Mariner's Astrolabe Found in 15th-Century Shipwreck Breaks Records
"You can only dream about finding such a rare and precious artifact."
The Warwick Manufacturing Group, an academic department at the University of Warwick, is usually concerned with the future. Its researchers use high-resolution lasers and 3D visualizations to create advanced materials for industries like automotive and aerospace. So, when they were called on by a shipwreck hunter curious to work with them on a rare new discovery, they were intrigued.
“Obviously, as engineers, you don’t get an awful lot of that every day,” Mark Williams, Ph.D., a professor of metrology at Warwick, tells Inverse. “So we were very keen to work with him.”
The shipwreck hunter was David Mearns, a marine scientist who has found the watery remains of over 24 doomed voyages. On Saturday, Mearns, Williams, and their collaborators announced the culmination of their joint effort: The discovery of the oldest-ever mariner’s astrolabe, a navigation tool used to determine the latitude of a ship at sea. Their feat, described in a new paper published in the International Journal of Nautical Archaeology, is now official in the Guinness Book of World Records.
Today, mariner’s astrolabes are prized and prestigious artifacts. To a 15th century explorer, they were everything. These navigation instruments were based off simplified versions developed by Arab astronomers and came into use on board ships around 1481. The astrolabe described in the paper was made as early as 1496.
“Ships today navigate by electronic means, principally GPS, so there is no comparison to how the first global explorers like Vasco de Gama and Christopher Columbus navigated their small wooden sailing ships,” Mearns tell Inverse. Mariner’s astrolabes were the best option for an explorer until their use died out around the mid-18th century.
The story of its discovery began when Mearns’ organization, Blue Water Recoveries, collaborated with Oman’s Ministry of Heritage and Culture in 2013. Oman’s Royal Navy supplied vessels to explore Al Hallaniyah, a large island off the southern coast of the Arabian Sea bordering the country.
There, in May 1503, two Portuguese armada ships called the Esmeralda and the Sâo Pedro sank after encountering a sudden and furious storm. They were originally a part of a military mission led by the famous explorer Vasco de Gama, the first European to reach India by sea. His uncle, Vicenté Sodré, ignored his orders to protect trading outposts and sailed to the Gulf of Aden to loot Arab ships. Sodré then sailed to Al Hallaniyah to evade a monsoon, where he later encountered viperous winds and went down with his ship. It’s believed that the astrolabe belonged to him.
Mearns and his team discovered the wreck site in 1998 and, because of the logistical challenges of working on such a remote island, they were unable to begin the excavation until 15 years later. In 2014, a year after the excavation began, Mearns was diving in a gully labeled “Z” and found a metal disc alone in the sand.
“I have conducted numerous shipwreck projects around the world, many in depths greater than 4,000 and 5,000 meters,” Mearns says. “But I have never worked harder and had such fun as I did diving with our British and Omani team every day on this rewarding project.”
“You can only dream about finding such a rare and precious artifact as an astrolabe, but then to find such a historically important one in relatively good condition was a huge bonus.”
The disk is thin and light, just 175 millimeters in diameter and 344 grams. The clean side of the disc is decorated with the coat of arms and armillary sphere that are clearly Portuguese in origin. Because of its size, shape, and what appeared to be remnants of a suspension ring, they suspected it was an early astrolabe. But they couldn’t be sure, so they called in Mearns and two other engineers who traveled to Muscat, Oman, in 2016 to scan it with lasers.
Using a portable, seven-axis Nikon laser scanner, the team created a 3D virtual model of the artifact. This process revealed a series of 18 scale marks spaced in uniform intervals along the limb of the disc. Ostensibly invisible to the human eye, these scale marks were placed at five-degree intervals, allowing independent experts at Texas A&M University to declare it the earliest known astrolabe found to date.
To Williams, the event was a delight.
“That sort of thing doesn’t happen every day,” he chuckles. “It could be a moment that’s once in a lifetime. You get to scan the oldest recorded device of its type and, not only that, but you helped identify what it was.”
Now, Sodré’s astrolabe joins the 104 other examples known to exist in the world as the oldest and the only known solid disc type with a verifiable provenance and age. Because of the known date of Sodré’s voyage, the likely date range for its manufacture is sometime between 1496 and 1501.
The process of exploration isn’t done yet. Mearns says the team is still writing academic papers on the artifacts recovered from the Sodré wreck site, and he’s planning another project with Oman’s Ministry of Heritage and Culture that will start later this year. What they could find may alter the historical record, as the current excavation not only revealed the astrolabe but the oldest ship bell ever unearthed.
A unique leaded‐gunmetal disc decorated with iconic Portuguese markings was recovered in 2014 during archaeological excavations at the Sodré shipwreck site in Al Hallaniyah, Oman. Initially, the identity and function of the disc was unknown, although it did possess characteristics suggesting it could be an astrolabe. Laser imaging of the disc post conservation revealed regular scale marks on the limb of its upper right quadrant. Accurate digital measurements of the marks show them to be graded at close to 5‐degree intervals, thus confirming the identity of the disc as a mariner’s astrolabe and the earliest known example discovered to date.