Diameter, not distance
Diameter measures across an object. Our diagrams compare body diameters on one linear scale. The spacing between objects is a layout choice, not an orbital distance. Saturn’s rings are excluded. Surface artwork is original illustration, not a map or photograph.
Mean sizes and uncertain boundaries
Planet and dwarf-planet values use twice the volume-equivalent mean radius in JPL’s physical parameters. The Moon and Ganymede use JPL satellite mean radii. The Sun uses twice NASA’s listed mean solar radius.
Betelgeuse uses a representative rounded diameter of 800 solar diameters based on ESO’s description. Its boundary is approximate and method-dependent. Derived ratios inherit that uncertainty; extra computed digits do not make the measurement more certain.
The mathematics
The diameter ratio is the larger diameter divided by the smaller. Spherical volume scales with the cube of diameter, so the volume ratio is that ratio cubed. It describes equivalent volume, not sphere packing, mass, or gravity. The marble model multiplies the chosen marble diameter by the ratio of the second object to the first.
Small objects and the across view
A locator outline may surround a tiny disk; the outline is not its size. In the across view, the line spans the larger diameter. Whole smaller bodies are drawn along it, with a remainder for a fractional diameter. For ratios over 80, only the first 20 bodies are drawn to keep the page responsive; the full ratio is still shown.
Scope
The starter collection compares roughly spherical bodies. Galaxies, nebulae, rings, orbital distances, and irregular dimensions need different measurement definitions and are not treated as interchangeable spherical diameters.