Solar System model

Solar System models, especially mechanical models, called orreries, that illustrate the relative positions and motions of the planets and moons in the Solar System have been built for centuries. While they often showed relative sizes, these models were usually not built to scale. The enormous ratio of interplanetary distances to planetary diameters makes constructing a scale model of the Solar System a challenging task. As one example of the difficulty, the distance between the Earth and the Sun is almost 12,000 times the diameter of the Earth.

If the smaller planets are to be easily visible to the naked eye, large outdoor spaces are generally necessary, as is some means for highlighting objects that might otherwise not be noticed from a distance. The Boston Museum of Science had placed bronze models of the planets in major public buildings, all on similar stands with interpretive labels. For example, the model of Jupiter was located in the cavernous South Station waiting area. The properly-scaled, basket-ball-sized model is 1.3 miles (2.14 km) from the model Sun which is located at the museum, graphically illustrating the immense empty space in the Solar System.

The objects in such large models do not move. Traditional orreries often did move, and some used clockworks to display the relative speeds of objects accurately. These can be thought of as being correctly scaled in time, instead of distance.

Permanent true scale models
Many towns and institutions have built outdoor scale models of the Solar System. Here is a table comparing these models with the actual system.

Other models of the Solar System: historic, temporary, virtual, or dual-scale
Several sets of geocaching caches have been laid out as Solar System models.