Somewhat off-topic, but regarding visualization, we're told that Andromeda is on a collision course with the Milk Way, but also that it is very unlikely that e.g. the Sun will actually collide with any other stars -- galaxies are approximately empty over all. I have always want to know what it would look like from Earth to see the stars of the two galaxies 'sliding across' the celestial sphere during the merge. Has anyone seen something like that? I search online for it every few years.