I recently made a scale model of the solar system in my back yard. The attached document describes how. This would be a good thing to do with your kids or grandkids -- and you'll learn something on an emotional level that you'll never learn from a book...

 

I did something similar for my earth science class when I was in 8th grade, back in the 1970s. I also tried to keep the length scale to reasonable accuracy and tried to position the planets around the sun in their actual orbital positions at that point in time. The planets were not perfectly scaled because I used household spherical objects for the sun and planets. However, the ratios were about right. The sun was a painted basketball. Jupiter was a small Christmas ornament, and then superballs, marbles etc. were used for the other planets. I was allowed to use the school grounds to place the objects, so I was able to keep the distance scale reasonably accurate. I even put a Halley's comet in there, which was a pinhead with long cotton strands glued to the pin.

Not only did I develop an appreciation for just how insignificantly small the Earth is, but I learned that the saying "... like trying to find a needle in a haystack" might just have well been "... like trying to find a marble in a grass-field".

 

I know some teachers that could use this lesson. My boy used to claim one of his high school teachers (who was primarily a coach) thought the pictures were to scale. I would doubt it except I remember some of the qualified idiots I had when I was in school.