The relic, a bronze disc which marine archaeologists name an ‘astrolabe’, was excavated from a shipwreck off the coast of Oman. It would have been used by mariners to measure the altitude of the sun during their voyages, and is believed to date from between 1495 and 1500.
Experts consider astrolabes to be rare and only 108 are known to be confirmed and catalogued.
This latest find is believed to be the earliest example of the ancient tool by several decades.
Earlier this week, the BBC reported the item was recovered from a Portuguese explorer which sank during a storm in the Indian Ocean in 1503.
The boat 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.
The Esmeralda was discovered by National Geographic grantee and shipwreck hunter David Mearns last year, after half a millenium resting hidden in her murky grave.
On March 15, 2016, Oman’s Ministry of Heritage and Culture (MHC) in cooperation with Blue Water Recoveries Ltd (BWR) of West Sussex, UK, announced the discovery and archaeological excavation of a Portuguese East Indiaman that was part of Vasco da Gama’s 1502-1503 Armada to India, later confirmed as the Esmeralda.
The ship, which sank in a storm in May 1503 off the Coast of Al Hallaniyah Island in Oman’s Dhofar region, is the earliest ship from Europe’s Age of Discovery ever to be found and scientifically investigated by a team of archaeologists and other experts.
History indicates it was being commanded by the maternal uncle of Vasco da Gama, Vicente Sodré; a descendent of the nobleman Frederick Sudley of Gloucestershire, UK.
Key individual artefacts that helped identify the wreck as Vicente Sodré’s nau, Esmeralda included an important copper-alloy disc marked with the Portuguese royal coat of arms and an esfera armilar (armillary sphere), which was the personal emblem of King Dom Manuel I; a bronze bell with an inscription that suggests the date of the ship was 1498; gold cruzado coins minted in Lisbon between 1495 and 1501; and an extraordinarily rare silver coin, called the Indio, that was commissioned by Dom Manuel in 1499 specifically for trade with India.
The extreme rarity of the Indio (there is only one other known example in the world) is such that it has legendary status as the ‘lost’ or ‘ghost’ coin of Dom Manuel.
In comments to the BBC, Mr. Mearns, from Blue Water Recovery, who led the excavation and is the author of The Shipwreck Hunter, said of the recently-confirmed Astrolabe: “It’s a great privilege to find something so rare, something so historically important, something that will be studied by the archaeological community and fills in a gap.”
The astrolabe was one of nearly 3,000 artefacts recovered from the Esmeralda during a series of dives.
“It was like nothing else we had seen and I immediately knew it was something very important because you could see it had these two emblems on it”, he said, adding: “One I recognised immediately as a Portuguese coat of arms… and another which we later discovered was the personal emblem of Don Manuel I, the King of Portugal at the time.”
According to the BBC, from the start, the excavation team believed the object was an astrolabe, but had doubts as they could not see any navigational markings on it.
However, a later analysis uncovered its hidden details.
Laser scanning work carried out by scientists at the University of Warwick revealed etches around the edge of the disc, each separated by five degrees.
This, the experts said, would have allowed mariners to measure the height of the sun above the horizon at noon to determine their location so they could find their way on the high seas.
Mr Mearns said: “We know it had to have been made before 1502, because that’s when the ship left Lisbon and Dom Manuel didn’t become King until 1495, and this astrolabe wouldn’t have carried the emblem of the King unless he was King.”