Abu Ali al-asan ibn al-asan ibn al-Haytham, generally called Al-Hazen in Europe is known in the West as “Ptolemaeus Secundus” or “Ptolemy the Second” based on his main astronomical work Al-Shukuk ala Batlamyus, generally translated as “Doubts Concerning Ptolemy”. He also wrote several important works concerning astrophysics and celestial mechanics as well.
Al-Hazen distinguished between astrology and astronomy. He rejected astrology as a science because it was not empirically based, but instead was mere guesswork. But also because it was antithetical to Islam.
In his most important work: “Doubts Concerning Ptolemy” Al-Hazen rejects Ptolemy because used conjecture, not observation to arrive at his theories. In this work as well as his other Al-Hazen promoted empirical, observational and experimental data as the only source of knowledge. In an early attempt to define the scientific method and rejected authority, for Al-Hazen the truth is sought for its own sake, but such truths are not self evident and the authorities are not error free.
In his “Doubts” Al-Hazen makes the following point regarding Ptolemy:
“Ptolemy assumed an arrangement that cannot be, and the fact that this arrangement produces in his imagination the motions that belong to the planets does not free him from the error he committed in his assumed arrangement, for the existing motions of the planets cannot be the result of an arrangement that is impossible to exist. . . For a man to imagine a circle in the heavens, and to imagine the planet moving in it does not bring about the planet’s motion.” (Ibn al-Haytham’s (Al-Hazen) doubts concerning Ptolemy”)
In his “The Model of the Motions of Each of the Seven Planets” Al-Hazen continued to accept the geocentric, or Earth centered solar system. But promoted an early version of what would later be called Occam’s Razor in the West and also suggested that the earth rotates on its axis. In this work Al-Hazen rejected cosmology and instead focused on planetary motion as an exercise in physical geometry.
In the astrophysical realm Al-Hazen determined that the planets must and did obey the laws of physics. 600 years before Newton, Al-Hazen also talked about a theory of attraction between physical masses, he seemed aware that the distances of the masses from each affected the acceleration of said bodies and also theorized that the weight of an object would vary depending on how far from the Earth’s center of mass it was.
Al-Hazen also determined that the so called celestial spheres were no solid matter and that “the heavens” were much less dense than the Earth atmosphere.
Sources:
Duhem, Pierre, To Save the Phenomena: An Essay on the Idea of Physical theory from Plato to Galileo, University of Chicago Press, 1969.
Sabra, A. I. “An Eleventh-Century Refutation of Ptolemy’s Planetary Theory”, Science and History: Studies in Honor of Edward Rosen, 1978.
Voss Don L., translator, “Ibn al-Haytham’s (Al-Hazen) doubts concerning Ptolemy”, University of Chicago Press, 1989
http://www.yawiki.org/proc/Astronomy+in+medieval+Islam (accessed 29 Jan 2011)
http://www.tutorgig.com/ed/Alhazen
