Commentary Par XXX 4-6

For mezzo as 'center of the sky,' in the sense of zenith, see Salsano (Sals.1974.1), pp. 222-24, and Chiavacci Leonardi (Chia.1997.1), pp. 825-26.  For centuries this was the standard gloss.  That is, commentators believed that Dante was referring to the midpoint of the Starry Sphere, directly overhead.  Porena (DDP Porena.Par.XXX.1-6 [= 'Nota finale' to this canto]) sharply objected.  How can the sky directly above an observer be the first part of the heavens seen growing lighter at the approach of dawn, when obviously the eastern horizon is?  He goes on to cite a text that, he says, explains this verse perfectly (Conv.III.ix.11-12), in which Dante discusses the obscuring qualities of the earth's atmosphere itself.  Most of the commentators who follow Porena accept his explanation (a few even crediting him).  See, for example, Bellomo (Bell.1996.1), pp. 52-53.  At least three aspects of Porena's argument are, however, problematic: (1) Dante does not say that the predawn sky grows lighter first at its zenith, only that it does so, and does so very gradually; (2) his description seems to imply invariable phenomena (i.e., celestial events that happen in the same manner every night at its juncture with dawn), while atmospheric hindrances are variable; (3) the relationship between this and the following terzina is such that the process initiated in this one is completed in that, which would at least imply a continuous movement in these celestial 'candles' becoming dimmer and finally being snuffed out.  In short, it seems unwise to jettison the old reading for Porena's.

For an extended argument in support of the notion that Dante conceived the Empyrean as a depiction of the 'eye of God,' even unto its extramissionary ray of sight, see Kay (Kay.2003.1).