Our Solar System
Regularities of the Solar System
- Orbits and spins
- All planets orbit near the ecliptic
- path of Sun on celestial sphere
- orbit of earth projected on celestial sphere
- All orbits counter-clockwise as seen from N of ecliptic
- Most planets have diurnal spin axis aligned with ecliptic
- Earth’s axis tilted 23.5 degrees (seasons)
- Sun’s spin axis also aligned with ecliptic
- sun rotates once/27 days (sunspots)
- Planets formed out of flattened, disk-like Solar Nebula
- demo with rotating water-balloon
- Planet’s composition -- inferred through density
- typical densities: Table 20-3
- water or ice 1 gm/cm3
- silicate rocks 3
- iron (Fe) 8
- H, He depends on compression, typically low