Oh, he knew this one, especially because Mo and West had used Cassiopeia last term in making their own asterism. His face fell for a moment before Mo's hand shot in the air. No reason to think on that with anything other than fondness or whatever. Right?

"What about Cepheus, Professor? It actually falls between Cassiopeia and the Little Dipper." And had once been part of a lovely asterism that looked like a Bludger and bat.