Geocentric
Ptolemy

Heliocentric
Copernicus

Earth at center

Sun at center

Explains

• Motion of Sun
• Motion of Moon
• Solar and Lunar Eclipses
• Phases of Moon

Explains

• Motion of Sun
• Motion of Moon
• Solar and Lunar Eclipses
• Phases of Moon

For the Apparent Motion of Planets

Retrograde Motion

• Needs Epicylces

• Consequence of Lapping

Inferiority of Mercury & Venus

• Must keep orbits aligned

• Interior to Earth

Predicts

• No Parallax

• Venus & Mercury:
  • New & Crescent
    phase only

Predicts

• Parallax

• Venus & Mercury:
  • Full range of phases
    New to Full