Build a solar system
This is an interesting exercise to visualise the true scale of space and the solar system.
Plug in the size you want your model Sun to be , and it calculates the size and distances of the planets to the scale you specify.
It also tells you the scale distances to a few stars, the speed of light in your scale and a few other intersting things. eg my Sun was a 100mm ball, so Betelgeuse was 37.5 metres in diameter !
