Because you asked: Eclipse Frequency

• Eclipse schedules for 2010, 2011, and beyond

Greek Cosmology: Geocentric

• Aristotle
  • physical principles
  • experimental evidence: round earth, no stellar parallax
• epicycles: animation
• Ptolemy
• enduring geocentrism: medieval cosmology

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 (animation, another animation)
3. P² = a³

• solar system orbit viewer
• inner solar system objects in real time