Timepiece Surfaces, Telling of Its Past
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 items were housed in the museum.
With no one at the museum in Verona knowing what the piece was, Ms. Gigante went to Italy for a closer look.
The brass device consisted of a thick circular plate into which fitted a series of other plates and dials. On the central plate, Ms. Gigante made out Arabic inscriptions and, seemingly everywhere, faint Hebrew markings, Western numerals and scratches that looked as if they had been keyed. “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,” she 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.
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. The tool reached Europe through the conquest of much of Spain by the Moors.
Ms. Gigante narrowed its provenance to 11th-century Andalusia, where Muslims, Jews and Christians had worked alongside one another. “As the astrolabe changed hands, it underwent numerous modifications, additions and adaptations,” she said. The original Arabic names of the signs of the zodiac were translated into Hebrew, indicating that it had 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. Another plate was etched with North African latitudes, which indicated that it may have been used in Morocco or Egypt. A series of Hebrew additions led Ms. Gigante to conclude that the astrolabe had 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,” she said.