6-Planet Mini Planetarium

A minimalist hand-driven planetarium that turns the six classical planets — Mercury, Venus, Earth, Mars, Jupiter, and Saturn — at astronomically accurate relative speeds. 10 cm wide, 5 cm tall. A desk piece that models the solar system (as it was known in the 1700s!).

Why only 6 planets?

I came across a gear train for a planetarium that was designed by Scottish astronomer James Ferguson in the mid-1700s. At the time, Uranus and Neptune had not been discovered. His design used a single stacked gear to drive 6 planets, and I thought it was cool! In order to print it however, I had to include a dedicated connector gear for Jupiter-Saturn, as the teeth would have been too small to be printed. Description of the model can be found page 300 here.

Parts Required

Requires 7 ball bearings with these diameters:

Sun = 12 mm

Mercury, Venus, Earth, Mars = 6 mm

Jupiter, Saturn = 8 mm

I included spheres for printing, but I think marbles or ball bearings would look much better. You can get all you need for approx €10 on ali express. I used a copper ball for Earth just to add distinction. 

Orbital Periods and Errors