re: Spiral Arm Rotation
This example of counter-rotation appears to be a result of a past collision or other encounter with another galaxy, a topic discussed in one of Raoul 's links. I know that stars are so far apart from one another that two galaxies could be forced to share the same volume without there being a risk of collision, or even gravitational interaction, between individual stars, although the gas and dust clouds would definitely crash together. Ah, HST! we certainly got our money's worth on that one!
"We are, by definition, in the very center of the observable region."
--Edwin Hubble, The Realm of the Nebulae