The Astrolabe
Author: Sarah Dard
Editor: Hira Islam
Housed within the magnificent observatories set up by the likes of Caliph Al – Mamun of Baghdad (arguably the first man in history to build an observatory) were large observational instruments designed and built to study the universe that so deeply intrigued early Muslim astronomers. These astronomers pioneered large observational instruments, which, due to their size, reduced the percentage of error in the measurement of celestial coordinates. Accuracy of measurement was not only critical to the reputation of the Muslim astronomers and the observatories from where they conducted their research and study, but it was vital in v determining daily prayer times. These large-scale, innovative tools were fundamental in advancing and developing an astronomical study that followed their inception. Early Muslim astronomers designed and built instruments and devices that included armillary spheres, large quadrants, sextants, and celestial globes. The most outstanding and influential of these instruments and devices, however, was the Astrolabe.
Astrolabes
American astrophysicist Dr. Harold Williams describes the Astrolabe as “the most important astronomical calculating device before the invention of digital computers and the most important astronomical observational device before the invention of the telescope.”
Figure 1- A working astrolabe, created by Mohamed Zakariya. The creation of this almost magical device requires a wealth of knowledge. Using ancient techniques, such an astrolabe can take three to six months to complete; it requires extensive geometrical calcula
The word “astrolabe” is derived from the Arabic word “asturlab,” which is a transliteration of a Greek word. While similar devices can be traced to earlier centuries, this instrument was fully developed and used in a multitude of forms by the early Muslim astronomers due to their need for determining prayer times and the “qibla” or direction of prayer (toward Mecca) with accuracy. Thus, the use of astrolabes remained common in the Islamic world up to the 1800s.
New treatises on the Astrolabe can be traced back to the early ninth century, the earliest being produced by Masha’Allah Ali Ibn Isa and Al Khwarizmi. The earliest surviving instrument dates back to the middle of the tenth century, built by an apprentice of Ali Ibn Isa in Baghdad. Islamic learning, including that of the Astrolabe, seeped into western Europe due to the Muslim presence in Spain from the eighth century. Thus, the earliest surviving Christian or Western instruments are from the 13th century onward.
Multiple astrolabes followed the initial models developed by the Muslim astronomers, the most popular being the planispheric Astrolabe. This type is characterized by the celestial sphere being projected onto the plane of the Equator. The Astrolabe is a two-dimensional model of the sky, showing how the sky looks at a specific place at a particular time. This calculation is done by drawing the sky on the face of the Astrolabe and marking it so that positions in the sky are easy to find. The astrolabes of the medieval Muslim astronomers varied in size, with some being portable, palm-sized devices and others being of a much larger scale – a few meters in diameter.
Astrolabes were the astronomical and analog computers of their time. These devices helped solve problems relating to the position of celestial bodies, like the sun and stars and time. Essentially, they were the pocket watches of medieval Muslim astronomers. The astrolabes could take altitude measurements of the sun; could tell the time during the day or night; or find the time of a celestial event such as sunrise, sunset, or culmination of a star. These determinations were made possible by the use of ingenious tables printed on the back of the astrolabes. These tables would contain information about curves for time conversions, a calendar for converting the day of the month to the sun’s position on the ecliptic, trigonometric scales, and a graduation of 360 degrees. They were based on the model of the Earth being at the center of a spherical universe, with an imaginary observer positioned at a particular latitude and time outside this sphere and looking down upon it.
On the Astrolabe that the astronomer was holding, the major stars in the sky were represented on a pierced metal plate, which was set into a larger flat circular holder called a mater. As the plate with the stars was pierced, the astronomer could see through it onto another plate beneath, with lines representing his particular geographical location. Several plates would be included in an astrolabe so that the astronomer could move about from one latitude to another. After using the sighting device on the back of the plate to determine the altitude of a star or the sun, the astronomer would rotate the pierced star map over the plate for his location to coincide with the sky at that time. Then, all sorts of calculations could be made. For the more accurate coordinates of celestial bodies necessary for detailed astronomical tables, astrolabes were used with other instruments, such as large quadrants and observational armillary spheres.
A highly sophisticated form of the Astrolabe, the universal Astrolabe, was developed in Toledo in the ninth century, and it revolutionized star mapping. Ali ibn Khalaf al Shakkaz, an apothecary or herbalist, and Al-Zarqali, an astronomer, played a critical role in this new development. The universal Astrolabe was a significant breakthrough because it could be used at any location. Ordinary astrolabes needed different latitude plates if they were moved because they were designed for a particular place and were latitude dependent. Another trailblazer in the history of the Astrolabe was a young engineer astronomer, Maryam al-Ijliya al-Astrulabi. Born in Aleppo, Syria, in 944, she was raised in a family of astronomers and instrument makers. She became a skilled astrolabe maker and worked at the famous Aleppo castle under the ruler Saif al-Dawla. She died in 967.
Figure 2- Maryam al-Ijliya al-Astrulabi. Source: https://www.istockphoto.com/photo/brass-astrolabe-a-madieval-astronomical-navigation-instrument-gm511666569-46609938
Astrolabes, and in particular universal astrolabes, were the cutting edge of technology, critical to the study and work of Muslim astronomers who were intrigued and fascinated by
the universe. Through these innovative and trailblazing scholars, the Astrolabe made it into Europe, where modern astronomy was born.
References
Al-Hassani, T. S. (2012). 1001 Inventions: The enduring legacy of muslim civilization. National Geographic.
Islamic Astrolabe: Science Museum Group Collection. Islamic astrolabe | Science Museum Group. (n.d.). Retrieved September 28, 2021, from https://collection.sciencemuseumgroup.org.uk/objects/co8228482/islamic-astrolabe-astrolabe.
Islamic science and Mathematics: The astrolabe. TeachMideast. (2016, July 7). Retrieved September 28, 2021, from https://teachmideast.org/articles/a-golden-age-of-science-and-mathematics/.
The Arabs and the advancement of astrolabes. SCIplanet. (n.d.). Retrieved September 28, 2021, from https://www.bibalex.org/SCIplanet/en/Article/Details?id=5198.
