From the moment it was discovered more than a century ago, scholars have puzzled over the Antikythera mechanism, a remarkable and baffling astronomical calculator that survives from the ancient world. The hand-powered, 2,000-year-old device displayed the motion of the universe, predicting the movement of the five known planets, the phases of the moon and the solar and lunar eclipses. But quite how it achieved such impressive feats has proved fiendishly hard to untangle. Now researchers at UCL believe they have solved the mystery – at least in part – and have set about reconstructing the device, gearwheels and all, to test whether their proposal works. If they can build a replica with modern machinery, they aim to do the same with techniques from antiquity. “We believe that our reconstruction fits all the evidence that scientists have gleaned from the extant remains to date,” said Adam Wojcik, a materials scientist at UCL. While other scholars have made reconstructions in the past, the fact that two-thirds of the mechanism are missing has made it hard to know for sure how it worked. The mechanism, often described as the world’s first analogue computer, was found by sponge divers in 1901 amid a haul of treasures salvaged from a merchant ship that met with disaster off the Greek island of Antikythera. The ship is believed to have foundered in a storm in the first century BC as it passed between Crete and the Peloponnese en route to Rome from Asia Minor. The battered fragments of corroded brass were barely noticed at first, but decades of scholarly work have revealed the object to be a masterpiece of mechanical engineering. Originally encased in a wooden box one foot tall, the mechanism was covered in inscriptions – a built-in user’s manual – and contained more than 30 bronze gearwheels connected to dials and pointers. Turn the handle and the heavens, as known to the Greeks, swung into motion. Michael Wright, a former curator of mechanical engineering at the Science Museum in London, pieced together much of how the mechanism operated and built a working replica, but researchers have never had a complete understanding of how the device functioned. Their efforts have not been helped by the remnants surviving in 82 separate fragments, making the task of rebuilding it equivalent to solving a battered 3D puzzle that has most of its pieces missing. Writing in the journal Scientific Reports, the UCL team describe how they drew on the work of Wright and others, and used inscriptions on the mechanism and a mathematical method described by the ancient Greek philosopher Parmenides, to work out new gear arrangements that would move the planets and other bodies in the correct way. The solution allows nearly all of the mechanism’s gearwheels to fit within a space only 25mm deep. According to the team, the mechanism may have displayed the movement of the sun, moon and the planets Mercury, Venus, Mars, Jupiter and Saturn on concentric rings. Because the device assumed that the sun and planets revolved around Earth, their paths were far more difficult to reproduce with gearwheels than if the sun was placed at the centre. Another change the scientists propose is a double-ended pointer they call a “Dragon Hand” that indicates when eclipses are due to happen. The researchers believe the work brings them closer to a true understanding of how the Antikythera device displayed the heavens, but it is not clear whether the design is correct or could have been built with ancient manufacturing techniques. The concentric rings that make up the display would need to rotate on a set of nested, hollow axles, but without a lathe to shape the metal, it is unclear how the ancient Greeks would have manufactured such components. “The concentric tubes at the core of the planetarium are where my faith in Greek tech falters, and where the model might also falter,” said Wojcik. “Lathes would be the way today, but we can’t assume they had those for metal.” Whether or not the model works, more mysteries remain. It is unclear whether the Antikythera mechanism was a toy, a teaching tool or had some other purpose. And if the ancient Greeks were capable of such mechanical devices, what else did they do with the knowledge? “Although metal is precious, and so would have been recycled, it is odd that nothing remotely similar has been found or dug up,” Wojcik said. “If they had the tech to make the Antikythera mechanism, why did they not extend this tech to devising other machines, such as clocks?”