So, we did a "science project" today, the kids and me. We made a scale model of the Solar System, out on the street, to get a visual impression of its true size. It was pretty amazing. It's a very easy project to do, takes a couple hours, and it's a lot of fun.
The Sun was a regular soccer ball, 23 cm (9") in diameter. Everything else was made to scale.
Mercury was a tiny 0.8 mm grain of sand, barely visible, about 10 m (30') away from the Sun.
Venus was a larger 2 mm grain of sand, 18 m (54') away from the Sun.