A letter from Marvel Comics' Star Wars:
-> ...someone made an astronomical error. On page 16, panel 5 [of issue #2], Han Solo says his ship "made the Kessel Run in less than twelve parsecs." I'll bet he can run the mile in less than 100 yards, too. A parsec is a measure of distance, approximately 3.26 light years. (A light year is about six trillion miles.) I expect my oofy, gilded no-prize by earliest mail.
We'd love to present you one, Mike, since you're right on target. However, we asked George about it, and he says he wrote that line for the movie on purpose, partly as an in-joke and partly to show that Han Solo was something of a bull artist who didn't always know precisely what he was talking about. So, we're afraid you'll have to take it up with Mr. Lucas himself! --Roy [Roy Thomas, writer and editor for the comic at the time]
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There are a couple more theories on the [link=http://www.starwars.com/databank/location/kessel/?id=bts]Official Star Wars site[/link].
Btw, the Ep3 teaser poster is there as well on the main page