Orrery demonstrating the transit of Venus

An orrery is a mechanical device demonstrating the relative positions and motions of planets and moons in the solar system. This example was made for the Royal Society to show the transit of Venus across the Sun as seen from the Earth. When the handle is turned Venus rotates around the Sun. The Royal Society sent Captain James Cook to Tahiti to time the transit; timing the event from different parts of the globe allowed astronomers to calculate an accurate distance to the Sun for the first time.