An orrery is a device used to model and predict the motion of planets and moons in our solar system. these devices are commonly mechanical in nature using a complex train of gears and lever arms to describe the motions. An example of this is the Antikythera mechanism from ancient Greece. While mechanical orreries are more common, electro-mechanical orreries using stepper motors and electronic control do exist.

orreries can come in a wide verity of sizes, levels of complexity and accuracy. From small desk top models to room filling behemoths. Some may only have the Earth sun and moon, while others have all 8 / 9 planets and the most complex even have all of there respective moons as well.

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