Silas watched the obviously mad professor, blank faced... weirdo. This McLaggen knew how to smile and nod, though. So that he did.

When the guy had finished his spiel Silas raised his hand and nodded. " Fair enough. And the Mister is not necessary either. Silas will do just fine. And to answeryour question: Earth rotates around sun. "

Maybe that answer would do... he thought Astronomy was rubbish, but his mum INSISTED he take it. Blah.