ALL of the students in my astrophysics class last semester had to give a final presentation. In one, a student showed everyone an image of our galaxy, the Milky Way , as viewed from Earth. The student then showed another image of a spiral galaxy, suggesting that it reflected our own. Because it was a class focused on stars – the students are taking on galaxies this semester – a question came from the audience: how can we get a picture of the whole Milky Way if we are inside it? We can’t.

In this sense, astrophysics is like a Midsomer …