The astrolabe is an ancient astronomical tool used to measure the position of the sun and the stars as well as solve problems of time. Inventors of the astrolabe re-created the sky on the face of the instrument and marked it so that celestial bodies were easy to find. Dating back to 1345-1355 C.E., this astrolabe is made of brass and was found in Spain, where it was introduced by Islamic astronomers after the Muslim conquest of the Iberian Peninsula in the 8th century [Glick 2005, 11]. Muslims used astrolabes to find the times of the sunrise and the rising of fixed stars and to help schedule morning prayers facing Mecca.
Although many variations existed, most ancient astrolabes were made of brass and were roughly six to eight inches in diameter. The front of the astrolabe is designed with two components: a fixed and rotating part. Latitude lines depicting the stereographic projection of the sky are present on the fixed part as well as scales representing time. The rotating part is designed to move with the daily rotation of the sky.
Astrolabes were constructed by hollowing out a brass disk, called the mater, which holds a set of thin brass plates. The plates, commonly called or climates, are inserted into the mater and are engraved with circles of altitude and lines of latitude. A rotating brass disk, called the rete, is fitted over the hollow disk. The rete includes pointers representing the number of fixed stars and a circle showing the projection of the sun’s path. The back of the astrolabe included scales for measuring angles and determining the sun’s longitude on any date.
One of the most important features of the astrolabe came about in al-Andalus in the eleventh century, when Muslim astronomers devised the single universal plate, which included markings for both equatorial and ecliptic coordinate systems. With this modification, the astrolabe no longer needed plates for different latitudes and eliminated the need to re-calculate the radii values at each use. This technology was not known outside of the Islamic world in al-Andalus at the time, but in the fourteenth century, it was perfected in Syria [Selin 1997, 87].
Muslim craftsmen forged intricate designs onto the faces of astrolabes, depending on the region the smiths were from. Since the time of Charlemagne (CE 742-814), the brass industry was capable of producing items of technical and artistic sophistication, and therefore, Islamic smiths were able to make use of this technology to forge elaborate and beautiful brass work. Brass had replaced bronze as the most prevalent copper alloy in Europe in the 6th and 7th centuries, so the craftsmen of Andalusia easily acquired brass from centers, such as Dinant and Huy on the Meuse River. In the 13th century, the brass industry was not only widespread in Europe, but also internationally, especially in West Africa [Ward 2008, 58].
By the 16th century, the astrolabe was a basic educational tool in mathematics and astronomy. It was largely replaced by the invention of the telescope, but those who were able to employ an astrolabe were considered educated and well-schooled. As for time-keeping, the pendulum clock and the chronometer replaced the astrolabe, making it a thing of the past. However, the workmanship behind beautiful astrolabes was evidence of the advancements of technology in metalwork.
Local Historical Context
Ancient Greek astronomers invented the astrolabe in the second century BCE to determine the position and altitude of celestial bodies. Hipparchus (150 BCE) is credited with constructing the first four ring astrolabe, but desciptions of the instrument’s concept and design do not appear until AD 150 when Ptolemy wrote Mathematical Syntaxis – later used by Islamic astronomers. During the Dark Ages, many Greek astrolabes and manuscripts were lost, specifically in the burning of the library in Alexandria, Egypt. This coupled with the sequestering of knowledge by the Church resulted in the loss of astronomical knowledge in the Western world.
However, from 12 AD to the 12th century, astrolabes were re-introduced to the Western world as Islamic astronomers sought out and uncovered the remaining Greek astrolabes and manuscripts. They expanded on the uses and technology of astrolabes and disseminated this knowledge as Islam was spreading throughout North Africa and southern Europe. Ibn al-Nadim, a 10th century bibliographer, states that al-Fazari was the first Muslim to make an astrolabe. He also states that astrolabe construction was centered in Harran and spread from there. Islamic astronomers expanded on the Greek version by introducing shadow squares and trigonometric grids on the backs and the azimuth curves representing different latitudes [Selin 1997, 87].
The earliest surviving Islamic astrolabes date back to the 9th century and historians agree that they are indeed modifications of the Greek design. Over 40 uses existed for the astrolabe, but Islamic astronomers primarily used the astrolabe to develop a calendar of astronomical events important to the Islamic faith, determine exact moments of sunrise and sunset for prayer times, and position mosques and direction of prayer toward Mecca.
The 9th century invention of tables by al-Farghani, which listed the radii of the circles on the plate of the astrolabe for each latitude degree, removed the need for mathematical calculation for these values on individual astrolabes. This suggests that astrolabes were widely distributed and manufactured in large numbers.
Astrolabes forged by Muslim craftsmen varied from region to region. In the Middle East, especially Baghdad, astrolabes were simple in design, but by the 10th century, a tradition of ornamentation and intricate metallurgy had began and continued in Europe for several centuries [Ward 2008, 58]. Construction of astrolabes after 1500 CE continued in Iran and India until the end of the nineteenth century [Selin 1997, 87]. These objects are remembered as beautiful instruments of the finest workmanship.
During the Middle Ages, Europe was plagued by Germanic invasions, deurbanization, and depopulation, resulting in a widespread disinterest in classical learning. However, the revival of knowledge and learning is evident in the Muslim world with its many advances in science and technology. As Islam was branching out from the Middle East into Europe and North Africa, so was Islamic innovation and technology, such as the astrolabe. Although the model for the astrolabe was derived from the Greeks, the Muslims re-created and improved it to make it a version representative of their culture.
Islamic scientists and astronomers are known for their extensive contributions to the world of math and science during the Middle Ages. Because of their curiosity and desire to innovate and re-discover ancient knowledge, they developed inventions and concepts that sparked a revival of learning in the European world. The long term use of the astrolabe demonstrates the longevity and usefulness of their inventions. From the 12th to the 17th century, the astrolabe was the main tool for time keeping and determining positions of celestial bodies. It wasn’t until the invention of more advanced technologies, such as the telescope, that the astrolabe became obsolete.
Glick, Thomas. Islamic and Christian Spain in the Early Middle Ages. Leiden, Netherlands: Martinus Nilioff, 2005.
Kusukawa, Sachiko, and Liba Taub. "An Islamic Astrolabe." Whipple Museum of the History of Science. Accessed April 17, 2011. http://www.hps.cam.ac.uk/starry/isaslabe.html.
Morrison, James. "Parts of an Astrolabe." The Astrolabe. Accessed April 18, 2011. http://www.astrolabes.org/astrolab.htm.
Selin, Helaine, ed. Encyclopaedia of the History of Science, Technology, and Medicine in Non-Western Cultures. Norwell, Mass.: Kluwer Academic Publishers, 1997.
Strode, Diana. "The Islamic Astrolabe: An Indicator of the Role of Islamic Astronomy during the Middle Ages." College of DuPage. Accessed April 18, 2011. http://www.cod.edu/middle/history/astrolabe.pdf.
Ward, Gerald, ed. The Grove Encyclopedia of Materials and Techniques in Art. New York: Oxford University Press, 2008.