Yeah, I'd probably figure both were physical objects, at least as large as mountains, pretty far away. There's no way I'd guess anywhere near the actual enormous sizes and distances. But the rest of the world is made of physical objects, so that would be what I'd expect of the sun and moon. Thinking that way is pretty core to who I am, and I would gravitate towards that even if it made me peculiar in my society, and if it's too far from the bounds of what a person in that society is able to believe then, like I said, that's just not identifiable as me anymore.