Ptolemy & Copernicus

Aristotle: On the

Heavens• Aristotle On

astronomy

• Read in Latin throughout the middle ages

• Renaissance: Greek original

Two realms – eternally separated

• Sublunar: ever changing, complicated, chaotic, human (i.e. lowly)

• Supralunar: eternal, no changes other than “perfect” (i.e. complete) circular motion, divine

Prescientific Explanations - Alchemy

• See online reading

• Casual observation of patterns in nature – Bubbles of air in water go

up, etc.

• Wrong theory/elements

• This leads to wrong world views

The Grand Mystification of the Cosmos

• Aristotle’s thoughts ossified and prevented progress

• Disempowerment of the inquisitive mind– Trapped in a realm of chaos, what can we do?

– There is no connection of what goes on on Earth and in the heavens, so how can we find out?

– We are lowly, how can we ask divine questions or question the word of God?

Sun, stand thou still!• King James Bible (Joshua 10:12)

Then spake Joshua to the LORD in the day when the LORD delivered up the Amorites before the children of Israel, and he said in the sight of Israel, Sun, stand thou still upon Gibeon; and thou, Moon, in the valley of Ajalon.

• Logic: So the Sun usually moves!

The Bible, Plato, Aristotle, Ptolemy, Aquinas

• Everyone and the Scripture agree on the explanation of the cosmos since over one thousand years

• And you want to doubt that ?! How DARE you!

The Copernican Revolution

“Strange” motion of the Planets

Planets usually move from W to E relative to the stars, but sometimes strangely turn around in a loop, the so called retrograde motion. (Explanation: next lecture!)

Ptolemy (~140 AD)

• Puts forth a complete geocentric model

• dominates scientific thought during the Middle Ages

• Longest lasting (wrong) theory ever: 1000yrs

Major Work: Almagest

Epicycles

• Ptolemy’s explanation of retrograde motion

• About 40(!) epicycles necessary to explain all observations complicated theory

Which two fundamental misconceptions made Ptolemy's geocentric model very complicated

and prevented it from adequately describing the movements of bodies in the Solar System?

I) The Sun is at the center of the universe. II) All heavenly bodies move in combinations of

perfect circles. III) The Earth is at the center of the universe.

IV) The stars never move. a) I and IV.

b) II only. c) III only. d) II and III.

The Medieval Setting

• Dominant Church

• 1000 years of relative stagnation

• Experimental research greatly reduced

• To answer a question:

“Study the Bible or Aristotle!”

The Renaissance Setting

• Invention of the print (1450) by Gutenberg

Books widely available!

(Think: Manuscripts vs Amazon.com)

• End of Middle Age Church Domination

• Back to the roots (renaissance=rebirth)

• Study of Arabic astronomers

• Intellectual movement

Nicolas Copernicus (1473–1543)

• Rediscovers the heliocentric model of Aristarchus BOOKS!

• Planets on circles needs 48(!) epicycles to explain

different speeds of planets• Not more accurate than Ptolemy

Major Work : De Revolutionibus Orbium Celestium

(published posthumously)

Copernicus’ heliocentric Explanation of retrograde planetary motion

See also: SkyGazer