I did some more OSC CMOS tinkering in the backyard last night
the result is here
I wanted to explore longer sub-exposure times (5 minutes) which gave the result above. Processing the data I noticed a subtle "ripple" in the CMOS dark frame data
...which I've also highlighted via an animation on the page linked above.
I suspect this is intrinsic to CMOS chips, but would be interested to hear from other CMOS camera users as to their experience with this low level noise pattern.