What is "sublunary sphere"

n. (context cosmology English) In geocentric cosmology, that region of the cosmos from the centre of the Earth to the moon, believed to be comprised of the four classical elements (earth, air, fire and water) and to be subject to generation and corruption.

The sublunary sphere is a concept in Aristotelian physics derived from Greek astronomy. It is the region of the geocentric cosmos below the Moon, consisting of the four classical elements: earth, water, air, and fire.

The sublunary sphere was the realm of changing nature. Beginning with the Moon, up to the limits of the universe, everything (to classical astronomy) was permanent, regular and unchanging – the region of aether where the planets and stars are located. Only in the sublunary sphere did the powers of physics hold sway.