The oldest known marine navigation tool has been excavated from a shipwreck that sank in a violent storm off the coast of Oman in 1503.Archaeologists say the navigation tool, known as an astrolabe, would have been used by mariners in the Age of Discovery to measure the position of the sun on trans-oceanic voyages.The item was recovered from a ship called 'Esmeralda', which sank in the Indian Ocean, killing all on board, including its captain who was the uncle of famous Portuguese explorer Vasco da Gama.Archaeologists say the astrolabe would have been used by mariners in the Age of Discovery to measure the position of the sun on trans-oceanic voyages. It is 17.5cm in diameter and less than 2mm thick.  It is believed to have been made between 1495 and 1500 and is the earliest known example by several decades. The disc has 18 evenly spaced gradations around the edge and each one is separated by five degrees. 

This would marines to measure the height of the sun so they could orientate themselves.  Since the late 50s they've been keeping a worldwide catalogue of every one that's been found. This is the 108th marine astolade discovered in the worldThe astrolabe, which is 17.5cm in diameter and less than 2mm thick, was used by mariners to measure the altitude of the sun during voyages.When the researchers found the object, no markings were visible.But scans by Warwick University showed etches around the edge of the object, each separated by five degrees – proving that it is an astrolabe.These markings 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.The artefact is also engraved with the Portuguese coat of arms and the personal emblem of Don Manuel I, the King of Portugal from 1495-1521.

Scientists say it is the earliest known example of an astrolabe by several decades.'The first reference to a maritime astrolabe was 1480 and the earliest one before ours was from a shipwreck that sank in 1533', David Mearns from Blue Water Recovery, who excavated the shipwreck, told MailOnline.'It is from a ship from the Age of Discovery - the pre-colonial period before empires were built', said Mr Mearns, who is also author of The Shipwreck Hunter.'Since the late 50s they've been keeping a worldwide catalogue of every one that's been found. This is the 108th marine astolabe discovered in the world.'Esmeralda was part of da Gama's second voyage to India and is the oldest ship ever found from Europe's Golden Age of Discovery.

The astrolabe was one of nearly 3,000 objects recovered from the wreck.Although it was found in 2014, It was not confirmed as a marine astrolabe until last month when the Institute of Nautical Archaeology at Texas A&M confirmed it.'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.' Mr Mearns told BBC.

​'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.Mr Mearns said he first recognised the Portuguese coat of arms and then the emblem of the King of Portugal - Don Manuel I.'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', he said.'

* ASTROLABE- an instrument formerly used to make astronomical measurements, typically of the       altitudes of celestial bodies, and in navigation for calculating latitude, before the development of the sextant. In its basic form (known from classical times), it consists of a disk with the edge marked in degrees and a pivoted pointer.- Google Search

Once upon a time: Atlantic: Great Sea Battles, Heroic Discoveries, Titanic Storms, and a Vast Ocean of a Million Stories. by Simon Winchester

"Variably genial, cautionary, lyrical, admonitory, terrifying, horrifying and inspiring…A lifetime of thought, travel, reading, imagination and memory inform this affecting account." —Kirkus Reviews (starred review)

Blending history and anecdote, geography and reminiscence, science and exposition, New York Times bestselling author Simon Winchester tells the breathtaking saga of the Atlantic Ocean. A gifted storyteller and consummate historian, Winchester sets the great blue sea's epic narrative against the backdrop of mankind's intellectual evolution, telling not only the story of an ocean, but the story of civilization.

​Fans of Winchester's Krakatoa, The Man Who Loved China, and The Professor and the Madman will love this masterful, penetrating, and resonant tale of humanity finding its way across the ocean of history.

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