We all see pictures of the Moon, on an almost daily basis and the real thing fairly often. The craters we see are all more or less circular. There must have been a lot of very oblique impacts from all directions so why don't we see a significant number of asymmetrical impact craters? I would have expected a meteorite which arrives on a glancing trajectory would produce a 'trench' shaped groove and not an almost perfect circular crater. Is there (there must be) a good answer to this question? I was looking at my Moon Map App with my son and we couldn't produce a good reason. I was wondering about a refraction-type explanation where the path gets bent 'towards the normal' but you can't avoid momentum conservation.