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The Universe According to Ptolemy, Second Century A.D.

Description
Ancient Astronomy

Ancient Greeks  
Used philosophical arguments to explain natural phenomena
Also used some observational data

Most ancient Greeks held a geocentric (Earth-centered) view of the universe
 “Earth-centered” view
Earth was a motionless sphere at the center of the universe
Stars were on the celestial sphere
Transparent, hollow sphere
Celestial sphere turns daily around Earth

Seven heavenly bodies (planetai)  
Changed position in sky
Seven wanderers
Sun
Moon
Mercury
Venus
Mars
Jupiter
Saturn

Ancient Greeks
Aristarchus (312–230 B.C.) was the first Greek to profess a Sun-centered, or heliocentric, universe
Planets exhibit an apparent westward drift
Called retrograde motion
Occurs as Earth, with its faster orbital speed, overtakes another planet

Ptolemaic system
A.D. 141
Geocentric model
To explain retrograde motion, Ptolemy used two motions for the planets
Large orbital circles, called deferents, and
Small circles, called epicycles
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