The Elizabethan Stage in Ashland, Oregon. Your dissertation defense won't get a stage like this, you'll probably get some random room in Harper or Burkle. But still, a dissertator can dream, right?
'Tis the season for Dissertation Defenses!
If you're planning one, good luck on ya! But if you're not, you might think about attending some.
At CGU, dissertation defenses are open to the public (For more on why this is, and why it's not a bad thing, see Prof. Lori Anne Ferrell's earlier remarks). Many departments send out mass e-mail invites announcing defense dates, times, and locations.
You should definitely attend defenses in your field: they help you see what kinds of questions are being asked, how certain professors do their defenses (you might get to see someone on your committee in action), and be able to visualize it for yourself: you're going to be in that room some day soon!
However, it is the unspoken rule that you should always ask the person who is defending for permission before showing up at their defense. Some people really don't mind strangers at their defenses, others don't even want their closest family members in the room. Proper etiquette and decency requires that you ask the person first.
You may feel awkward about attending a defense of someone you don't know. If so, just send them an e-mail. Say hey, I'm really interested in your topic and I'd like to attend your defense. Would that be okay with you? I'm sure they'd appreciate the gesture.
Some people who attend defenses take notes and give them to the defending student (and newly minted Ph.D.!) later. Often they're so "in the zone" and stressed out during the defense that they don't remember all the details later, and many appreciate having the little notes you take during their defense. It also helps you stay focused - a defense on a dissertation you haven't read can be pretty arduous to listen to.