Dante describes nine celestial spheres, excluding the Empyrean, in Paradiso.
Beatrice guides Dante through the Moon, Mercury, Venus, the Sun, Mars, Jupiter, Saturn, the Fixed Stars, and the Primum Mobile. These spheres belong to the material cosmos and are arranged concentrically around Earth according to the medieval geocentric model.
The ninth sphere is the Primum Mobile, or “First Moved,” which Dante presents as the outermost physical heaven. Its motion is caused directly by God and, in turn, drives the movement of the other celestial spheres. Dante associates it with angels and with the highest activity of the created universe.
The Empyrean is different: it is beyond physical space and time, and is the true abode of God and all the blessed souls. This is why the structure is often summarized as nine material spheres plus one non-material realm. A common mix-up is counting the Empyrean among the celestial spheres, which produces ten; Dante’s heavenly structure contains ten regions overall, but only nine celestial spheres.