My Father-In-Law often asks me how scientists can 'experiment' on stars if they are indeed so far away. I can't get over to him how things work. May be I shouldn't even start with this news: Astronomers simulate how white dwarf stars merge and become a supernova
Interesting, oh and I'd probably attempt metaphore. Start by describing how they found the circumference of the earth with two sticks and a guy pasing a measured distance then convey that it is the same kind of thing. Little measurements from a long way away along with the best understanding and ideas of the time.
Either that or get him the box set of the Cosmos tv series which is a good watch if you are into science.