Commentary Par I 61-63

Venturi (DDP Venturi.Par.I.62-63) believes that this additional brightness was caused by the sight of the Moon, now grown larger in its appearance because Dante is so much higher.  However (and as Lombardi [DDP Lombardi.Par.I.61-63] correctly objects), this cannot be the sphere of the Moon, which awaits Beatrice and Dante in the next canto, but is the sphere of fire, in the outermost situation of the four elements that constitute our earth (water and earth, then air, and finally fire), a solution at first proposed in 1333 or so by the Ottimo (DDP Ottimo.Par.I.58-63).  And see verse 115 of this canto ('This instinct carries fire up toward the moon'), where the sphere of fire is apparently again alluded to.  However, some early commentators (e.g., Benvenuto [DDP Benvenuto.Par.I.58-63]) and some recent ones as well (e.g., Singleton [DDP Singleton.Par.I.61-63]) deny this, the first insisting that Dante had passed this zone on the Mount of Purgatory, the second observing that Dante does not definitively refer to this important boundary of the earth's atmosphere, thus leaving the question unresolved. However, Benvenuto either has conflated what Dante says about the limits of normal earthly weather to the ante-purgatorial precincts (see [Purg XXI 41-60]) with the location of the sphere of fire or he simply misconstrues details in the earthly paradise, since he claims that we frequently learn in that part of the poem that it is found lower down; as for Singleton's objection, this would not be the first time that Dante withholds information that we would like to have (e.g., how he entered Hell, how he crossed Acheron, etc., etc.) on the good ground that we would find such information simply too challenging to our already challenged credence in the givens of this poem.  He probably felt forced, since there are nine of them, to account for his passages through the boundaries that constitute the starry spheres; but he may have felt that he could finesse the sphere of fire, thus avoiding the need to explain how he passed through it unscathed (in contrast one thinks of the lengthy and detailed description of Dante's difficult passage through the wall of fire around the seventh terrace [[Purg XXVII 10-57]]).

On this tercet see Carroll (DDP Carroll.Par.I.49-64): '"The light of the moon shall be as the light of the sun, and the light of the sun shall be sevenfold, as the light of seven days, in the day that the Lord bindeth up the hurt of his people, and healeth the stroke of the wound" (Isaiah 30:26).  This represents the vast increase of knowledge which would have come to Adam had he remained in his first estate, and which Dante receives because he has regained it, -- not the direct vision of the Divine Essence, but power to see the sparks which it flung forth -- its operations and effects in creation.'