StarTools

I never understood the flux module until I tried it. This is with the default settings: m42 flux

Clear skies,
Steve

Careful application is key! In its basic form, it's a "useful" artefact creator, based on self-similarity (aka "fractal") analysis; if it looks like a feature is similar to another in the image, then chances are that feature is flagged as "more valid" detail.

The latter flagging of "more valid detail" (and also its counterpart "less valid detail") can then be used in more (or less) sophisticated ways to manipulate the image. In its basic form, it can accentuate those parts of the image that are considered "more valid detail". In more sophisticated use, the "more vs less valid detail" metric can be used to drive other algorithms, such as sharpening or noise reduction.

YMMV, but astrophotography tends to deals with a fairly high amount of recurring detail at various scales, so tends to be a good candidate. It's a module that needs careful application however, as artefacts can quickly take over when not used carefully. Personally I like using it as an "intelligent" sharpener after switching Tracking off to give it that little bit of extra acuity in some cases, right before I save my final image.