An archeological company investigating a Portuguese shipwreck has recovered what is believed to be the earliest navigation tool ever found.
The device, called an astrolabe, was used to sight the height of the sun to determine the ship’s latitude, or distance from the equator.
The astrolabe came from the shipwreck of the Portuguese vessel Esmerelda, which sank in the Indian Ocean in 1503. The ship, part of the fleet of Portuguese explorer Vasco De Gama, sank during a storm near the island of Al Hallaniyah, which is owned by Oman.
De Gama was the first European to reach India by sea in 1498, a discovery that opened the way for an age of colonialism and trade between Europe and Asia.
The wreck was discovered in 1998 by the British archeological company, Blue Water Recoveries. Blue Water eventually managed to work out terms with the Omani government to allow exploration. The astrolabe turned up during undersea excavation at the site in 2014.
The details of the 7-inch bronze disc are caked with patina. What looked to be the crest of the King of Portugal and the Portuguese coat of arms was visible on one side; the other seemed smooth.
“I knew immediately when I saw it that this was a very, very important object. I could see the royal coat of arms on it,” said David Mearns of Blue Water Recoveries, who led the recovery effort.
“The Portuguese were at the forefront of developing astrolabes at sea. The oldest reference of them using them at sea is about 1480. The previous oldest was on a ship from 1533,” Mearns said.
“This is the oldest maritime astrolabe.”
Researchers contacted professor Mark Williams of Warwick Manufacturing Group (WMG), which is part of the U.K.’s University of Warwick. Williams and his team used 3-D scanning technology to uncover a series of markings, each five degrees apart, which sailors would have used to sight the sun.
“It was fantastic to apply our 3-D scanning technology to such an exciting project and help with the identification of such a rare and fascinating item,” said Williams in a statement released by the University of Warwick.
The astrolabe, which preceded the sextant, works in a similar fashion. A sailor would line up the base line with the horizon and sight the height of the sun above the horizon at exactly noon. The resulting numbers could be used to calculate the ship’s current latitude.
This astrolabe is believed to have been used between 1495 and 1500. The crest was identified as belonging to Don Manuel I, who was king of Portugal between 1495 and 1521.
“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,” David Mearns said in a statement.
“It was like nothing else we had seen.
“It adds to the history, and hopefully astrolabes from this period can be found.”
More than 2,800 artifacts have been recovered from the wreckage of the Esmerelda so far.
The astrolabe is currently in the possession of the National Museum of Oman.