Review
Kepler I, II and III
- planetary orbits are mostly close to circles
- only Mercury, Mars and Pluto have eccentricity > 10%
- Comet orbits are very non-circular
- long, narrow ellipses. High eccentricity
- some long period comets eccentricity nearly 100%
- essentially a parabola
- orbit originates in Oort cloud, 10,000 AU from sun
- example: Halley’s comet
- period is 76 y
- perhelion distance is < 1 AU
- What is aphelion distance?
- KIII implies a3 = 762 = 5800
- 103 = 1000, 23 = 8, so a somewhat less than 20, i.e. a = 18
- major axis = 2a = 36 AU
- aphelion distance between 35 and 36 AU, beyond Neptune