The device, used by sailors in the early years of the 16th century, was discovered while studying the remains of a Portuguese ship that was part of the second Indian expedition of Vasco da Gama and sank in the Arabian Sea during a storm on April 30, 1503. In addition to it, a ship's bell was found among the wreckage, which, most likely, is also the oldest artifact of this kind that fell into the hands of scientists.
The astrolabe was invented by the ancient Greeks in antiquity and was then used for the needs of the then fundamental science, that is, to determine the height of celestial bodies above the horizon and all kinds of calculations based on it, up to the preparation of astrological forecasts. The astrolabe was also used in architecture, but there were simpler tools. Then antiquity ended, the astrolabe was forgotten in Europe, but the ingenious instrument was preserved from the Arabs, from whom the Europeans adopted it again somewhere in the 11th-12th centuries.
Disassembled astronomical astrolabe.
The sea astrolabe, invented by the Portuguese in the 15th century, was a very simplified version of the "classic." It was impossible to perform complex calculations with the help of many discs and arrows on it, and the sailors did not need them. It was enough for the navigator to determine the height above the horizon of the Sun or the North Star. Therefore, the device was reduced to a graduated disk with an arrow, which had to be pointed at the celestial object of interest. The disk was thick and heavy so that its mass damped the vibrations of the device during rolling.
This is how the sea astrolabe looks like, kept in the collection of the House-Museum of Christopher Columbus on the island of Gran Canaria. Until recently, it was considered the oldest in the world. But apparently this is not the case.
Astrolabe from a museum in Gran Canaria.
The found bronze disc with the coat of arms of Portugal, 175 mm in diameter and weighing 344 grams, was analyzed by scientists from the University of Warrick (UK), who traveled to Muscat, Oman in November 2016 to collect laser scans of the most important artifacts found at the crash site. Its examination was carried out back in 1998 by the Blue Water Recovery Ltd. company, but it has only now come to a thorough study of some of the finds.
Using Nikon's handheld 7-axis laser scanner capable of capturing elevations in excess of 50,000 points per second with an accuracy of 60 microns, a 3D virtual model of the artifact was created.
Promotional video:
3-D model of the find.
Analysis of the results revealed a series of 18 marks located at regular intervals along the disc limb.
Further analysis showed that the distance between the scale marks was equivalent to 5-degree intervals. This was critical evidence that it was the astrolabe.
The object thus turned out to be the oldest known marine astrolabe. There are not so many of them - there are only 104 of them preserved in the world.
Sergey Sysoev