Abdelhamid Sabra and Roshdi Rashed are in agreement that experimentation, identified by the Arabic verbal noun iʿtibār, was a part of Ibn al-Haytham’s theory of proof. They also agree that the term has a variety of meanings: simple observation, thought experimentation, and actual experimentation. The former attributes the source of this idea and the term to be the Arabic translations of Ptolemy’s _Almagest_, whereas the latter shows the source to be Ptolemy’s _Optics_. More importantly, Sabra states that Ibn al-Haytham’s experimentations were only “confirmatory” and not “discovery experimentation”, and thus, did not lead to revealing anything new about properties of light besides what was already known. This viewpoint portrays Ibn al-Haytham’s inquiry of knowledge to be unable of making discoveries.
Ibn al-Haytham’s treatise _On the quiddity of the trace on the face of the moon_, seems to present a significant discovery in the realm of celestial natural philosophy (physics) by applying experimentally (albeit of confirmatory nature) developed theory of light to the observations of the lunar color. His theory-based analysis of the visible color variation on the lunar surface shows that the moon is a heterogenous body with parts that are substantially different from one another. This is a theoretical-based finding that goes against the simplicity of the makeup of the superlunary world as one of the foundations of Aristotelian doctrine of celestial physics. The latter was the dominant theory in the natural philosophy of the time. Further, Ibn al-Haytham proceeds to explain what in the lunar matter causes this difference in the light of the interaction between light and matter as described in his theory of light in his _Optics_.
Thus, in this treatise, Ibn al-Haytham is taking a theory from the physical part of optics to the celestial natural philosophy whereby he analyzes his observation, and consequently, makes a discovery. I ask to what extent this treatise along with its underlying optical theory can be seen as a process of experimentally developing a theory and applying it to make a discovery and to explain a phenomenon. To answer this question, I analyze Ibn al-Haytham’s arguments in this treatise and trace his references to his _Optics_ and his treatise _On the Light of the Stars_ to show to what extent and how his arguments and their underlying theories are based on experiments and systematic observations, and to what extent on the casual observations, thought experiments, or unproven assumptions.