Betelgeuse is a red giant (some say supergiant) star in the constellation Orion. You can easily spot it on a clear night: it's at a straight angle to Orion's Belt, and it's reddish (more so than Mars). It's pretty impressive. I recommend you find it and point it out to your friends. People really should look up at the sky now and then.
That said, I thought you were supposed to pronounce it as Beatle Jews.
Now it turns out there's this kitsch-y comedy from the Year of Our Lord's Grace 1988, titled "Beetlejuice," in which there's a character (a ghost, I think, I didn't see the whole movie) from Betelgeuse whose name is Beetle Juice. Either it's a tacky joke of some sort, or I'm missing something here. I'm not a movie buff.
What am I missing? What's the joke?