3D scanning technology reveals that a circular artifact extracted from an ancient shipwreck is the oldest known astrolabe in the world.
Photo by David Mearns, National Geographic
An astrolabe is an elaborate tool historically used by astronomers and navigators to measure a celestial body’s inclined position in the sky. Thus, the tool can survey, identify celestial bodies such as stars and planets, and determine latitude. Now, an excavation of the Esmeralda, a ship that belonged to famed Portuguese explorer Vasco da Gama, has yielded the oldest known astrolabe so far.
The Esmeralda, which sank in 1503, hails from a period of time known as Europe’s Age of Exploration. The ship was part of a fleet that Vasco da Gama took with him on his search for a route from Europe to India, which occurred from 1502 to 1503. Initially, the shipwreck of the Esmeralda was discovered in 1998 and excavated between 2013 to 2015. These excavations produced the astrolabe, which was extracted from the sand on the sea floor.
Photo by Philip Koch
The team that excavated the artifact published a study in which they theorized that the artifact had been a navigation tool. Researchers also believe that the artifact is about 500 years old, having dated back sometime between 1495 and 1500. The artifact is just one of 3,000 others recovered from the shipwreck, but it holds a particular significance.
"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," says Blue Water Recovery’s David Mearns.
Photo by WMG, University of Warwick
On the top half of the disk was a Portuguese royal coat of arms, which was identified to have belonged to Portuguese king Dom Manuel I. This helped the researchers date the artifact, since Dom Manuel I became king in 1495, and the Esmeralda left Lisbon in 1502. Thus, the astrolabe should have been made sometime between these years.
The presence of the royal coat of arms also indicated that the artifact was an important component of the ship. The researchers had already guessed that it was an astrolabe, but they didn’t see any of the characteristic markings of the disk.
Thus, scientists at the University of Warwick used a laser scanner that produced 80,000 measurement points per second to produce 3D images. The scans and imaging revealed that etches on the edge of the disc, each separated by five degrees.
An extremely rare coin, called an indio, that was also on the Esmeralda.
"The markings were very fine and, due to damage to the surface, almost invisible to the human eye," said Mark Williams, a University of Warwick professor. "The resolution of the 3D data allowed us to zoom in and identify the marks and subsequently characterize them."
The markings would have helped navigators measure how high the sun was and determine their location. Mariners’ astrolabes, of which the Esmeralda astrolabe was one, are quite rare. In fact, the one on the Esmeralda was only the 108th to be catalogued so far.
Interestingly, the astrolabe isn’t the only rare artifact found in the ancient shipwreck of the Esmeralda. Divers also found a coin that is so rare that there is only one other of its kind known to exist.
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