The Ptolemaic universe from Andrew Borde’s The First Book of the Introduction of Knowledge, 1542.
Medieval cosmology was centered around the concept of the Ptolemaic universe, named after Greek astronomer Ptolemy (ca. 150 CE). In this geocentric (earth-centered) model, the earth was the motionless center of the universe, with the rest of the universe revolving around it in spheres. Ptolemy’s work was based on Aristotle’s (384-322 BCE) idea of an ordered universe, divided into the sublunary, or earthly, region which was changeable and corruptible, and the heavenly region, which was immutable and perfect. Aristotle posited that the heavens contained 55 spheres, with the Primum Mobile, “Prime Mover” or “First Movable”, giving motion to all the spheres within it.
Centermost in this cosmology was the Earth. The sublunary sphere was comprised of the four elements (earth, water, fire, and air). Next followed the spheres of the 7 planets (which included the sun and the moon). After these came the Circle of the Fixed Stars (including the signs of the Zodiac). Outermost in this scheme was the Primum Mobile, sometimes divided into three spheres of the Crystalline Heaven, the First Movable, and the Empyrean, or highest heaven.
While not scientifically supportable, this cosmology was eagerly embraced and adapted to fit Medieval theology. The Prime Mover became the Christian God, the outermost sphere became heaven, and the earth was the center of God’s attention. The spheres, moved by the Prime Mover, existed and rotated in perfect harmony, creating the “music of the spheres.” Man, habitant of the sublunary sphere which was corruptible since Adam’s fall, could no longer hear this music. This world view gave rise to further Medieval philosophical explanations of man’s place in the universe, such as the concept of corresponding planes, and the idea of the Great Chain of Being, so prominent in Boethius and Chaucer, for example.
By the 17th century, the Copernican and Galilean models gained ground, and replaced this world view. It was still an attractive philosophical construction and one that persisted for a long time in the collective Renaissance consciousness. Milton, who chose to use the Ptolemaic cosmology for his Paradise Lost, was not alone in Renaissance literature to hold on to the Medieval world view, if not in scientific earnest, as a poetical conceit (cf. Donne’s “The First Anniversary” and “Good Friday, 1613”).