The Geocentric or Ptolemaic Notion of the Universe
This system of explaining the apparent motion of the moon, sun, planets and stars around the earth - the "geocentric" (Greek ge or gea = "earth") was current until overturned by the Galilean - Copernician heliocentric (Greek helios = "sun") in the 17th century (the Roman Catholic church did not officially abandon it until the beginning of the 19th century).
This is a system that imagines the "heavenly bodies" rotating each in its own "sphere", and the whole around the earth. Their apparent motion, as seen from the earth, could be accounted for by assuming very complex rates and angles of rotation of each sphere.
This system could be made, and was made, complex enough to appear to account for this motion, given the relative inaccuracy of naked-eye observations. But its real purpose was not scientific, but ideological; it was only secondarily a reflection of systematic observation. It purported to demonstrate that the structure of the observable universe conformed to the hierarchical system which elite medieval thinkers imposed on the natural and social world on earth, and so to reinforce authoritarianism. In addition, it had to conform to the account of Creation in Genesis, so that the supposed infallibility of the Bible as Word of God could be confirmed. These ideological purposes were far more important than explaining observable phenomena, as the condemnation of Galileo later showed.
The Sublunary Sphere
This diagram imagines the universe split in half like an onion, revealing the "spheres" with the Earth at the center, the most important, but at the same time the most imperfect, of God's creations. The area within the Moon's "sphere" was called the "sublunary sphere" (from Latin sub = "under" and luna = "moon"). As the Moon was the only heavenly body that appeared to change, to wax and wane, it was taken as a sign of the Mortality which entered the Earth as a result of the Fall of Man due to Original Sin, the sin of Adam and Eve, according to the account in Genesis. Similarly, even the mountains, valleys, and other irregularities of Earth were interpreted as "imperfections" or deviations from the original perfect Creation -- it was assumed that the earth, like the rest of the universe, must have originally been perfectly spherical, since the sphere is a "perfect" shape, and God is the "perfect" Being.
This conception of the universe is also a hierarchy, therefore, but in reverse. If you imagine a pie-shaped piece cut from the flat "slice" above, it would also resemble a triangle, much like those I've diagrammed here for the universal order, or here for the societal order, except that the point, or apex of the triangle, is not the "most worthy", but the "least worthy" -- the Earth, site of Original Sin. In fact, the Earth is both the "most" and the "least" noble -- the pinnacle of the divine creative plan, and the only part of the divine Creation sullied by Original Sin and thereby bereft of its pristine perfection.
Fortune and the Sublunary Sphere
As the site of Original Sin, the Earth is ruled by "Fortune" -- mortality, or death, and mutability, or change, which is a foreshadowing of death and an aspect of it (from Latin mors = "death" and mutare = "to change"). Go here to see some selections from Boethius' Consolation of Philosophy and the doctrine of Fortune.
https://msuweb.montclair.edu/~furrg/mel/ptolemaic.html | firstname.lastname@example.org | verion 09.23.2018