THESE pictures are of the plate of a mariner’s astrolabe, the earliest known, which was raised in 2014 from a wreck off the coast of Oman. The complete instrument would also have had a rotating pointer, called an alidade, mounted on a pin running through the central hole. The plate itself is 17.5cm in diameter, but less than 2mm thick, and has recently been examined by scanning with a laser beam, by Mark Williams of the University of Warwick, in Britain. Dr Williams used the laser to create a high-resolution, three-dimensional “point cloud” of individual spots on the plate’s surface. This reveals detail invisible to conventional photography. The blue picture, showing the reverse side of the plate from the natural-light picture, is a result of such a scan.
Esmeralda, the vessel the astrolabe came from, was part of Vasco da Gama’s second expedition to India. Between 1497 and 1499 da Gama had led the first fleet to travel from Europe to India and back. He…Continue reading
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