How Do We Know the Shape and Size of Our Galaxy?

How do we know the shape and size of our galaxy? It's not all that easy to answer, but we can tell something about its shape even with our eye. With things like infrared astronomy now, we can see through dust so we can see further than we could before. And then brilliant, amazing missions like Gaia,. which have mapped so many stars, getting up for a billion stars. We'll catch up with you later in the show to take on some listener questions. I hear you've got a special guest this week as someone who used to be my boss. But is he now?