The Leiden Sphaera

You’re now in Vroesenpark, but this story isn’t about the park itself. It’s about Adriaen Vroesen, the mayor the park is named after, and his special invention: the Sphaera, a mechanical planetarium from the seventeenth century.

Around 1670, Vroesen designed this impressive model of the solar system. It showed how the planets orbit the sun, which was a groundbreaking idea at the time.

The Sphaera was a technical marvel. Mathematician Nicolaas Stampioen calculated the gears, and clockmaker Steven Tracy built the mechanism, powered by a four-meter pendulum. Around it, a band with the twelve zodiac signs rotated, carefully matched to the movements of the sky.

Vroesen enjoyed it only briefly. In 1672, he was removed from office for political reasons and fled the country. The Sphaera was forgotten and donated to Leiden University in 1710.

In 1931, it found a place in a museum but was badly damaged during World War II. During restoration, the zodiac was accidentally assembled in the wrong order—a mistake never corrected.

Today, the Sphaera is still on display at the Rijksmuseum Boerhaave.