Answer: A Dutch Living Room

In the Dutch city of Franeker, there is a small and unassuming home that houses a planetarium on the ceiling of its living room. The intricate and mechanically driven model of our solar system is over 230 years old and, as such, is the oldest functioning planetarium in existence—and if you want to get very technical about it and perhaps even learn a new word today, it’s the oldest functioning orrery, or mechanical model of the solar system, in the world.

How, exactly, did a small home in the Netherlands become a planetarium? To answer that question, we have to dig into the history of one brilliant but amateur Dutch astronomer by the name of Eise Eisinga. The son of a wool worker, Eisinga wasn’t allowed to go to school but was, instead, compelled to study his father’s craft. Despite this, he educated himself and published his first work on astronomy at the age of 17. Later in life, he even served as a professor at the Franeker Academy.

Eisinga began work on his planetarium during the summer of 1774. Earlier that same year, Reverend Eelco Alta published a book claiming that an impending conjunction of the Moon and the planets Mercury, Venus, Mars, and Jupiter would cause all five cosmic bodies to collide, with the result being that the Earth would be pushed out of its orbit and burned by the Sun. This prediction caused an inordinate amount of panic among the public and Eisinga, as a service to the public, began working on an intricate model of the solar system in order to show that the prediction and its foretold outcome was false.

The entire project took 7 years (far more than the 6 months Eisinga had originally predicted) and featured a complex system of wooden rings fitted with thousands of hand-forged nails to serve as cog-teeth. Despite its age, the apparatus still tracks the placement of planets in our solar system with precision—a testament to both the quality of the construction and the knowledge of the builder.