The Observed Sky

• stars: celestial sphere
• Sun and planet motion in celestial sphere: real-time movies of the Sun (LASCO C3 camera on SOHO)
• planets: retrograde motion

Greek Cosmology: Geocentric

• physical principles
• experimental evidence
• retrograde motion explained via epicycles: animation
• Ptolemy

Nicholas Copernicus

• heliocentric model
• retrograde motion explained (animation)

Tycho Brahe

• nova stella discovery; present view (X-ray vision)
• precision astrometry

Johannes Kepler & Kepler's Laws

1. Orbits are ellipses
2. Equal areas in equal times
3. P² = a³

• inner solar system objects in real time