Caption: A simulated Airy diffraction pattern with intensity in grayscale.

Features:

1. An Airy diffraction pattern is the diffraction pattern of a plane waves impinging on a circular aperture in a screen that is parallel to the wave fronts.

2. The setup enforces circular symmetry about the axis that is perpendicular to the screen and passes through the center. This axis can be considered the optical axis of the system.

3. The source in most astronomical application is a point light source at optical infinity.

4. The Airy diffraction pattern consists of a bright central diffraction fringe surrounded by concentric alternating dark and bright fringes which are called Airy rings.

5. To digress, why don't we notice the Airy diffraction pattern and other diffraction patterns for light in everyday life?
   1. First note that diffraction is an effect of physical optics. Geometrical optics is the limit of physical optics in which light can be treated as light rays neglecting light's wave nature.

   2. Part of the answer to the question is that diffraction patterns are partially averaged away by overlapping effects. There are usually multiple light beams giving overlapping diffraction patterns. Also diffraction is wavelength-dependent. Thus, polychromatic light gives rise to overlapping and partially canceling diffraction patterns.

   3. However, even for a single light beam of monochromatic light, diffraction is often not noticeable.

   4. As aforementioned, diffraction is wavelength-dependent.

      If λ << L (where L is the characteristic length of the aperture or obstacle that cuts the wavefronts), then the diffraction pattern alternating dark and bright fringes are very tiny about the bright central fringe which approximates an ideal beam of light rays.

   5. In the ideal limit as λ/L → 0, you just have no diffraction. This is geometrical optics limit where light is treated as consisting of light rays.

   6. Since we are never in the ideal limit of of geometrical optics exactly, the dark and bright fringes are present just at the edge of shadows if not washed out which they often are.

   7. A shadow is where the overall diffraction pattern intensity has asymptotically gone to zero.

   8. Now visible band (fiducial range 0.4--0.7 μm) has wavelengths much smaller than most everyday apertures and obstacles that we notice.

      So the diffraction patterns at the edges of shadows are usually too minute to be observed by casual observation.

      But actually, we'd notice them pretty often if they weren't generally partially averaged away as discussed above.

   9. Diffraction can be readily seen using intense monochromatic light from a laser and small apertures or obstacles.

   10. For more elucidation, see the Light Diffraction videos:
       1. Young's Double Slit Experiment Well Jack Maxwell (the great, great, great grandson of Jim Maxwell) never uses slits, but it's still pretty nifty what you can do with laser pointer and some pencil leads. Actually, I think Jack M is relying on Babinet's principle: "the diffraction pattern from an opaque body is identical to that from a hole of the same size and shape except for the overall forward beam intensity." He doesn't seem to know this. So his single slit acts as a double slit and his double slit acts as triple slit.
       2. Diffraction of Light A tutorial, not a quick show. Too long for the classroom.

6. Let us now return to the Airy diffraction pattern after our bracing digression into generality.

7. The Airy diffraction pattern is only readily noticeable when light wavelength λ is comparable to or greater than the aperture diameter D.

8. As λ grows smaller than D, the Airy rings become very narrow and asymptotically vanish leaving only shadow and the bright central Airy disk.

9. In this case the characteristic length scale of the aperture is the diameter D. Thus, in the limit of λ/D → 0, you just have geometrical optics.