• Ptolemy (A.D. 100 – 170)

• Planet – Greek for wanderer – retrograde motion

• Book: Almagest – codified the work of Greek astronomers in a system that survived for over a millennium

• Ptolemaic or Geo-Centric System

• Athens is center of universe

• Dark Ages end – Arab guardians of this ancient wisdom returned it to Europe to become Christian Dogma.

Nicolaus Copernicus (1473 – 1543)• Devout Scholar – Canon of the Church

• Questioned Ptolemaic System – bothered by it’s complexity/arbitrariness

• Works out as pure ‘Mathematical Exercise”

• New View – Heliocentric or Copernican view of solar system

• Afraid to publish – 1543 – put on index of forbidden books as “False & Altogether Opposed to Holy Scriptures” until 1835

Tycho Brahe (1546 – 1601)• Noble Danish family• Twin brother was a stillborn• Raised by Jorgen – Admiral of Danish Navy• Great interest at university – mathematics• Silver Nose – duel over “better mathematician”• Career shaping events:

1. Eclipse of sun

2. New star in Cassiopeia – Nova

3. Observatory - (Sextant) on island, best in the world – 20 year nightly project to catalog observations.

Johannes Kepler (1571 – 1630)

• University of Tubingen – career plan was to be a Lutheran minister

• Studied under astronomers

• Exiled (mother called a heretic/witch)

• Joined Brahe – 1600 after working as an astrologer for Austria Prince

• Goal: ascertain true nature of planetary motions – a convinced believer of Copernican system.

Resolution: Kepler’s Laws of Planetary Motion

1. The planets travel in elliptical orbits with the sun at one focus.

2. The area swept out by the line drawn from the sun to a planet is the same in equal time intervals.

3. The square of the time each planet’s period (‘year’) is directly proportional to the cube of the mean distance between planet and sun.