And yet I'm not sure this works out. Is it at all reasonable for a habitable planet to have a supergiant which is close enough to produce Moon-like levels of illumination?
Or what about other galaxies--- would they be visible as low-magnitude objects? Wikipedia says a handful are: http://en.wikipedia.org/wiki/List_of_ga
As Marissa pointed out, this seems like a detail that causes the reader to withdraw from the story to think about rather than one which keeps the story moving.