1 Darth Vader: My master?
1 Emperor: Yes, Lord Vader? I sense something disturbing you. What is it?
2 Darth Vader: You know sound doesn't travel through space, right?
3 Emperor: Yes, of course.
4 Darth Vader: So why do our TIE fighters broadcast a radio beacon so that Rebel fighters can hear us coming in from their rear quadrant?

2012-11-23 Rerun commentary: I thought I'd talked about this somewhere on a later strip, but a search doesn't turn it up. So to prevent the tide of e-mails from readers, here goes:

Sound of course, does not travel through space. Except, apparently, in the movies, in which people spaceships seem to be able to hear other spaceships flying past or firing guns at them.

An actual, reasonable explanation for this is that the ships have sensors that let them detect other ships and stuff flying around them, and then they generate sound inside the ship for the benefit of humans, because then the people inside gain the useful ability to hear other ships flying up behind them.

This is probably the single most sensible explanation for a standard piece of Hollywood stupidity ever devised in the entire history of ridiculous movie conventions. It actually makes more sense than not having the sounds. Impressive.