From [Wikipedia](http://en.wikipedia.org/wiki/Epicyclic_gearing): **Epicyclic gearing** or **planetary gearing** is a gear system consisting of one or more outer gears, or *planet* gears, revolving about a central, or *sun* gear. … Epicyclic gearing systems also incorporate the use of an outer ring gear or *annulus*, which meshes with the planet gears.

Built with [D3.js](http://mbostock.github.com/d3/).