normalised irradiance profile for a circular aperture.
(bottom): The irradiance pattern, showing the central Airy disk surrounded by a series of rings with reduced intensity.
Airy Disk - The Airy Disk is a disk of light from a star that forms at the focal plane of an optical system instead of a point. The stars we see in the night sky are so far away that they are essentially point sources.
Airy disk always visible; arcs frequently seen on brighter stars.
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Airy disk always visible; short arcs constantly seen.
A. Is the Airy disk clearly visible, even though highly mobile and sometimes merged with background light?
" NO: Go to B.
" YES: Go to C.
This breaks down due to the practical limits imposed by the atmosphere, whose random nature disrupts the single spot of the Airy disk into a pattern of similarly-sized spots covering a much larger area (see image of binary on right).
This is a traditional criterion for image quality and is the ratio of maximum intensity of the point spread to that of a theoretically perfect point source image (Airy disk). A perfect (no distortion) diffraction limited image would have R = 1.0.
What is Resolution is a short page with a number of images comparing resolution as Airy disks and as astronomical images.
Questions
What is the relationship between the diameter of the primary mirror of a telescope and its sensitivity?
 See also: Disk, Diffraction, Wavelength, Light, Star
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