Moon Spots: Moon, Paradiso 2   In addition to explaining the appearance of dark areas on the lunar surface, the episode of the "moon spots," comprising exactly one-hundred verses (2.49-148), establishes an important general lesson for understanding Paradise. Beatrice informs Dante--and the reader--that the usual ways of attaining knowledge, through sensory perception and even the use of reason, are insufficient for grasping fully the spiritual realities of the heavens. In posing his question to Beatrice, Dante right away dismisses the popular belief for the lunar marks (2.49-51): God adorned Cain with thorns, as punishment for murdering his brother Abel, and exiled him to the Moon--"Cain with his thorns," as Virgil put it when telling time by the Moon in Hell (Inf. 20.124-6). Instead, Dante attributes the appearance of dark areas to the presence of denser and rarer portions of the lunar body (2.55-60), a rational, pseudo-scientific hypothesis that the poet vigorously supported in his earlier philosophical treatise (Convivio 2.13.9). Beatrice's refutation of this view points to the limits of reason and the need for an alternative theory of knowledge in Paradise.   Beatrice develops her argument with the confident hand of a scholastic master. She first objects to Dante's claim that dense and rare matter is the underlying cause of the moon spots: this would imply, by analogy, that a single formal principle (density) determines the varying luminosity of the stars when in fact multiple formal principles must engender multiple stellar powers (manifested by different gradations of brightness) (2.64-72). Turning back to the Moon, Beatrice delineates two possible configurations, both unacceptable, implied by Dante's reasoning. 1) The lunar body contains a section that is rare (i.e. transparent) through and through, which cannot be true because sunlight would then shine through the Moon during an eclipse (2.79-81); 2) the Moon contains alternating section of rare and dense matter, with the dark spots caused by light reflected from dense matter located deep within the lunar body. Rebutting Dante's rational explanation with a rational argument of her own, Beatrice asks Dante (and us) to imagine an experiment in which light (from a candle located just behind the viewer) is reflected from three mirrors (two would actually suffice), on e of which is placed further away from the light source than the other two. The reflected image of light, she argues, would be smaller in the more distant mirror but no less bright than the image reflected from the other mirrors. Thus dense matter further back in the lunar body could not be the reason for the dark spots (2.85-105).   The answer to this celestial question, according to Beatrice, therefore requires a more metaphysical approach (2.112-48). The uniform divine power, distributed among the stars, is unfolded and multiplied down through the heavens. The compounds formed from different powers joined to different planetary bodies then display varying luminosity not only among the stars but also within the Moon (and presumably the other planetary bodies as well).