Timelines of Events

• 465 BCE

  • Empedocles claims that there are four elements: earth, water, air, and fire. Aristotle argues that the stars and planets are made of a fifth element, aether.

• 387 BCE

  • Eudoxus, a pupil of Plato, proposes that the planets are housed inside of transparent, rotating spheres.

• 355 BCE

  • Heraclides, a Greek philosopher, asserts that the Earth spins but the sky remains still.

• 12th century

  • Thomas Aquinas, an Italian Catholic priest, starts imparting the ideas of Aristotle.

• 1577

  • Tycho Brahe calculated that the Great Comet is farther away from Earth than the moon.

• 1687

  • In his Philosophiae Naturalis Principia Mathematica, Isaac Newton explains force.

The Geocentric Model

• Aristotle, from Macedonia, was one of the most influential Western philosophers, believing that the universe was governed by physical laws.

  • He attempted to explain these through deduction, philosophy, and logic.

• He believed that the positions and brightness of stars and constellations are fixed.

• He claimed that the moon, sun and planets seem to move constantly around Earth, he believed that their motion is circular and their speed is constant..

• Observing Earth's shadow on the moon's surface during a lunar eclipse convinced him that Earth was a sphere.

• He came to the conclusion that the universe revolved eternally around a spherical Earth that remained still in space.

• Aristotle thought that the atmosphere of Earth was also stationary.

• Friction occurred at the top of the atmosphere between the atmospheric gases and the rotating sky above.

  • Volcanic gas emissions rose to the top of the atmosphere on a regular basis.

  • Comets are formed when ignited by friction; shooting stars are produced when friction is ignited quickly.

• His logic was widely accepted until the 16th century.

Facts about Aristotle

• Aristotle thought the universe was finite and spherical. He also thought the earth was a sphere, much relatively small than the stars.

• He used lunar eclipse observations to back up his theory, claiming that if the earth weren't spherical, lunar eclipses wouldn't display segments with a curved outline.

  • He stated that when a person travels north or south, they do not see the same night stars, nor do they appear in the same positions in the sky.

• The four fundamental elements of earth, air, fire, and water were widely believed to exist at this time.

  • Aristotle thought that there was a fifth element, called aether, which he thought was the fundamental composition of the celestial bodies.

• He had a hierarchical conception of the cosmos and distinguished clearly between the heavens and the earth.

• Aristotle believed that there are three different types of motion: rectilinear, circular, and mixed.

  • According to his hypothesis, the four elements mainly moved in straight lines. Water and air fell in between the movements of the earth and fire. His aether, the fifth element, whirled around.

  • Aristotle also thought that every planet traveled along a distinct path.

• His hierarchical conception of the cosmos had a significant impact on medieval thinkers, who modified it.

  • The ability to pose specific questions about the universe and inspire those who came after him to seek solutions was Aristotle's contribution to astronomy.