Scientists have discovered the world's oldest astrolabe -- an ancient device used for navigating at sea -- which was part of Portuguese explorers Vasco da Gama's second voyage to India in the fourteenth century.
The Guinness World Records independently certified the astrolabe excavated from the wreck site of a Portuguese Armada Ship as the oldest in the world.
They also certified a ship's bell -- dated 1498 -- recovered from the same wreck site also as the oldest in the world.
The scientific process of verifying the disc as an astrolabe by laser imaging is described in the International Journal of Nautical Archaeology.
The Sodre astrolabe is believed to have been made between 1496 and 1501 and is unique in comparison to all other mariner's astrolabes.
Mariner's Astrolabes were used for navigating at sea by early explorers, most notably the Portuguese and Spanish.
They are considered to be the rarest and most prized of artefacts to be found on ancient shipwrecks and only 104 examples are known to exist in the world, according to the researchers from the University of Warwick in the UK.
They were first used at sea on a Portuguese voyage down the west coast of Africa in 1481. Thereafter, astrolabes were relied on for navigation during the most important explorations of the late 15th century, including those led by Bartolomeu Dias, Christopher Columbus and Vasco da Gama.
It is the only solid disk type astrolabe with a verifiable provenance and the only specimen decorated with a national symbol: the royal coat of arms of Portugal.
As the earliest verifiable mariner's astrolabe it fills a chronological gap in the development of these iconic instruments and is believed to be a transitional instrument between the classic planispheric astrolabe and the open-wheel type astrolabe that came into use sometime before 1517, researchers said.
The thin 175 millimetres diameter disk weighing 344 grammes was analysed by a team who travelled to Muscat, Oman in November 2016 to collect laser scans of a selection of the most important artefacts recovered from the wreck site.
Using a portable 7-axis Nikon laser scanner, capable of collecting over 50,000 points per second at an accuracy of 60 microns, a 3D virtual model of the artefact was created.
Analysis of the results revealed a series of 18 scale marks spaced at uniform intervals along the limb of the disk.
Further analysis showed that the spacing of the scale marks was equivalent to 5-degree intervals.
This was critical evidence that allowed independent experts at Texas A&M University to include the disk in their global inventory as the earliest known mariner's astrolabe discovered to date.
"Using this 3D scanning technology has enabled us to confirm the identity of the earliest known astrolabe, from this historians and scientists, can determine more about the history and how ships navigated," said Mark Williams from the University of Warwick.