For 2,000 years, celestial observers mapped the heavens with astonishingly precise instruments called astrolabes, which looked like large, old-fashioned vest-pocket watches and enabled users to determine time, distance, height, latitude and even (with a horoscope) the future.
Recently, an astrolabe dating to the 11th century turned up at the Fondazione Museo Miniscalchi-Erizzo in Verona, Italy. Federica Gigante, a historian at the University of Cambridge, first noticed it in a corner of a photograph while searching online for an image of Ludovico Moscardo, a 17th-century nobleman and collector whose miscellany was housed in the museum.
Gigante became familiar with astrolabes at the University of Oxford’s History of Science Museum, where she had been a curator of Islamic scientific instruments. “The museum in Oxford has the world’s largest and finest assemblage of astrolabes, spanning the ninth century to the 19th,” she said. Upon learning that no one on staff at the museum in Verona knew what the piece was, Gigante went to Italy for a closer look.
There, a curator brought her to a side room where she stood by a window and watched the sunlight illuminate the relic’s brass features. The device consisted of a thick circular plate into which fitted a series of other plates and dials. On the central plate, Gigante made out Arabic inscriptions and, seemingly everywhere, faint Hebrew markings, Western numerals and scratches that looked as if they had been keyed.
“In the raking light, I realized that this wasn’t just an incredibly rare ancient object, but a powerful record of scientific exchange between Arabs, Jews and Christians over nearly a millennium,” Gigante said.
Astrolabes are believed to have been around at the time of Apollonius of Perga, a Greek mathematician from the third century B.C. known as the Great Geometer; and Hipparchus, a founder of trigonometry who estimated the distances of the sun and the moon from Earth and cataloged at least 850 stars.
Muslims learned of the gadget through the translation of Hellenistic and Byzantine texts into Arabic. Islamic scholars refined the mechanism, and by the ninth century A.D. the Persians were using astrolabes to locate Mecca and ascertain the five periods of prayer required each day, as stated in the Quran. The tool reached Europe through the conquest of much of Spain by the Moors, a branch of the Islamic Arab population that invaded the Iberian Peninsula in A.D. 711.
By analyzing the Verona astrolabe’s design, construction and calligraphy, Gigante narrowed its provenance to 11th-century Andalusia, where Muslims, Jews and Christians had worked alongside one another, particularly in the pursuit of science. “As the astrolabe changed hands, it underwent numerous modifications, additions and adaptations,” Gigante said. The original Arabic names of the signs of the zodiac were translated into Hebrew, a detail that suggested that the relic had at one point circulated within a Sephardic Jewish community.
One side of a plate was engraved in Arabic with the phrase “for the latitude of Cordoba, 38° 30’”; on the other side “for the latitude of Toledo, 40°.” A handful of latitude values were corrected, some multiple times. Another plate was etched with North African latitudes which indicated that, during the instrument’s travels, it may have been used in Morocco or Egypt. A series of Hebrew additions led Gigante to conclude that the astrolabe had eventually reached the Jewish diaspora in Italy, where Hebrew, rather than Arabic, was used.
“Basically, carving in the revisions was like adding apps to your smartphone,” Gigante said. — NYT
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