The Royal Eise Eisinga Planetarium is an 18th-century orrery in Franeker, Friesland, Netherlands. It is currently a museum and open to the public. The orrery has been on the top 100 Dutch heritage sites list since 1990 and in December 2011 was placed on a provisionary list of future UNESCO World Heritage Site candidates. It is the oldest working orrery in the world.
The museum consists of the planetarium room, a screening room where documentaries are shown, and special exhibits based on modern astronomy. Other parts on permanent display are Eisinga’s former wool combing establishments and a collection of historical astronomical instruments.
Historical astronomical instruments in the collection include Georgian telescopes and an 18th century octants and tellurium, an educational model of the Sun, Earth and Moon.
An orrery is a planetarium, a working model of the solar system. The orrery is painted with royal blue glimmer and outlined in shiny gold paint. The sun is painted at the center of the ceiling. The Earth is represented by a golden orb dangling on a wire. The zodiac is also depicted. The clockwork-like mechanical planetarium moves as it does in reality at a reduced scale. The planetarium is very exact, but is not perfect. The pendulum, for instance, is made of a single type of metal so it is influenced by temperature fluctuations.
The "face" of the model looks down from the ceiling of what used to be his living room, with most of the mechanical works in the space above the ceiling. It is driven by a pendulum clock, which has 9 weights or ponds. The planets move around the model in real time, automatically. (A slight "re-setting" must be done by hand every four years to compensate for the February 29th of a leap year.) The planetarium includes a display for the current time and date. The plank that has the year numbers written on it has to be replaced every 22 years.
According to en.wikipedia