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READ: The Missing Link? — The Maragha Observatory

From Ptolemy to Copernicus and Galileo, thinkers have debated what the Universe looked like for centuries. Ultimately, scholars moved from an Earth-centered model to a Sun-centered model. How did we get there?

The Missing Link? The Maragha Observatory

By Eman M. Elshaikh
From Ptolemy to Copernicus and Galileo, thinkers have debated what the Universe looked like for centuries. Ultimately, scholars moved from an Earth-centered model to a Sun-centered model. How did we get there?

Planetary revolutions

Television with breaking news is a composite image of the Earth orbiting the Sun, Breaking News lower thirds banner, and television, all via Freepik.
Or at least it was big news to people living in the sixteenth century, when this revolutionary idea challenged people’s understanding of the Universe. Ancient astronomers like Ptolemy (100–170 CE) believed that the Earth was at the center of the Universe. They thought the Sun, stars, and planets revolved around Earth. This belief persisted—although some questioned it—for many hundreds of years. By the sixteenth century, however, astronomers like Copernicus (1473–1543 CE) and Galileo (1564–1642 CE), started challenging Ptolemy’s model. They put the Sun at the center. This heliocentric (Sun at the center) model of the Universe shocked people at the time. The Catholic Church even jailed Galileo for claiming it.
Like all scholars, Copernicus and Galileo came up with their ideas using the knowledge of those who came before them. What was this earlier knowledge? About 1,400 years separated Copernicus from Ptolemy. But we don’t hear much about the people who came between—who carried on the collective learning conversation between these major figures. For centuries, scholars had been slowly chipping away at the Earth-at-the-center model. The tenth-century Arab astronomer, Ibn al-Haytham (965–1040 CE), for example, questioned Ptolemy’s model. He pointed out several contradictions and claimed that Ptolemy’s idea about how different planets fit together simply didn’t work. An even earlier Arab astronomer, al-Battani (858–929 CE), calculated the movement of the Sun and the planets. His carefully recorded observations were cited by Copernicus many times.
So while Copernicus is famous for challenging Ptolemy, there have been missing links in history’s centuries-long chain of thinkers who contributed to this debate. Thanks to the work of many invisible giants like Ibn al-Haytham and al-Battani, it was possible for scholars who came later to construct a serious challenge to such a long-accepted view of the Universe. Many of these invisible giants were astronomers working during the Golden Age of Islam.

A golden age during a dark age

The scholars between Ptolemy and Copernicus were part of a vibrant tradition of astronomy in the Islamic world. These scholars were supported largely by the wealthy rulers of Islamic empires, and together their work launched a period of scientific and cultural achievement called the Islamic Golden Age. By building on the knowledge of Greek, Indian, Chinese, Babylonian, Persian, and Arab thinkers before them, scholars were able to make new observations and discoveries.
Astronomy was a major field for these scholars. For Muslims of this period, astronomy was a practical science that was important for religious practice. By measuring the movement of the Sun, Moon, and stars, Muslim scientists determined the times for daily prayers, set the dates for the lunar calendar, and precisely calculated the direction of Mecca from any location. This knowledge was valuable to Muslim political and religious leaders.
As a result, many Muslim rulers built observatories—special buildings for studying astronomy. Among the most famous and important of these was the Maragha Observatory. There, scholars seriously challenged Ptolemy’s Earth-at-the-center system, which had been accepted for many centuries.
The geocentric or Earth-centered model of the Universe, which places the Earth at the center of planetary orbits. Ptolemy was one thinker who proposed this model, which was accepted for centuries after Ptolemy’s death. By BHP and Peter Quatch, CC BY-NC 4.
The heliocentric or Sun-centered model of the Universe, which places the Sun at the center of planetary orbits. Copernicus was arguably the first scholar to propose this model. By BHP and Peter Quatch, CC BY-NC 4.0.

The Maragha Observatory

In the thirteenth century, the Mongol ruler Hulagu Khan conquered a big part of the Islamic world. After founding the Ilkhanate of Persia, he destroyed the city of Baghdad, along with the many books in its famed House of Wisdom. Despite the Mongols’ destruction of scientific knowledge in this unfortunate case, they also supported its creation. Like the Arab and Persian rulers who came before them, Mongol rulers supported scholars, especially astronomers. In addition to the practical importance of astronomy to Islam, Mongol rulers believed that studying the stars would help them make decisions and predict the future, so they brought astronomers from across their massive empire to their courts.
Once he had finished his wars of conquest, Hulagu Khan worked with the great Persian astronomer Nasir al-Din al-Tusi, and built the Maragha Observatory in Persia. It was the most advanced observatory in the world at the time. It attracted astronomers from across the Islamic world and from as far away as China. Under Mongol rule, astronomers from across Eurasia shared ideas, which sped up new developments in collective learning.
Maragha astronomers recorded their astronomical observations and calculations in the massive library at the observatory. Using these observations, they came up with new ideas about how the planets moved. One of the most important of these new ideas was called the “Tusi couple,” named after Nasir al-Din al-Tusi many centuries later. The Tusi couple may sound like the screen name of a pair of adorable lovebirds on Instagram, but it’s actually a mathematical idea. Astronomers used the Tusi couple to create models of a small circle rotating within a larger one, and then track the motion of the rotation. It helped astronomers understand how different celestial bodies revolve around one another.
Ibn al-Shatir, a Syrian astronomer, built on this work. Using the Tusi couple, Ibn al-Shatir corrected Ptolemy’s calculations about distances between planetary bodies. Ibn al-Shatir wanted to create a model of the Solar System that fit with the observations he and others had made. His model was much more accurate than Ptolemy’s. While the models coming out of the Maragha Observatory kept the Earth at the center, they made crucial changes to Ptolemy’s model and moved our collective understanding closer to a Sun-centered model.

The missing link?

Neither Nasir al-Din al-Tusi nor Ibn al-Shatir understood the Sun was at the center of the Solar System. Still, their work may have provided the foundation for Copernicus’s heliocentric model. OK, words like “may have” are frustrating when you want to know if something is true, but not all historians agree on this. The “conversations” among Copernicus, Ptolemy, and the Maragha scholars were spread out over 14 centuries. It’s hard to prove how these ideas developed, moved, or changed, but it’s still important to look for connections.
On the one hand, some historians of science argue that scholars like al-Tusi and Ibn al-Shatir influenced Copernicus’s heliocentric system. They use this evidence to support their claims:
  1. The work of these scholars had been translated and spread around Eurasia for centuries before Copernicus’s time. It’s logical to assume that an educated man like Copernicus would have come across their work.
  2. There are similarities between Copernicus’s diagrams and mathematical arguments and those of the Maragha scholars. Some of Copernicus’s models of planetary rotations used mathematical ideas that were nearly identical to the Tusi couple. Some historians even argue that the diagrams are labeled similarly to Ibn al-Shatir’s.
  3. Without this link, it’s more difficult to explain how Copernicus made the leaps that led to his conclusion that the Sun is at the center of our Solar System.
On the other hand, other historians disagree. They don’t think the Maragha Observatory scholars influenced Copernicus’s heliocentric system. They use this evidence to support their claims:
  1. While Copernicus cited scholars like al-Battani, he never mentioned al-Tusi or Ibn al-Shatir. (Of course, scientists of this era often borrowed freely from one another and reworked each other’s ideas without giving direct credit.)
  2. These Islamic scholars didn’t have a heliocentric model. In fact, their models are pretty different from Copernicus’s.
  3. There may be similarities in mathematical ideas, but these mathematical ideas are used very differently.
  4. Even if there are some similarities, these historians argue that it’s possible to have similarity without direct influence. They could be independent discoveries.
Historians will continue to debate these questions. You might say that historians are still learning about collective learning. Who learns it? Who collects it? How, over thousands of years, is knowledge shared, moved, changed, translated, improved, and challenged? No matter how historians answer these questions, it’s important to keep revealing the influence of invisible giants like Ibn al-Haytham, al-Battani, al-Tusi, Ibn al-Shatir, and many others. Only then can we start to make connections that allow us to tell our Big History more fully.
Author bio
Eman M. Elshaikh holds an MA in social sciences from and is pursuing a PhD at the University of Chicago, where she also teaches writing. She is a writer and researcher, and has taught K-12 and undergraduates in the US and in the Middle East. Eman was previously a World History Fellow at Khan Academy, where she worked closely with the College Board to develop curriculum for AP world history.

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