Sublunary sphere
The changing realm below the Moon in classical cosmology.
The sublunary sphere is a concept from Aristotelian physics and Greek astronomy, denoting the region of the geocentric cosmos below the Moon. It was composed of the four classical elements—earth, water, air, and fire—and was considered the realm of changing nature, where the powers of physics held sway. Above the Moon, from the lunar sphere to the limits of the universe, everything was thought to be permanent, regular, and unchanging, composed of aether.
- Field
- Aristotelian physics, Greek astronomy
- Key concept
- Region below the Moon composed of four classical elements
- Associated thinkers
- Plato, Aristotle, Avicenna, Thomas Aquinas
- Contrasted with
- Celestial sphere (aetheric realm of planets and stars)
- Historical role
- Foundation for geocentric cosmology and medieval worldview
Lore & Background
Aristotle formulated the fully developed theory of a sublunary sphere in antiquity, linking it to geocentrism and a spherical Earth. Avicenna carried the Aristotelian idea of generation and corruption being limited to this sphere into the Middle Ages. Medieval scholastics like Thomas Aquinas discussed the division between celestial and sublunary spheres in his work Summa Theologica, drawing on earlier philosophical traditions.
Reader's Guide
The sublunary sphere was central to the Aristotelian worldview, defining a sharp boundary between the corruptible, changeable Earth and the perfect, unchanging heavens. This concept shaped medieval and Renaissance thought, creating what C. S. Lewis called a 'great divide' from aether to air, from heaven to nature. However, the theories of Copernicus began to challenge this distinction, and Tycho Brahe's observations of a nova and comets in the supposedly unchanging heavens further undermined the Aristotelian view. Thomas Kuhn saw scientists' new ability to see change in the 'incorruptible' heavens as a classic example of a paradigm shift. The concept also appeared in literature: Dante envisaged Mt. Purgatory as reaching above the sublunary sphere, and Samuel Johnson praised Shakespeare's plays for exhibiting 'the real state of sublunary nature'.
Did You Know?
- Only in the sublunary sphere did the powers of physics hold sway, according to classical astronomy.
- Tycho Brahe's observations of a nova and comets undermined the Aristotelian view of unchanging heavens.
More in Ancient Greek astronomy 1-24
Spotted an error? Know more?
Reader corrections go straight into our review queue. Suggest an edit · How this site is sourced