The solar system is a big place, and while Colin's testing the shuttle, Sarah and Matthew have a visitor.David drops by to explain a bit about relativity and distance within the solar system and the universe in general.And watch out for mighty Zordon of the Orcs.Things to LearnWhat happens when you're travelling close to the speed of light?What's a light second?How fast are you travelling right now, and why don't you realise it?Why do two trucks seem to take ages over passing each other?