Seriously Sirius

Conversation with my boy and my 20 year old brother:

Me: "Anders, what is the name of the ocean the Titanic sailed across?"
Boy: "The Atlantic.  It was the North Atlantic."
Brother: "The Atlantic is between Europe and America?"
Boy: "Yes."
Brother, seemingly surprised: "Huh."

Me: "Do you know what the ocean on the other side of the United States is called?''
Boy: "Polaris?"
Me: "No, the Pacific.  Polaris is the name of the North Star.  Remember?"
Boy: "Oh, yeah.  Polaris.  Betelgeuse is another star."
Brother, staring incredulously: "What??"
Me: "I bet Uncle Paul didn't know that."
Boy: "Really?"
Brother: "Not really..."
Me: "So do you know any other star names?"
Boy, thinking: "The dog star? ...um..."
Me: "YES! Sirius is the dog star's name."
Boy: "Oh yeah!  Um, is it called 'serious' cause it's really really true?"