The first thing we need to do is to determine the scale to be used to scale down the solar system . We can determine the scale working on the planet furthest from the sun ( identified with PFS from now on ) . Once we have calculated the scale for this planet , we can apply it to all the orbits of the other planets to build the full scaled down model of the solar system Consider this question If the diameter of the PFS's orbit must be reduced down to 1/ 2 mile , then the radius of PFS's orbit should be reduced to .. ? " The answer to this question has to be put in cell D18 , while the reduced diameter of the PFS's orbit has to be put in cell E 18