Orrery is a clockwork model of the solar system. I am trying to emulate one in 2D. Now, to emulate, I need to know what goes on inside. Can someone please explain the basic principle behind the clockwork? Or direct me to a resource that will explain all the machinery inside a simple Orrery.


The principle is almost exactly the same as a watch or clock, but instead of three concentric axles, you need 9 for the planets.

Have a google for Orrery kit - there are loads available. It is really all simple maths - you just need to know relative orbital periods in order to calculate cog sizes. enter image description here (picture from curiousminds.co.uk) For moons, you do add a little complexity in the form of a transmission to support the Earth, so that the difference in movement can move the Moon.

  • $\begingroup$ Okay! Well after a whole lot of googling, I wasn't able to come upon a resource that would give me the gear ratios. Where do I get these from? $\endgroup$ – Ranveer Jan 12 '14 at 14:25
  • $\begingroup$ You can work them out pretty easily from orbital periods: 0.24 0.62 1 1.88 11.86 29.46 84.01 164.8 for Mercury to Neptune. $\endgroup$ – Rory Alsop Jan 12 '14 at 14:31
  • $\begingroup$ Also, a quick google for Orrery gear ratio comes up loads of results, including a set of spreadsheets with all the info you need. $\endgroup$ – Rory Alsop Jan 12 '14 at 14:45

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