STS112 Lecture Notes - Lecture 3: Ptolemy, Nicolaus Copernicus, De Revolutionibus Orbium Coelestium
8 Jun 2018
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Week 3: Ptolemy
Ptolemy
• Claudius Ptolemaeus was born in c. AD 90 – c. AD 168 as a Roman citizen with Greek origins
• Wrote a number of works with various topics including: The Almagest, the Geography and the Tetrabiblos
• Ptolemy’s work carried through late antiquity as part of the scholarship undertaken in Ancient Rome in
centres such as Alexandria
The Almagest
• Was preserved and carried down through time after the decline of the Roman Empire (fall of Rome 476 AD)
via Arabic scholars who highly valued ‘Classical Greek Natural Philosophy’ and Ptolemy’s work
• Great synthesis of Astronomy/Natural Philosophy from Ancient Greece and Babylonian Astronomical tables
and Ptolemy’s own observations
Ptolemaic System
• Provides a guide to accurately (by the standards of the time) predict positions of Sun, Moon and the Planets
• Worked with the key ingredients of Classical Greek natural philosophy and largely Aristotelian Cosmology
• Famous for using various geometric devices based on circles to assist in providing accurate calculations of
Planetary Motion
Issues with Ptolemaic System
• Each planetary calculation seemed to rely on its own system of circles to fit with observation and help
prediction
• Various constructions could yield the same results
Week 3: Copernicus
Copernicus
• Nicholas Copernicus, born in 1473 and died in 1543, is mainly known for his book ‘De Revolutionibus’
which was published in the year of his death
• Born in region bordering what today we think of Poland and Germany, he spent much of his life in this
backwater
• Copernicus was strongly attached to the church where his uncle was a Bishop
• Became a Canon in the Cathedral at Frauenberg from 1512-1543 which allowed him the opportunity and
resources to do Astronomy
• Developed helio-centric model of the Cosmos (Sun centered) with the Earth just another planet moving
around the Sun and rotating on its axis amongst other more subtle, tilts and motions to help account for
seasons etc.
• Believed that unlike Ptolemy all the parts of his system were necessary for its coherence
• Argued against the appropriateness of the earth as the centre of the Cosmos – Earth was a place of
imperfection and change whereas the Sun was the source of light and life and therefore was more
appropriate to place in the centre.
Copernican System
• No centre of all the celestial circles or spheres
• All the spheres rotate around the sun as their midpoint, so the Sun is the ‘centre’ of the Universe
• Had difficulty in explaining the moving earth
• Copernicus’s work was criticised by Martin Luther (1483-1546) one of the key figures of the Reformation
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