Asymmetric propeller blades

On a recent flight to Copenhagen (actually, to Bergen, but that’s another story) I happened to sit with a great view of one of the plane’s propellers. And it struck me how asymmetrical the dark areas caused by the moving propeller above and below the axis looked!

I guessed the explanation would have to be that the propellers were asymmetric in some way, too. Kept me entertained until I saw this:

What could have happened there? Why would there be a seam between completely different patterns of clouds?

I guess there is no reason there shouldn’t be, especially since the cloud / no cloud border is often quite sharp, too. But still, pretty intriguing!

But then a pretty approach to Cph:

And finally: a good view of the propellers. Ha!

And now that I am writing this I am wondering. What’s the difference between asymmetric and asymmetrical? Googling has to wait, I have a plane to catch…