Periode: 1682

Afmetingen: H: 75,0 cm B: 19,0 cm D: 65,0 cm

Inventarisnummer: V09997

In 1680 Christiaan Huygens proposed to the Paris Academie Royale des Sciences to design a planetarium that could predict planet conjunctions. The French minister Jean Baptiste Colbert endorsed Huygens’ plan, and the Dutchman set to work. In 1681 Huygens left Paris for The Hague, taking the plans for his planetarium with him, and in February 1682 he wrote to Colbert that he had engaged the local clock maker Johannes van Keulen to realise his plans. Six months later the planetarium was finished and Huygens presented Colbert with a bill of 620 ecus: 520 for the clock maker and 100 for himself. The bill however was never paid. Colbert died before Huygens could deliver the planetarium. Eventually the instrument remained in Huygens’ personal estate, until it was bequeathed to Leiden University by his descendant Alexander Jerome Royer in 1809.

The deceivingly plain exterior of the planetarium hides a complex instrument. The planetarium is driven by a clock that propels a central axle to one revolution per year. This axle drives the rings with the pins representing the planets. The trajectories of the planets are eccentric circles; to Huygens this was the best way to simulate their ellipsoid courses in the solar system. The complex machinery worked so well that its biggest deviation – that of the planet Venus – was only three and a half degrees in twenty years. With the crank on the side of the planetarium the planets could be arranged into past as well as future conjunctions, in order to study them.

A.C. van Helden, Rob H. van Gent, De Huygenscollectie, Leiden 1995, pp.16-17