I know you're interested in astronomy and I file that away about you.
"Oh, wow! Do you like independent films? Know any good indie theaters around here? What's the last film you saw?""Oh, i found that film rather intriguing. What did you think of the concepts presented?" (or, even sneakier, mention a few then slowly branch it out)
I know you're into film, maybe I can ask you questions about special effects or something depending on what you say.
Yep, this is basically what I do!Its a few lines, if they don't bite you waste a short amount of time. If they do, interesting conversation. Difficult?