Dude, that was outer space!

P.S. That link from Embry is so fascinating. One question I had though is I didn't quite follow why planes go to a higher altitude as they burn off fuel. Is it because they are lighter and therefore need a lower angle of attack and hence less power? Also, why are turbojet engines more efficient in colder air? I'm sorry physics isn't my stronghold, but airplanes have always fascinated me!