RECENTLY, I was giving a tour of the University of New Hampshire’s department of physics and astronomy to a guest who isn’t a scientist. Among the many questions he asked was: “How does this stuff show up in the real world?” The kind of stuff I do, I explained, is mostly just knowing things for the sake of our big-picture understanding of the universe and our place in it.

Later, I realised I had made a mistake in not giving a practical example based on the class I am teaching, an introduction to stellar astrophysics. The topic can seem as …