Moving the earth
With the benefit of hindsight, it is easy to see that the Islamic astronomers’ basic assumptions were flawed. Of course Copernicus showed in the mid-16th century that the earth does move, circling around the sun with the planets. But even this concept failed to give correct predictions until Kepler showed that the paths of the planets through space are not perfectly circular, but slightly elliptical. And it would have made no sense in terms of existing theories of how the celestial machine held together. It required the addition of Newton’s theory of gravity to complete the picture and show how it all worked.
In conventional accounts, the narrative seems to leap straight from Ptolemy to Copernicus, and to show how Copernicus had the great insight to see that the earth is not fixed, as Ptolemy said it was, but circles around the sun and spins on its axis. In this narrative, the ultimate Islamic contribution to the big picture seems comparatively small or even misguided. The Arab astronomers may have been diligent and ingenious, it seems, but they were barking up the wrong tree in backing the fixed-earth model, and it required Copernicus’s brilliant insight to set things right.
Copernicus acknowledged that some of the data he needed to prove his theory came from the charts of al-Battani and al-Bitruji, but that was all that apparently came from the Arab astronomers. Yet there are clues that this is not the full story.
Islamic source
In 1957, the historian Otto Neugebauer noticed a similarity beween an illustration in Copernicus’s first key book Commentariolus (1514), in which he first set out his idea that the earth moves, and one in ibn al-Shatir’s book in which he answered the problems of the moon’s motion. The similarity was so striking that it seemed hard not to believe that Copernicus had seen ibn al-Shatir’s book. Intrigued, Neugebauer delved deeper for connections between Copernicus and the Islamic astronomers, and soon found another apparent illustration match in Copernicus, this time with al-Tusi’s 1260 Tadhkira, in which he explains the Tusi Couple. Again the similarity was marked, even including an apparent mistake in the copying of an Arabic letter in al-Tusi’s illustration.
Many historians now believe that Copernicus drew directly from the work of the Islamic astronomers in providing proofs for his theories. Recent research has suggested that West European astronomers were far more aware of Arabic work at the time than was imagined. Indeed many may actually have spoken, or at least read, Arabic, including Guillaume Postel, a lecturer at Paris University in the early 16th century, whose highly technical notes in Arabic can clearly be seen on an Arabic astronomical text in the Vatican library.
The Arab contribution
Of course, Copernicus made the great breakthrough suggestion that the earth moved, but the argument is that it was simply yet another step down the road away from the Ptolemaic model. Indeed, at the time, in some ways it seemed like a backward step, since ibn al-Shatir’s work had matched a believably real theory with observations to a remarkable degree. Yet Copernicus’s idea did not. No one at the time could explain how the universe could possibly fit together without the earth at its centre – and Copernicus’s model made considerably less accurate predictions than ibn al-Shatir’s. These problems, as much as any theological problems that the Roman Catholic Church might have had, needed to be solved before most astronomers could accept that the earth moves.
There is no doubt that Copernicus’s idea of a heliocentric (sun-centred) universe was a seismic shift in scientific thinking. But it was a revolution waiting to happen. The way was paved by the gradual chipping away at the edifice of the Ptolemaic system over the centuries by countless Arabic astronomers, both with their observations and their often ingenious theories.
With the benefit of hindsight, it is easy to see that the Islamic astronomers’ basic assumptions were flawed. Of course Copernicus showed in the mid-16th century that the earth does move, circling around the sun with the planets. But even this concept failed to give correct predictions until Kepler showed that the paths of the planets through space are not perfectly circular, but slightly elliptical. And it would have made no sense in terms of existing theories of how the celestial machine held together. It required the addition of Newton’s theory of gravity to complete the picture and show how it all worked.
In conventional accounts, the narrative seems to leap straight from Ptolemy to Copernicus, and to show how Copernicus had the great insight to see that the earth is not fixed, as Ptolemy said it was, but circles around the sun and spins on its axis. In this narrative, the ultimate Islamic contribution to the big picture seems comparatively small or even misguided. The Arab astronomers may have been diligent and ingenious, it seems, but they were barking up the wrong tree in backing the fixed-earth model, and it required Copernicus’s brilliant insight to set things right.
Copernicus acknowledged that some of the data he needed to prove his theory came from the charts of al-Battani and al-Bitruji, but that was all that apparently came from the Arab astronomers. Yet there are clues that this is not the full story.
Islamic source
In 1957, the historian Otto Neugebauer noticed a similarity beween an illustration in Copernicus’s first key book Commentariolus (1514), in which he first set out his idea that the earth moves, and one in ibn al-Shatir’s book in which he answered the problems of the moon’s motion. The similarity was so striking that it seemed hard not to believe that Copernicus had seen ibn al-Shatir’s book. Intrigued, Neugebauer delved deeper for connections between Copernicus and the Islamic astronomers, and soon found another apparent illustration match in Copernicus, this time with al-Tusi’s 1260 Tadhkira, in which he explains the Tusi Couple. Again the similarity was marked, even including an apparent mistake in the copying of an Arabic letter in al-Tusi’s illustration.
Many historians now believe that Copernicus drew directly from the work of the Islamic astronomers in providing proofs for his theories. Recent research has suggested that West European astronomers were far more aware of Arabic work at the time than was imagined. Indeed many may actually have spoken, or at least read, Arabic, including Guillaume Postel, a lecturer at Paris University in the early 16th century, whose highly technical notes in Arabic can clearly be seen on an Arabic astronomical text in the Vatican library.
The Arab contribution
Of course, Copernicus made the great breakthrough suggestion that the earth moved, but the argument is that it was simply yet another step down the road away from the Ptolemaic model. Indeed, at the time, in some ways it seemed like a backward step, since ibn al-Shatir’s work had matched a believably real theory with observations to a remarkable degree. Yet Copernicus’s idea did not. No one at the time could explain how the universe could possibly fit together without the earth at its centre – and Copernicus’s model made considerably less accurate predictions than ibn al-Shatir’s. These problems, as much as any theological problems that the Roman Catholic Church might have had, needed to be solved before most astronomers could accept that the earth moves.
There is no doubt that Copernicus’s idea of a heliocentric (sun-centred) universe was a seismic shift in scientific thinking. But it was a revolution waiting to happen. The way was paved by the gradual chipping away at the edifice of the Ptolemaic system over the centuries by countless Arabic astronomers, both with their observations and their often ingenious theories.
