I'm a bit concerned over Space Engine's representation of them... while making them look exactly how they would to the naked eye isn't feasible (or fun), I don't like the idea of seeing totally false colors or shapes. How realistic are the depictions?
1. It seems like nebulae are going to be totally false color in the next version, which is disappointing. Correct me if I'm wrong, but those pictures don't give me an impression of realism.
2. How much of the visible light of galaxies is generated by stars? Seems like the star density in SE above the Milky Way's core is just as thick as in the arms, but that isn't shown in the galaxy model. If this is realistic, then maybe the arms are more visible due to having lots of gas/dust.