I noticed when entering custom footer text that when I centered, it centered to the main content width and not the full site width.
The same is true for the header. When centering a text header (not using an image in this scenario) that the header text, like the footer text, centers to the width of the content (default is 620px), and to the left of an "invisible" sidebar space.
Before I make my own modifications to Asteroid I wanted to mention this in the event someone wants to have a perfectly centered header and footer without regard to the main content and sidebar widths.
Maybe in a future update? ;)
Thanks again for a terrific theme. You've done a fantastic job on the theme and the helpful options under Appearance when the theme is active are well-done.