Machines · Study 072
Orrery
A clockwork model of the solar system. Mercury to Saturn circle the Sun at their true relative speeds, one Earth year every six seconds.
What you're looking at
Each planet rides a brass arm turning at a rate set by its real orbital period: 88 days for Mercury, 225 for Venus, a year for Earth, 1.9 years for Mars, 11.9 for Jupiter and 29.5 for Saturn. The Moon circles Earth about thirteen times a year. Distances and sizes are compressed to fit, as they are on any tabletop model.
The idea behind it
Mechanical planetaria became fashionable in the early 1700s, and the name comes from the Earl of Orrery, who commissioned one of the first. Getting the gear ratios right is the whole art: a pair of wheels with 83 and 44 teeth, for example, approximates the ratio between the Mars and Earth years closely.
Try this
Move the pointer to the right to run the clockwork faster, up to twenty years a second.
