Kepler’s Laws of Planetary Orbits: All deduced from observations 1. Orbits are ellipses 2. Plane Velocity Varies as it orbits 3. P 2 = A 3. Ptolemy. Copernicus – doesn’t quite get it right – still needs epicycles. Tycho’s Insane Model. Kepler’s Ultimate Resolution. An Ellipse:.
An Ellipse: epicycles
Eccentricity of Mars orbit means variations in Earth-Mars distance at opposition
Kepler’s Second Law – Equal areas in Equal Times distance at opposition
This requires the planet to move fastest when its closest to the sun
P = orbital period measured in units of years
A = orbital distance, measured in units of AU (1 AU = 1
Astronomical Unit = distance from the Earth to the Sun
But, he has no dynamical basis for understanding why these laws exist.