> Traditionally (pre-ai) you would use another image of the same part of the sky and negate the items that you want to remove from the image.

I'm not an astrophotographer, so I'm interested about why that method would work for stars. Are not stars fixed in relation to the images taken? I could see how the technique would work with planets, maybe, but not stars.

Why does the technique not work with aircraft? Because they generally fly on fixed routes?