John Donne (1572-1631 A.C.E.) is a poet best known for his use of metaphysical conceits . His poetry and prose reflect a deep knowledge and understanding of theology, astronomy, law and alchemy (The Norton Anthology of English Literature, 1233). During Donne's lifetime, the Copernican Revolution erupted around him -- he refers to both the old and the emerging astronomy theories: the Ptolemaic vs. the Copernican universe. In his poetry especially, Donne uses grandiose expression to describe what his speaker is feeling. Astronomical theory, therefore, with it's elaborate and infinite construction, presented itself as a perfect conceit for Donne.
Ancient Greek astronomers developed the first theories on the structure of the universe. Plato (428-327 B.C.E.) had believed that a circle was the perfect shape and the universe was comprised of concentric spheres surrounding the earth; the planets, sun and moon circled the earth, following uniform circular motion (Seeds 46). It was also believed that our universe was hierarchal, divided into 2 separate parts: the Earth and the Heavens. The separate spheres were comprised of the basic elements of earth, water, air, and fire. The earth was within what was known as the sublunary sphere: that which was enclosed by the orbit of the Earth. The Celestial, outer sphere, was comprised of all other heavenly bodies (the planets, stars, sun and moon) and controlled by God and angels.