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.
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.
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.
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.
[1] https://en.wikipedia.org/wiki/Schlieren_photography [2] https://en.wikipedia.org/wiki/Shadowgraph