In his commentary on Aristotle's Meteorology, Avempace presented his own theory on the Milky Way galaxy. Aristotle believed the Milky Way to be caused by "the ignition of the fiery exhalation of some stars which were large, numerous and close together" and that the "ignition takes place in the upper part of the atmosphere, in the region of the world which is continuous with the heavenly motions." On the other hand, Aristotle's Arabic commentator Ibn al-Bitriq considered "the Milky Way to be a phenomenon exclusively of the heavenly spheres, not of the upper part of the atmosphere" and that the "light of those stars makes a visible patch because they are so close." Avempace's view differed from both, as he considered "the Milky Way to be a phenomenon both of the spheres above the moon and of the sublunar region." The Stanford Encyclopedia of Philosophy describes his theory and observation on the Milky Way as follows:

Avempace also reported observing "two planets as black spots on the face of the Sun." In the 13th century, the Maragha astronomer Qotb al-Din Shirazi identified this observation as the transit of Venus and Mercury. However, Avempace cannot have observed a Venus transit, as there were no Venus transits in his lifetime.

Avempace worked under the mathematician Ibn al-Sayyid. He was given the privilege to add a commentary to Ibn al-Sayyid's work on geometry and Euclid's Elements. Furthermore, he viewed astronomy as part of mathematics. Avempace's model of the cosmos consists of concentric circles, but no epicycles. Avempace starts with a good kinematic definition of motion and construes it as a force. According to Avempace regarding freely falling objects, what is moved as the heavy body falls, is the heavy body and what moves it downward is its 'gravity' or its 'form' or 'nature'.

What follows is also found in Text 71:<blockquote> “This resistance offered to the moving body by the medium does not occur in the way Aristotle has established in the fourth book when he discussed the void. The velocity of a body is not inversely proportional to the density of the medium, but it is the retardation the motion is subject to by virtue of the medium, which is proportional to the density. If what Aristotle said was true, natural motion in a supposed void would not meet any resistance and it would not take time but be instantaneous. Also, the motion of the heavenly spheres, which do not traverse a medium, would occur instantaneously. We see these motions occurring with different finite velocities: the motion of the fixed stars is very slow; the daily motion is very fast. These differences in velocity are due to the fact that the movers of the spheres differ in nobility and the more noble a mover, the faster is the motion of the sphere moved by it.” In this commentary, Avempace discusses the morphology of various plants and attempts to classify them based on their similarities. He also writes about the reproductive nature of plants and their supposed genders based on his observations of palm and fig trees. Kitab al-nabat was written in Arabic and has most recently been translated into Spanish.

Tributes

In 2009, a crater 199k km (62&nbsp;mi) from the South Pole of the Moon was designated The Ibn Bajja crater by the International Astronomical Union (IAU) in his honor.

Notes

References

  • Marcinkowski, M. Ismail (April 2002), "A Biographical Note on Ibn Bajjah (Avempace) and an English Translation of his Annotations to al-Farabi's Isagoge", in Iqbal Review (Lahore, Pakistan), vol. 43, no. 2, pp.&nbsp;83–99.
  • The Diwan Attributed to Ibn Bajjah (Avem pace), D. M. Dunlop, Bulletin of the School of Oriental and African Studies, University of London, Vol. 14, No. 3, Studies Presented to Vladimir Minorsky by His Colleagues and Friends (1952), pp.&nbsp;463–477
  • (PDF version)
  • Ibn Bajja-Stanford Encyclopedia of Philosophy
  • Muslim Philosophy on Ibn Bajjah
  • Catholic Encyclopedia: Avempace