Knock Knock, Whose There… It's Space : Classifications Part Deux

Purely by coincidence, the second episode of the first season and this episode - the second episode of the second season - are about how we classify things in space! Benjamin is, shall we say, just a little obsessed about how scientists categorize stars, planets, nebulae, black holes and quasars - and he asks Kovi to explain it all in a kind of quasi-quiz/Q&A conversation. Say it three times fast, "Chthonian..."