If this is moving towards the edge of the frame then it’s likely to be caused by an intrusion in the lens cell. Completely normal, sometimes the spacer (wedges) separating the lens’ intrude a fraction into the optical path.
There are three 0.1mm thick aluminium spacers about 10x4mm that sit between the crown and flint of a Tak doublet. Have seen similar effects on bright stars with that scope.
I found not diffraction spikes, but three "flares" on an old ED80 I got.
After investigation I tracked it down to the collimation screws (which acted on the edge of one of the elements) Easing these screw solved the problem.
Been 100% for the last few years.
I thought that maybe one of Muskies reindeer had blown up. There's so many of those things going up at the moment that one of them is bound to have a collision with something.
Possible causes's now stand at:
UFO, Galaxy, OTA intrusion, spider and exploding satellite.
Guys an girls, we have to get serious.
So I looked at the Zernike model of aberrations.
Circular wavefront profiles associated with aberrations may be mathematically modeled
using Zernike polynomials.
Developed by Frits Zernike in the 1930s, Zernike's polynomials are orthogonal over a circle of unit radius.
A complex, aberrated wavefront profile may be curve-fitted with Zernike polynomials to yield a set of fitting coefficients
that individually represent different types of aberrations....
