To whomever is interested, I guess...
I suggest that at night clear air turbulence might be detected using a telescope trained on an ahead star. I hypothesise that seeing (the term astronomers use) would be worse in conditions of CAT in the aircraft's path.
What you are talking about is a variation of Schlieren photography [1] or shadowgraph [2]. I'm no expert in these kind of experimental techniques, but you are correct in that they can identify regions of turbulence.<p>A problem is that a lot of these techniques need a clean background to really see the streaks or shimmers associated with turbulence. In a laboratory setting, this isn't a problem, but an aircraft isn't always pointed straight up or at a clean background. This seems more plausible during takeoff when the nose is more pointed to the sky than cruise or landing, but even during takeoff it seems like a stretch. Also, I doubt that a single star would provide a good enough light source to really distinguish between clear-air turbulence, clouds, or even birds for that matter. It is an interesting idea but unfortunately I do not think it would work in practice.<p>[1] <a href="https://en.wikipedia.org/wiki/Schlieren_photography" rel="nofollow">https://en.wikipedia.org/wiki/Schlieren_photography</a>
[2] <a href="https://en.wikipedia.org/wiki/Shadowgraph" rel="nofollow">https://en.wikipedia.org/wiki/Shadowgraph</a>