Portrait of Aristotle Courtesy of Corbis-Bettmann.

Aristotle was a Greek philosopher who lived between 384-322 B.C. He was one of the greatest thinkers of the world and his written works encompassed all major areas of thought: logic, science, metaphysics, ethics, and politics.

Aristotle mistakenly believed that the Earth was at the center of the universe and made up of only four elements: earth, water, air, and fire. He also thought that celestial bodies such as the sun, moon, and stars, were perfect and divine, and made of a fifth element called ether. Aristotle's conception of the universe lasted for almost 2000 years, until Copernicus presented his heliocentric theory.