(in Ptolemaic astronomy) the outermost of the 10 concentric spheres of the universe, making a complete revolution every 24 hours and causing all the others to do likewise.
astronomythe outermost empty sphere in the Ptolemaic system that was thought to revolve around the earth from east to west in 24 hours carrying with it the inner spheres of the planets, sun, moon, and fixed stars
"the first source of motion," mid-15c., from Medieval Latin (11c.), literally "the first movable thing;" see prime (adj.) + mobile. A translation of Arabic al-muharrik al-awwal "the first moving" (Avicenna).
