Historian finds rare astrolabe from the 11th century – 03/16/2024 – Science

For 2,000 years, observers mapped the heavens using astrolabes, surprisingly precise instruments that looked like large old-fashioned pocket watches and allowed them to determine time, distance, height, latitude, and even (with a horoscope) the future. .

Recently, an astrolabe dating back to the 11th century appeared at the Fondazione Museo Miniscalchi-Erizzo in Verona, Italy.

Federica Gigante, a historian at the University of Cambridge, first noticed it in the corner of a photograph while searching online for an image of Ludovico Moscardo, a 17th-century collector whose objects are kept at the museum.

Federica became familiar with astrolabes at the Museum of the History of Science at the University of Oxford, where she was curator of Islamic scientific instruments. “The museum in Oxford has the largest and best collection of astrolabes in the world, spanning from the 9th century to the 19th century,” she said.

Discovering that none of the museum staff in Verona knew what the piece was, she headed to Italy to take a closer look.

There, a curator took her to a side room where she stood next to a window and watched the sunlight illuminate the reliquary’s brass features. The device consisted of a thick circular disc into which other discs and dials were fitted. On the central disk, the historian identified Arabic inscriptions and, seemingly everywhere, faint Hebrew markings, Western numerals and scratches that appeared to have been engraved.

“In the oblique light, I realized that this was not just an incredibly rare ancient object, but a powerful record of scientific exchange between Arabs, Jews and Christians over nearly a millennium,” Federica said.

Astrolabes are believed to have existed in the time of Apollonius of Perga, a third-century BC Greek mathematician known as the Great Geometer; and Hipparchus, one of the founders of trigonometry who estimated the distances of the Sun and Moon from Earth and cataloged at least 850 stars.

Muslims learned of the device through the translation of Hellenistic and Byzantine texts into Arabic. Islamic scholars refined the mechanism, and by the ninth century AD, the Persians were using astrolabes to locate Mecca and determine the five prayer periods required each day, as stated in the Quran. The tool arrived in Europe through the conquest of much of Spain by the Moors, an offshoot of the Islamic Arab population that invaded the Iberian Peninsula in 711 AD.

By analyzing the design, construction and calligraphy of the Verona astrolabe, Federica estimated that the instrument had its origins in Andalusia in the 11th century, where Muslims, Jews and Christians worked together, especially in the pursuit of science.

“As the astrolabe changed hands, it underwent countless modifications, additions and adaptations,” said the historian. The original Arabic names of the zodiac signs were translated into Hebrew, a detail that suggested the reliquary circulated at some point within a Sephardic Jewish community.

One side of a plaque was engraved in Arabic with the phrase “to the latitude of Córdoba, 38° 30′”; on the other side “to the latitude of Toledo, 40°.” Some latitude values ​​have been corrected sometimes.

Another plate was engraved with North African latitudes, which indicated that during the instrument’s travels it may have been used in Morocco or Egypt. A series of additions in Hebrew led Federica to conclude that the astrolabe ultimately reached the Jewish diaspora in Italy, where Hebrew rather than Arabic was used.

“Basically, sculpting the revisions was like adding apps to your smartphone,” Gigante said.