It is actually a small disk, known as the Airy disk
, surrounded by a series of diffraction rings, with the first ring being prominent and the rest dim.
At the focus the image of a star appears as a small bright disk surrounded by concentric rings of diminishing brightness, known as Airy disk
or diffraction spot.
As a result, constructive and destructive interference occurs, forming a so-called Airy disk
instead of an infinitely small focused point.
This pattern is called the Airy disk
after George B.
Doesn't an obstruction make the center of the Airy disk
A scope with a central obstruction shows a slightly larger Airy disk
(the bright center of a star's diffraction pattern) than an unobstructed aperture.
The smallest focused spot is called the Airy disk
, which depends on the wavelength of light and the aperture of the optical system.
After slight tweaks to the telescope's collimation, the optics yielded classic Airy disk
diffraction patterns around stars at high powers, and double stars such as Epsilon Lyrae were well resolved.
The result is an Airy disk
that is 16 times brighter.
Viewed at high power, stars looked "textbook perfect," with little evidence of spherical aberration disturbing their Airy disk
patterns, and there was no hint of astigmatism distorting them into ellipses or other odd shapes from malformed or pinched optics.
The size of the Airy disk
is determined by the telescope's aperture and the light's wavelength.
And at these magnifications, stars appeared as textbook-perfect Airy disks
surrounded by a bull's-eye pattern of uniformly illuminated diffraction rings, which decreased in brightness outward from the Airy disk