It is difficult to make models of objects in the solar system because the sizes of the bodies and the distances between them are so extreme that they cannot both be shown accurately at the same time in any convenient model.

Huge differences in size

  • The Sun is more than 100 times wider than Earth, so if a model Sun is made a comfortable “medium” size, the planets must be tiny specks to keep the same scale.
  • Some planets and moons are only a fraction of Earth’s size, which makes them almost invisible in a scale model if the larger bodies are shown realistically.

Enormous distances between objects

  • The distance from Earth to the Sun is almost 12,000 times Earth’s diameter, so a truly to‑scale layout would spread over hundreds of meters or more, even if the planets were only a few centimeters across.
  • To fit everything into a classroom, poster, or yard, model makers must shrink distances much more than sizes (or vice versa), so at least one of those aspects becomes unrealistic.

Can’t match both size and distance

  • Using a single scale for both planet diameters and their orbital distances “doesn’t really work,” because it forces either the planets to become too small to see or the model to become too large to use.
  • Most physical solar system models therefore exaggerate planet sizes relative to their separations, or compress distances while keeping planets big enough to notice, sacrificing strict accuracy for practicality.

Motion and behavior are complex

  • Real solar system objects move in elliptical orbits, at different speeds, and in three dimensions, with gravitational interactions that are hard to copy in a simple classroom or desktop model.
  • Mechanical models (orreries) can show relative motions, but usually drop true scale and simplify orbits and speeds so the device can actually be built and understood.

Limits of materials and detail

  • No model can fully reproduce surfaces, atmospheres, temperatures, or internal structures of planets, so things like gas giant atmospheres or ring systems are always simplified impressions.
  • Because all models have these limitations, they are best seen as tools to highlight specific ideas—such as relative order, basic sizes, or orbital paths—rather than perfect copies of the real solar system.

TL;DR: It is difficult to make models of objects in the solar system because the size differences, vast distances, complex motions, and material limits mean you cannot show everything accurately and conveniently at once.

Information gathered from public forums or data available on the internet and portrayed here.