Scans reveal secrets of the world's oldest navigation tool

The late fifteenth century astrolabe, which is believed to be the earliest known marine navigation tool, was used by mariners to measure the altitude of the sun during voyages.

It was excavated by Blue Water Recoveries, who could not see any navigational markings on it so they took it WMG’s Professor Mark Williams, who conducts scanning analyses, to reveal the artefact’s invisible details.

Scans proved it was an astrolabe because markings were found etched around the edge of the object, each separated by five degrees. These would have allowed mariners to measure the height of the sun above the horizon at noon to determine their latitude so they could find their way on the high seas.

The technology at WMG was able to accurately scan the item to within 0.1mm and reproduce a high-resolution 3D model.

Prof Williams said: “It was fantastic to apply our 3D scanning technology to such an exciting project and help with the identification of such a rare and fascinating item.

“Usually we are working on engineering-related challenges, so to be able to take our expertise and transfer that to something totally different and so historically significant was a really interesting opportunity.”

The astrolabe is a bronze disc, which measures 17.5cm in diameter, and is engraved with the Portuguese royal coat of arms and the personal emblem of Don Manuel I, the King of Portugal from 1495-1521.

It is believed to date from between 1495 and 1500, and was recovered from the wreck of a Portuguese explorer vessel which sank during a storm in the Indian Ocean in 1503.

The ship was called the Esmeralda and was part of a fleet led by Portuguese explorer Vasco da Gama, the first person to sail directly from Europe to India.