To invent the scientific method, 17th century scientists had to overthrow the old world views of great scientists, particularly Aristotle. Aristotle believed Earth was at the center of the solar system and did not move. Instead, everything else, including the sun, moon, other planets, and fixed stars, moved around Earth. He also believed that all celestial bodies were made from Quintessence, a type of matter. This matter could not be corrupted or changed. The other four types of matter Aristotle believed existed were Earth, Air, Water, and Fire. He believed that Earth made a man heavy, Air was to breathe, Water was used for internal organs such as blood, and Fire made the heart. He also believed that celestial bodies followed crystalline spheres and had epicycles, an orbit within the orbit. Aristotle believed that motion was unnatural and objects wanted to be at rest. He explained the movement of celestial bodies by saying that the Quintessence had a natural motion, which he called uniform circular motion. He said the spheres on which the heavenly bodies move turn forever because it is in their nature to do so. Aristotle was very important and admired, so people assumed that his ideas were true. Thus, these ideas from Aristotle were "obstacles" to the scientific revolution. .
A few scientists that challenged Aristotle's ideas were Copernicus, Brahe, Gilbert, Kepler, Galileo, Descartes, and Newton. Their ideas and discoveries made it impossible to maintain the old world view. Copernicus believed that Earth was not at the center of the universe and it revolved around the sun. He made a theory that Earth rotated once a day and revolved around the sun once a year. He published his book On the Revolutions of the Heavenly Orbs, which explained his theory. Brahe was an astronomer who discovered a nova in 1572. He observed the star for months and published a monogram on it in 1573.
