A mistake opened the modern sky. The first object widely logged as a nebula, a faint smudge in Andromeda, was not a local gas cloud at all but a separate galaxy, a stellar metropolis far beyond the Milky Way. Through early telescopes it looked diffuse, unresolved, its starlight smeared into a single patch.That mislabel was not simple ignorance; it was a theory locking the door. Under the dominant ...More