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• Ptolemy (A.D. 100 – 170)
• Planet – Greek for wanderer – retrograde
• 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
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
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.