The Leiden Sphaera — the dynamic model of the solar system pictured above — was built around 1670 by Dutch clockmaker Steven Tracy. The impressive cosmic model measures 1.5 meters across, and is believed to be the first model of its kind to represent the motions of our Solar System's planets and moons in a heliocentric model.

There's just one problem: the Sphaera's constellations are all backwards. And nobody has noticed until now.

Govert Schilling — astronomy writer and contributing editor of Sky & Telescope Magazine — recently noticed the stellar-reversal when the mechanical model (known in astronomical circles as an orrery) was unveiled to the public following an intensive, year-long restoration:


The twelve patterns of stars in the zodiac are displayed in separate gold-plated reliefs around the "equator" of the Sphaera. Each constellation is pictured in reverse, as it would appear reflected in a mirror - a common practice on celestial globes. As seen from the Earth, in the interior of the globe, the constellations would have the correct orientation, but as seen from the outside, they appear flipped horizontally. For instance, the head of the Lion on the Leiden Sphaera points to the left, whereas looking up to the sky from Earth, it points to the right.

To keep things consistent, the order in which the twelve constellations are displayed should of course also be mirror-reversed. But, as I noticed last week, that's not the case with the Sphaera: the Lion's head points towards the Virgin, not towards the Crab, as it does in the sky.

So did Tracy, the orrery's 17th century creator, simply botch the first attempt at a heliocentric model of the Solar System? Evidently not.

According to Schilling, the blame for the improperly placed constellations rests not with its designer, but with those who are thought to have restored the Sphaera after it was severely damaged during World War II.


"It must have been repaired shortly after the war," explains Hans Hooijmaijers, head of collections at Museum Boerhaave, where the Sphaera is currently on display. "But this has not been documented."

But there is evidence to support Hooijmaijer's hypothesis. An engraving of the Sphaera that dates all the way back to 1711 depicts the orrery with its constellations in the correct order, as does a photograph of the model taken back in 1930. But a photo taken in 1948 shows the device in its present, misrepresented form.

According to Rosalijn van Ijken, who worked on the model's most recent restoration, it's a pity that nobody ever took the time to inspect old representations of the Sphaera closely enough to notice that the constellations had been mirror-reversed, "but I wouldn't call it negligence," she explains. "I just put the constellations back in the order in which I found them. I don't know anything about astronomy."

[Via New Scientist]