From Jason Allemann:
A LEGO Orrery featuring the Earth, Moon and Sun. I tried to focus on making the rotation and movements as accurate as possible without making it too complex. It can be powered manually using the crank, or with a Power Functions M-Motor.
The relative sizes and distances between the objects is obviously not to scale, a concession often taken with these models. It’s also missing the tilt of the Earth and inclination of the Moon’s orbit. Perhaps some things that could be added in the future.
Building instructions and more information can be found here.