This has been nagging at me for quite some time:
Where are the cannons that are seen firing above the cockpit of the Millenium Falcon?
Their use can be distinctly seen approximately 40 seconds after dropping out of hyperspace near what was Alderaan. A lone patrolling TIE fighter overtakes them and Han throws a quick switch in the ceiling, firing as the fighter zooms past.
I just rewatched the scene mentioned above, just to confirm I'm not imagining things. Then I went and looked at various shots of the Falcon, models and in the movies.
Just to be safe, I allowed that it might actually have been the TIE that took a quick pot-shot, but to me it's definitely Han shooting first (har har!)
There's nothing I can identify as looking like cannons above the cockpit.