[gufcfmpn] Density-accurate orrery

Construct a model of the solar system in which the density of the sun and planets is accurate (i.e., accurate, to-scale masses and sizes).  It should be possible to hold each object in one's hands to feel its heft (or lack thereof).  For the sun, it may be better to provide a sample of material.

Or have the planets hang as pendula, so people can get a feel of their inertial mass by pushing them and observing their period.

Fortunately, we have no white dwarf or neutron stars in our solar system; their densities cannot be approximated by normal materials.