Copernican Revolution & History Of Astronomy

What was the Copernican Revolution?

A 16th century shift from an Earth-centered model of the universe to a sun-centered model (geo-centric → heliocentric models)

What were the old beliefs and models at the time before the 16th century Copernican Revolution (1501-1600 AD)?

The Ptolemaic system by Claudius Ptolemy

Aristotle’s Homocentric Sphere Model of the universe

Eudoxus’s concentric sphere model

What does geocentric mean?

Earth-centered

What does heliocentric mean?

Sun-centered

What are some ways people looked at time and the sky?

Obelisks

Stonehenge

The Sun Dagger

What does retrograde mean and what is retrograde motion?

Typically means something is moving or performing backwards; opposite to the normal or expected direction

Could you give me an example?

All the planets in our solar system orbit the sun in the same direction; prograde. But Earth orbits the sun faster than some other planets. When Earth passes a slower moving outer planets, the planet appears to stop and move backward, then continuing to move forward; retrograde — or opposite our orbits direction.

Who expanded upon Greek astronomer Apollonius of Perga with a geocentric model of retrograde motion?

Claudius Ptolemy, with his geocentric model of explaining the phenomenon of retrograde motion

Who ended up proving that Ptolemy’s model of retrograde motion of the planets is an optical illusion?

Nicolaus Copernicus

How did Nicolaus Copernicus improve upon Ptolemy’s model after he proved his retrograde model was an illusion?

By shifting the center of the universe from the Earth to the Sun, a concept known as heliocentrism

What are some main differences between Ptolemy and Copernicus’s model?

Ptolemy’s model used epicycles, based orbitals of planets on estimated distances, used an equant point to make planetary speeds match, though did note that plants actually do change speed — whilst Copernicus’s model found planets the closest to the sun move the fastest, removed the equant, and proposed that we (the Earth) orbit the Sun.

Who proved that both these theories were wrong?

Johannes Kepler

What did he do?

Johannes Kepler discovered that planets orbit the sun in ellipses, the sun isn’t exactly the center, and proved that planets do not move at a constant speed

Who was another person (besides Kepler) who was able to help overturn Earth-centered models?

Galileo, by discovering 4 moons orbiting Jupiter and not the Sun, and also discovering phases in Venus that would have only made sense if Venus was orbiting something other that Earth (the Sun).

Why wasn’t Copernicus’s model adopted immediately after it had been proposed, even if it was heliocentric?

It was still based on perfect circles and epicycles.

What are the three key hallmarks of science?

Modern science seeks explanations for observed phenomenon that rely solely on natural causes (meaning no spirits, or aliens)

Models must make testable predictions that will force us to revise or abandon the model if they do not agree with observations (must be real world, measurable, and able to withstand testing)

Must explain and use models that are as simple as possible (must be reasonable and simple).