The solar system is a magnificent display of physics and gravity. Huge planets spinning around the sun, each in their own orbit. Somehow not hitting each other in the process. Models that show how the solar system moves over time (an Orrery) can be extremely complicated. This Lego MOC of the Solar System is created by Thomas Rodger. There is a lot of math involved in trying to get the speeds of the planets as accurate as possible. And, that is with out Pluto! The designer has figured that this Lego Orrery is about 96.5% accurate. It uses one power functions motor to drive everything, which adds up to be about 4,000 Lego pieces. There are instructions on how to build this yourself that have been made available, but if you need to buy everything it will cost around $350-$600. Even though a lot of the pieces are common and cheap, there are some extremely rare ones found in the gear rack system. A very interesting note, is that brand new gears are needed. As any wear and tear will effect how this model works. Make sure to check out the video to see it in action!
You can find out more about this model, and how to get instructions on how to build it over here: https://rebrickable.com/mocs/MOC-38774/jollyrodger/8-planet-solar-system/
There is a neat video showing just how this Lego Solar System works, go watch it below or over here: https://youtu.be/CvNbTaAXOz4