I remember how, as a physics student, I was pretty amazed to find that a CD I had lying around created inference rings from the sun shining on it and that I could quite accurately calculate the spacing of the track on the disk. I considered the sun to be a thermal light source - something that should not result in any interference. My conclusion at the time was, that the I was looking at single-photon interference and that the 'lateral coherence length' of the photons coming from the sun must be large. I didn't follow up on this, I'm ashamed to say. But it must me the prerequisite for the attempt to increase the effective aperture of the telescopes.

Another thought that came to me - we already know of a technique to store phase information from coherent sources for practically indefinitely, which is holography. Can anyone tell whether that would be an option for the use case?

edit: I should have spent a little more thought on this comment, but I mostly wanted to get it out of my head and maybe have others pick up on it. The issue with holography is, that the image is created by interference of a reference beam and the reflections from an object. Here, we don't want to image an object, but the light source itself. Maybe we can learn something about the light source when we have multiple holograms created with reference objects...