Click here and go to the Live Interstellar Hangout Event page.
Choose "Yes", you're going to watch. That will put the event right into your Google calendar, so you'll get a reminder.
Post a question. If you click the video on the Event page, you'll be able to post a question which we'll see when the broadcast goes live on Wednesday.
Join the conversation using the hashtag #InterstellarHangout. You can post comments and questions on Google+ or Twitter.