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

Several towns and institutions have built outdoor scale models of the Solar System. Here is a table comparing these models.

An Exploration of Scale

Power & Light District to Union Station, Kansas City, Missouri (2008)
Space Center Houston, Texas (2008)
Corpus Christi, Texas (2009)

Several sets of geocaching caches have been laid out as solar system models.

Most classroom globes are 41 cm (16 inches) in diameter. If the Earth were reduced to this size, the Moon would be a 10 cm (4 in) baseball floating 12 metres (40 feet) away. The Sun would be a beach ball 14 stories tall (somewhat smaller than the Spaceship Earth ride at Epcot) floating 5 kilometres (3.1 mi) away. While a complete model to this scale has never been built, a Solar System built centered in Washington DC, London, or Sydney, to that scale (approximately 1:31 000 000) would look like this:

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