Orreries, mechanical models of the solar system, are not about proper scale, but they are good for better understanding the basic positions and motions of the planets and moons in our solar system.
As far as accuracy goes, it’s not too far off the real thing. Each rotation of the crank represents one day, and the Earth rotates once with every turn. The Moon orbits the Earth every 28 days, the sun makes a full rotation every 25 days, and the Earth orbits the Sun every 375 days.
Watch these next: Allemann’s Sisyphus kinetic sculpture made with LEGO, The Jules Verne-Themed Sanderson Orrery, and building the solar system to scale in the Nevada desert.
via BBC. Thanks, Betsy.