The Copernican Model

Timelines of Events

• 350 BCE
  • Aristotle sets Earth at the center of the universe.
• 270 BCE
  • Aristarchus suggests a sun-centered (heliocentric) universe with distant stars.
• 150 CE
  • Ptolemy publicizes the Almagest.
• 1576
  • Thomas Digges, an English astronomer, proposes modifying the Copernican system by removing its outer edge and replacing it with a star-filled unbound space.
• 1605
  • Johannes Kepler uncovers that orbits are elliptical.
• 1610
  • Galileo Galilei strengthened the heliocentric perspective by discovering Jupiter's moons and Venus's phases.

Nicolaus Copernicus

• In 1473, he was born in Torun, Poland.
• From 1491 to 1495, he learned astronomy, philosophy, and mathematics at the University of Kraków.
• From 1496 to 1497, he studied astronomy and canon law at the University of Bologna in Italy.
• In 1497, he was established as canon of the cathedral in Frombork, Poland.
• From 1501 to 1505, he studied Medicine, Greek, and Law at the University of Padua, Italy. He returned to Frombork and lived there for the rest of his life.
• By 1508, he had begun to formulate his sun-centered universe model.
• He did not finish this work until 1530, though he did publicize a summary of his ideas in 1514.
• Copernicus postponed publishing the full version of his theory until the last weeks of his life, fearing ridicule or persecution.
• In 1514, he published Commentariolus.
• In 1543, his De revolutionibus orbium coelestium (On the Revolutions of the Celestial Spheres) is published.

Geocentric Era

• According to Aristotle and Ptolemy, the Earth was a stationary point at the center of the universe, surrounded by everything else. For 1,800 years, this model has persuaded everyone.
• According to the Aristotelian Geocentricsm, each of the planets was contained within an invisible concentric sphere that rotated around Earth at a constant speed.
• In Ptolemy's revision of the Aristotelian model, the planets were not attached to the concentric spheres by themselves but rather to circles that were connected to them — the epicycles.
  • These were suborbits that the planets traveled in circles around, with the sun serving as their central pivot point.
• Ptolemy’s modifications became hugely complicated.
• His proposal was dismissed as ridiculous by geocentrists, who held that the Earth's rotation would generate powerful winds that would cause anything on its surface to just fly away.
• In 250 CBE, Aristarchus of Samos first raised the possibility that Earth might revolve around the sun.
• However, proponents of geocentrism have also long claimed that the "lack of stellar parallax" is a scientifically sound argument against the validity of Aristotelian theories.

Copernican Revolution

• Copernicus' theory was founded on a number of fundamental precepts.
  • First, the Earth rotates on its axis every day, accounting for the majority of the daily movements of the stars, sun, and planets across the sky.
  • Second, Copernicus proposed that the sun, not Earth, which is merely one of the planets and orbits the sun at varying rates, is the object of cosmic gravitation.
• If Earth and a different planet, such as Mars, both orbit the sun at different rates, taking different amounts of time to complete each revolution, they will alternately be close to and far from the sun on different sides.
• Furthermore, the apparent retrograde motion was elegantly explained by the heliocentric model.
• According to Copernicus, the distance between the Earth and the sun is a little portion of the distance between the Earth and the sun and the stars.
• Supporters of geocentrism have maintained for centuries that the only explanation for the lack of parallax is that Earth is stationary.
  • The alternative is that the parallax was present but was too small to be detected with the available equipment due to the stars' great distance from Earth.
• Copernicus also proposed that Earth is located at the center of the lunar sphere.
• Copernicus clung to the idea that all celestial body motions were caused by objects moving inside of invisible spheres, and that these motions had to be exact circles.
• Later, the work of Johannes Kepler replaced the concept of circular orbits with that of elliptical orbits, thereby eradicating the majority of the remaining flaws in Copernicus's model.