Common-sense interpretation: concentric spheres in uniform circular motion around the stationary earth

Concentric spheres. Confronted with the overwhelming impression of the night sky, it was natural to think of the stars as fixed on an immense sphere rotating around the North Pole at a constant rate forever. By far the two brightest objects in the sky, the Sun and Moon behaved very similarly: they too also moved across the sphere of the heavens but at a slightly slower pace than the stars. And the same held for the other five planets -- Mercury, Venus, Mars, Jupiter, and Saturn -- aside from the curious phenomenon of retrograde motion, which called for a separate explanation.

The fifth essence. Observing the heavens, Aristotle concluded that they must be composed of a fifth element, different from the four which made up the terrestrial realm. Everything composed of earth, water, air, and fire is mutable and corruptible, coming into being and passing away; but no change can be perceived in the celestial realm aside from local motion or change of place. Moreover, while the natural motion of the four terrestrial elements was towards or away from the centre of the cosmos in a straight line, the natural motion of the heavenly bodies appeared to be uniform circular motion around that centre. Aristotle therefore inferred that the cosmos above the terrestrial sphere (that is, from the moon upwards) was not made out of any of the mutable terrestrial elements but must be composed of a different, unchangeable substance, the fifth element or 'quintessence', which he called aether (αἰθήρ).

The core conception. This elegant conception of the heavens provided the idealized basic conception of the cosmos from Greek antiquity into the sixteenth century. It offered in one simple and comprehensible package both a basic mathematical model of the celestial motions (a series of concentric spheres, centred on the earth, rotating with uniform circular motion) and a physical explanation (since this motion was regarded as the natural).

This elegant core conception was crucial to the longevity of the geocentric cosmology. The problem was that it was only very generally congruent with the observed motions of the heavenly bodies. As the Greeks began to observe the heavens more closely, this simple cosmological model needed to be altered; and the most it was altered, the more it lost the elegant simplicity which was its most attractive characteristic.  

Image. This arrangement is depicted in this image from the standard textbook on the subject, the Tractatus de sphaera (c. 1230) of Johannes de Sacrobosco (c.1195–c.1256), here in an Italian translation from 1537.  

At the centre of this cosmology is the earth (Terra, consisting of the three continents, Evropa, Africa, and Asia). Around the earth are the spheres of water (Agva, corresponding to the oceans and other bodies of water), air (Aria), and fire (Fvoco). 

Above the spheres of the four terrestrial elements come the spheres of each of the seven ancient planets, each with its sign: 1. ☾ the Moon, 2. ☿ Mercury , 3. ♀ Venus , 4. ☉ the Sun , 5. ♂ Mars , 6. ♄ Jupiter , and 7. ♃ Saturn. Above these are 8. the firmament or sphere of the fixed stars (with the signs of the zodiac), 9. the crystalline sphere, and 10. the 'primum mobile' or prime mover, which sets all the others in motion.

Further resources. For Aristotle's views: G.E.R. Lloyd, Aristotle: The Growth and Structure of his Thought (Cambridge, 1968), pp. 133-9. A summary of Sacrobosco's De sphaera is available on the Starry Messenger website in Cambridge. The complete treatise in English translation is available here.