Aristotle was the student of Plato, but unlike his teacher he focussed on his surroundings. Plato focused his attentions on perfect forms, Aristotle focused his attentions on the physical world he could see.

Aristotle was enamored with the sun, the moon and the stars. Although the earth had physical imperfections, the heavenly bodies were the essence of the divine - perfect in their circular shape and movement.  Thus for Aristotle the perfect/imperfect dualism in life occurred not between things seen and unseen (as it had for Plato), but between the imperfect things seen on earth and the perfect things seen in the heavens. He was the first earth observer.

More Info
http://www.ucmp.berkeley.edu/history/aristotle.html